Fugro has been awarded six contracts by the National Maritime Safety Authority (NMSA) of Papua New Guinea. The hydrographic survey packages are expected to contribute to capacity development in the country, which has more than 5,000 kilometers of coastline.
The surveys will be conducted using a combination of Fugro’s Airborne Lidar Bathymetry (ALB) and multi-beam echo sounder (MBES) sensors, and a seamless dataset will be delivered to the NMSA.
“As a pioneer of ALB development, Fugro has a solid track record in applying this advanced technology for mapping shallow water environments safely and cost- effectively,” said Paul Seaton, Fugro’s regional business development manager for Asia Pacific.
The surveys in deeper waters will be performed by vessel, and Fugro will also conduct a comprehensive tides campaign throughout the survey area.
The contracts are part of the Asian Development Bank-funded Maritime Waterways Safety Project that aims to improve the safety and efficiency of the country’s international and national shipping in coastal areas and waterways. By improving the maritime environment and making coastal shipping safer, the project will facilitate travel, trade and tourism for rural communities.
Fugro has also begun a hydrographic survey encompassing an area of Norwegian waters of 15,000 square kilometers. The contract was awarded by the Norwegian Hydrographic Service and has a value of 34.5 million NOK (approximately €3.8 million).
The survey is part of the MAREANO program, for which Fugro has successfully completed a number of surveys since 2006. The Norwegian program maps depth and topography, sediment composition, contaminants, biotopes and habitats. It takes place in the Barents Sea with various areas located above the 78th parallel and typical water depths ranging from 80 to 3,500 meters.
SATELLITES. I have been fascinated by them ever since I was a child. My interest in satellites and space in general led me on my career path, which began with an undergraduate degree in physics at the University of Waterloo. Although it was an applied physics program and I did work terms at Atomic Energy of Canada, I was more interested in astronomy than nuclear physics and took all the astronomy courses I could. That, in turn, led me to pursue a Ph.D. in experimental space science doing research in the application of very long baseline (radio) interferometry (VLBI) to geodesy. As a postdoctoral fellow at MIT, I worked on ranging data from the U.S. and Soviet laser reflectors placed on the surface of Earth’s natural satellite — the moon.
I continued my interest in VLBI and lunar laser ranging for a while after I arrived at the University of New Brunswick in 1981 but I quickly got involved with satellite Doppler positioning and that was when I heard my first satellite signals through the speaker of a Canadian Marconi CMA-722B Doppler receiver. At that time, Doppler positioning was being quickly supplanted by GPS and so my interest naturally migrated to the new system. GPS and the other global navigation satellite systems have been a consuming interest ever since.
That interest includes helping to develop techniques for precision positioning and navigation — ones that minimize as much as possible the effect of various sources of error that plague GPS measurements. One such technique is precise point positioning or PPP, which uses primarily precise carrier-phase measurements along with an accurate model of those measurements to obtain position accuracies down to the centimeter level.
Although often carried out with recorded data, PPP with real-time GPS orbit and clock correction streams has become an established technique for land, air and sea applications. However, the use of real-time corrections for precise positioning of satellites has not been attempted yet although a number of low-Earth-orbit (LEO) satellite missions could benefit from such a capability. Future satellites with altimeter and radio-occultation payloads may require real-time precise-orbit determination to enable onboard processing of science data for forecasting or now-casting of meteorology data, open-loop instrument operation of radar payloads, or quick-look onboard science data generation. Precise real-time orbit information could also be used for maintaining the formations of closely-spaced satellite constellations.
In this month’s column, our authors discuss the results of realistic simulations they have carried out to precisely position a LEO satellite using a source of real-time GPS corrections actually transmitted by a network of geostationary satellites. Even accounting for data outages, 3D positioning accuracies better than a decimeter have been obtained. Precision on board? Not right now but likely coming real soon.
Precise point positioning (PPP) with real-time orbit and clock correction streams has become an established technique over the past decade. Several free as well as commercial sources of precise correction streams are available through the internet or via a satellite link to geostationary satellites.
Many applications exist for land, air and sea applications, but use of real-time corrections for precise positioning has not extended into orbit yet, although a number of low Earth orbit (LEO) satellite missions have a demand for precise orbit determination (POD). Mission requirements often allow for a relatively high latency for the availability of the precise orbit products, thus ground-based, near-real-time processing is sufficient. However, future satellites with altimeter and radio-occultation payloads may require real-time POD to enable onboard processing of science data for short-term forecasting or now-casting of meteorology data, open-loop instrument operations of radar payloads, or quick-look onboard science data generation. Also, precise real-time orbit information may be used for constellation maintenance of satellite formations. Despite early technology readiness demonstrations by the Jet Propulsion Laboratory carried out one decade ago to transmit real-time corrections via geostationary relay satellites to LEO spacecraft, this technique has so far not been implemented and used in a space mission.
