DOT serves as the civil lead for the GPS and chairs the CGSIC in this capacity. NAVCEN is assigned duties as deputy chair and executive secretariat for the CGSIC.
Subcommittees of the CGSIC for Timing, State and Local Government, International Information, and Survey, Mapping and Geosciences will hold meetings Sept. 25, and a summary of these meetings will be presented to the CGSIC plenary session Sept. 26.
The keynote speaker for this year’s plenary session will be Keith Conner, Ph.D., Senior Engineer, Science and Technology First Responders Group, U.S. Department of Homeland Security.
Presentations include:
Operational status and modernization of the GPS constellation of satellites
U.S. Space-Based Position, Navigation and Timing policy
GPS augmentation systems
Briefings from the National Aeronautics and Space Administration (NASA) and the National Parks Service
Information related to U.S. engagement with other international Global Navigation Satellite Systems as well as a variety of applications of the use of GPS
The full agenda is available. CGSIC presentations will be posted online shortly after the meeting ends.
Even a GNSS receiver that can supply raw pseudorange and carrier-phase measurements now costs only a few hundred dollars, and in this month’s column, a couple of researchers from Down Under pit a couple of these receivers up against a couple of survey-grade receivers. Did this cheap receiver turn out to be a good thing?
By Robert Odolinski and Peter J.G. Teunissen
ALL GOOD THINGS ARE CHEAP; ALL BAD ARE VERY DEAR. That’s what the famous American essayist (and surveyor) Henry David Thoreau wrote in his diary on March 3, 1841. He was likely referring, in part, to the cheapness of the things he came across in nature such as birdsong or the plants and trees on the shores of Walden Pond and the dearness of some luxuries and comforts of civilization, which he tended to eschew. But what has that got to do with GPS, you might ask?
When they were first introduced in the late 1970s and early 1980s, GPS receivers were very dear. Many of them sold for anywhere from $50,000 to $250,000, which would be equivalent to about twice those amounts in today’s dollars. The first civilian receivers were large bulky affairs. As I documented in this column in April 1990 (“Smaller and Smaller: The Evolution of the GPS Receiver”), the “first commercially available GPS receiver was the STI-5010 built by Stanford Telecommunications Inc. It was a dual-frequency, C/A- and P-code, slow-sequencing receiver. Cycling through four satellites took about five minutes, and the receiver unit alone required about 30 centimeters of rack space. External counters, also requiring rack space, made pseudorange measurements. An external computer controlled the receiver and computed positions.” While it could be transported in a small truck (and some were), it was not designed for portability and ease of use by surveyors or geodesists.
Then, in 1982, Texas Instruments introduced the first relatively compact civil GPS receiver, the TI 4100, also known as the Navstar Navigator. And as I also noted in that column more than 15 years ago, this “receiver could make both C/A- and P-code measurements along with carrier-phase measurements on both L1 and L2 frequencies. Its single hardware channel could track four satellites simultaneously through a multiplexing arrangement. The 37 × 45 × 21-centimeter receiver/processor had a handheld control and display unit and an optional dual-cassette data recorder for saving measurements for post-processing. The unit, although portable, weighed 25 kilograms and consumed 110 watts of power (the receiver doubled as a hand warmer). Field operation required a supply of automobile batteries.”
My, how things have changed. Beginning around 1990, receivers steadily got smaller and smaller and cheaper and cheaper. Survey-grade GNSS (not just GPS) receivers can now be purchased for well under $10,000 and consumer-grade units sell for as little as a hundred dollars or less. And, of course, the GNSS modules inside smartphones and other devices cost manufacturers only a couple of dollars or so.
But even a GNSS receiver that can supply raw pseudorange and carrier-phase measurements now costs only a few hundred dollars, and in this month’s column, a couple of researchers from Down Under pit a couple of these receivers up against a couple of survey-grade receivers. Did this cheap receiver turn out to be a good thing?
Read on to find out.
GPS has been the number-one positioning tool for a range of applications during the past few decades. The integration of the emerging global navigation satellite systems, such as the Chinese BeiDou Navigation Satellite System (BDS), can give improved precise (millimeter- to centimeter-level) real-time kinematic (RTK) positioning. When BDS is combined with GPS, about double the number of satellites are visible in the Asia-Pacific region, which can make single-frequency RTK and low-cost receiver RTK positioning possible.
In this article, we will analyze the performance of L1 GPS + B1 BDS in Dunedin, New Zealand, using low-cost receivers. We compare their performance to that of L1+L2 GPS survey-grade receivers.
First, we describe the GPS+BDS functional and stochastic models and the data used for our evaluations. Least-squares variance component estimation (LS-VCE) is used as a means to determine the code and phase (co)variances to formulate a realistic stochastic model. (An incorrect stochastic model will deteriorate the ambiguity resolution and consequently the achievable positioning precisions.)
Having correctly defined the stochastic model, we focus on the positioning performance. We investigated the ambiguity resolution and positioning performance, both formally and empirically, for customary and high-elevation cut-off angles. The high cut-off angles are used to mimic situations when low-elevation multipath is to be avoided. Lastly, we compared all our results between using low-cost and survey-grade antennas.
GPS+BDS POSITIONING MODEL
The model that we used for positioning is given as follows. Assume that sG + 1 GPS satellites are tracked on fG frequencies and sB + 1 BDS satellites on fB frequencies. As we apply system-specific double-differencing (DD), one pivot satellite is used per system. The total number of DD phase and code observations per epoch then equals 2 fGsG + 2 fBsB. We assume for now that cross-correlation between frequencies as well as code and phase is absent. The combined multi-frequency short-baseline GPS+BDS model is then defined as follows.
