As announced by Russian Deputy Prime Minister Dmitry Rogozin on May 13, 2014, GPS tracking stations co-sponsored by U.S. interests have stopped making their data available to scientists and others.
The tap on the flow of data from 11 stations was turned off starting on May 31. The data flow included hourly and daily data files from the stations as well as the real-time flow of data over the Internet.
In an item entitled “On Execution of the Instructions of the Government of the Russian Federation,” the website of Roscosmos, the Russian Space Agency, reported:
“In accordance with the instructions of the Government of the Russian Federation, the Russian Space Agency in conjunction with the Federal Agency scientific organizations on June 1, 2014, implemented measures to avoid the use of information from the global seismographic network stations operating on the signals of the GPS system and located in the Russian Federation, for purposes not covered by existing agreements, including military uses.” (As translated by Google Translate.)
It should be pointed out that none of the affected stations contribute to the day-to-day running of GPS; that is, they are not part of the GPS command and control network. They are stations participating in the work of the International GNSS Service, which provides data and products to scientists and other researchers for different purposes including geodesy, geodynamics, orbital mechanics, and atmospheric studies.
It is believed that the Russian move is a tit-for-tat exercise in response to sanctions by western countries following recent events in Ukraine. However, the Russians say that the action was initiated by the refusal of the U.S. to enter into negotiations on the placement of Russian-operated GLONASS tracking stations on U.S. territory. Russia wishes to expand its global network of differential correction and monitoring stations, which could conceivably be also used to supply data for GLONASS command and control purposes.
What isn’t widely known is that Roscosmos already uses sites on U.S. territory for monitoring the availability and health of the GLONASS satellites as the map below clearly shows.
A sixth GPS IIF satellite was launched aboard a United Launch Alliance Delta 4 rocket from Cape Canaveral at 8:08 p.m. EDT May 16.
The satellite, designated GPS IIF-6 and built by Boeing, is one of the next-generation GPS satellites, incorporating improvements to provide greater accuracy, increased signals, and enhanced performance for users.
According to Boeing, each GPS IIF satellite has greater navigational accuracy through improvements in atomic clock technology and a new civilian L5 signal to aid commercial aviation and search and rescue operations.
Interestingly, the rocket is the first to be tracked via GPS instead of by radar.
United Launch Alliance’s Atlas and Delta rockets are transitioning to GPS metric tracking for range safety functions, which protect the public and property should a launch vehicle veer off course. The move is a money-saving upgrade to the military’s aging range infrastructure.
A special avionics system on the launcher transmitted the location. For decades, most rockets launching from Cape Canaveral, Florida, and Vandenberg Air Force Base, California, have been tracked by C-band radar.
Two more GPS IIF satellites are scheduled to launch before the end of the year.
Galileo FOC Satellites Reach Spaceport
Galileo’s first two full operational capability (FOC) satellites arrived in Kourou, French Guiana, on May 7, in preparation for launch this summer.
Manufactured by OHB in Bremen, Germany, with navigation payloads contributed by Surrey Satellite Technology Ltd. in Guildford, UK, these satellites — the first of 22 full-capability models — had spent several months at ESA’s Technical Centre, ESTEC, in Noordwijk, the Netherlands, where they underwent exhaustive testing in simulated space conditions.
The Galileo satellites are named for the children who won a painting competition organized by the European Commission in 2011. Doresa and Milena, the first two FOC satellites, will be launched together aboard a Soyuz rocket, joining the four Galileos already in orbit. Adam, the third Galileo FOC satellite, is now undergoing testing under space conditions at ESTEC. Anastacia, the fourth Galileo FOC satellite, will begin final testing at OHB in Bremen before being shipped to ESTEC.
“A steady stream of satellites is foreseen, coming from OHB to ESTEC for acceptance testing and then on to French Guiana,” said an ESA official.
Arianespace is already facing an exceptionally crowded launch manifest in 2014. A well-informed source opined, “If one were to hazard a guess, here is the most likely scenario: O3b arrives ready for launch several weeks ahead of Galileo and secures the June launch. Galileo moves to August and is promised a second launch in the autumn. O3b’s planned second launch in 2014 is moved to early 2015, as is the planned third launch of Galileo.
“The effect of these schedule slips on the cost of the Galileo program, which is about a year late — cost overruns that Tajani has vowed will not be paid by the commission — is a subject for another day.”
New Loran at 5 Meters
The red track is based on raw eLoran data without any corrections. The transparent blue line is made by GPS-RTK and is widened to 10 meters, giving the required ± 5-meter limits of eDLoran. The white line is output from the eDLoran receiver, which stays within the borders of the 10-meter-wide transparent blue line.
Dutch consultants Reelektronika showed results from a prototype enhanced differential Loran (eDLoran) system, extensively tested in the Europort (Rotterdam) area, at the European Navigation Conference held in April. The tests achieved accuracies of 5 meters. A full technical article describing the equipment, methodology, and test results will appear in the July issue of GPS World.
Harbor pilots require accuracies of 5 meters and some form of robustness or back-up for GNSS systems in case of jamming, unintentional interference, system failure, or other disruption.
The current eLoran system cannot get better than 10-meter accuracy. The new eDLoran opens up new possibilities for multiple applications:
Installing eDLoran reference stations is fast, simple, and cost effective.
As there is no data channel bandwidth limitation, multiple reference stations can be installed, which offers increased reliability and makes the system more robust against terrorism and lightning damage.
A single or multiple eDLoran servers can be installed in a protected area. There is hardly a practical limit in the number of differential reference stations to serve.
CNAV on L2C and L5 Initiated
On April 28, U.S. Air Force Space Command began broadcasting civil navigation (CNAV) messages on all operational GPS satellites capable of transmitting the L2C and L5 signals. L2C is designed for commercial needs and L5 meets safety-of-life transportation requirements.
“These new CNAV messages will enable manufacturers to develop and test advanced civil receivers and make for a more robust position, navigation, and timing (PNT) solution available to the civilian public,” said Maj. Gen. Robert E. Wheeler. “We do not anticipate any GPS satellite outages or legacy degradations as a result of the pre-operational deployment of these frequencies, and those currently using the GPS Standard Positioning Service should not be impacted.”
Initial CNAV broadcast occurs at a reduced data accuracy and update frequency compared to GPS signals in use today. In December 2014, CNAV data updates will increase to a daily rate, bringing L2C and L5 signal-in-space accuracy on par with legacy signals. However, derived position accuracy cannot be guaranteed during the pre-operational deployment. These signals are primarily used to test various equipment and should be employed at the users’ own risk; not used for safety-of-life or other critical purposes.
The Air Force will broadcast L2C messages with the health bit set “healthy,” as was the case during a June 2013 test. L5 messages will be set “unhealthy,” but as experience grows with L5 broadcast and implementation of signal monitoring is achieved, this status may change upon review.
Tony, I do take issue with the suggestion that the International GNSS Service (IGS) is somehow inferior and not reliable. I understand that Veripos is a commercial service designed for specific markets, but in central New South Wales (most populous state of Australia) it is 800 kilometers to the nearest base station.
You mention “So Veripos and other commercial providers overcome the weaknesses of IGS by providing a worldwide network that is well maintained — an infrastructure designed for high reliability and availability. Each base station has dual-redundant receiver and communications links.”
The IGS has 400+ base stations. How many does Veripos have? If a station goes down on the IGS there are still 399+ backups.
“There are three processing centers, two active and one on warm standby.”
The IGS has seven processing centers using different algorithms and combined solutions.
“There are seven geostationary satellites with a large degree of coverage overlap.”
OK, IGS is not a real-time service —yet… but some sites are.
How does Veripos handle coordinate dynamics (station velocities)?
Don’t get me wrong, Veripos looks like a very good service for its clients, but please don’t bag the IGS, which I liken to the United Nations of geodesy. Many good people and nations contribute (through their taxes which support infrastructure and personnel) to this service for the benefit of all.
Thanks for putting together this article. It’s good to know more about Veripos, and I hope to try it out soon.
Our survey editor Eric Gakstatter chimed in with this comment:
Good points. Have you used the IGS service yet? I’d like to give it a spin.
Craig Roberts replied:
Not me personally, but one of my students and some researchers have. You can download some open-source software (there are a few options) and try it out. Early days for the RT IGS but results seem encouraging. Still the standard issues with initialization times for RT PPP processing. We are also looking at the LEX message from QZSS which graces our shores thanks to the Japanese. Basically investigating near real-time positioning options for remote locations in the absence of CORS networks and/or mobile phone coverage.
Tony Murfin added:
No IGS bashing from me. IGS is a different tool of a different color. Point of the article is that if you want to run a business requiring PPP performance, you need to use a commercial service. If your application can stand some potential down-time and tolerate longer initiation times — for university and engineering R&D for instance — IGS is perfect. It’s free of charge and accurate and as reliable as you need. Good luck with IGS, it’s a great system!
