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One-Centimeter Orbits in Near-Real Time: The GPS experience on OSTM/Jason-2 4

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One-Centimeter Orbits in Near-Real Time: The GPS experience on OSTM/Jason-2 4

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Abstract

The advances in Precise Orbit Determination (POD) over the past three decades have been driven in large measure by the increasing demands of satellite altimetry missions. Since the launch of Seasat in 1978, both tracking-system technologies and orbit modeling capabilities have evolved considerably. The latest in a series of precise (TOPEX-class) altimeter missions is the Ocean Surface Topography Mission (OSTM, also Jason-2). GPS-based orbit solutions for this mission are accurate to 1-cm (radial RMS) within three to five hours of real time. These GPS-based orbit products provide the basis for a near-real time sea-surface height product that supports increasingly diverse applications of operational oceanography and climate forecasting.

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... There are 2 levels of GPS solutions for space based radio arrays. One is to have Real Time Gipsy (RTGx) running on all of the spacecraft, this gives an approximate location to within 22 ns that is good enough to synchronize the taking of data between the duty cycles of all the spacecraft [37]. ...
... These projected separations are important, and will be used later in the pipeline to simulate the synthetic beam of the array.Using models of the GNSS sidelobes and expected signal strengths at the SunRISE altitude, we generate a set of (3-D) position and timing uncertainties for each S/C. These values were given by the GNSS-Inferred Positioning System and Orbit Analysis Simulation Software package (GipsyX)[37]. This software has been successfully leveraged for many Low Earth Orbiting missions such as Jason-1, Jason-2/OSTM, and GRACE. ...
Thesis
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... The used GPS receiver is a BlackJack receiver built by Spectrum Astro Inc. It features 16 dual frequency channels and is connected to a patch antenna with choke rings (Haines et al., 2011), shown inA secondary mission goal is to provide observations for a real time forecasting system of ionospheric irregularities. The system will be used to forecast possible navigation or communication outages for United States military forces (de La Beaujardière, 2004).To accomplish the scientific objectives the satellite is equipped with six different sensors to study the Earth's ionosphere. ...
Thesis
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Chapter
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Chapter
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recision orbit determination (OD) methodologies have evolved over the past 50 years through research by astrodynamics specialists from industry, university, and government organizations. Refinements have included improvements in mod- eling techniques from analysis of satellite tracking data over a wide range of orbits. Methods have been developed to evaluate force models and the enhancement of model fidelity using a variety of geodetic-quality satellites placed into orbit since the early days of the space program and continuing today. This article provides an over- view of OD methodologies and their evolution as well as a brief description of modern OD and estimation methods that are being used routinely in the 21st century by the astrodynamics community. The subject matter should also be useful reading for the nonspecialist.
Article
The U.S./French Jason-1 oceanographic mission is carrying state-of-the-art radiometric tracking systems (GPS and DORIS) to support precise orbit determination (POD) requirements. The performance of the systems is strongly reflected in the early POD results. Results of both internal and external (e.g., satellite laser ranging) comparisons indicate that the root-mean-square (RMS) radial accuracy is in the range of 1–2 cm. This paper reviews the POD strategy underlying these orbits, as well as the challenging issues that bear on the understanding and characterization of an orbit solution at the 1 cm level. It also describes a GPS-based system for producing science-quality orbits in near real time to support emerging applications in operational oceanography.
Article
The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1–2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone.
Article
To achieve maximum benefit from the altimetric data collected by the French-aAmerican TOPEX/POSEIDON spacecraft, radial orbit accuracy of 10 cm or better is required. This unprecedented requirement led the French Space Agency Centre National d'Etudes Spatiales (CNES) to develop a new high-accuracy tracking system, Doppler orbitography and radiopositioning integrated by satellite (DORIS), and a new precision orbit production facility, the Service d'Orbitographie DORIS. A global effort produced new models and a new orbit determination strategies. The result of these efforts has been assessed after 1 year of operation. The original goal has clearly been met, and the TOPEX/POSEIDON orbits produced by NASA and CNES agree beter than the 5 cm root mean square (RMS) level in the radial direction. At this level of accuracy, traditional techniques cannot correctly describe the actual orbit error, and some new procedures are proposed.