The system-specific DD phase and code observation vectors are denoted as φ* and p*, respectively, with * = {G, B} where G = GPS and B = BDS. The single-epoch GNSS model of the combined system is given as
(1)
and
(2)
in which
is the combined phase vector,
is the combined code vector,
is the combined integer ambiguity vector,
is the real-valued baseline vector,
is the combined phase random observation noise vector,
is the combined code random observation noise vector, and
D[.] denotes the dispersion operator.
The entries of the baseline design and wavelength matrices are given as
where is the x 1 vector of 1s, is the differencing matrix, is the unit matrix, the geometry-matrices GG and GB contain the undifferenced receiver-satellite unit direction vectors for GPS and BDS, respectively, is the wavelength of frequency , denotes the Kronecker product, and “diag” and “blkdiag” indicate diagonal and block diagonal matrices, respectively. The entries of the positive definite variance matrices are given as
(3)
where , denote the phase and code standard deviation, respectively, and the satellite elevation-angle-dependent weight.
The model in Equation 1 applies to short baselines, and thus the ionospheric and tropospheric delays are assumed absent. The broadcast ephemerides are used to obtain the satellite coordinates. Further, the Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) technique is used to estimate the integer ambiguities a. The observation noise vectors εand e, respectively, are zero-mean vectors, provided that no multipath is present in Equation 1.
EXPERIMENT SETUP
The GNSS receivers we used are depicted in FIGURE 1. Firstly, two low-cost single-frequency receivers were set up to collect L1+B1 GPS+BDS data for two days. These receivers cost a few hundred U.S. dollars. Since the patch antennas we used have been shown to have less effective signal reception and multipath suppression in comparison to survey-grade antennas, the receivers that collected data for two days were additionally connected to such antennas. These antennas have a cost of slightly more than US$1,000 per antenna. To compare the low-cost solution to a survey-grade receiver-solution, two such receivers (which cost several thousand U.S. dollars) were connected to the same survey-grade antennas through splitters and collected L1+L2 GPS data. A detection, identification and adaption procedure was used to eliminate any outliers.
FIGURE 1. Low-cost single-frequency receivers collecting GPS+BDS data for single-baseline RTK, with patch antennas (left) and survey-grade antennas (right) on Jan. 4–6 and Jan. 6–8, 2016, respectively. Survey-grade dual- frequency GPS receivers were connected to the same survey-grade antennas simultaneously to truly track the same GPS constellation.
FIGURE 2 depicts the corresponding redundancy of the two receiver models (that is, the number of observations minus the number of estimated unknowns) together with the number of satellites over 48 hours (30-second epoch interval). The number of BDS satellites (magenta lines) is overall smaller than when compared to GPS (blue lines) in Dunedin. However, Figure 2 also shows that the model strength of L1+B1 GPS+BDS, as measured by its redundancy, is almost similar to that of L1+L2 GPS except for some hours at the middle of the two days. This implies that the two receiver models can potentially give competitive RTK ambiguity resolution and positioning performance. This is however only true if the receiver code and phase observation noise would be of similar magnitude between the receivers used, hence the need for an analysis of the receiver observation precision.
FIGURE 2. Redundancy (left) and number of satellites (right) of L1+B1 GPS+BDS and L1+L2 GPS during Jan. 6–8, 2016, (48 hours) for an elevation cut-off angle of 10°.
In our receiver evaluations, we determined a set of reference ambiguities by using a known baseline and treating them as time-constant parameters over the two days in a dynamic model.
LOW-COST RTK POSITIONING
The code and phase variances were estimated by LS-VCE using data independent from the data used for the following positioning analysis. The variances are needed to formulate a realistic stochastic model, whereas an incorrect stochastic model will deteriorate the ambiguity resolution and consequently the achievable positioning precisions. TABLE 1 depicts the corresponding estimated standard deviations (STDs) used for our positioning models.
TAB LE 1. Zenith-referenced undifferenced code and phase standard deviations estimated by least-squares variance component estimation.
Table 1 shows that the code precision of L1 GPS and B1 BDS improves significantly when the survey-grade antennas are used instead of patch antennas (49 centimeters STD for L1/B1 that decreases to about 30 centimeters), due to their better signal reception and multipath suppression abilities. For testing our stochastic model, we used data that is independent from the data used to estimate the code/phase precision.
Positioning Performance. The single-epoch (instantaneous) RTK positioning results for 24 hours data are shown in FIGURE 3, with ambiguity-float solutions shown at the top and ambiguity-fixed solutions at the bottom. Only the correctly fixed solutions are depicted as determined by comparing the instantaneously estimated ambiguities to the set of reference ambiguities. The 95% empirical and formal confidence ellipses and intervals are shown in green and red, respectively. They were computed from the empirical and formal position variance matrices. The empirical variance matrix was estimated from the positioning errors as obtained from comparing the estimated positions to precise benchmark coordinates. The formal variance matrix used was determined from the mean of all single-epoch formal variance matrices.
FIGURE 3. Horizontal (north (N), east (E)) position scatter and corresponding vertical (U) time series of the float (top) and correctly fixed (bottom) L1+B1 GPS+BDS single-epoch RTK solutions for an elevation cut-off angle of 10°. The 95% empirical and formal confidence ellipses and intervals are shown in green and red, respectively. The 24 hour (30 second) period is 22:00-22:00 UTC Jan. 5-6, 2016, for patch antennas in (a) and 21:48-21:48 UTC Jan. 8-9, 2016, for survey-grade antennas in (b), which are periods independent of the periods used to determine the stochastic model through the code/phase STDs in Table 1.
Figure 3 shows a good fit between the formal and empirical confidence ellipses/intervals, which thus illustrates realistic LS-VCE STDs in Table 1 that were used in the stochastic model. Note also the two-order of magnitude improvement when going from float to fixed solutions, and that the low-cost receiver plus survey-grade antenna has the most precise ambiguity-float positioning solutions.