Performance of the Galileo Single-Frequency Ionospheric Correction During In-Orbit Validation
By Roberto Prieto-Cerdeira, Raül Orús-Pérez, Edward Breeuwer, Rafael Lucas-Rodriguez, and Marco Falcone
OFF TO A GOOD START. That’s how we might characterize the European Galileo satellite navigation system. The official beginning of the Galileo program occurred on May 26, 2003, when the European Union and the European Space Agency officially agreed on the first stage of the program (although some work on system concepts took place earlier). The first two prototype or development satellites, Galileo In-Orbit Validation Element-A (GIOVE-A) and GIOVE-B, were launched on December 28, 2005, and April 26, 2008, respectively. The satellites successfully validated key technologies for the full Galileo constellation and secured the system’s frequency allocations.
The first two In-Orbit Validation (IOV) satellites were launched by a single rocket on October 21, 2011, and the third and fourth IOV satellites were similarly launched on October 12, 2012. The two GIOVE satellites and first two IOV satellites provided an opportunity to use Galileo-only receiver measurements and after-the-fact precise satellite orbit and clock data to compute the position of a receiver’s antenna. Joined by two colleagues, I was pleased to report our successful attempt using dual-frequency carrier-phase and pseudorange data collected on May 17, 2012, in an article in the September 2012 issue of this magazine. The two GIOVE satellites were subsequently retired.
The four IOV satellites began transmitting navigation messages with valid ephemerides in March, 2013, and this paved the way for the first real-time single-frequency pseudorange Galileo position fix using the broadcast messages on the morning of March 12 at the Navigation Laboratory of the European Space Research and Technology Centre in Noordwijk, the Netherlands. The position fix included compensation for the effect of the ionosphere on the Galileo signals.
The signals from GNSS satellites travel through the ionosphere on their way to receivers on or near the Earth’s surface. The free electrons populating this region of the atmosphere affect the propagation of the signals, changing their speed and direction of travel. This results in a delay in the arrival of the modulated components of the signals (from which pseudorange measurements are made) and an advance in the phases of the signals’ carrier waves (affecting carrier-phase measurements). The ionosphere is a dispersive medium for radio signals, so by making measurements simultaneously on two frequencies transmitted by a satellite, most of the effect of the ionosphere can be removed. However, single-frequency devices such as most vehicle navigation and handheld receivers don’t have the luxury of dual-frequency correction. These devices must rely on a single-frequency correction model. The coefficients for such a model are included in the navigation messages transmitted by all GPS satellites. Known as the Ionospheric Correction Algorithm or Klobuchar Algorithm, it removes at least 50 percent of the ionosphere’s effect.
The Galileo satellites also include the parameters of an ionospheric algorithm, called NeQuick G, in their navigation messages. In this month’s column, the Galileo system design team describes the novel European way for modeling the ionosphere for single-frequency users and compares its performance to the current GPS approach.
“Innovation” is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. Write to him at lang @ unb.ca.
Radiowave propagation of GNSS signals is affected by the Earth’s atmosphere and the characteristics of the local environment surrounding the receiver. GNSS systems are based on the broadcasting of radiowave ranging signals in the microwave domain (mainly in the so-called L-band, although some new systems like the Indian Regional Navigation Satellite System are also expected to broadcast in the S-band). These electromagnetic signals may suffer from a number of impairments as they propagate from a satellite to a receiver. In considering these effects, we can divide the Earth’s atmosphere into two parts: the electrically neutral atmosphere (primarily the lowest part, the troposphere), whose main effect is a group delay on the navigation signal due to water vapor and the gas components of the dry air, which, for microwave frequencies, is non-dispersive (independent of frequency); and the ionosphere, the ionized part of the atmosphere. The local environment may affect the navigation signal in various ways, too, such as signal fading or complete signal blockage by vegetation or obstacles such as buildings, and multipath, where the signal is broadened in the time and frequency domains due to reflections and diffraction by surrounding objects. In this article, we will discuss the effect of the ionosphere on GNSS signals and how it is being dealt with by the Galileo satellite navigation system.
The ionosphere owes its existence to solar radiation, primarily extreme ultraviolet light. The radiation ionizes the atoms and molecules in the upper atmosphere at heights of less than a hundred kilometers to a few kilometers above the Earth’s surface, producing a sea of ions and free electrons (collectively known as a plasma). This region is responsible for a number of dispersive (frequency-dependent) effects on navigation signals. Chief among these is a persistent delay of the pseudorandom noise (PRN) ranging codes (and the advance of the phase of the underlying carrier waves), thereby introducing positioning and timing errors if not compensated for. Signals are also susceptible to scintillations — rapid variations of amplitude and/or phase of the signals due to diffraction and refraction caused by plasma irregularities. Furthermore, the ionosphere can bend the signal path, resulting in a slightly longer path than the straight path, and rotate the polarization of the signal.
The ionospheric refractive index (the ratio of the speed of propagation of electromagnetic waves in a vacuum to the speed of their propagation in a medium) is related to the number of free electrons along the propagation path. For this purpose, the total electron content (TEC) is defined as the electron density in a cross-section of 1 square meter, integrated along a slant (or vertical) path between two points (such as a satellite and a receiver). It is often expressed in TEC units (TECU) where 1 TECU = 1016 electrons per meter squared = 0.1624 meters of delay at the GPS L1 frequency. According to the electron density, the mechanisms responsible for such ionization, and the dynamics, the ionosphere is usually sub-classified in layers of different characteristics: D, E, F1, and F2, with the latter largely responsible for the ionospheric effects on GNSS.
All of the propagation effects due to the ionosphere depend on a number of factors such as time of the day, location, season, and solar activity. There is also an interaction between solar activity, the ionosphere, and the Earth’s magnetic field, which, at times, can result in a significant disturbance of the ionosphere, as happens during geomagnetic storms. On a long timescale, solar activity follows a periodic, approximately 11-year, cycle. And spatially, the behavior of the ionosphere can be broadly classified into four main regions: the equatorial anomaly regions, located at around ±15-20º on either side of the magnetic equator, usually presenting the largest TEC values; mid-latitude regions, where the daytime TEC values are usually less than half the values found in the equatorial anomaly regions; and the auroral and polar regions, which present moderate TEC values but with larger variability than at mid-latitudes due to the characteristics of the geomagnetic field.
If we ignore some smaller, higher-order terms, the ionospheric group delay (the delay of the “group” of waves making up the PRN ranging code modulations) may be expressed in meters as 40.3 sTEC / f2, where sTEC is slant TEC in electrons per meter squared, calculated along the straight propagation path between receiver and satellite, and f is the carrier frequency in hertz. This effect introduces ranging errors of several meters if not corrected. The higher order terms usually account for differences at the millimeter level (rising to centimeter level during extreme ionospheric disturbances) and may be safely neglected for code ranging. The effect on the carrier phase has the same magnitude as the code delay, but of opposite sign, meaning that the carrier phase is advanced while propagating through the ionosphere. Since the group delay is dispersive, its effect can be mitigated using linear combinations of signals at two separate frequencies.
For single-frequency receivers, GNSSes often rely on correction models driven by broadcast data. For example, with GPS, the Ionospheric Correction Algorithm (ICA, also known as the Klobuchar algorithm) uses eight broadcast coefficients to describe the ionosphere, which is represented as a two-dimensional thin-shell model (the vTEC is assumed to be concentrated in a two-dimensional shell at a given height, relying on an analytical mapping or obliquity function to convert between vTEC and sTEC depending on the elevation angle of the received signal). This model is very efficient in terms of computational complexity, and it usually removes more than 50 percent of the ionospheric error, particularly at mid-latitudes.
Galileo and NeQuick G
Galileo provides dual-frequency services able to mitigate the effects of the ionosphere, but also services to single-frequency users. For a Galileo single-frequency receiver, an algorithm has been developed based on an adaptation of the NeQuick electron density model.
With the launch of the Galileo In-Orbit Validation (IOV) satellites and the initial navigation message broadcast, for the first time the end-to-end performance of the single-frequency correction algorithm for Galileo could be analyzed. The objective of the IOV phase was to launch the first four operational Galileo satellites and to deploy the first version of a completely new ground segment. During this phase, the European Space Agency (ESA) needed to validate — in the operational environment — all space, ground, and user components and their interfaces, prior to full system deployment, including the single-frequency correction algorithm performance starting from April 2013. Results were obtained for the period up to March 2014, coinciding with the maximum of solar cycle 24 and including three equinoxes with increased solar activity. In this article, we present performance results showing that the algorithm is capable of correcting more than 70 percent of the ionospheric group delay error under nominal ionospheric conditions, using only the reduced Galileo infrastructure during IOV (four satellites and a partial set of the Galileo sensor or monitoring stations).