Article
The TOPEX/POSEIDON (T/P) altimeter satellite has recently become an integral part of NOAA's operational satellite system for monitori ng the oceans. The transformation was achieved through the joint efforts of NOAA, JPL, and NAVOCEANO. Since late 1996, this team has produced accurate T/P sea level observations with a delay of only two daysófast enough to be included in NOAA's weekly ocean model run. Operational assimilation began in March 1997. The T/P data improve both the ocean initial conditions and the sea surface temperature forecast s with lead times of up to 6 months.
Article
Until now, TOPEX/Poseidon precise orbits were needed only for the production of Geophysical Data Record files, and thus were not required until about 5 weeks after data acquisition. Recent developments in operational oceanography now require the rapid delivery of precise altimeter data within days, and possibly hours, of data acquisition. The processing of the altimeter measurements can be accomplished according to this schedule, and the only difficulty rests with the production of the precise orbit ephemerides. The long delay involved in the current production scheme results from the necessity to collect laser tracking data from ground stations and also from the need to wait for the final and most accurate values of the solar activity and Earth orientation parameters. A reduction in the orbit production delay forces the processing to deal with DORIS data only and with predicted values for the parameters. In addition, this reduces the amount of validation that can be performed before delivery. Fortunately, the spatial and temporal coverage of the DORIS tracking system is such that the DORIS data by itself is sufficient to produce a precise orbit. Also, predictions of solar activity and Earth orientation parameters have improved considerably over the last few years, so that using them instead of actual data does not significantly degrade the orbit accuracy. Using this strategy, DORIS orbits have been computed on a daily basis within 24 to 48 hours of data acquisition. And since the beginning of October 1997, these orbits have been included on the Posëdon Interim Geophysical Data Record files for all cycles when this altimeter is on. Evaluations of these daily orbits reveal that their radial accuracy is very close to that of the standard precise orbits ephemerides.
Article
The Jason-1 altimeter satellite and its follow-on mission Jason-2/OSTM were launched in December 2001 and June 2008, respectively, to provide the scientific community with a high-accuracy continuous record of observations of the ocean surface topography. Both missions carry on board three state-of-the-art tracking systems (DORIS, GPS, SLR) to meet the requirement of better-than-1.5 cm radial accuracy for the operational orbit included in the geophysical data record (GDR) product.This article outlines the common set of models and processing techniques applied to both Jason reprocessed and operational orbits included in version C of the GDR, referred to as GDR-C standards for precision orbit determination (POD), and describes the systematic components of the radial error budget that are of most interest for the altimeter data analysts. The nonsystematic component of the error budget, quantified by intercomparison of orbits using similar models or with reduced dependency on the dynamic models, is generally at or below 7 mm RMS (root-mean-square). In particular, the average daily RMS of the radial difference between the JPL and CNES reduced-dynamic orbits on Jason-2 is below 6 mm. Concerning the dynamic models employed, the principal contributors to residual systematic differences appear to be the time varying gravity and solar radiation pressure, resulting in geographically correlated periodic signals that have amplitudes at the few-mm level. Concerning the drifts of the orbits along the North/South direction, all solutions agree to better than the 1 mm/year level.
Article
We assess the accuracy of JPL's estimated OSTM/Jason-2 Global Positioning System (GPS)-determined orbits based on residuals to independent satellite laser ranging (SLR) data, compared with orbits produced by different software from different data (SLR/DORIS), Geophysical Data Record version C (GDR-C) orbits, and altimeter crossover tests. All of these tests are consistent with sub-cm radial accuracy: high elevation SLR residual standard deviation lies at 6.8 mm, RMS differences from GDR-C in the radial component typically fall below a cm, and altimeter crossovers from JPL orbits have a variance 89 mm smaller than altimeter crossovers from GDR-C orbits. Although RMS differences between radial components of different orbit solutions typically lie below a cm, we observe systematic dependences on both time and geography.The improved precision and accuracy of JPL's OSTM/Jason-2 orbit solutions rely on a new algorithm for applying constraints to integer carrier phase ambiguities. This algorithm is sufficiently robust to improve solutions despite half-cycle carrier phase identification issues in OSTM/Jason-2's BlackJack receiver. Although Jason-1 receiver performance differs, our algorithm should extend to Jason-1 processing (during the time span of nominal GPS receiver operations).