Ambiguity Resolution and Positioning Performance for Higher Cut-Off Angles. We subsequently investigated the low-cost L1+B1 GPS+BDS performance for high elevation cut-off angles, so as to mimic situations in urban canyon environments or when low-elevation-angle multipath is present and is to be avoided. We have made comparisons to the survey-grade L1+L2 GPS results. It has been shown that a good ambiguity resolution performance does not necessarily imply a good positioning performance, so we investigated what effect this has on our positioning models.
The following integer least-squares (ILS) success rates (SRs) are thus computed based on epochs with the condition of positional dilution of precision (PDOP) ≤ 10 and averaged over all epochs over two days of data. By including and excluding epochs with large PDOPs, we can show how the positioning performance of the different models is affected by poor receiver-satellite geometries. To better understand how this exclusion of epochs with large PDOPs also influenced the empirical ambiguity-correctly-fixed positioning performance, we constructed TABLE 2, which shows the corresponding positioning STDs for two days of data. These STDs were computed by comparing the estimated positions to precise benchmark coordinates. In addition to the positioning performance, we depict in Table 2 the corresponding empirical ILS SR for full ambiguity-resolution, which is given by the ratio of the number of correctly fixed epochs to the total number of epochs.
TABLE 2. Single-epoch empirical STDs (N, E, U) of correctly fixed positions for the three positioning models together with their ILS SR for four elevation cut-off angles and 48 hours of data (Jan. 4–6 and Jan. 6–8, 2016). The empirical STDs and ILS SRs are also shown when conditioned on PDOP ≤ 10.
Table 2 shows that the L1+B1 low-cost receiver plus patch antenna combination has (as expected) smaller SRs in comparison to those when the survey-grade antenna is used. This latter combination has comparable SRs to the (PDOP-conditioned) SRs of the survey-grade L1+L2 GPS receiver for cut-off angles up to 25°.
In support of better understanding Table 2, FIGURE 4 shows typical positioning results for the different receiver and antenna combinations with elevation cut-off angles of 10° (top two rows) and 25° (bottom two rows). The first and third rows show the local horizontal (N, E) positioning scatterplots and the second and fourth rows the vertical (U) time series over two days of data. The float solutions are depicted in gray, and incorrectly and correctly fixed solutions in red and green, respectively. The zoom-in is given to better show the spread of the correctly fixed solutions with millimeter-centimeter level precisions. The formal ambiguity-float STDs are also shown under the up time series to reflect consistency between the empirical and formal positioning results.
FIGURE 4. Horizontal (N, E) scatterplots and vertical (U) time series for L1+B1 low-cost receiver with patch antenna (first column) with 99.5% (89.8%) ILS SR, L1+B1 low-cost receiver with survey-grade antenna (second column) with 100% (97.8%) ILS SR, and survey-grade L1+L2 GPS (third column) with 100% (94.1%) ILS SR, using 10° (top two rows) and 25° (bottom two rows) cut-off angles respectively (Jan. 4–6, 2016, for low-cost receiver with patch antenna and Jan. 7–8, 2016, for the low-cost and survey-grade receivers with survey-grade antennas). The SRs are conditioned on PDOP ≤ 10 and computed based on all epochs. Below the vertical time series, the ADOP is depicted in blue color, the 0.12-cycles level as red, and ambiguity-float vertical formal STDs are shown in gray.
We also depict in Figure 4 the ambiguity dilution of precision (ADOP) as an easy-to-compute scalar diagnostic to measure the intrinsic model strength for successful ambiguity resolution. The ADOP is defined as
(cycles) (4)
with n being the dimension of the ambiguity vector, the ambiguity variance matrix, and |.| denoting the determinant. ADOP gives a good approximation to the average precision of the ambiguities, and it also provides for a good approximation to the ILS SR. The rule-of-thumb is that an ADOP smaller than about 0.12 cycles corresponds to an ambiguity SR larger than 99.9%.
Figure 4 shows that more solutions are incorrectly fixed (red dots) when the ADOPs (blue lines) are larger than the 0.12 cycle level (red dashed lines). The figure also reveals that the L1+B1 low-cost receiver plus patch antenna combination achieves an ILS SR (99.5%) similar to that of the survey-grade L1+L2 GPS receiver (SR of 100%) for the cut-off angle of 10°. This ILS SR corresponds to the availability of correctly fixed solutions (green dots) with millimeter-centimeter level positioning precision over the two days. The L1+L2 GPS receiver has, moreover, large ambiguity-fixed positioning excursions at the same time as the formal STDs are large for the cut-off angle of 25° due the poor GPS-only receiver-satellite geometry for this high cut-off angle. This is also reflected by the corresponding relatively large ambiguity-fixed STDs depicted in Table 2 that are improved from decimeter- to millimeter-level when the PDOP ≤ 10 condition is applied. Figure 4 also shows that the L1+B1 low-cost receiver with the survey-grade antenna has a larger SR of 97.8% when compared to the PDOP-conditioned SR for L1+L2 GPS of 94.1% for the cut-off angle of 25° (see also Table 2), owing to the use of BDS that significantly improves the receiver-satellite geometry.
Finally, we also tested the low-cost receiver-solution (with survey-grade antennas) for a baseline length of 7 kilometers, where (small) residual slant ionospheric delays are present. It was shown that this combination still has the potential to achieve ambiguity resolution and positioning performance competitive with the survey-grade receiver-solution.