POD accuracy of a few decimeters or less with real-time corrections has been demonstrated repeatedly by various groups. For these studies, it was assumed that the required real-time precise orbit and clock products are continuously available on board the LEO satellite. Even though a network of several distributed geostationary Earth orbit (GEO) relay satellites may achieve seamless coverage in the equatorial region, gaps at high latitude close to the North and South Poles may occur. The extent of these gaps depends on the gain pattern of the transmitting antenna of the GEO relay satellite. Likewise, the availability of corrections depends on the LEO orbit characteristics, the gain pattern and mounting of the receiving antenna and the attitude profile of the LEO satellite. Most Earth observation and altimeter missions are launched into polar orbits to achieve global coverage. Up-to-date real-time corrections may therefore not be available for POD processing over the polar regions, which are typically also affected by reduced GNSS satellite visibility. As a result, the positioning performance will be degraded during this part of the orbit.
To study the effects of interrupted availability of precise correction data, we simulated real-time POD using real flight data of the Swarm-C satellite, a representative LEO satellite orbiting Earth at an altitude of about 440 kilometers in a polar orbit with approximately 87° inclination. The satellite was launched into orbit in Nov. 2013 and is part of a three-satellite constellation of identical spacecraft with the mission objective to study Earth’s magnetic field and the electric field in the atmosphere (see FIGURE 1). The orbital period is 93 minutes. The satellite is equipped with a dual-frequency GPS receiver and two zenith-pointing POD antennas. The receiver provides dual-frequency GPS observations of up to eight satellites simultaneously. For the analysis, we selected a test data period of Feb. 1–15, 2016.
FIGURE 1. Close-up view of the Swarm-C satellite with Swarm-A and -B in the background (artist’s impression). The satellites’ booms point in the anti-flight direction. Two GPS antennas are located on the top side of each satellite’s structure (Credit: ESA-AOES-Medialab).
We processed the GPS observations using a high-performance navigation filter together with precise real-time orbit and clock corrections provided by Fugro, a Dutch multi-national company that provides a multi-GNSS real-time PPP service tailored for maritime applications. The complete processing emulates real-time onboard POD and only uses information available up to the current epoch being processed. This information includes GNSS observations and ephemerides as well as satellite attitude information and predicted Earth orientation parameters.
We assessed POD accuracy by comparing the results of the real-time POD filter to a reference orbit, which was generated with a least-squares reduced-dynamics POD and precise post-processed GPS orbit and clock products. Correction data gaps over the polar regions were realistically simulated. During such gaps, an onboard POD filter cannot use the most recent corrections and may have to use outdated orbit and clock correction information for several minutes. We investigated the impact of outages of different durations on the positioning accuracy.
REAL-TIME ORBIT AND CLOCK PRODUCT
Fugro’s G4 reference station network consists of 45 geodetic receivers distributed worldwide, which deliver real-time multi-constellation GNSS observations and ephemerides to the processing centers located in Norway and Germany. Precise orbit and clocks are then computed in real time for all constellations and broadcast to the users via seven L-band geostationary satellites. GNSS orbits are computed using a batch process with hourly updates, and clocks are estimated at a 1-Hz rate in real time. G4 supports GPS, GLONASS and BeiDou. Galileo corrections will be made available to customers as soon as Galileo enters initial operational capability. The broadcast coverage ensures that the majority of users can receive corrections simultaneously through two independent satellite beams, thus ensuring redundancy and increased availability for critical operations at sea (see FIGURE 2).
FIGURE 2. Fugro’s G4 global GNSS station network for real-time orbit and clock generation. Colored dots at the equator show the positions of the geostationary relay satellites. Colored circles indicate the GEO access areas.
Additionally, uncalibrated phase delays (UPDs) for GPS are also estimated and broadcast in real time, which allows integer carrier-phase ambiguity resolution for PPP users requiring higher levels of accuracy. Typical real-time GPS orbit accuracy is 3–4 centimeters root-mean-square (rms) when compared with International GNSS Service final products. GPS clock accuracy is generally better than 0.1 nanoseconds (standard deviation). The accuracy of these products guarantees that end-user position accuracy is a few centimeters in real time. One of the objectives of our study is to determine whether the same level of accuracy can be achieved for real-time LEO POD.
ONBOARD NAVIGATION FOR LEO POD
The precise real-time orbit- and clock-products are used in a Kalman-filter-based real-time navigation algorithm, which has been developed for use in onboard navigation systems for LEO satellites. The algorithm is capable of processing single- or dual-frequency measurements and can be used with pseudoranges only or with both pseudorange and carrier-phase measurements. In the configuration used for this study, the filter processes dual-frequency pseudorange and carrier-phase GPS observations. The state vector comprises 12 + n states: satellite position and velocity vectors, receiver time offset, scaling coefficients for atmospheric drag and solar radiation pressure, empirical accelerations in radial-, along- and cross-track directions, and n carrier-phase ambiguities, one for each satellite tracked. The prediction model of the satellite’s trajectory considers accelerations due to Earth’s gravity field, luni-solar perturbations, drag, solar-radiation pressure, thrust and empirical accelerations.
Although the data is processed post facto in this study, the algorithm emulates a true real-time process by only using past and current observations in the data cleaning and quality control. Furthermore, the limited resources of a satellite onboard processor are taken into account by using only a reduced gravity field model of 70 × 70 terms and fixed Earth-orientation parameters. When processing dual-frequency pseudorange and carrier-phase measurements, typical 3D rms positioning errors are about 50 centimeters with GPS broadcast ephemerides and approximately 10 centimeters with precise orbit and clock products. The algorithm has flight heritage through the use in the Phoenix eXtended Navigation System (XNS) on board the PROBA2 PRoject for OnBoard Autonomy satellite.