Article
Plans are presented for flying a Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system on SPOT platforms. DORIS is designed for precise orbit positioning for use as part of the Topex/Poseidon payload. The measurement precision of DORIS depends upon the characteristics of Ultra Stable Oscillators (USOs). Laboratory experiments testing the stability of the USOs for long, medium, and short term behavior are presented.
Article
The Jason-1 Operational Sensor Data Record (OSDR) is intended as a wind and wave product that is aimed towards near-real-time (NRT) meteorological applications. However, the OSDR provides most of the information that is required to determine altimetric sea surface heights in NRT. The exceptions include a sufficiently accurate orbit altitude, and pressure fields to determine the dry troposphere path delay correction. An orbit altitude field is provided on the OSDR but has accuracies that range between 8-25 cm (RMS). However, tracking data from the on-board BlackJack GPS receiver are available with sufficiently short latency for use in the computation of NRT GPS-based orbit solutions. The orbit altitudes from these NRT orbit solutions have typical accuracies of < 3.0 cm (RMS) with a latency of 1-3 h, and < 2.5 cm (RMS) with a latency of 3-5 h. Meanwhile, forecast global pressure fields from the National Center for Environmental Prediction (NCEP) are available for the NRT computation of the dry troposphere correction. In combination, the Jason-1 OSDR, the NRT GPS-based orbit solutions, and the NCEP pressure fields can be used to compute sea surface height observations from the Jason-1 mission with typical latencies of 3-5 h, and have differences with those from the 2-3 day latency Interim Geophysical Data Records of < 5 cm (RMS). The NRT altimetric sea surface height observations are potentially of benefit to forecasting, tactical oceanography, and natural hazard monitoring.
Article
We have used GPS carrier phase integer ambiguity resolution to investigate improvements in the orbit determination for the Jason-1 satellite altimeter mission. The technique has been implemented in the GIPSY orbit determination software developed by JPL. The radial accuracy of the Jason-1 orbits is already near 1 cm, and thus it is difficult to detect the improvements gained when the carrier phase ambiguities are resolved. Nevertheless, each of the metrics we use to evaluate the orbit accuracy (orbit overlaps, orbit comparisons, satellite laser ranging residuals, altimeter crossover residuals, orbit centering) show modest improvement when the ambiguities are resolved. We conservatively estimate the improvement in the radial orbit accuracy is at the 10–20% level.
Article
Precise measurements of sea surface height from the Jason-1 and Jason-2/Ocean Surface Topography Mission satellite altimeter missions are being generated within seven and four hours, respectively, of real time by applying high accuracy orbit altitudes to their near-real-time altimetry products. The near-real-time orbit altitudes have respective accuracies of <2 and <1 cm (RMS), and the corresponding sea surface height measurements have accuracies of <4.0 and <3.5 cm, respectively. These near-real-time orbit solutions are computed using GPS-based precise orbit determination for Jason-2, and Jason-1/Jason-2 sea surface height crossover differences for Jason-1.