CONCLUSIONS
In this article, we evaluated a low-cost L1+B1 GPS+BDS RTK setup and compared its ambiguity resolution and positioning performance to a survey-grade L1+L2 GPS solution in Dunedin, New Zealand. The LS-VCE procedure was used to determine the variances of the low-cost receivers. The estimated variances are needed so as to formulate a realistic stochastic model, otherwise the ambiguity resolution and hence the achievable positioning precisions would deteriorate.
Since we analyzed a short baseline, the LS-VCE variances were shown to likely be affected by multipath. To mitigate multipath we connected the low-cost receivers to survey-grade antennas with better signal reception and multipath suppression abilities. It was shown that the survey-grade antennas can significantly improve the performance for the low-cost receivers so that the code/phase noise estimates more resemble that of survey-grade receivers. The LS-VCE STDs were furthermore shown to be realistically estimated for an independent time period.
We also demonstrated that the low-cost receivers can give competitive instantaneous ambiguity resolution and positioning performance to that of the survey-grade receivers. This is particularly true when the low-cost receivers are connected to survey-grade antennas.
ACKNOWLEDGMENTS
This article is based on the paper “On the Performance of a Low-cost Single-frequency GPS+BDS RTK Positioning Model” presented at the 2017 International Technical Meeting of The Institute of Navigation held Jan. 30-Feb. 1, 2017, in Monterey, California.
Ryan Cambridge at the School of Surveying, University of Otago, collected the low-cost receiver data. Author Peter J.G. Teunissen was supported by an Australian Research Council Federation Fellowship. All of this support is gratefully acknowledged.
MANUFACTURERS
The low-cost receivers used in the research were u-blox EVK-M8T receivers. The survey-grade receivers were Trimble NetRS receivers. The patch antennas were u-blox ANN-MS antennas, while the survey-grade antennas were Trimble Zephyr 2 GNSS antennas.
ROBERT ODOLINSKI conducted his Ph.D. studies at Curtin University, Perth, Australia, from 2011 to 2014. His research focus is next-generation multi-GNSS integer ambiguity resolution enabled precise positioning. In 2015, Odolinski started his position as a lecturer/research fellow in geodesy/GNSS at the School of Surveying, University of Otago, New Zealand.
PETER J.G. TEUNISSEN is a professor of geodesy and navigation and the head of the Curtin GNSS Research Centre, Curtin University. He is also with the Department of Geoscience and Remote Sensing, Delft University of Technology, Delft, The Netherlands. His research interests include multiple GNSS and the modeling of next-generation GNSS for high-precision positioning, navigation and timing applications.
FURTHER READING
• Authors’ Conference Paper
“On the Performance of a Low-cost Single-frequency GPS+BDS RTK Positioning Model” by R. Odolinski and P.J.G. Teunissen in Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, Jan. 30 – 1 Feb., 2017, pp. 745–753.
• Authors’ Related Work
“Single-Frequency, Dual-GNSS Versus Dual-frequency, Single-GNSS: A Low-cost and High-grade Receivers GPS-BDS RTK Analysis” by R. Odolinski and P.J.G. Teunissen in Journal of Geodesy, Vol. 90, No. 11, 2016, pp. 1255–1278, doi:10.1007/s00190-016-0921-x.
“Combined BDS, Galileo, QZSS and GPS Single-frequency RTK” by R. Odolinski, P.J.G. Teunissen and D. Odijk in GPS Solutions, Vol. 19, No. 1, 2015, pp. 151–163, doi:10.1007/s10291-014-0376-6.
“Instantaneous BeiDou+GPS RTK Positioning With High Cut-off Elevation Angles” by P.J.G. Teunissen, R. Odolinski and D. Odijk in Journal of Geodesy, Vol. 88, No. 4, 2014, pp. 335–350, doi: 10.1007/s00190-013-0686-4.
“The Future of Single-Frequency Integer Ambiguity Resolution” by S. Verhagen, P.J.G. Teunissen and D. Odijk in Proceedings of the VII Hotine-Marussi Symposium on Mathematical Geodesy, Rome, June 6–10, 2009, edited by N. Sneeuw, P. Novák, M. Crespi and F. Sanso, International Association of Geodesy Symposia, Vol. 137, 2012, pp. 33–38, doi:10.1007/978-3-642-22078-4 5.
“Centimeter-Level Positioning for UAVs and Other Mass-Market Applications” by C. Mongredien, J.-P. Doyen, M. Strom and D. Ammann in Proceedings of ION GNSS+ 2016, the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, Sept. 12–16, 2016, pp. 1441–1454.
“Initial Assessment of the COMPASS/BeiDou-2 Regional Navigation Satellite System” by O. Montenbruck, A. Hauschild, P. Steigenberger, U. Hugentobler, P.J.G. Teunissen and S. Nakamura in GPS Solutions, Vol. 17, No. 2, 2013, pp. 211–222, doi:10.1007/s10291-012-0272-x.
• LAMBDA
“On the Reliability of Integer Ambiguity Resolution” by S. Verhagen in Navigation, Vol. 52, No. 2, Summer 2005, pp. 99–110, doi: 10.1002/j.2161-4296.2005.tb01736.x.
“ADOP in Closed Form for a Hierarchy of Multi-frequency Single-baseline GNSS Models” by D. Odijk and P.J.G. Teunissen in Journal of Geodesy, Vol. 82, 2008, pp. 473–492, doi: 10.1007/s00190-007-0197-2.
By Christopher Ball, 412th Test Wing Public Affairs
What happens when GPS isn’t available?
A collection of U.S. Department of Defense units and universities found out when they gathered at Edwards Air Force Base, California, to evaluate various aerial platforms in a degraded GPS environment this summer.
The week-long test event called DT NAVFEST — short for Developmental Test Navigation Festival — was the first large-scale program of its kind, according to James Cook, KC-46A project manager with the 418th Flight Test Squadron.