The results of the real-time navigation algorithm were compared against reference orbit solutions generated with a precise reduced-dynamics POD, which is based on a least-squares fit using the final orbit products of the Center for Orbit Determination in Europe (CODE). Independent validation through satellite-laser-ranging measurements suggests an accuracy of the reference solution of a few centimeters.
POD WITH CORRECTIONS
For the precise real-time POD analysis, the navigation filter uses orbit and clock corrections together with GPS broadcast data. To assess the best possible real-time POD performance, the GPS observations from Swarm-C are processed with continuously available corrections. To take into account the latency in the clock correction generation process, the corrections are processed in the filter with an assumed delay of 10 seconds. The results for the 3D orbit errors are shown in FIGURE 3.
FIGURE 3. 3D orbit errors of the real-time navigation filter with continuous precise orbit and clock corrections based on Fugro’s products. The errors are plotted over argument of latitude u, where the northern-most point on the orbit corresponds to u = +90° and the southern-most point is u = −90°. 3D rms orbit errors are 6.8 centimeters.
The position errors of the two weeks of data are plotted vs. argument of latitude u, which is the sum of a satellite’s true anomaly and argument of perigee. As a result, the equator crossings of the satellite correspond to u = 0° and u = 180°. As the satellite proceeds along its orbit, it moves from left to right through the plot. The northern-most point on the orbit is reached at u = +90°, the southern-most point is u = −90°. The results show that a 3D rms LEO orbit accuracy of 6.8 centimeters can be achieved with the Fugro real-time orbits and clocks.
In addition, orbit and clock corrections are also generated based on the precise final orbits and clocks from CODE, which are used for the generation of the reference orbit solution. These corrections are also processed in the real-time navigation filter with the same settings as Fugro’s product. Comparison to the reference solution yields 3D rms orbit errors of 6.0 centimeters. This result demonstrates that the use of the real-time orbits and clocks only leads to a small degradation in the orbit accuracy compared to the use of post-processed GPS products.
EFFECTS OF CORRECTION DATA GAPS
The analysis in the previous section has shown that the use of real-time corrections enables high orbit accuracy when the corrections are continuously available. However, in an on-orbit scenario, the demodulator, which keeps track of GEO satellites and delivers corrections to the navigation filter, may not be able to track them continuously for various reasons. Even though dedicated GEO satellite networks for space-borne applications, like NASA’s Tracking and Data Relay Satellite System (TDRSS) or the European Data Relay Satellite (EDRS) system, potentially offer a seamless service volume for LEO users anywhere on the globe, this may not be feasible with a GEO network originally intended for ground-based users. These satellites typically have a more focused beam, which potentially hinders reliable data transmission in polar regions. This situation is depicted in FIGURE 4, which shows the approximate access areas of the GEO satellite network used to transmit Fugro’s corrections. It also depicts the ground track of two orbital revolutions of the Swarm-C satellite, which leaves the access areas at latitudes beyond approximately 80° N/S.
FIGURE 4. Coverage area of the GEO satellite network for orbit- and clock-correction dissemination (colored circles) and Swarm-C satellite ground track (black). Dotted lines indicate the assumed coverage area limits at 66° N/S and 75° N/S.
Even if the beamwidth of a GEO satellite’s antenna allows for a continuous link at high latitudes, the receiving satellite demodulator on board the LEO spacecraft will have to switch signal reception to another GEO satellite when the tracked satellite drops out of the field of view. These switches typically happen in polar regions. The acquisition of the new GEO signal is not a trivial task, as it is done under unfavorable conditions at the edge of the service area and requires, for example, correct prediction of the expected Doppler shift due to relative motion the GEO and LEO satellites. Thus, interruptions in the correction data streams are likely to occur and the extent of these interruptions depends on how the switching mechanism is implemented in the demodulator and how fast the acquisition of the new GEO satellite’s signal takes place.
It is worth mentioning in this context that GEO signal reception depends not only on the transmitting antenna gain pattern, but also on the gain pattern of the receiving antenna on the LEO satellite, the antenna placement on the satellite structure as well as its attitude profile. Experience has shown that satellite design constraints may prevent the antenna from being placed in the most favorable position. Operational constraints can force the satellite not to be oriented in the preferred way for GNSS and GEO signal reception. Instead, priority must often be given to the optimal orientation of body-fixed solar panels for maximum power generation or the pointing of payload sensors, such as optical instruments, to certain target directions.
To study the impact of correction data outage on the LEO POD, we defined reduced-coverage areas. The first scenario limits the reception of correction data beyond latitudes of 66° N/S. In the case of Swarm-C at approximately 440-kilometers altitude, the outage intervals over the North and South Poles extend to 13 minutes at maximum. In the second case, the corrections are received up to 75° N/S, which corresponds to a maximum outage of 8 minutes, twice per orbit. The smaller coverage area serves as a worst-case scenario, whereas the larger service area is more representative of the expected on-orbit performance.
Prediction of Orbit- and Clock-Corrections. When up-to-date corrections are no longer available due to an outage in the GEO satellite link, the last received set of corrections must be extrapolated. Up to a certain prediction interval, this method still provides more precise orbit and clock information than the broadcast ephemerides and thus yields better positioning results. The prediction of orbit and clock information is therefore crucial to bridge correction outages and still maintain a precise positioning solution. The following analysis assesses the errors introduced by only extrapolating the orbit and clock corrections. In addition to these errors, the modeling of the observations is also affected by the absolute errors in the real-time orbit and clock product.