Chapter
The basic concept of satellite altimetry is to measure the range from the satellite to the sea surface. The altimeter transmits a short pulse of microwave radiation with known power toward the sea surface. The pulse interacts with the rough sea surface and a part of the incident radiation reflects back to the altimeter. The chapter emphasizes on the correction algorithms applied to the dual-frequency altimeter onboard the TOPEX/POSEIDON (T/P) satellite. This state-of-the-art altimeter sets the standard for future altimeter missions as it is significantly more accurate than any of the other altimeters that have been launched to date. To provide assurance that the performance requirements for altimeter measurement accuracy are met or exceeded, extensive calibration and validation (cal/val) are important elements of altimeter missions. Cal/val embraces a wide variety of activities, ranging from the interpretation of information from internal-calibration modes of the sensors to the validation of the fully corrected sea-level estimates using in situ data. The chapter concludes with a summary of the T/P mission design and an assessment of the performance of the T/P dual-frequency altimeter in addition, as well as an overview of future altimeter missions.
Article
JPL's BlackJack receiver currently represents the most widely used geodetic grade GPS receiver for space applications. Using data from the CHAMP science mission, the in-flight performance of the BlackJack receiver has been assessed and the impact of various software updates performed during the 2.5 years since launch is described. Key aspects of the study comprise the channel allocation, anomalous data points, and the noise level of the code and carrier data. In addition, it has been demonstrated that the code measurements collected onboard the CHAMP satellite are notably affected by multipath errors in the aft-looking hemisphere, which can be attributed to cross-talk between the occultation antenna string and the primary precise orbit determination antenna. For carrier smoothed 10 s normal points, the code noise itself varies between a minimum of 5 cm at high elevations and 0.5 m (C/A) to 1.0 m (P1, P2) at 10° elevation. Carrier-phase data exhibit representative errors of 0.2 to 2.5 mm. The results of the CHAMP GPS data analysis contribute to a better understanding and possible improvement of the BlackJack receiver and support the design of optimal data editing and weighting strategies in precise orbit determination applications.
Article
DIODE (DORIS Immediate Orbit on-board Determination) is a real-time on-board orbit determination software, embedded in the DORIS receiver. The purpose of this paper is to focus on DIODE performances. After a description of the recent DORIS evolutions, we detail how compliance with specifications are verified during extensive ground tests before the launch, then during the in-flight commissioning phase just after the launch, and how well they are met in the routine phase and today. Future improvements are also discussed for Jason-2 as well as for the next missions.
Article
The TOPEX/Poseidon, Jason-1 and Jason-2 set of altimeter data now provide a time series of synoptic observations of the ocean that span nearly 17 years from the launch of TOPEX in 1992. The analysis of the altimeter data including the use of altimetry to monitor the global change in mean sea level requires a stable, accurate, and consistent orbit reference over the entire time span. In this paper, we describe the recomputation of a time series of orbits that rely on a consistent set of reference frames and geophysical models. The recomputed orbits adhere to the IERS 2003 standards for ocean and earth tides, use updates to the ITRF2005 reference frame for both the SLR and DORIS stations, apply GRACE-derived models for modeling of the static and time-variable gravity, implement the University College London (UCL) radiation pressure model for Jason-1, use improved troposphere modeling for the DORIS data, and apply the GOT4.7 ocean tide model for both dynamical ocean tide modeling and for ocean loading. The new TOPEX orbits have a mean SLR fit of 1.79 cm compared to 2.21 cm for the MGDR-B orbits. These new TOPEX orbits agree radially with independent SLR/crossover orbits at 0.70 cm RMS, and the orbit accuracy is estimated at 1.5–2.0 cm RMS over the entire TOPEX time series. The recomputed Jason-1 orbits agree radially with the Jason-1 GDR-C orbits at 1.08 cm RMS. The GSFC SLR/DORIS dynamic and reduced-dynamic orbits for Jason-2 agree radially with independent orbits from the CNES and JPL at 0.70–1.06 cm RMS. Applying these new orbits, and using the latest altimeter corrections for TOPEX, Jason-1, and Jason-2 from September 1992 to May 2009, we find a global rate in mean sea level of 3.0 ± 0.4 mm/yr.