“DT NAVFEST was established to provide a locally more realistic GPS jamming environment in which aircraft platforms and unmanned aerial vehicles could evaluate their performance under a degraded GPS signal,” Cook said. “Other locations around the U.S. provide such environments, but having it locally allowed for direct program input and cost savings to customers by not having to deal with the logistics costs of deploying to those locations.”
Cole Johnson, technical lead for NAVFEST, explained how they create a degraded GPS environment.
“GPS signals are super faint,” he said. “Imagine a 30-watt lightbulb 12,000 miles in space. So it doesn’t take much interference for your smartphone’s GPS to lose lock on such a low power signal. Interference could occur from walking in a dense forest, through a canyon, inside a building, driving among skyscrapers, or from GPS jammers. The end effects of GPS jammers aren’t much different than the other causes of interference, they all make it harder for your GPS receiver to pick out faint GPS signals from the air, except jammers do it by adding noise to the environment.”
Teams from the University of Illinois Champagne Urbana and Stanford University were invited to the first-ever DT NAVFEST at Edwards Air Force Base to test their projects in a GPS degraded environment. (Photo: U.S. Air Force/Wei Lee)
The GPS jammers and support came from the 746th Test Squadron at Holloman Air Force Base, New Mexico.
According to Wei Lee, test safety engineer with the 412th Test Wing, the universities were invited to participate in DT NAVFEST on a trial basis with the hope of expanding to other institutions in the future.
“Live GPS jamming data is extremely difficult for academic labs to obtain due to the complexity of working with the Federal Aviation Administration and regional first responders,” Lee said. “It is crucial that the Department of Defense support basic research and development that is ongoing in our nation’s top academic institutions. Many of the low technology readiness level projects will eventually migrate from academic labs to defense industry and military applications. Allowing the labs to participate on a non-interference basis is a win-win situation.”
To minimize the effect on the local community and air traffic, planning of the GPS jamming was initiated months in advance. According to Johnson, the GPS jammers had a vertical reach of upwards of 30,000 feet, so the first step was contacting the FAA, which provided a list of “green” times when commercial air traffic was at its lowest. This led to the testing being performed between 1 and 6 a.m. on test days.
Johnson said the team performed extensive modeling and simulation to identify how far the GPS interference would reach. “Not just at 30,000 feet, but ground level as well.”
The models suggested a small part of the Antelope Valley — a couple of small towns around Edwards — could be affected. “We wanted to err on the side of caution, so we constructed a huge list of emergency services from the Antelope Valley to contact.”
The team also set up phone lines the FAA and any emergency service could call up during testing and request the jammers to be turned off.
The 746th Test Squadron from Holloman Air Force Base, New Mexico, provided an array of GPS jamming equipment and support for DT NAVFEST at Edwards Air Force Base. The jammers provided a degraded GPS environment for testing multiple aerial platforms throughout the week. Testing was done from 1 to 6 a.m. each day to minimize impact on the community and civilian air traffic. (Photo: U.S. Air Force/Cole Johnson)
Cook said the event was extremely successful, judging by the feedback from the customers.
“For a first-of-its-kind event, it executed fairly smoothly, thanks to the test team and customers’ direct involvement,” he said. “The technical knowledge and support from the 746th TS was awesome. And the support given to this program from 412th Test Wing all the way down to the Airman on the ground providing direct support.”
Arianespace will launch four new satellites for the Galileo constellation, using two Ariane 62 versions of the next-generation Ariane 6 rocket from the Guiana Space Center in French Guiana.
The Ariane 62 rocket. (Image: Arianespace)
The contract will be conducted by the European Space Agency (ESA) on behalf of the European Commission (DG Growth) and the European Union.
This is the first ESA first contract to use the company’s new rocket.
Stéphane Israël, Arianespace chief executive officer, and Paul Verhoef, director of Navigation at the European Space Agency (ESA), signed the launch contract for four new satellites to join the European satellite navigation system Galileo. The contract will be conducted by ESA on behalf of the European Commission (DG Growth).
These launches are planned between the end of 2020 and mid-2021, using two Ariane 62 launchers — the configuration of Europe’s new-generation launch vehicle that is best suited for the targeted orbit. The contract also provides for the possibility of using the Soyuz launch vehicle from the Guiana Space Center, if needed.
Both missions will carry a pair of Galileo spacecraft to continue the constellation deployment for Europe’s satellite-based navigation system. The satellites, each weighing approximately 750 kg, will be placed in medium earth orbit (MEO) at an altitude of 23,222 kilometers and be part of the Galileo satellite navigation constellation.
An ESA video about Ariane 6 is below:
Galileo is the first joint infrastructure financed by the European Union, which also will be the owner. The Galileo system incorporates innovative technologies developed in Europe for the greater benefit of citizens worldwide.
A total of 18 Galileo satellites already are in orbit. Fourteen of these satellites were launched two at a time by Soyuz launchers, with the last four orbited on a single Ariane 5 ES mission in November 2016. Two more Ariane 5 ES missions are planned on December 12, 2017 and in the summer of 2018.
Following the signing of this latest contract, Stéphane Israël, CEO of Arianespace, issued this statement:
“Arianespace is especially proud to have won this first launch contract for the Ariane 6 from its loyal customers and partners, the European Commission (DG Growth) and ESA. We are very pleased to have earned this expression of trust from the European Commission; by choosing to continue the deployment of the Galileo constellation with two Ariane 62 launches, they become the first confirmed customer for our next-generation heavy launcher, which is slated to make its initial flight in the summer of 2020. Through this decision, which adds two additional launches to follow the already-scheduled Ariane 5 ES flights, the European Commission and ESA are clearly indicating a key commitment to Arianespace’s next generation of launchers, which reaffirms more than ever its mission to ensure Europe’s autonomous access to space.”