The satellite clock offsets are estimated based on predicted orbits. Therefore, the radial, along-track and cross-track components of the orbit corrections can be computed so that prediction errors over a predefined time interval are minimized. Taking advantage of this, the prediction errors are typically less than 1 centimeter even for extrapolation times of 12 minutes and therefore have negligible effect on the POD.
In the case of the satellite clock offset, corrections are only available up to the present epoch. Thus, the extrapolation is done based on a fit through the past hour of data.
The results for the rms clock extrapolation errors over interpolation intervals of 0–15 minutes are displayed in FIGURE 5.
FIGURE 5. Clock extrapolation errors (rms) for different GPS block types for a linear clock extrapolation polynomial fitted through one hour of data. The results reflect the GPS constellation on Feb. 1, 2016. The largest errors are obtained for the two Block-IIF satellites SVN 38 (PRN 08) and SVN 65 (PRN 24) operated on cesium clocks (light-blue diamonds) and the rubidium clock of Block IIR-A satellite SVN 45 (PRN 21) (red diamonds).
The errors have been computed for clock data of Feb. 1, 2016, for each GPS satellite independently and are color-coded depending on the satellite type. It becomes obvious that the newest generation of Block IIF satellites with their rubidium atomic clocks yield the smallest extrapolation errors. After 15 minutes, the most stable clock has an rms error of approximately 0.10 nanoseconds and the least stable Block IIF rubidium clock does not exceed extrapolation errors of 0.15 nanoseconds. It is interesting to note that two Block IIF satellites are operated on cesium atomic clocks, which are significantly less stable than the rubidium ones. Their maximum rms clock extrapolation error (plotted in light blue) amounts to approximately 0.45 nanoseconds and 0.60 nanoseconds at the longest time interval of 15 minutes. The satellites of the GPS Block IIR (both the earlier IIR-As and the later IIR-Bs, which have a different transmitting antenna panel) and the IIR-M generations are equipped with less stable atomic clocks, which exhibit extrapolation errors of 0.15–0.25 nanoseconds. The Block IIR-A satellite SVN 45 plotted in red exhibits a clearly reduced stability, possibly an indication of degraded performance of its operational rubidium clock. The clock extrapolation error amounts to 0.40 nanoseconds at 15 minutes.
POD with Real-Time Correction Data Gaps. For the simulation of GEO-link outages in the real-time POD, the navigation filter starts extrapolating the orbit and clock corrections when the LEO satellite exceeds the latitude threshold. The 3D rms orbit errors are shown in FIGURE 6.
FIGURE 6. 3D orbit errors of real-time navigation filter results plotted over argument of latitude u, where the northern-most and southern-most point on the orbit correspond to u = +90° and u = −90°, respectively. Corrections are available between 66° S and 66° N (Figure 6a) and 75° S and 75° N (Figure 6b). The orange color indicates outage periods of the GEO-link when extrapolated corrections are used. 3D rms errors are 8.5 centimeters (Figure 6a) and 7.5 centimeters (Figure 6b).FIGURE 6. 3D orbit errors of real-time navigation filter results plotted over argument of latitude u, where the northern-most and southern-most point on the orbit correspond to u = +90° and u = −90°, respectively. Corrections are available between 66° S and 66° N (Figure 6a) and 75° S and 75° N (Figure 6b). The orange color indicates outage periods of the GEO-link when extrapolated corrections are used. 3D rms errors are 8.5 centimeters (Figure 6a) and 7.5 centimeters (Figure 6b).
The top plot depicts the conservative threshold of 66° N/S and the bottom plot refers to the threshold of 75° N/S. The orange color marks the time periods during which the corrections are extrapolated. It becomes obvious that the position solution degrades for increasing extrapolation intervals. In the case of the conservative latitude threshold, the maximum 3D position error is 38 centimeters and the rms error is 8.5 centimeters. For the latitude threshold of 75° N/S, the maximum error reduces to 33 centimeters and the rms to 7.5 centimeters. The plot also shows that the largest orbit errors typically do not appear at the end of the extrapolation interval, but shortly afterwards. The reason for this effect is that the systematic extrapolation errors in the clock corrections cause the filter state to diverge. When up-to-date corrections become available again, the filter requires a certain time to recover and converge back.
The degradation of the orbit accuracy is not only affected by the errors due to the clock extrapolation alone; the reduced GPS satellite visibility and unfavorable geometry over the North and South Poles also has an impact on the orbit determination performance. The resulting higher dilution of precision or DOP further amplifies the errors in the modeling of the GPS clock offset. Also, with only eight tracking channels available, the onboard receiver cannot track all visible satellites, leading to reduced measurement redundancy. Additional degradation of orbit accuracy is also caused when observations of GPS satellites are rejected in the data screening process due to the errors introduced by the extrapolation of corrections. Nevertheless, even for the conservative latitude thresholds for orbit and clock corrections, a 3D rms POD accuracy of less than 10 centimeters can be achieved with sufficient margin. This is an important result, since sub-decimeter POD accuracy is a key mission requirement for many space missions, such as radio occultation satellites.