The Algorithm. The Galileo single-frequency correction algorithm is based on an adaptation of the three-dimensional NeQuick electron density model, driven by an effective ionization level calculated with three broadcast ionospheric coefficients.
The original NeQuick model is a three-dimensional and time-dependent ionospheric electron density model based on an empirical climatological representation of the ionosphere, which predicts monthly mean electron density from analytical profiles, depending on solar-activity-related input values: sunspot number or solar flux, month, geographic latitude and longitude, height and UT. It allows us to calculate the TEC through numerical integration of electron density along a path between a beginning and an end point crossing the ionosphere. As an example, a global vTEC map obtained with NeQuick is illustrated in FIGURE 1. The first version of this model (NeQuick1) was incorporated into a previous version of the International Telecommunication Union (ITU) recommendation ITU-R P.532 for TEC estimation in radiowave propagation predictions. Researchers have continued development of the model with updated formulations, and version NeQuick2 is the one currently recommended by the ITU.
FIGURE 1. Global vTEC map obtained with the NeQuick electron density model for a sunspot number of 150 at 13h UT in the month of April (grid resolution 2.5 degrees × 2.5 degrees).
The NeQuick model has been adapted for Galileo single-frequency ionospheric corrections (for convenience, the Galileo version is known as NeQuick G) in order to derive real-time predictions based a single input parameter, Az, which is determined using three coefficients broadcast in the navigation message. The three coefficients are used in a second-degree polynomial as a function of the modified dip latitude (MODIP) of the receiver, to determine Az, which replaces the solar flux input parameter of the parent NeQuick model, with the following equation:
(1)
where ai0-2 are the three broadcast coefficients. MODIP is expressed in degrees. A grid table of MODIP values versus geographical location is provided together with the algorithm. A map showing five different MODIP regions is presented in FIGURE 2, each region usually presenting different behavior.
FIGURE 2. MODIP regions. Contours are modified dip latitudes.
The performance of the Galileo single-frequency ionospheric algorithm, designed to reach a correction capability of at least 70 percent of the ionospheric code delay, had been assessed in the past using GPS data only and using GPS plus Galileo In-Orbit Validation Element satellite data for an offline estimation of the broadcast parameters.
Since the first successful autonomous real-time Galileo-based position fix on March 12, 2013, the Galileo navigation messages have been broadcast by the four IOV spacecraft to the external user community, including the ionospheric broadcast parameters determined with IOV-only observations.
Experiment Period and Performance Indicators
To analyze the performance of the single-frequency ionospheric correction, a number of performance indicators were used:
The root-mean-square (RMS) error of the ionospheric model in meters of L1 code delay, for one station and one day.
The relative correction capability, expressed as an RMS percentage, defined as:
(2)
where STECref is the reference STEC and STECNeQuickG is the STEC obtained with the Galileo correction model. The factor 66 is used to avoid the fact that small absolute errors, which are relatively large due to small reference values, inflate the correction capability; it is linked to a target correction of 70 percent with a minimum absolute threshold of 20 TECU (30 percent of 66 TECU is about 20 TECU).
Performance verification has been assessed for the period from April 2013 to March 2014, which includes the secondary peak of the current solar maximum. The Galileo broadcast data used for this test are the Az coefficients broadcast by the four Galileo IOV satellites. It is important to remember that during the period of this assessment, the IOV infrastructure was reduced with respect to the target full operational capability, including the generation of the ionospheric parameters: four IOV satellites (no other GNSS satellites were used in the estimation) and a reduced number of monitoring stations.
Since the ionospheric correction performance assessment can be done independently of the Galileo signals and analysis of performance is preferred over independent data and locations, reference STEC estimated using dual-frequency observables from GPS at stations from the International GNSS Service (IGS), distributed around the world, were selected for the correction capability performance assessment. This resulted in observations of six to nine satellites for any epoch and with more than 120 stations per day, which assured good global coverage for the test. Performance has been computed individually for each set of broadcast parameters. For this aspect of ionospheric correction assessment, the differences between GPS and full constellation Galileo geometries are considered to be negligible.
As a reference for comparative purposes, for some cases the results have been compared to those obtained with the GPS ICA correction model using the broadcast parameters from GPS satellites.
The reference ionosphere STEC values were computed using dual-frequency carrier-phase GPS observables from IGS stations at a sampling rate of 300 seconds, and using IGS final global ionospheric maps (GIMs) to level the geometry-free combination of carrier phases. In this context, the IGS GIMs are employed to align the geometry-free or ionospheric combination, LI, to compute the ambiguity term (BI) for each satellite-to-receiver arc: (3)
where LI represents the linear combination between signals at frequencies f1 and f2; is the ionospheric delay in meters of LI; and BI is composed of several terms: station and satellite phase inter-frequency biases ( and respectively), LI phase ambiguity (λ1N1j – λ2N2j), phase wind-up, multipath, and noise. And i corresponds to the station and j to the satellite.
Then, in order to compute the corresponding BI term for each satellite-receiver continuous arc, the sTEC prediction of the GIM (sTECGIM_map) is computed for each satellite ionospheric pierce point, and then the average is computed as follows: (4)
where the indices i, j, and α correspond to the receiver, satellite, and arc indicator respectively, and the average is performed over the corresponding continuous (no cycle slips) arc (α) of data. is estimated following the mapping function and the procedures to interpolate in space and time recommended by IGS for GIM maps represented in ionosphere-exchange (IONEX) format.
With this estimation, the aligned STEC can be obtained as: (5)
which is the STEC used as an accurate sTEC estimation or “truth” reference value.
Results
The first analysis that we performed was the daily RMS error and correction capability for all stations. Most days have shown very promising performance. To see different levels of performance, results for one “bad” day and one typical “good” day, in the period of experimentation, are presented in FIGURE 3. It is observed that even for the “bad” day, the correction capability is above 70 percent, except for some stations in the equatorial regions. This performance is exceeded significantly for the “good” day, with RMS residual ionospheric errors below 1.5 meters for L1 even at low latitudes.
FIGURE 3a. Performance of the Galileo single-frequency ionospheric correction when using the E11 satellite broadcast, “bad day” RMS error in meters of L1.FIGURE 3b. Performance of the Galileo single-frequency ionospheric correction when using the E11 satellite broadcast, “good day” RMS error in meters of L1.FIGURE 3c. Performance of the Galileo single-frequency ionospheric correction when using the E11 satellite broadcast, “good day” correction capability in percent.FIGURE 3d. Performance of the Galileo single-frequency ionospheric correction when using the E11 satellite broadcast, “good day” correction capability in percent.
The evolution of the RMS residual error both for Galileo NeQuick G and GPS ICA from April 2013 to March 2014 are presented in FIGURE 4. In this figure, ionospheric activity at the equinoxes is clearly observed in the degradation of performance, and the influence of increased solar activity from October 2013 to March 2014 is also evident.
FIGURE 4. Global daily RMS ionospheric residual error in meters of L1 after correction with Galileo NeQuick G (red) and GPS ICA (blue) from April 2013 to March 2014.
The residual error of the Galileo correction model is already at the level of the expected capability for the full constellation. It also shows better performance as compared to the GPS ICA model, especially at equatorial latitudes.
The level of correction capability for each station for the Galileo NeQuick G model and the GPS ICA model are presented in FIGURE 5 for a quiet day in May 2013 and an active day during the spring equinox in 2014.
FIGURE 5a. RMS correction capability (percent, with a lower bound of 20 TECU) of Galileo NeQuick G correction models for day 127, 2013.FIGURE 5b. RMS correction capability (percent, with a lower bound of 20 TECU) of GPS ICA correction models for day 127, 2013.FIGURE 5c. RMS correction capability (percent, with a lower bound of 20 TECU) of Galileo NeQuick G correction models for day 80, 2014.FIGURE 5d. RMS correction capability (percent, with a lower bound of 20 TECU) of GPS ICA (right) correction models for day 80, 2014.
Effect in the Positioning Domain. We have performed two analyses to assess the correction performance in the positioning domain: one using GPS observables and one with Galileo-only observables. In both cases, we used three ionospheric delay mitigation methods: the dual-frequency ionosphere-free combination, the single-frequency GPS ICA correction algorithm, and the single-frequency Galileo NeQuick G correction algorithm.
The performance of the correction algorithm in the positioning domain using GPS observables was performed with data from two stations: Noordwijk in The Netherlands (a mid- to high-latitude station) and Malindi in Kenya (a low-latitude station) for the day of year (doy) 172 of 2013. Results are presented in FIGURES 6 and 7 showing good performance of the NeQuick G correction, in particular at low latitude. The results do not include code smoothing neither for single-frequency nor dual-frequency positioning. In the results, it may be observed that, as expected, the noise level for single-frequency positioning is much lower than that of ionosphere-free, but a higher bias may be present (the residual mean ionospheric error).