The second satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has started transmitting navigation signals. QZS-2, or Michibiki-2, was launched on June 1, 2017, and joins its predecessor QZS-1 (Michibiki-1), which has been in orbit since September 2010.
Both satellites have been placed into inclined geosynchronous, elliptical orbits, which enable extended satellite visibility periods over Japan and are characteristic features for this regional navigation system.
The third satellite QZS-3 was launched on Aug. 19, 2017, into a geostationary orbit. If all goes according to plan, a fourth satellite in an eccentric orbit will follow by the end of this year and complete the constellation.
Three of six new Lockheed Martin-developed receivers are now deployed at U.S. Air Force monitoring stations to maintain the accuracy of GPS satellite signals.
In June, the first Monitor Station Technology Improvement Capability (MSTIC) receiver became operational at Cape Canaveral Air Force Station, Florida. Upgrades continued at USAF monitoring stations at Kwajalein Atoll and Hawaii. These upgrades from early 1990s technology are part of an overall effort to modernize the current GPS ground control system, known as the Architecture Evolution Plan Operational Control Segment.
MSTIC software-defined radio technology replaces legacy receivers’ hardware-based application-specific integrated circuit platform. MSTIC leverages commercial off-the-shelf hardware without the need for custom firmware. Standard interfaces and architecture configurability simplify sustainment and enable MSTIC software to migrate to new hardware platforms as commercial vendors increase processing power, improve reliability and enhance cybersecurity. MSTIC enables remote application of mission-specific software updates to improve performance and enable reception of modernized GPS signals, according to the company.
The three remaining GPS Monitoring Stations will be upgraded with MSTIC receivers by the end of 2017.
The navigation payload before integration into the second GPS III SV, which now is in environmental testing. (Photo: Harris)
GPS III Payloads Delivered
Harris Corporation has delivered the third of 10 advanced navigation payloads to Lockheed Martin. The payloads will increase accuracy, signal power and jamming resistance for GPS III satellites. They feature a Mission Data Unit (MDU) with a 70-percent digital design that links atomic clocks, radiation-hardened computers and powerful transmitters, enabling signals three times more accurate than those on current GPS satellites. The new payloads also boost satellite signal power, increase jamming resistance by eight times and help extend the satellite’s lifespan.
The payload was integrated into GPS III SV03 over the summer. The first navigation payload is integrated aboard GPS III SV01, which is in storage awaiting expected 2018 launch.
Harris announced it is in full production and on target to deliver the fourth GPS III navigation payload to Lockheed Martin in fall. Harris is also developing a fully digital MDU for the U.S. Air Force’s GPS III Space Vehicles 11+ acquisition. The new MDU will be demonstrated in fall 2017 and provides even greater flexibility, affordability and accuracy versus existing GPS satellites.
Next GLONASS-M Readied
The Russian navigation satellite GLONASS-M 52 moved from ISS-Reshetnev Company’s assembly plant to the Plesetsk Cosmodrome launch site about 800 km north of Moscow in August. One of the system’s ground spares, it was built more than two years ago and stored awaiting launch. The satellite is due to launch in September.
There are six GLONASS-M satellites in ground reserve.
Esri has published a Hurricane Irma Resource Catalog in advance of the Category 4 hurricane cutting through the Caribbean islands on its path toward Florida.
The catalog features read-to-use applications compiled by the Esri Disaster Response Program (EDRP). EDRP is an around-the-clock service that helps with monitoring events online, discovering useful content, augmenting software and obtaining assistance from Esri experts.
To see the track of the hurricane, Esri provides its hurricane map.
Resources include:
Hurricane Public Information Map (PIM)
Hurricane Impact Summary
Hurricane Force Wind Impact Summary
Storm Surge and Flooding
Storm Surge Inundation
Hurricane Evacuation Zones
Waze Alerts – Hurricane Irma
Florida 511 – Real-Time Traffic Information
Hurricane Irma Photo Story Map
Airport and Port Status
NOAA Real-Time Coastal Observations
Florida Division of Emergency Management Open Data
Waze alerts light up Florida highways as people evacuate. (Image: Esri)
Hurricane Harvey is the first major catastrophe in which drones have been used on a large scale by both government and commercial operators, said Ken Long, an analyst at the Freedonia Group.
UAVs are also likely to find widespread use if Hurricane Irma either directly strikes or skirts the east coast of Florida early next week, as current projections show.
In addition to helping keep emergency workers safe by allowing them to look for people trapped by floodwaters and inspect damage in high-risk areas, drone use can speed up the recovery process. Drones can be flown over structures such as fuel tanks, power lines and railroad tracks before they can be reached by land, enabling government agencies and utilities to identify what is in most urgent need of repair.
They also allow insurance adjusters to more quickly process claims, enabling rebuilding efforts to get underway faster. Farmers Insurance reports that an insurance inspector using a drone can complete up to eight times the number of home inspections each day than he or she otherwise would be able to do.
When Hurricane Harvey first made landfall in Texas on Aug. 25, the Federal Aviation Administration (FAA) set up a temporary but extensive no-fly zone over Houston and nearby areas to help protect first responders in helicopters and other manned aircraft. This flight ban included all drone operations except those specifically approved by the FAA.
https://youtu.be/XRdUV4WqnDE
In the 10 days that followed Hurricane Harvey, the FAA issued more than 100 separate authorizations for drone use in the Houston area, according to the Wall Street Journal. Some of the applications for drone use were reviewed and approved by the FAA within hours, an unusually fast turnaround time for an agency that typically takes days or weeks to make decisions.