To assess the effects of the absolute orbit and clock errors in the real-time orbit and clock product on the POD, we repeated the same processing procedure with corrections generated based on the CODE final products. In this case, the POD with the conservative latitude threshold of 66° N/S yields 7.2 centimeter 3D rms orbit errors, and the threshold of 75° N/S leads to 3D rms errors of 6.5 centimeters. These results confirm that the use of the real-time product leads to only a small degradation of the POD performance. The results for the orbit determination with continuous and limited availability of corrections are summarized in TABLE 1. In addition, a real-time POD with uncorrected broadcast ephemerides (BCEs) yields an accuracy of 36.4 centimeters.
Table 1. Overview of 3D rms orbit errors (in centimeters) for real-time POD based on different orbit and clock products and different latitude limits for the availability of precise corrections. The age of data (AoD) indicates the extrapolation interval of the corrections.
SUMMARY AND CONCLUSIONS
Onboard orbit determination simulations for the Swarm-C satellite with real-world flight data and precise real-time orbit and clock products from Fugro have achieved sub-decimeter 3D rms orbit errors. When the GPS orbit and clock corrections are continuously available, 6.8 centimeters 3D rms can be achieved. With conservative assumptions for correction data gaps at latitudes beyond 66° N/S, the 3D rms errors are still just 8.5 centimeters. This result fulfills the accuracy requirements of, for example, radio occultation missions with sufficient margin. This is an important result, as it allows us to shift the POD process from the ground into the spacecraft for future missions and thus provide a precise orbit solution without delay, with possible implications for onboard processing of science data, now-casting of meteorology data, or open-loop instrument operation of radar payloads.
Even though a small degradation of the POD accuracy is noticeable in the case of correction data gaps, the dissemination of precise orbit and clock corrections for LEO users is a competitive approach to a global centimeter-level augmentation service using high-rate data channels in the navigation signal itself. This service is presently only offered by the Quasi-Zenith Satellite System (QZSS) on the Michibiki L-band Experiment (LEX) signal and is limited to regional users.
The extrapolation error of the GPS satellite clock corrections has been identified as the main contributor to the error budget. The introduction of additional precise atomic clocks into the GPS constellation in the course of the GPS Block III deployment or the use of the Galileo satellites with their ultra-stable passive hydrogen masers in a multi-GNSS POD promise further improvements. Also, the use of Fugro’s uncalibrated phase delays to fix integer ambiguities in the POD would also lead to improved orbit results.
Having demonstrated the overall fitness of the concept, the development of an onboard real-time POD demonstrator will be the next step. This hardware unit requires a space-enabled dual-frequency GNSS receiver with a geodetic choke-ring antenna, an onboard processing unit for the navigation filter, and a demodulator unit with a suitable antenna, to receive and demodulate the corrections and provide them for the use in the POD.
ACKNOWLEDGMENTS
This article is based on the paper “Precise Onboard Orbit Determination for LEO Satellites with Real-Time Orbit and Clock Corrections” presented at ION GNSS+ 2016, the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation, held Sept. 12–16, 2016, in Portland, Oregon.
The European Space Agency is acknowledged for the provision of Swarm-C GPS measurements. The Center for Orbit Determination in Europe is acknowledged for providing their precise GPS orbit and 5-second high-rate clock products for the POD reference solution.
ANDRÉ HAUSCHILD is a member of the scientific staff of the GNSS Technology and Navigation Group at DLR’s German Space Operations Center (GSOC), Oberpfaffenhofen, near Munich.
JAVIER TEGEDOR works as a GNSS scientist for Fugro Satellite Positioning AS in Oslo, Norway, focusing on the enhancement of Fugro’s high-accuracy positioning services and solutions.
OLIVER MONTENBRUCK is head of the GNSS Technology and Navigation Group at DLR/GSOC.
HANS VISSER works for Fugro-Intersite BV in the Netherlands monitoring the Fugro network.
MARKUS MARKGRAF is a senior research engineer in the GNSS Technology and Navigation Group at DLR/GSOC.
FURTHER READING
Authors’ Conference Paper
“Precise Onboard Orbit Determination for LEO Satellites with Real-Time Orbit and Clock Corrections” by A. Hauschild, J. Tegedor, O. Montenbruck, H. Visser and M. Markgraf 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. 3715–3723.
Earlier Work in On-Orbit High-Accuracy Positioning
“Real-time Clock Estimation for Precise Orbit Determination of LEO-Satellites” by A. Hauschild and O. Montenbruck in Proceedings of ION GNSS 2008, the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation, Savannah, Georgia, Sept. 16–19, 2008, pp. 581–589.
“Autonomous and Precise Navigation of the PROBA-2 Spacecraft” by O. Montenbruck, M. Markgraf, J. Naudet, S. Santandrea, K. Gantois and P. Vuilleumier in Proceedings of AIAA/AAS Astrodynamics Specialist Conference and Exhibit, Honolulu, Hawaii, Aug. 18–21, 2008, paper AIAA 2008-7086, doi: 10.2514/6.2008-7086.
“Extremely Accurate On-Orbit Position Accuracy Using NASA’s Tracking and Data Relay Satellite System (TDRSS)” by M. Toral, F. Stocklin, Y. Bar-Server, L. Young, and J. Rush in Proceedings of the 24th AIAA International Communications Satellite Systems Conference, San Diego, California, June 11–14, 2006, doi: 10.2514/6.2006-5312.