FIGURE 6a. Horizontal GPS positioning error on L1 using single-frequency NeQuick G correction (blue), L1 and GPS ICA (red) and dual-frequency ionosphere-free (green) for mid-latitude station in Noordwijk (doy 172, 2013).FIGURE 6b. Vertical GPS positioning error on L1 using single-frequency NeQuick G correction (blue), L1 and GPS ICA (red) and dual-frequency ionosphere-free (green) for mid-latitude station in Noordwijk (doy 172, 2013).FIGURE 7a. Horizontal GPS positioning error on L1 and single-frequency NeQuick G correction (blue), L1 and GPS ICA (red) and dual-frequency ionosphere-free (green) for low-latitude station in Malindi (doy 172, 2013).FIGURE 7b. Vertical GPS positioning error on L1 and single-frequency NeQuick G correction (blue), L1 and GPS ICA (red) and dual-frequency ionosphere-free (green) for low-latitude station in Malindi (doy 172, 2013).
Positioning domain analysis with Galileo-only observations using the four Galileo IOV satellites, and applying the NeQuick G correction, was evaluated for a station in Washington, D.C., for doy 245, 2013, including E1-only, E5a-only, and dual-frequency E1-E5a ionosphere-free observations. (E1 is centered at the GPS L1 frequency, while E5a is centered at the GPS L5 frequency.) These results are presented in FIGURE 8. The single-frequency positioning performance is considered promising considering the limited number of satellites.
FIGURE 8a. Horizontal Galileo IOV positioning error on E1 and single-frequency NeQuick G correction (blue), E5a and single-frequency NeQuick G correction (red) and dual-frequency E1-E5a ionosphere-free (green) for mid-latitude station in Washington (doy 245, 2013).FIGURE 8b. Vertical Galileo IOV positioning error on E1 and single-frequency NeQuick G correction (blue), E5a and single-frequency NeQuick G correction (red) and dual-frequency E1-E5a ionosphere-free (green) for mid-latitude station in Washington (doy 245, 2013).
Conclusions
The performance of the Galileo single-frequency ionospheric correction algorithm, based on NeQuick G, was evaluated using the broadcast navigation messages from the four Galileo IOV satellites, both in correction capability and in the positioning domain for the period April 2013 to March 2014. Despite the reduced infrastructure (broadcast ionospheric parameters estimated using only the IOV satellites at a limited number of monitoring stations), the performance shows promising results, in particular for low-latitude regions where the ionosphere is more problematic and, as expected, it has been confirmed that the correction performance is correlated with solar activity.
Acknowledgments
The NeQuick electron density model was developed by the Abdus Salam International Center of Theoretical Physics in Trieste, Italy, and the University of Graz in Austria. The adaptation of NeQuick for the Galileo single-frequency ionospheric correction algorithm (NeQuick G) was performed by ESA and involved the original developers of NeQuick and other European ionospheric scientists under various ESA projects.
Note to Manufacturers
The publication of the NeQuick G model and the Galileo single-frequency correction algorithm is under preparation for public release by the European Commission.
ROBERTO PRIETO-CERDEIRA is a propagation engineer in the European Space Agency (ESA) at the European Space Research and Technology Centre (ESTEC) in Noordwijk, The Netherlands, responsible for the activities related to radiowave propagation for GNSS and satellite mobile communications.
RAUL ORUS-PEREZ is a propagation engineer at ESTEC, working on activities related to radiowave propagation in the troposphere and ionosphere for GNSS and other ESA projects.
EDWARD BREEUWER is the system integration and verification manager in the Galileo Project Office at ESTEC, responsible for the organization and coordination of all testing activities at the system level. He had overall responsibility for the IOV test campaign.
RAFAEL LUCAS-RODRIGUEZ is the Galileo Services Engineering Manager for the Galileo project at ESTEC.
MARCO FALCONE is the System Manager in the Galileo Project Office at ESTEC.
FURTHER READING
• Development of NeQuick Ionospheric Model
“A New Version of the NeQuick Ionosphere Electron Density Model” by B. Nava, P. Coïsson, and S.M. Radicella in Journal of Atmospheric and Solar-Terrestrial Physics, Vol. 70, No. 15, December 2008, pp. 1856–1862, doi: 10.1016/j.jastp.2008.01.015.
“A Family of Ionospheric Models for Different Uses” by G. Hochegger, B. Nava, S.M. Radicella, and R. Leitinger in Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science, Vol. 25, No. 4, 2000, pp. 307–310, doi : 10.1016/S1464-1917(00)00022-2.
“An Analytical Model of the Electron Density Profile in the Ionosphere” by G. Di Giovanni and S.M. Radicella in Advances in Space Research, Vol. 10, No. 11, 1990, pp. 27–30, doi: 10.1016/0273-1177(90)90301-F.
• Evaluation of the Galileo Single-Frequency Ionospheric Model
“Assessment of NeQuick Ionospheric Model for Galileo Single-Frequency Users” by A. Angrisano, S. Gaglione, C. Giola, M. Massaro, and U. Robustelli in Acta Geophysica, Vol. 61, No. 6, December 2013, pp. 1457–1476, doi: 10.2478/s11600-013-0116-2.
“GIOVE-A Experimentation Campaign: Ionospheric Related Data Analysis” by R. Orus and R. Prieto-Cerdeira in Proceedings of NAVITEC 2008, the 4th ESA Workshop on Satellite Navigation User Equipment Technologies: GNSS User Technologies in the Sensor Fusion Era, Noordwijk, The Netherlands, December 10–12, 2008.
“Assessment of the Ionospheric Correction Algorithm for GALILEO Single Frequency Receivers” by R. Prieto-Cerdeira, R. Orus, and B. Arbesser-Rastburg in Proceedings of NAVITEC 2006, the 3rd ESA Workshop on Satellite Navigation User Equipment Technologies, Noordwijk, The Netherlands, December 11–13, 2006.
“Advanced Ionospheric Modelling for GNSS Single Frequency Users” by M.A Aragón Ángel and F. Amarillo Fernández in the Proceedings ofPLANS 2006, the Institute of Electrical and Electronics Engineers / Institute of Navigation Position, Location and Navigation Symposium, San Diego, California, April 24–27, 2006, pp. 110–120, doi: 10.1109/PLANS.2006.1650594.
• GPS Ionospheric Model
“Ionospheric Time-delay Algorithm for Single-frequency GPS Users” by J.A. Klobuchar in IEEE Transactions on Aerospace and Electronic Systems, Vol. AES-23, No. 3, May 1987, pp. 325–331, doi: 10.1109/TAES.1987.310829
Tri-Band Multi-Constellation GNSS in Smartphones and Tablets
This article presents a single-chip BeiDou/Galileo/GLONASS/
GPS/QZSS/SBAS architecture for use in cell phones and tablets. The authors explain the advantages to end users of multiple constellations. They also examine the details of system interchangeability, multi-system issues, and how assisted-GNSS data operates with all constellations, including BeiDou.
By Frank van Diggelen and Kathy Tan
With GPS, GLONASS, SBAS, BeiDou, QZSS, and Galileo there are over eighty operational satellites. Why do we need all these satellites in the first place? The answer is simple: in urban environments we want a few (six to eight) good satellites with an unobstructed line-of-sight (LoS) to the receiver and good horizontal dilution of precision (HDOP). In order to achieve this, we need many more satellites in space than any single constellation. In this article, we address the following issues.
Receiver intersystem RF bias with a tri-band front-end. BeiDou uses a different RF section than GPS/Galileo/QZSS/SBAS and GLONASS. As a result, there is a receiver intersystem bias between BeiDou and each of these other systems—not just because BeiDou is on a different frequency, but because of the different RF path through the receiver. We explain how this bias is calibrated and removed.
In the space segment there are intersystem biases primarily caused by differences in time standards. We discuss time management and show how the different systems can be made interoperable.
BeiDou Assistance. In order to realize the benefits mentioned, we need infrastructure deployment for BeiDou assistance in accordance with 3GPP standards. We will discuss what is available, and what is left to do.
Coverage outside of China. Europeans can see more BeiDou satellites than Galileos. At the time of writing (March 2014) they could see approximately twice as many. Thus, when used in a multi-GNSS receiver, BeiDou is far from being just a regional system. We will provide coverage analysis, and live-test data, including a focus on Europe.
Finally, we will demonstrate all of the above in practice, explaining and showing how interchangeability is achieved, and where first fixes can be computed with no more than one of each satellite type.
Figure 1 illustrates the point referenced at the beginning, that we need many more satellites in space than any single constellation.
All of the lines in Figure 1 show signals that were actively tracked by the receiver at the position shown on the right. The orange lines are to satellites that are blocked, but the reflected signal is tracked. We do not want to use these measurements if we can help it, so we need many satellites to provide enough LoS signals.
Let’s look at the HDOP of the LoS signals. In this example, the HDOP for the three LoS GPS satellites was 50. For the three LoS GLONASS satellites, the HDOP was 45. However, with the combined GNSS constellation, the HDOP for the six LoS satellites was 2.2. In other words, we expect about a 20x accuracy improvement by using the combined constellation.