Article
The DORIS system has been developed to provide high accuracy orbit determination and beacon positioning. It is fully operational and has been working for 10 years with Spot-2, Spot-3, Spot-4 and Topex-Poseidon. This uplink radio-electrical system is based upon precise doppler measurements made with the dual-frequency signals emitted by the 50 autonomous beacons distributed homogeneously over the Earth surface. The DORIS Control Center performs system monitoring (on board receivers and ground beacons), receivers programming, data processing and archive.On board gathering of the measurements allows a precise on board autonomous real-time computation of the orbit. Experienced on board of Spot-4 since 1998, DIODE (the Navigation software) has demonstrated that on-board real-time orbits are now feasible with a few meters accuracy and an availability better than 99% over 3 years, even through manæuvers.Today, Earth observation missions, altimetry, oceanography, imaging, etc. and satellite constellations navigation often ask for a real time on board orbit restitution with a accuracy, or even better.Including an extended force model (40×40 Earth gravitational fields, moon and sun attractions, etc.), the last issue of DIODE is able to compute the orbit in real-time on board of the satellite, with an expected accuracy of RMS on the radial component.To be launched in 2001, Envisat-1 and Jason-1 are both equipped with a DORIS 2nd generation receiver: unfortunately, flight results will not be available in time to be presented in the paper. Future flights will occur in the next years (Spot-5, Cryosat, Pléiades, etc.).
Article
The ability of radar altimeters to measure the distance from a satellite to the ocean surface with a precision of the order of 2 cm imposes unique requirements for the orbit determination accuracy. The orbit accuracy requirements will be especially demanding for the joint NASA/CNES Ocean Topography Experiment (Topex/Poseidon). For this mission, a radial orbit accuracy of 13 centimeters will be required for a mission period of three to five years. This is an order of magnitude improvement in the accuracy achieved during any previous satellite mission. This investigation considers the factors which limit the orbit accuracy for the Topex mission. Particular error sources which are considered include the geopotential, the radiation pressure and the atmospheric drag model.
Article
TOPEX/POSEIDON is the first space mission specifically designed and conducted for studying the circulation of the world's oceans. The mission is jointly conducted by the United States and France. A state-of-the-art radar altimetry system is used to measure the precise height of sea level, from which information on the ocean circulation is obtained. To meet the stringent measurement accuracy required for ocean circulation studies, a number of innovative improvements have been made to the mission design, including the first dual-frequency space-borne radar altimeter capable of retrieving the ionospheric delay of the radar signal, a three-frequency microwave radiometer for retrieving the signal delay caused by the water vapor in the troposphere, an optimal model of the Earth's gravity field and multiple satellite tracking systems for precision orbit determination. Additionally, the satellite also carried two experimental instruments to demonstrate new technologies: a single-frequency solid-state altimeter for the technology of low-power, low-weight altimeter and a Global Positioning System receiver for continuous, precise satellite tracking. -from Authors
Article
The objectives and conclusions reached during the Seasat Precision Orbit Determination Experiment are discussed. It is noted that the activities of the experiment team included extensive software calibration and validation and an intense effort to validate and improve the dynamic models which describe the satellite's motion. Significant improvement in the gravitational model was obtained during the experiment, and it is pointed out that the current accuracy of the Seasat altitude ephemeris is 1.5 m rms. An altitude ephemeris for the Seasat spacecraft with an accuracy of 0.5 m rms is seen as possible with further improvements in the geopotential, atmospheric drag, and solar radiation pressure models. It is concluded that since altimetry missions with a 2-cm precision altimeter are contemplated, the precision orbit determination effort initiated under the Seasat Project must be continued and expanded.
Article
NASA is pursuing two key applications of differential positioning with the Global Positioning System (GPS): sub-decimeter tracking of earth satellites and few-centimeter determination of ground-fixed baselines. Key requirements of the two applications include the use of dual-frequency carrier phase data, multiple ground receivers to serve as reference points, simultaneous solution for use position and GPS orbits, and calibration of atmospheric delays using water vapor radiometers. Sub-decimeter tracking will be first demonstrated on the TOPEX oceanographic satellite to be launched in 1991. A GPS flight receiver together with at least six ground receivers will acquire delta range data from the GPS carriers for non-real-time analysis. Altitude accuracies of 5 to 10 cm are expected. For baseline measurements, efforts will be made to obtain precise differential pseudorange by resolving the cycle ambiguity in differential carrier phase. This could lead to accuracies of 2 or 3 cm over a few thousand kilometers. To achieve this, a high-performance receiver is being developed, along with improved calibration and data processing techniques. Demonstrations may begin in 1986.