“Toward Decimeter-Level Real-Time Orbit Determination: A Demonstration Using the SAC-C and CHAMP Spacecraft” by A. Reichert, T. Meehan and T. Munson in Proceedings of ION GPS 2002, the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation, Portland, Oregon, Sept. 24–27, 2002, pp. 1996–2003.
Real-Time Precise Orbit Determination
“Integer Ambiguity Resolution on Undifferenced GPS Phase Measurements and Its Application to PPP and Satellite Precise Orbit Determination” by D. Laurichesse, F. Mercier, J.-P. Berthias, P. Broca and L. Cerri in Navigation, Journal of The Institute of Navigation, Vol. 56, No.2, Summer 2009, pp. 135–149.
Swarm Constellation GPS Receiver
“Precise Science Orbits for the Swarm Satellite Constellation” by J. van den IJssel, J. Encarnação, E. Doornbos and P. Visser in Advances in Space Research, Vol. 56, No. 6, September 2015, pp. 1042–1055, doi: 10.1016/j.asr.2015.06.002.
High-Performance Navigation Filter
“Precision Real-time Navigation of LEO Satellites Using Global Positioning System Measurements” by O. Montenbruck and P. Ramos-Bosch in GPS Solutions, Vol. 12, No. 3, 2008, pp. 187–198, doi: 10.1007/s10291-007-0080-x.
“(Near-)real-time Orbit Determination for GNSS Radio Occultation Processing” by O. Montenbruck, A. Hauschild, Y. Andres, A. von Engeln and C. Marquardt in GPS Solutions, Vol. 17, No. 2, April 2013, pp. 199–209, doi: 10.1007/s10291-012-0271-y.
Fugro Precise Real-Time Orbit and Clock Corrections
“The New G4 Service: Multi-Constellation Precise Point Positioning Including GPS, GLONASS, Galileo and BeiDou” by J. Tegedor, D. Lapucha, O. Ørpen, E. Vigen, T. Melgård and R. Strandli in Proceedings of ION GNSS+ 2015, the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation, Tampa, Florida, Sept. 14–18, 2015, pp. 1089–1095.
Fugro’s laser airborne depth sounder (LADS) technology is being deployed in New Zealand to assist in relief efforts following the damaging 7.9 magnitude earthquake near Christchurch on Nov. 14.
At the request of the New Zealand Government, the Royal Australian Navy LADS flight is to conduct a rapid hydrographic survey of the seafloor in the coastal margins of the north east coast of the South Island.
“We will fly over the area and collect hydrographic survey data, which will reveal what has happened below the waterline, and identify any shifts in the ocean floor which mariners need to be aware of,” explained Flight Lieutenant Commander Susanna Hung, who is serving as the mission’s commanding officer.
The navy’s airborne lidar bathymetry (ALB) system has been developed by Fugro for safe, high speed and cost effective surveys of shallow coastal areas. Under a long-term contract to the RAN, Fugro provides the LADS technology, a de Havilland Dash 8-202 aircraft and support services.
Fugro’s LADS technology is being deployed following the Nov. 14 New Zealand earthquake.
The airborne survey equipment is operated by navy personnel from the main cabin of the aircraft to rapidly collect high resolution data of the seafloor. Fugro’s system incorporates sophisticated sensors that utilize a high-powered laser, innovative scanner and receiver optics technology.
The survey tool complements traditional hydrographic survey methods (such as hull-mounted multibeam echo sounders) to support nautical charting and coastal zone management applications in the nearshore/shallow water environment. The speed of deployment and safe operating capability make it an ideal solution to confirm the safety of navigation and locate new hazards such as is now required in the earthquake affected area.
“The New Zealand deployment by RAN LADS is an excellent example of how our innovative technology can assist in the safety of navigation and management of the marine environment,” said Paul Seaton, Fugro’s regional business development manager.
Fugro has been awarded a five-year survey contract by the United States Army Corps of Engineers (USACE). Task orders under this indefinite delivery, indefinite quantity (IDIQ) type contract will support architect and engineering survey and mapping support services for the military, civil and federal agencies of the corps team, Mobile District.
Using a variety of airborne sensors and systems, including topographic lidar, bathymetric lidar, digital cameras and multispectral/hyperspectral imagers, Fugro will provide integrated data collection and processing in support of the USACE’S National Coastal Mapping Program.
Other services within the scope of the contract include photogrammetry, vessel based hydrographic surveying, topographic and boundary surveying, conventional and GNSS surveying, terrestrial and mobile lidar scanning and geographic information system (GIS) development and production.
Fugro has been awarded a supply arrangement by the Canadian Hydrographic Service (CHS) to provide vessel-based hydrographic survey services. Under the contract, CHS will procure hydrographic surveys as needed, anywhere in Canada, to enhance its capacity for data acquisition and processing in support of its nautical charting program.
Hydrographic survey data from ports, harbors, nearshore and offshore regions will be acquired and processed using Fugro’s vessels, equipment and personnel. The resulting data will be used by CHS to update its nautical charts.
The supply arrangement, together with a supply arrangement for airborne lidar bathymetry (ALB) awarded in 2013, will enable Fugro to support Canada in its plans to implement an integrated multi-platform methodology to hydrographic surveying anywhere in Canada, including the Arctic region.