There are many places and times in cities where we see just one or two direct LoS signals from a particular constellation, and we need more than just GPS and GLONASS to get the desired number of good signals, thus explaining the desire and need for all available constellations.
We’ll now look at the coverage provided by BeiDou2, which has five Geostationary satellites (GEOs), five inclined Geosynchronous satellites (GSOs), and four Medium Earth Orbit satellites (MEOs). With this 14-satellite constellation, the global coverage is as shown in Figure 2. This figure shows the percentage of time in a day that four or more BeiDou satellites are visible above a 10-degree mask angle. In the Asia-Pacific region, where the GEOs and GSOs are positioned, the coverage is predictably 100 percent. In fact, there are seven or eight BeiDou satellites visible in much of this region most of the time.
Figure 2. BeiDou2 global coverage.
As shown in Figure 3, outside the Asia-Pacific region the coverage is also interesting. We see that at least four BeiDou satellites are available over Europe about half of the time. This is quite significant given the previous discussion; even one or two extra satellites can make all the difference in an urban environment. Another notable fact is that, for now at least, Europe can see more BeiDou than Galileo satellites.
Figure 3. BeiDou coverage over Europe. The different colors show the percent of time that four or more BeiDou satellites are visible above a 10° mask angle.
Technical Requirements
There are five significant technical requirements that we want to satisfy when creating a multi-GNSS receiver for consumer applications:
Three Separate RF Paths. To acquire and track all of the satellites already mentioned, we need three separate RF paths. Details follow in Section 3 (Front-End Architecture).
Search and Track capability for all visible GNSS satellites. The receiver must have the ability to search a very large number of code-frequency bins at once.
Host-Based. As much as possible, we want to make use of the host application processor (AP) and memory. This allows for tight integration with assistance data (which is coming from the host), other sensors, and other wireless data (such as Wi-Fi and Bluetooth for indoor locations). A host-based architecture also keeps size and cost as low as possible.
With Host-Offload. A significant trend in location applications is the need for “always-on low power” location. The host AP cannot be used for continuous position updates, since it draws too much power. So, while we want host-based location when the host AP is active (such as when navigating with turn-by-turn directions and a map), we also want a host-offload capability so that the GNSS chip can compute positions internally while the host is asleep.
Interchangeability. The ultimate requirement for multi-system GNSS is the ability to use any combinations of satellites as if they were all in the same constellation. This is summarized as “any four satellites will do.”
Front-End Architecture
From a cell phone/tablet perspective, the signals in space are all in the L1 band, with frequencies as shown in Figure 4. The key architecture feature of the GNSS front-end is that it should have three separate RF chains for the three separate frequencies-of-interest; see Figure 5.
Figure 4. Frequencies-of-interest for GNSS in cell phones.Figure 5. Front-end architecture showing three RF chains.
Baseband Architecture
The preferred architecture of a chip, as shown in Figure 6, is host-based to take advantage of the large host CPU when it is active. When the host CPU is asleep, a small, low-power, on-chip CPU is leveraged for background “always on” location. This enables applications such as geofencing to run without significantly reducing battery life.
Figure 6. Block diagram of the preferred architecture, showing a host-based configuration that includes a host-offload capability for geofencing and position caching on-chip when the host is asleep.
When the host is active, such as when you are actively using the phone for turn-by-turn navigation, the host AP is on and we want to make as much use as possible of the host AP and memory. This allows for tight integration with assistance data coming from the host, other sensors, and other wireless data (such as Wi-Fi and Bluetooth for indoor locations). A host-based architecture also keeps size and cost as low as possible, even with host-offload capability, which adds very little to the size of the chip.
Receiver Intersystem RF Biases
With the three different bands of frequencies, we will get RF group delays in the receiver front-end. These must be calibrated out by the receiver’s designer as part of the chip’s system design. If the group delay between BeiDou and GPS is not calibrated, it will lead to approximately three meters of bias between the two systems (Figure 7). Once it is calibrated, there is essentially no bias.
Figure 7. L1 frequency spectrum for BeiDou2, GPS, Galileo, QZSS, SBAS, and GLONASS.
Satellite Intersystem Biases
Different GNSS constellations run off their own master clocks; referenced to different realizations of UTC. GPS is referenced to UTC (USNO), QZSS is referenced to UTC (NICT), GLONASS to UTC (SU), BeiDou to UTC (NTSC), and Galileo to UTC (INRIM). GLONASS UTC (SU) differs from the others by 3 hours.
Furthermore, different systems treat leap seconds differently. This is indicated by the red arrows in the clocks in FIGURE 8. GPS, QZSS, BeiDou and Galileo system times are continuous and ignore leap seconds. Thus, each system time is ahead of UTC by a number of leap seconds. GPS time started in 1980 in synch with UTC; there have been 16 leap seconds since, so now GPS is 16 seconds ahead of UTC. QZSS and Galileo system times were started in synch with GPS. BeiDou system time was started in 2006 in synch with UTC; there have been 2 leap seconds since, so now BeiDou is 2 seconds ahead of UTC. GLONASS system time, on the other hand, includes leap seconds.
Apart from this, each of the different realizations of UTC is within several nanoseconds of the others.
To combine measurements from these different systems and avoid any time-induced intersystem biases, we need to resolve the time offsets. Each system transmits the delta-time between its system time and the systems that preceded it, as listed in Figure 8. To combine the systems, we either need to decode these data messages or obtain the delta-time values from Assisted GNSS.
Figure 8. Intersystem time differences and broadcast delta-time values from each system.
Note, however, that in the BeiDou broadcast Nav message the intersystem time-offset data values are all set to zero (even though the true offsets are not zero).
Assisted-GNSS Including BeiDou
Assisted GNSS, or A-GNSS, increases sensitivity and decreases the time-to-first-fix of a receiver by providing assistance data in the form of the receiver’s approximate position, time and frequency, as well as all data that the receiver might decode from the broadcast signals. The assistance data may also include data beyond what is broadcast, in particular, let’s focus on BeiDou time offsets. The BeiDou time offset to the other systems is included in the BeiDou broadcast Nav message as shown in Figure 8; however, at present these data values are all set to zero (even though the true offsets are not zero). Thus, in order to get these offsets and integrate BeiDou properly into a combined GNSS system, one must compute the offsets at a reference station and provide them as part of the assistance data, as shown in Figure 9.
Figure 9. A-GNSS provides broadcast satellite data over some other wireless network, as well as time-offsets between the different pairs of systems.
Commercial Implementation
The preferred architecture described in this article has been implemented in a commercial GNSS receiver that is now available for commercial host-based products, such as cell phones and tablets. The chip, Broadcom’s BCM47531, is the first consumer GNSS chip with a tri-band front-end capable of acquiring and tracking satellites from GPS, SBAS, QZSS, GLONASS, and BeiDou constellations, simultaneously; and operating in host-based mode for navigation and in host-offload mode for Always-On location.
Broadcom has collaborated with leading smartphone manufacturers to launch the first wave of BeiDou enhanced consumer smartphones. Figure 10 shows one of these smartphones being tested in Europe. Note the number of BeiDou satellites in view. As predicted by the availability plots shown earlier, there are many BeiDou satellites in view (in this case, six).
Figure 10. GPS/GLONASS phone and GPS/GLONASS/BeiDou phone being tested in Warsaw, Poland. Note the six BeiDou satellites (red) that are seen and tracked by the BeiDou phone.
Interchangeability: Any Four
Now that we have addressed all of the major issues related to integrating different GNSS systems (in particular BeiDou), we can demonstrate the payoff.This is the achievement of interchangeability, where any GNSS satellites can be used together, as if they all belong to a single constellation. Figures 11 and 12 show assisted cold starts, where first fixes are obtained with no prior knowledge other than that provided by A-GNSS data. In each case, we show a different combination of satellites; including one satellite from each of four different constellations, and all four from BeiDou.
Figure 11. Interchangeability: Position fix with 1 GPS satellite, 1 GLONASS, 1 QZSS, and 1 BeiDou. The receiver is in Perth, Australia, where all of these constellations can be seen.Figure 12. Interchangeability: Assisted cold start, first fixes. Blue numbers show the satellites used in the position fix (top: two GPS and two BeiDou; middle: one GPS, one GLONASS, and two BeiDou; and bottom: four BeiDou only). The receiver is in San Jose, California, where four BeiDou satellites can be seen some of the time (some of the BeiDou GSOs can be seen and all the BeiDou MEOs can be seen for a few hours each day).