With the exception of a handful of flights conducted by media firms, all of the approved operations were for drones used in conjunction with, or on behalf of, government agencies. Drones were used to inspect bridges, roadways and power lines; assess the condition of oil refineries and water plants; and survey coastal damage.
As the flood waters continued to recede and flight restrictions were eased or lifted, insurance companies — including Allstate, Farmers Insurance, Travelers and USAA — began to use drones to assess property damage and speed claims processing.
However, drone use by insurance companies and other commercial users is limited by FAA rules that do not allow them to be flown above 400 feet, outside the visual line of sight of the operator, or above people not directly involved in their operation, unless a waiver is granted.
These regulations could change with a 2018 FAA reauthorization bill being considered by Congress.
“The demonstrated usefulness of drones in Hurricane Harvey response and recovery efforts could well influence the content of that legislation,” Long said.
Even if the current FAA regulations remain in place, U.S. commercial drone demand will expand rapidly from what is currently an extremely small market base, according to the Freedonia Group’s Drones (UAVs) study. “Non-military government use of drones will also climb at a robust rate through 2020,” Long said.
Both commercial and non-military government market gains will be fueled by further improvements in drone designs, making them more capable and easier to operate, customized for use in specific applications and cost-saving.
Taoglas has launched a range of small-form-factor ultra-wideband (UWB) antennas specifically designed to enable centimeter-level positioning and angle-of-arrival applications.
The FXUWB10, UWC.01 and UWCCP.01 ultra-wideband antennas by Taoglas.
Applications include asset tracking, follow-me drones, healthcare monitoring, smart home services and other applications that demand high-performance indoor localization capabilities, the company said.
The antennas offer high efficiencies across a wide spectrum of frequency bands, from 3 GHz to 10 GHz.
Indoor wireless positioning has long been hampered by technologies that were not designed for this purpose, such as Bluetooth, Wi-Fi and assisted GPS.
Ultra-Wideband. UWB is a low-power digital wireless technology that offers significant increases in location precision and range while transmitting large amounts of digital data short distances over a wide spectrum of frequency bands. UWB’s low-power requirements offer increased battery life of sensors and tags, leading to reduction in overall operational costs.
Taoglas’ range of UWB antennas, designed in Taoglas’ Munich, Germany, engineering center, features both state-of-the-art flexible embedded UWB antennas and UWB embedded SMT chip antennas. According to the company, the flexible FXUWB range of antennas were developed utilizing a “peel and stick” assembly process, attaching securely to non-metal surfaces via 3M adhesive with a flexible micro-coaxial cable mounting.
The UWB chip antennas are designed to be surface mounted directly onto a printed circuit board (PCB). Both series of antennas help designers future-proof devices, keeping costs low while covering all common UWB commercial bands.
“Today’s emerging applications require very precise indoor localization of assets, objects and people,” said Ronan Quinlan, co-CEO for Taoglas. “UWB can work as a type of ‘indoor GPS’ to help solve the precision dilemma for indoor applications, bringing much greater levels of precision than current technologies. We optimize complex antenna performance parameters such as the Group Delay, Polarization and Fidelity Factor. Taoglas’ first-to-market line of UWB antennas are designed to help our customers capitalize on this need for real-time precision localization.”
Autonomous Antenna. One antenna that Taoglas co-developed exclusively with DecaWave is the UWCCP.01 circularly polarized chip antenna, a mass-market antenna specifically designed to enable a new generation of autonomous applications.
The DecaWave DW1000 chip.
The UWB antennas were designed for use with the DecaWave DW1000 chip and are also compatible with any other UWB sensor modules on the market, the company added. Since its launch in December 2013, more than 3.5 million units of the DW1000 have shipped across multiple industries.
From real-time location of people and assets in factories, hospitals and mines, to automotive keyless entry systems, to drones, connected home and sports, the accurate location and secure communications capability of the DW1000 has already taken numerous applications to new heights.
“Antennas play a key role in our customers’ applications. Performance is a given for customers but the capability to adapt to the constraints of the applications — size, shape, electronics environment — is equally important as end products get smaller and smaller,” said Ciaran Connell, CEO and co-founder, DecaWave. “DecaWave is really pleased to partner with Taoglas, as their expertise is not only in delivering high-performance, off-the-shelf antennas, but also to provide customization services that will be highly beneficial to our customers.”
Tallysman, a manufacturer of high-performance GNSS antennas and related products, has released two high-gain (50dB) GNSS antennas: the TW3152 and TW3752.
High-gain GNSS antennas are useful in situations where long cable runs are required, such as in timing systems and GNSS re-radiator systems, the company said.
The TW3152 provides reception of GPS L1. The TW3752 provides reception of GPS L1, GLONASS G1, BeiDou B1 and Galileo E1 signals. Both antennas employ Tallysman’s Accutenna technology, which provides a high degree of multipath signal rejection through the full bandwidth of the antenna.
According to Tallysman, the antennas are triple filtered to prevent the saturation of the front-end LNA by strong near frequency and harmonic signals, which are a growing concern throughout the world.
These antennas are available with a choice of radome shape (flat or conical), color of radome (white or grey), as well as a wide variety of connectors.
The second Lockheed Martin GPS III satellite completes a test simulating a strenuous launch environment.
The launch is the most strenuous part of a satellite’s life. To survive the extreme sound wave pressure and pounding vibrations generated by more than 700,000 pounds of thundering rocket thrust, spacecraft need a solid, reliable design if they hope to arrive operational on orbit.
On July 13, Lockheed Martin’s second, fully assembled GPS III space vehicle (SV) completed a realistic simulation of its future launch experience and passed this critical acoustic environmental test with flying colors, the company said.