Article
A reduced-dynamic technique for precise orbit determination of low earth satellites is described. This technique optimally combines the conventional dynamic technique with the nondynamic technique which uses differential GPS continuous carrier phase to define the state transition. A Kalman filter formulation for this reduced-dynamic technique is given. A covariance analysis shows that when neither the dynamic nor the nondynamic technique is clearly superior, the reduced-dynamic technique appreciably improves the orbit accuracy. Guidelines for selecting a near-optimum weighting for the combination are given. Sensitivity to suboptimal weighting is assessed.
Article
The largest nongravitational forces that will be acting on the TOPEX satellite will be those due to incident and emitted radiation on the spacecraft surfaces. In order to minimize the effects of these forces on orbit determination, a detailed model is being developed so that they may be predicted accurately. This model requires a precise description of the spacecraft shape and orientation, an evaluation of the solar and Earth radiation impinging on the surfaces, and a determination of the radiation being emitted from the surfaces as they heat and cool throughout the orbit. The TRASYS software system is used to evaluate the solar and Earth radiation (albedo and infrared) striking each surface of the spacecraft. This software has been modified to include an Earth radiation model that follows the seasonal variations in albedo and infrared radiation. The SINDA software system is then used to determine the transient temperatures of the spacecraft surfaces. Orbital thermal histories of significant features are given. These temperatures are used to determine the force exerted on each surface due to thermal emission. The emission forces are combined with the incident radiation forces to determine the total force acting on the satellite.
Article
(Previously announced in STAR as N80-20749)
Article
In this paper a computational scheme is presented for accurately predicting the farfield amplitude and phase characteristics of Global Positioning System (GPS) antennas flush-mounted to a corrugated groundplane. The algorithm developed is particularly well-suited in beamshaping of (GPS) antennas in order to provide a high level of multipath rejection. The usefulness of the analytical model has been verified by the excellent agreement achieved between experimental data and predicted amplitude and phase patterns
Gravity Model Improvement: A Decade Preparing for TOPEX/Poseidon: George Born, Byron Tapley and Jim Marsh
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Gravity Model Improvement: A Decade Preparing for TOPEXlPoseidon
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LEMOINE, F.G., LUTHCKE, S., ROWLANDS, D., KLOSKO, S., and ZELENSKY, N. "Gravity Model Improvement: A Decade Preparing for TOPEXlPoseidon: George Born, Byron Tapley and Jim Marsh," George H Born Symposium, American Astronautical Society, Boulder CO USA, May 13-14,2010.
An Introduction to Satellite Altimetry Satellite Altimetry and Earth Science: A Handbook of Techniques and Applications
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The I-Centimeter Orbit: Jason-l Orbit Determination Using
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LUTHCKE, S., ZELENSKY, N., ROWLANDS, D., LEMOINE, F. and WILLIAMS, T. "The I-Centimeter Orbit: Jason-l Orbit Determination Using GPS, SLR, DORIS and Altimeter Data," Marine Geodesy, Vol. 26, No. 3-4, 2003, pp. 399-421, doi: 10.10801 714044529.
Re-sults of an Automated GPS Tracking System in Support of
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MUELLERSHOEN, R.I., LICHTEN, S., LINDQWISTER, U., and BERTIGER, W. "Re-sults of an Automated GPS Tracking System in Support of TOPEXIPOSEIDON and Haines et al. GPSMet," Proceedings of the 1995 international Technical Meeting of the institute of Navigation (JON GPS 1995), Palm Springs, 1995, pp. 183-193.
An Introduction to Satellite Altimetry,” Satellite Altimetry and Earth Science: A Handbook of Techniques and Applications, International Geophysics
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