Multi-Constellation Robustness
While this article was being edited, the GLONASS system provided us with the most dramatic demonstration yet of the need for, and benefits of, multi-constellation receivers. On April 2, 2014, the GLONASS system failed spectacularly for a period of 11 hours. Receivers that used GPS and GLONASS had very large position errors, or no positions at all. While the receiver discussed in this article, the BCM47531, operated seamlessly. This receiver tracked GPS, GLONASS, QZSS and BeiDou satellites, correctly identified the faulty GLONASS satellites, and automatically stopped using them.
The details of the incident are as follows: The GLONASS control system uploaded incorrect orbit data to several satellites. When receivers used these satellites they had position errors of hundreds of meters, or no positions at all. At that time, the BCM47531 was being tested alongside a GPS/GLONASS receiver, and we have the data to show what happened. The receiver using only GPS/GLONASS suffered position errors of ten thousand meters, and long periods with no position at all; at the same time the multi-constellation receiver produced continual positions with normal accuracy. Figure 13 shows the test data — the left most image shows the route being driven, the middle image shows the data from the GPS/GLONASS receiver, and the right image shows the data from the BCM47531 multi-GNSS receiver. Figure 14 shows the details of the multi-GNSS receiver, you can see that no GLONASS satellites are being used.
FIGURE 13. Side-by-side tests of GPS/GLONASS receiver and multi-constellation receiver during the GLONASS incident of April 2, 2014. The GPS/GLONASS receiver produced errors of ten thousand meters and long periods with no position at all, while the multi-constellation BCM47531 operated seamlessly.FIGURE 14. Detail from the multi-constellation receiver when there is a problem with some satellites. The errors are recognized automatically by algorithms comparing the measurements to redundant measurements from the extra constellations, and the erroneous signals are not used.
This incident may raise the question: Why use GLONASS at all, why not just GPS? The answer is that in urban canyons, such as where this test was done, GPS alone does not have enough satellites to give the performance now expected in consumer products — for the reasons explained in the beginning of this article. Also, GPS, although it has been more reliable than GLONASS, is not immune to failures or jamming itself. The lesson of this incident is that reliability and accuracy comes from the combination of all the available constellations, with a receiver that can use the signals interchangeably.
Conclusion
We have shown the preferred architecture for a consumer GNSS receiver that includes all of the available constellations. We have addressed the major requirements of such a receiver for the consumer market, in particular, for cell phones and tablets. A receiver that meets these requirements is now available, the Broadcom BCM47531, has been designed into a new generation cell phones and tablets for 2014. Finally, we have shown how, with this receiver, the ultimate GNSS goal of interchangeability can be achieved.
Frank van Diggelen is vice president of technology at Broadcom Corporation, a consulting professor at Stanford University, and inventor of coarse-time GNSS navigation, co-inventor of Long Term Orbits for A-GNSS, and author of A-GPS: Assisted GPS, GNSS, and SBAS.
Kathy Tan is a senior principal engineer at Broadcom Corporation. She has worked on GNSS development and Assisted GNSS for Ashtech, Magellan, Global Locate and Broadcom. She received her MS and BS in electrical engineering from Fudan University, China.
Putting GNSS into use within much larger aggregates of systems shows the greatest promise yet for earthly good. Goodness knows, we have experienced plenty of benefit from GPS applied over 25+ years, from back-up and fill-in provided by GLONASS, and with further synergy anticipated from Galileo and BeiDou. But we ain’t seen nothing yet. Two presentations this month at the Geospatial World Forum in Geneva show that teamed with other, non-navigation satellite systems and the ensuing big data sets, GNSS leads the way into 21st-century illuminated knowledge and enlightened action. The European GNSS Agency supports many innovative prototypes to drive Galileo market penetration, and the International Centre for Earth Simulation envisions building a Virtual Earth to better understand the real world.
Galileo and EGNOS Seek Market Penetration
Carlo des Dorides, executive director of the European GNSS Agency (GSA), presented experience, results, and a broad call for proposals for future application developers in the “geoSMART + Infrastructure Development” plenary session of the Geospatial World Forum, held May 6–9 in Geneva, Switzerland. The GSA is tasked with market development for the European GNSS programs, EGNOS and Galileo, and its viewpoint is of necessity rosy on user uptake.
In a side note before we look at these market-development efforts, des Dorides showed a figure that I had not seen before, one which claims that signal noise from the four orbiting Galileo satellites is noticeably less than that encountered on current GPS and GLONASS combined solutions. Another piece of the portrait we began at the magazine with post-processing PPP using two Galileo GIOVE and two IOV satellites as reported here, and then using four IOV satellites to do differential carrier-phase positioning as reported here.
chart: Galileo GIOVE
The GSA has funded many small-to-medium enterprise projects, and some of these may actually take off, that is, achieve sustainability through consumer or industry payment. The double edge of stimulus spending such as this is that products may or may not be created, and corresponding business models may or may not be built, with a truly hardened eye towards cash flow. Such a product or service’s only sustainable mode may turn out to be, after all, through government funding. Nevertheless, these are valiant efforts.
To be fair, the primary goal of these projects is to get Galileo and EGNOS into more widespread use, thus encouraging manufacturers of receivers, smartphones, tablets and so on to include Euro GNSS capability in their products. Establishing self-sustaining downstream enterprises is secondary.
Emerging from three successive stages of the current framework program for R&D spending, des Dorides cited “10 Patents or registered trademarks,
33 commercialized products/services, 69 working prototypes, an overall portfolio of roughly 90 R&D projects with a budget of around €70 million.”
“And more is expected!” he added.
Among the GSA projects he singled out for further description:
SAFEPORT: Safe Port Operations using EGNOS safety-of-life services for vessel traffic management, with a successful prototype demonstration in Dublin port. SAFEPORT has been in the market since January 2013. As commercial-targeted service, or perhaps a government agency (such as a port authority)-targeted one, this may have a return-on-investment prospect.
WalkEGNOS, a social web 2.0 mapping solution with a web site following the social network approach, enabling hikers and bikers to share theirs tracks. This produces “new opportunities for high-quality leisure/ touristic services, and value for search and rescue operations.” I am dubious, myself, as to whether hikers or commercial tour services would pay for such services, but it’s certainly worth the effort (and the government money) exploring the possibility through application development. The service is now available; you must register to use (free of charge).
GOLDEN-ICE, applying EGNOS GPS corrections to enhance accuracy for precise salt-spreading for road safety. On the market.
INCLUSION, a location-based service offering motor-impaired persons, such as those confined to a wheelchair, improved mobility in safe conditions, helping them navigate traffic safety problems and limited accessibility of public transport. On the market.
Other applications available for use include ASPHALT for high-precision paving, SCUTUM for transportation of dangerous goods, and COSUDEC for surveying of coastal waters. Further programs and results are here.
The Whole Earth
In easily the most mind-blowing presentation of the conference, founder and president Bob Bishop of the International Centre for Earth Simulation spun a vision of Big Data Earth Science, using the world’s largest computing resources (talk of exoflops and exobytes and “the human mind cannot comprehend these large volumes of data” supplied by many orbiting imagery satellites and other sensor inputs) to model the Whole Earth: surface, subsurface, ocean, atmosphere, and social economics.
Earth observing satellites are generating big data sets.
The Centre’s mission is “Helping guide the successful transformation of human society in an era of rapid climate change and frequent natural disasters.”
In its prospectus, Bishop writes “The key to solving problems in weather, climate and environmental science is high performance computing. Nature can only be accurately described and computed from equations that take account of complex, non-linear interactions between multiple natural systems, i.e. rivers, lakes, oceans, mountains, forests, dust, pollution, cloud cover, snow cover, ice, polar regions, etc. Such equations of motion are so interconnected and intertwined that they can only be managed when all aspects are held in big memory and computed simultaneously. Only then can we begin to address the systemic risks associated with natural disasters and planetary change.”
The ICES Foundation supports Open Science, which incorporates a combination of open data files, open source code, and open access publications. Much of the data supplied by the following organizations, upon whose resources ICES draws, is either directly produced by or referenced to GPS/GNSS data:
Global Observing Systems Information Center and the U.S. National Oceanic and Atmospheric; the European Space Agency and Centre for Space Records; the U.S. Geological Survey; the U.S. National Aeronautics and Space Administration; the European Union’s Joint Research Centerthe U.S. National Center for Atmospheric Research; the U.S. Naval Research Laboratory; the European Commission’s Infrastructure for Spatial Information in the European Community (INSPIRE); and many more.
Bishop warned of both sequential and synchronous collapse of natural systems, leading to cascading crises. His language and message bear some resemblance to Al Gore’s An Inconvenient Truth, but Bishop, whose previous 40-year professional career had him responsible for building and operating the international aspects of Silicon Graphics Inc., Apollo Computer Inc., and Digital Equipment Corporation, has assembled some actual practical tools to apply to the many problems.
The immediate goal is modeling, simulation, visualization, and ultimately understanding of the whole, leading to new forms of civic engagement and insights as to risk, safety, food, water, and energy.
Earth observing satellites are generating big data sets — Really Big!