During acoustic testing, GPS III SV02 was blasted with deafening sound reaching 140 decibels in a specialized test chamber equipped with high-powered horns. (Photo: Lockheed Martin)
During acoustic testing, the GPS III SV02 satellite was continuously blasted with sound reaching 140 decibels in a specialized test chamber equipped with high-powered horns. For comparison, that is about as loud as an aircraft carrier deck and human hearing starts to be damaged back at about 85 decibels, the company said. The test uses sound loud enough to literally shake loose anything not properly attached.
“With this launch-simulation test, we are talking about sophisticated, advanced satellite technology and electronics enduring tremendous forces and then working flawlessly afterward,” said Mark Stewart, Lockheed Martin’s vice president for Navigation Systems. “Passing this test with GPS III SV02 further validates the robustness of our GPS III design. We credit this success and risk-retirement to all the pathfinding work we accomplished early in the program.”
The GPS III SV02 satellite is part of the U.S. Air Force’s next generation of GPS satellites and will bring critical new capabilities to the warfighter. GPS III will have three times better accuracy and up to eight times improved anti-jamming capabilities.
Spacecraft life will extend to 15 years, 25 percent longer than the newest GPS satellites on-orbit today. GPS III’s new L1C civil signal also will make it the first GPS satellite to be interoperable with other international global navigation satellite systems.
GPS III SV02 is Lockheed Martin’s second GPS III satellite to successfully complete acoustic testing. The company’s first satellite, GPS III SV01 — which is in storage awaiting its expected 2018 launch — completed acoustic testing in 2015.
The GPS III SV02 satellite is now being prepared for Thermal Vacuum (TVAC) testing this fall, where it will be subjected to extreme cold and heat in zero atmosphere, simulating its on-orbit life. The satellite is expected to be delivered complete to the Air Force in early 2018.
GPS III SV02 is the second of 10 GPS III satellites Lockheed Martin is contracted for and is assembling in full production at the company’s GPS III Processing Facility near Denver. The $128 million, state-of-the-art manufacturing factory includes a specialized cleanroom and testing chambers designed to streamline satellite production.
Lockheed Martin’s GPS III satellite design includes a flexible, modular architecture that allows for the insertion of new technology as it becomes available in the future or if the Air Force’s mission needs change. Satellites based off this design are already proven compatible with both the Air Force’s next generation Operational Control System (OCX) and the existing GPS constellation.
Facebook’s Open Cellular group is developing a cost-effective, software-defined, wireless-access platform to improve connectivity in remote areas of the world, the company said.
The TW2643POC employs Tallysman’s Accutenna technology in a magnet mount, passive right-hand circularly polarized antenna for the reception of all of the GNSS constellations (GPS L1/GLONASS G1/ Galileo E1/ BeiDou B1) plus Iridum: 1559 to 1626.5 MHz frequency band.
According to Tallysman, it is certified and specially designed to maximize the performance of Iridium Voice and Data Modems plus the upper GNSS band (1559–1606 MHz).
The TW2643POC is housed in an IP67 compliant housing and is REACH and RoHS compliant.
Enclosed in its protective container, Galileo Full Operational Capability (FOC) Flight Model 21 (FM21) is seen departing ESA’s ESTEC Test Centre on Aug. 24. Photos courtesy of the European Space Agency
News from the European Space Agency
The last of 22 Galileo satellites has departed the European Space Agency’s (ESA) Test Centre in the Netherlands. This concludes the single longest and largest scale test campaign in the establishment’s history, ESA said.
Cocooned in a protective container for its journey — equipped with air conditioning, temperature control and shock absorbers — the final Galileo satellite left the establishment by lorry on Aug. 24.
ESA’s Test Centre at ESTEC in Noordwijk, the Netherlands, houses a collection of test equipment to simulate all aspects of spaceflight. It is operated for ESA by private company European Test Services (ETS) B.V.
In May 2013, the Test Centre began testing the first of 22 Galileo “Full Operational Capability” (FOC) satellites, having previously performed the same function for the very first Galileo “In-Orbit Validation” satellite under a separate contract.
Pictured is a Galileo Full Operational Capability satellite being removed from the Phenix thermal vacuum chamber after a fortnight-long “hot and cold” vacuum test.
The Galileo FOC satellites had their platforms built by OHB System AG in Germany, incorporating navigation payloads coming from Surrey Satellite Technology Ltd. in the United Kingdom. They then traveled on to ESTEC to be subjected to the equivalent vibration, acoustic noise, vacuum and temperature extremes that they will experience for real during their launch and orbit, plus testing of their radio systems.
With a steady stream of satellites coming off the production line, the challenge for the combined ETS and OHB team overseeing Galileo testing was to put them through all necessary tests on a rapid and efficient basis, while also keeping the Test Centre accessible to other European missions requiring its unique services.
A total of 14 FOC satellites have since joined the first four IOV satellites in orbit, forming an 18-strong constellation that began Initial Services to global users on Dec. 15, 2016. The next four FOC satellites are scheduled for launch on an Ariane on Dec. 5.
Europe’s Galileo navigation satellites orbit 23 222 km above Earth to provide positioning, navigation and timing information all across the globe.
“For the first time in more than four years, there are no Galileo satellites in the Test Centre, but hopefully this will not be the end of our association with the programme,” said Jörg Selle, managing director for ETS. “The contract for making the next eight Galileo satellites — known as Batch 3 — was also awarded to OHB last June, and ETS will be bidding for the contract to test these satellites too.”
“The availability of the ETS facilities in ESTEC have substantially contributed to the programme,” said Paul Verhoef, ESA director of the Galileo Programme and navigation-related activities. “We thank ETS for their professionalism and support over this extended period.”
The final Galileo travelled back to OHB in Germany for some final refurbishment ahead of its launch together with another three satellites in December.