Fugro provides International Hydrographic Organization (IHO) compliant survey services to numerous governments throughout the world.
ROCIS is an airborne system for mapping surface current conditions over a wide area of ocean for current-sensitive offshore operations.
Fugro and technology partner Areté Associates have successfully delivered near real-time, synoptic, surface current data to characterize Loop Current and Loop Current eddy conditions in the U.S. Gulf of Mexico during a period of intense current conditions.
Over the course of the five-month program, Fugro used the new ROCIS (Remote Ocean Current Imaging System) to survey currents over a distance of more than 125,000 kilometers — the equivalent of 3 times around the world.
ROCIS is the first commercially available system of its kind and represents a step change in technology for mapping surface current conditions over a wide area of ocean for current sensitive offshore operations.
Optimizing recent advances in remote sensing and aerial survey, Fugro and Areté Associates developed a system that uses a combination of digital camera technology and highly accurate positioning systems, together with advanced algorithms, to derive surface currents from wave spectra measurements. It can be installed on a suitable survey aircraft, together with an inertial navigation system augmented by Fugro’s Starfix satellite positioning system.
Current data are reviewed in real time on board the aircraft, providing continuous assessment of data quality and the location of strong currents. Within an hour of the aircraft landing the system produces a “quick-look” map of the currents over the area while processed data files are available a few hours later.
During the program, ROCIS data supported day-to-day operational planning and enhanced the accuracy of 3D hydrodynamic current forecast modeling.
The key technical benefits of ROCIS are the near synoptic, wide area, high resolution, high integrity surface current measurements that allow sub-mesoscale circulation to be measured and monitored. During a four-hour flight, the system can survey ocean currents at 250-meter intervals over a track of 900-1,100 kilometers. To map currents over a similar distance using traditional methods would take a combination of four vessels 24 hours. Given sufficient daylight hours, two ROCIS flight missions can be conducted each day.
ROCIS services can be provided to single or multiple clients to monitor offshore current conditions over specific locations or a broad area. The system can also provide support in emergency situations such as oil spill and search and rescue, as well as in oceanographic research programs.
Fugro and Areté Associates are working on further development of the ROCIS system and services, including the use of expendable probes and the incorporation of additional airborne sensors. In 2016 Fugro will add a second ROCIS unit to further enhance its support of offshore operations.
Mahon Bay, Nova Scotia, Canada, is one of the many sites that Fugro will survey this winter.
Fugro has been awarded new task orders by the Canadian Hydrographic Service (CHS) to conduct airborne lidar bathymetry (ALB) surveys in Eastern and Central Canada, Fugro announced in a news release on Dec. 15. The task orders, which have been issued under a supply arrangement Fugro holds with the CHS, are in support of their nautical charting programs and involve the survey of multiple sites along the coasts of Quebec, Newfoundland and Labrador, Prince Edward Island, Nova Scotia and Central Canada.
Fugro’s ALB systems will be used to acquire hydrographic survey data and seabed imagery in shallow coastal waters, where the acquisition of similar information by traditional vessel-based acoustic methods is inefficient, expensive and unsafe. The data will fill gaps in shallow water and junction with existing deeper water data that have been acquired previously by CHS vessels. All data will be acquired to International Hydrographic Organization (IHO) Order 1B, an international standard for conducting hydrographic surveys, and will ultimately be used to update CHS’s nautical charts.
Fugro provides ALB products and services worldwide to public and private sector clients as a rapid and cost-effective solution to nearshore hydrographic survey needs where scale of the project, time constraints and user safety are of primary concern.
Fugro has been awarded a three-year contract by PGS for the provision of precise satellite positioning systems for its seismic vessel fleet. PGS is a leading global provider of marine seismic and electromagnetic services, data acquisition, imaging, reservoir services and multi-client library data.
Fugro, provider of precise satellite positioning to the offshore oil and gas industry, will supply PGS vessels with a number of independent GNSS. These systems include Fugro’s recently launched Starfix.G4 — a commercial GNSS service to utilize all available GNSS systems (GPS, GLONASS, Galileo and BeiDou), giving sub-decimeter accuracy — and Starfix.G2+, a global service offering centimeter accuracy in both position and height.
In addition to precise vessel positioning, PGS will benefit from a new generation of positioning technology for their seismic sources and tailbuoys. Meeting the high demand for robustness and quality in the offshore industry, this proactive technology provides independent decimeter and centimeter positions and heights for remote (seismic source and tailbuoy) operations.
Cerys James, vice president technical at PGS, remarked, ”Reliable, precise positioning technology is essential for modern seismic operations. The solution supplied by Fugro will ensure our entire fleet has highly accurate vessel positioning, along with precise source and streamer positioning.”
Fugro has extended its integrated survey services to help improve efficiency in coastal management and enable more informed decision-making. A new agreement with global specialist EOMAP enables the creation of integrated bathymetric survey products that comprise elements from Satellite Derived Bathymetry (SDB), Airborne LiDAR Bathymetry (ALB) and traditional acoustic survey technologies. The integrated data and product solutions will provide clients with outstanding value and unmatched coverage, Fugro said.