I’m stepping in just for this month as a self-invited guest columnist, giving a brief look at the trailblazing work of the International Centre for Earth Simulation.
Look for both Eric Gakstatter and me at the ESRI User Conference in July, where Eric will also host a webinar on the hottest trends in mapping. We hope to accommodate a live audience at the webinar. If you’re not attending ESRI, attend the webinar anyway! For a top-level look at conference doings, register free.
In easily the most mind-blowing presentation of the Geospatial World Forum held recently in Geneva, Bob Bishop of the International Centre for Earth Simulation spun a vision of Big Data Earth Science, using the world’s largest computing resources (talk of exoflops and exobytes and “the human mind cannot comprehend these large volumes of data” supplied by many orbiting imagery satellites and other sensor inputs) to model the Whole Earth: surface, subsurface, ocean, atmosphere, and social economics.
The Centre’s mission is “Helping guide the successful transformation of human society in an era of rapid climate change and frequent natural disasters.”
In its prospectus, Bishop writes “The key to solving problems in weather, climate and environmental science is high-performance computing. Nature can only be accurately described and computed from equations that take account of complex, non-linear interactions between multiple natural systems, i.e. rivers, lakes, oceans, mountains, forests, dust, pollution, cloud cover, snow cover, ice, polar regions, etc. Such equations of motion are so interconnected and intertwined that they can only be managed when all aspects are held in big memory and computed simultaneously. Only then can we begin to address the systemic risks associated with natural disasters and planetary change.”
The ICES Foundation supports Open Science, which incorporates a combination of open data files, open source code, and open access publications. Much of the data supplied by the following organizations, upon whose resources ICES draws, is either directly produced by or referenced to GPS/GNSS data: Global Observing Systems Information Center and the U.S. National Oceanic and Atmospheric Adminisration; the European Space Agency and Centre for Space Records; the U.S. Geological Survey; the U.S. National Aeronautics and Space Administration; the European Union’s Joint Research Center; the U.S. National Center for Atmospheric Research; the U.S. Naval Research Laboratory; the European Commission’s Infrastructure for Spatial Information in the European Community (INSPIRE); and many more.
Slides from Bishop’s Geneva presentation are available here. These, however, of necessity lack some of the video and Flash Player simulations that he showed at the conference, revealing truly a dynamic planet in all aspects.
Bishop warned of both sequential and synchronous collapse of natural systems, leading to cascading crises. His language and message bear some resemblance to Al Gore’s An Inconvenient Truth, but Bishop, whose previous 40-year professional career had him responsible for building and operating the international aspects of Silicon Graphics Inc., Apollo Computer Inc., and Digital Equipment Corporation, has assembled some actual practical tools to apply to the many problems.
The immediate goal is modeling, simulation, visualization, and ultimately understanding of the whole, leading to new forms of civic engagement and insights as to risk, safety, food, water, and energy.
The highest court in the European Union has granted the right to be forgotten by a search engine. Will location privacy be next on the docket? We are seeing the beginnings of the in-car smartphone-type apps market and are watching for approaching hockey-stick style growth that is a year or two away. Google has added rich, engaging features to maps. And we take a look at results from indoor location advertising. Read more.
The European Court (EU) of Justice, made a curious and powerful ruling on privacy. The court stated that upon request, Google is obliged to remove reputation-hurting information that is generated by searching a person’s name. Like Mr. González, who brought this case to court, many of us have things in our distant past that we don’t want to be aired each time we are Googled. Perhaps it is an old bankruptcy or a youthful prank gone bad. The continuous re-airing of this information can make it hard for people to move forward in their lives. But while the court rule serves a purpose, it is poorly conceived and vague. The administrative complexity for search engines to comply is staggeringly onerous. And the information that it seeks to shield will still reside in websites.
How does this relate to location privacy? The EU Court of Justice is in the mood for privacy restrictions, and the use and handling of location data may be in their scopes. Also, sensitive location information can turn up in Google searches. A person in the EU will be able to request to have it shielded. Location information can be revealing. There may be records of check-ins from the café outside a rehab center or other treatment center, for instance.
Market, Fast Approaching. Companies are falling over each other for a piece of a new market about to burst open — software apps within vehicles. Analysts at IHS Automotive expect there will be 370 million smartphone apps for cars in use by 2020, a hefty growth from the 6.9 million units projected by the end of this year. Aha Radio is in Honda cars. General Motors is embedding Pandora, the music streaming app. 4G Internet connectivity will be in some GM and Audi models next year. BMW is opening app stores, this year in Europe and next year in the U.S.
The Players. Google and Apple (Google Projected Mode and Apple CarPlay) are poised to together dominate the market for auto apps integration, but other companies are in pursuit as well, including MirrorLink, Aha by Harman, and Ford Sync AppLink. North America is ahead of the global rush. Let’s hope some money flows into Detroit.
Google v. Apple. Information about Googles’ Projected Mode is scarce. Daimler posted an ad for a software engineer to help implement Google’s new in-car system, referred to as “Google Projected Mode.” The employment ad described Project Mode as a way to “seamlessly integrate” Android smartphones into a dashboard’s head unit. There is no mystery about Apple’s CarPlay, an extension of IOS. CarPlay simplifies the in-car experience by offering the same look and feel as an iPhone.
GM Pulls Ahead. Ford was the early automotive leader to offer smartphone-type apps with its Sync system, but more recent versions of the offering have had issues. They weren’t alone. Other car makers have had confusing interfaces that often contained annoying bugs. IHS now predicts that vehicle OEM adoption and integration will be led by General Motors. “Apps for autos are growing rapidly and will have a profound impact on auto infotainment and connectivity in the next decade,” said Egil Juliussen of IHS Automotive. “Auto apps will influence the competitive landscape among auto manufacturers and will even change the brand market share between them. OEMs will have to keep up to remain competitive.”
Better Google Maps. Google’s navigation system will now offer less congested or otherwise quicker routes during navigation, a byproduct of Google’s purchase of Waze. In addition, the navigation system will now advise on the best traffic lane, replacing less precise directions such as “keep left at the fork.” Google has partnered with cab provider Uber to show how long it would take to get home via cab when searching for public transit or walking directions. Google maps also now enable users to save entire cities for offline use.
Indoor Location Pays? In order for retailers to adopt indoor location technology, there needs to be clear returns. “A body of information is now gathering that verifies the effectiveness of these technologies,” reports Dominque Bonte of ABI Research. “We can see how limited trials are showing increases of advertising local search click-through rates from 0.1 to 3.5 percent, indoor location applications increasing basket sizes 10 percent, and how smartphones are significantly changing the cross channel shopping habits of users.”
Not everyone is talking up the accuracy of indoor positioning. Arlington, Virginia-based Telecommunications Industry Association says the technology, which is seen as the one way location-based services providers will be able to capture consumer interest, is not ready. In other LBS news, AT&T has come out with data pricing for its connected vehicle initiatives.
In a recent FCC filing, the Telecommunications Industry Association said that indoor positioning technology is not sufficiently developed to support ongoing wireless E-911 location accuracy requirements.
While TIA supports the FCC’s goal to improve location accuracy, “Imposing location accuracy mandates at this time would be premature, given the nascent stage of the technology that will be needed to accomplish the Commission’s objectives, and should neither favor nor disfavor specific technologies,” said the association in its filing.
The NPRM proposes a requirement to achieve “rough” indoor location information, TIA said. It proposes to require providers to provide horizontal information for wireless 911 calls that originate indoors, specifically a caller’s location within 50 meters.
TIA also disagrees with an FCC proposal to require mobile operators to provide z-axis, which is vertical location within 3 meters of a caller’s location, for 67 percent and 80 percent of indoor wireless 911 calls — ranging from three to five years after adoption. Again, TIA says that the technology is not fully developed.
TIA quoted AT&T’s filing: “[The] time [is] right to begin discussing Indoor Location Accuracy for E-911” but the “FCC should be careful to ensure that any proposed rules on location accuracy are aligned with proven capabilities of the current state of technology and they should set realistic accuracy benchmarks that the industry and public safety can embrace.”
The location industry has been counting on indoor positioning, with its beacons and Wi-Fi enhancements, to jump-start a location-based services market that always seems to have tremendous potential, but the numbers don’t back it up. Some big-time analysts have said that while the promise of indoor positioning is huge, it just isn’t there technically yet.
In fact, one analyst said that the biggest technological breakthrough last year was indoor mapping. Such major retailers as Home Depot and Lowes launched indoor maps with product search locators. These same analysts say that indoor Wi-Fi positioning is not accurate enough for macro location.
The big deal coming up is how FCC positioning accuracy regulations will affect beacons or Bluetooth low energy for micro location and proximity services.
TIA said it supports initial FCC location accuracy requirements back to 2007. However, don’t ask TIA for more location regulation. “To date, the development of 911 and E911 location accuracy technologies and applications has been fostered by a voluntary and consensus-based standards process. This process has proven quite successful to date, and the Commission should refrain from imposing regulations that could slow additional development,” the association said.