“Teaming with EOMAP augments our considerable survey and satellite imagery capabilities and will allow a timely and cost-effective nearshore bathymetry review facility for clients whose own bathymetric holdings are either very old or very sparse — or both,” said Don Ventura, hydrographic business development manager at Fugro. “This service will help coastal zone management and engineering teams, environmental scientists and hydrographic agencies to focus on their immediate needs and to make more informed decisions on subsequent, efficient data acquisition and management.”
EOMAP’s robust technology platform can process satellite images and deliver global bathymetric and benthic habitat data over the full range of temporal and spatial resolutions through its proprietary, sensor-independent Modular Inversion Processor (MIP). This both complements and augments services already provided by Fugro, to provide even more spatial data solutions to suit a wide variety of budgets and purposes.
“We are very pleased to provide our Satellite Derived Bathymetric products and services to Fugro,” said Matthew Bergin, Vice President of Business Development at EOMAP. “We believe that this agreement will create a unique, one-stop technology resource to meet the demanding requirements of both commercial and government customers.”
Fugro has been awarded a contract by subsea contractor DeepOcean for the provision of precise satellite positioning for its fleet.
The contract is valid for three years and also includes the new vessels in DeepOcean’s expanding fleet. The DeepOcean fleet will be equipped with hardware and software developed by Fugro, providing independent positioning solutions on each vessel.
Under the contract, Fugro will supply DeepOcean with three independent decimeter-level satellite navigation systems. Also part of the contract delivery are Fugro’s Starfix.G2+ system, which has a 3D accuracy approaching that of GNSS RTK systems, and Fugro’s Starfix.G4 satellite correction service.
Starfix.G2 is a GPS and GLONASS positioning system based on orbit and clock corrections generated from Fugro’s own expanded network of dual system reference stations. Starfix.G2 is a precise point positioning (PPP) technology, which distinguishes itself from the traditional differential approach as satellite errors are not lumped together but estimated per source, per satellite. The GPS/GLONASS orbit and clock corrections are computed separately, free of ionospheric and tropospheric effects.
Starfix.G4 is a GPS, GLONASS, Galileo and BeiDou positioning system based on orbit and clock corrections generated from Fugro’s network of reference stations. Like Starfix.G2, Starfix.G4 also uses PPP technology. The GPS/GLONASS/Galileo/BeiDou orbit and clock corrections are computed separately, free of ionospheric and tropospheric effects.
DeepOcean is an integrated provider of services and technologies for the subsea industry, including offshore services for oil and gas, offshore renewables and electrical power transmission industries, with offices in Norway, UK, Holland, Brazil, Mexico and Singapore.
Fugro has commissioned an additional airborne laser bathymetry system to underpin its position in the development and application of bathymetric LiDAR technology. The combined Fugro LADS Mk 3 and Riegl VQ-820-G systems provide seamless measurements and mapping of nearshore and shallow water environments. The increased capability will enable Fugro to deliver simultaneous topographic and bathymetric surveys in multiple geographical areas.
With high power and frequency, the combined systems achieve superior coverage that minimizes gaps and outperforms lower energy alternatives and single-sensor systems in all conditions, particularly in difficult environments, Fugro said. They are highly adaptable and small enough to be installed in a variety of light aircraft.
With continued operations across the Middle East during 2015, Fugro will also begin a South West Pacific ALB survey campaign following the award of projects in multiple locations to support nautical charting, coastal engineering, scientific assessments, coastal management, benthic habitat mapping and climate change initiatives.
Since 2012, Fugro has operated simultaneous topographic and bathymetric LiDAR systems in France, Japan, New Zealand and the Middle East. Successful results from Japanese coastal areas include returns from the Fugro LADS Mk3 sensor to 50 meters while recent surveys in Saudi Arabia had even more impressive results, with 65-meter depth returns. The deep water returns combined with high-density shallow water and near coastal returns result in a seamless dataset from ridge to deep reef.
Fugro has introduced its high-accuracy G2+ service, designed to benefit offshore operators around the globe who require positioning and measurement accuracy at centimeter level.
G2+ is an enhancement of Fugro’s G2 service (based on GPS and GLONASS). The service uses highly advanced GNSS augmentation algorithms developed in house. The code and carrier-phase signals transmitted by GPS and GLONASS satellites are monitored globally by Fugro’s worldwide network of reference stations.
These observations are processed centrally in real-time using the company’s proprietary algorithms to generate precise corrections which are used to augment the standard signals broadcast by GPS and GLONASS satellites.
Customers receive corrections via seven high-powered communications satellites, providing at least two independent G2+ data sources. The new satellite positioning service will be particularly beneficial when seeking to measure latitude, longitude, elevation and speed with high accuracy in real-time, Fugro said.
Applications include offshore construction, survey services, vessel monitoring and structural monitoring. The ultra-high accuracy enables the real-time correction of tidal changes — which impact the accuracy of seabed mapping — as well as the real-time monitoring of the motion of floating and fixed structures.
The 3D accuracies of the system approach those of GNSS RTK (real-time kinematic) systems while avoiding the need for an RTK base station or local transmission link, overcoming the logistical challenges and range limitations associated with coastal RTK systems, Fugro said.
The launch of G2+ follows the recent launch of Fugro’s G4 satellite correction service, which takes advantage of all four global navigation satellite systems: GPS, GLONASS, BeiDou and Galileo.