AT&T Announces Connected Car Pricing
AT&T Mobility said standalone pricing for new LTE-enabled OnStar service will be $5 or $10 per month, depending on whether the driver is an OnStar subscriber. The company said it will allow customers, with a GM LTE-capable vehicle, to add the car as another device for $10 — which is the same price as a tablet.
OnStar subscribers will get coverage ranging from $5 for 200 MB of data per month to $50 for 5 GB. GM is also allowing customers to buy one-time data packages.
At this year’s CES, General Motors announced its first LTE-enabled vehicles — in which AT&T Mobility is powering the LTE network for GM’s OnStar service. The first LTE-enabled vehicles, which will be available this summer, are Impala, Spark, Volt, Orlando, Spark RV, Silverado, Silverado HD, Malibu, Equinox and Corvette Stingray. GM plans to have 30 Chevrolet, Buick, GMC and Cadillac vehicles LTE-equipped by the end of the year.
AT&T also made recent deals to provide connectivity for Ericsson Connected Vehicle Cloud which connects to the AT&T Drive platform for automakers.
CEA Hosts CES on the Hill
Members of Congress and their staff had the opportunity to observe location technology during the Consumer Electronics Association’s recent CES on the Hill event in Washington. Exhibiting companies include Origo Safe, distracted driving; AT&T Drive; DashIt; Qualcomm, which showed off a geofencing product around schools; and RideScout.
Washington-based Ridescout is a cool, and free, mobile app that allows a user to find the nearest subway, bus, taxi, bikeshare, sedan service, carshare, pedi-cab or carpool. A user can choose from a list of options by proximity, cost or arrival time.
“We launched in November in Washington, D.C. We are in Austin, San Francisco, Boston, Chicago and planning several new markets,” said Steve Carroll, Ridescout vice president of operations.
The app, which is on the iOS and Android platforms, generates revenue by sharing with the ride providers, large organizations and universities and the public transport network, Carroll said.
Some of Ridescout’s partners include Mozio, RidePost, Metro of Washington, Bandwagon, Sidecar, Car2Go, Arlington Transit, Capital Bikeshare, Yellow Cab, DC Circulator and Dash.
RideScout, founded by two Army veterans, was hatched when founder and CEO Joseph Kopser wanted an application to show him the best way to get to work in the Washington area. He could not find one and started the company with Craig Cummings. The company initially launched an alpha product at South by Southwest in 2013.
Though it was the first to combine all modes of transportation in a single application, the company has some competition. Of course this competition is from the 800-pound location gorilla, Google.
Google, with its Google Maps platform, shows the directions to the nearest transportation mode. Now it is incorporating Uber, which is an on-demand transportation provider.
This is not the first time Google has launched a product in an effort to dominate a market place or niche. When it launched Google Maps in 2009, it put the hurt on many companies in the location industry, which underwent a three-year period of consolidation, company closings and layoffs.
A panorama from the GNSS tide gauge at Onsala Space Observatory. When satellites pass over the sky, the GNSS tide gauge uses signals direct from the satellite and signals reflected off the sea surface to measure the sea level. Photo: Johan Löfgren
A new way of measuring sea level using satellite navigation system signals, for instance GPS, has been implemented by scientists at Chalmers University of Technology in Sweden. Sea level and its variation can easily be monitored using existing coastal GPS stations, the scientists have shown.
Measuring sea level is an increasingly important part of climate research, and a rising mean sea level is one of the most tangible consequences of climate change. Researchers at Chalmers University of Technology have studied new ways of measuring sea level that could become important tools for testing climate models and for investigating how the sea level along the world’s coasts is affected by climate change.
Johan Löfgren and Rüdiger Haas, scientists at Chalmers Department of Earth and Space Sciences, have developed and tested an instrument that measures the sea level using a GNSS tide gauge.
”The global mean sea level is rising because of climate change, but the change depends on where you are in the world,” says Rüdiger Haas. “We want to be able to make detailed measurements of sea level so that we can understand how coastal societies will be affected in the future.”
When satellites pass over the sky, the GNSS tide gauge uses signals direct from the satellite and signals reflected off the sea surface to measure the sea level. Photo: Johan Löfgren
The GNSS tide gauge uses GPS and GLONASS signals. BeiDou and Galileo will be added in the future.
”We measure the sea level using the same radio signals that mobile phones and cars use in their satellite navigation systems,” says Johan Löfgren. “As the satellites pass over the sky, the instrument ‘sees’ their signals — both those that come direct and those that are reflected off the sea surface.”
Two antennas, covered by small white radomes, measure signals both directly from the satellites and signals reflected off the sea surface. By analyzing these signals together, the sea level and its variation can be measured, up to 20 times per second. The sea level time series is rich in physical phenomena such as tides (caused mostly by the gravitational pull of the Moon and the Sun), meteorological signals (high and low pressure), and signals from climate change. Through advanced signal processing, these signals can be studied further.
The new GNSS tide gauge can measure changes in both land and sea at the same time, in the same location. That means both long-term and short-term land movements (post-glacial rebound and earthquakes) can be taken into consideration.
”Now we can measure the sea level both relative to the coast and relative to the center of the Earth, which means we can clearly tell the difference between changes in the water level and changes in the land,” says Johan Löfgren.
This summer, other high-precision instruments will be installed to work with the Onsala GNSS tide gauge, in collaboration with SMHI, the Swedish Meteorological and Hydrological Institute.
The GNSS tide gauge at Onsala Space Observatory uses signals from satellite navigation systems like GPS to measure the sea level. Photo: Johan Löfgren
”Our tide gauge station will become part of a network of stations along the coast of Sweden that will be able to monitor changes in the water level to millimeter precision well into the future,” says Gunnar Elgered, professor at Chalmers Department of Earth and Space Sciences.
The scientists have also shown that existing coastal GNSS stations, installed primarily for the purpose of measuring land movements, can be used to make sea-level measurements.
”We’ve successfully tested a method where only one of the antennas is used to receive the radio signals. That means that existing coastal GNSS stations — there are hundreds of them all over the world — can also be used to measure the sea level,” says Johan Löfgren.
More about the research
The method is described in two new scientific articles:
This work was previously reported in these publications:
Larson, K.M., J. Lofgren, and R. Haas, Coastal Sea Level Measurements Using A Single Geodetic GPS Receiver, Adv. Space Res., Vol. 51(8), 1301-1310, 2013, doi:10.1016/j.asr.2012.04.017, 2013.
Larson, K.M., R. Ray, F. Nievinski, and J. Freymueller, The Accidental Tide Gauge: A Case Study of GPS Reflections from Kachemak Bay, Alaska, IEEE GRSL, Vol 10(5), 1200-1205, doi:10.1109/LGRS.2012.2236075, 2013.
Altus Positioning Systems has introduced its new APS-NR2 RTK surveying receiver. The new product is being previewed at the 2014 Geo Business conference and exhibition in London May 28-29, and will be commercially available in July.
“The APS-NR2 provides a powerful combination of high GNSS RTK performance, light weight, low power consumption, versatile Quad-band modem, remote Web-based access and connectivity with Esri’s cloud-based platform,” said Neil Vancans, Altus president and CEO. “The result is a versatile product designed to enhance productivity and minimize downtime in the field for a wide range of surveying and geolocation jobs.”
The APS-NR2 is Altus’ second-generation RTK rover, building on the highly successful APS-3 product series. It features an easily accessible on-board web interface and integrated Wi-Fi for easy remote configuration and status monitoring, as well as Bluetooth for real-time data streaming, providing true cable-free operation. In parallel to RTK positioning, data can be recorded on a removable 2-GB SD memory card for post-processing.
The APS-NR2 is built around a low-power 132-channel GPS/GLONASS L1/L2/L2C SBAS receiver, which offers robust RTK performance, as well as DGPS capability. The internal 3.5G Quad-band GSM/GPRS/EDGE cellular modem supports RTK network connectivity. Dual internal cellular antennae ensure a positive signal lock and minimize disruptions due to dropped calls.
The new Altus receiver comes with two Li-Ion batteries. It has a built-in USB battery charger, as well as a separate two-bay external charger. The batteries are hot-swappable, allowing uninterrupted productivity on the job.
With Altus’ open-architecture philosophy, the user has a choice of data collector software from Carlson SurvCE, MicroSurvey FIELDGenius or direct interface to Esri ArcGIS Online, as well as proprietary customer-developed software.
The APS-NR2 doesn’t sacrifice essential processing power or connectivity and still weighs only 0.7 kg (1.5 lbs). The compact receiver is just 69 mm (2.7 in) high and 167 mm (6.6 in) in diameter. The rugged unit is waterproof to IP67 and has an operating temperature range of -40 to +85°C.
