5‐cm‐Precision aircraft ocean altimetry using GPS reflections

Lowe, S.; Zuffada, Cinzia; Chao, Yi; Kröger, Peter; Young, Larry; LaBrecque, John L.

doi:10.1029/2002gl014759

Cited by 185 publications

(112 citation statements)

References 12 publications

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“…High quality and dense sampling of geospatial and environmental information is expected not only for coastal management but also for scientific research, e.g., [11]. The increasing demands of coastal applications have motivated excellent efforts in the altimetry community to improve coastal applicability, including proposing new altimetry concepts (Ka-band altimetry [12], delay-Doppler altimetry [13,14], wide-swath altimetry [15], GNSS altimetry [16], constellations of altimeters [17]) and reprocessing conventional altimeter data [18][19][20]. In the last decade, a series of projects were supported by some space agencies and research institutions, aiming to retrieve valid altimeter data as close as possible to the coast.…”

Section: Introductionmentioning

confidence: 99%

Improving Jason-2 Sea Surface Heights within 10 km Offshore by Retracking Decontaminated Waveforms

et al. 2017

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Abstract:It is widely believed that altimetry-derived sea surface heights (SSHs) in coastal zones are seriously degraded due to land contamination in altimeter waveforms from non-marine surfaces or due to inhomogeneous sea state conditions. Spurious peaks superimposed in radar waveforms adversely impact waveform retracking and hence require tailored algorithms to mitigate this problem. Here, we present an improved method to decontaminate coastal waveforms based on the waveform modification concept. SSHs within 10 km offshore are calculated from Jason-2 data by a 20% threshold retracker using decontaminated waveforms (DW-TR) and compared with those using original waveforms and modified waveforms in four study regions. We then compare our results with retracked SSHs in the sensor geophysical data record (SGDR) and with the state-of-the-art PISTACH (Prototype Innovant de Système de Traitement pour les Applications Côtières et l'Hydrologie) and ALES (Adaptive Leading Edge Subwaveform) products. Our result indicates that the DW-TR is the most robust retracker in the 0-10 km coastal band and provides consistent accuracy up to 1 km away from the coastline. In the four test regions, the DW-TR retracker outperforms other retrackers, with the smallest averaged standard deviations at 15 cm and 20 cm, as compared against the EGM08 (Earth Gravitational Model 2008) geoid model and tide gauge data, respectively. For the SGDR products, only the ICE retracker provides competitive SSHs for coastal applications. Subwaveform retrackers such as ICE3, RED3 and ALES perform well beyond 8 km offshore, but seriously degrade in the 0-8 km strip along the coast.

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Section: Introductionmentioning

confidence: 99%

Improving Jason-2 Sea Surface Heights within 10 km Offshore by Retracking Decontaminated Waveforms

et al. 2017

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“…Assuming that coherent scattering is negligible, the bistatic scattering coefficient was derived under the geometric optics limit, for a sea surface model with Gaussian distribution of the slopes, and a final expression of the "waveform" was derived. During the last decade, additional experimental [5][6][7][8] and theoretical [9][10][11][12] works have been performed to investigate the feasibility of this bistatic radar system to perform accurate ocean altimetry, usually with open-loop receivers, and using a model of the scattering geometry to center the delay and Doppler tracking windows.…”

Section: Introductionmentioning

confidence: 99%

Empirical Results of a Surface-Level GNSS-R Experiment in a Wave Channel

Carreño-Luengo

Camps

2015

Remote Sensing

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Abstract:The scattering of GNSS signals over a water surface is studied when the receiver is at a low height, as in GNSS-R coastal altimetry. The precise determination of the local sea level and wave state from the coast will provide useful altimetry and wave information as "dry" tide and wave gauges. An experiment has been conducted at the Canal d'Investigació i Experimentació Marí tima (CIEM) wave channel for two simulated "sea" states. The GNSS-reflectometer used is the P(Y) and C/A ReflectOmeter (PYCARO) instrument, a closed-loop receiver with delay and Doppler tracking loops that uses the conventional GNSS-R technique for the GPS C/A code. After retracking of the scattered GPS signals, the coherent and incoherent components have been studied. To reproduce the transmitted GPS signals indoors, a Rohde and Schwarz signal generator is used. It is found that, despite the ratio of the coherent and incoherent components being ~1, the coherent component is strong enough that it can be tracked. The coherent component comes from clusters of points on the surface that approximately satisfy the specular reflection conditions ("roughed facet"). The Pearson's linear correlation coefficients of the derived "sea" surface height with the wave gauge data are: 0.78, 0.85 and 0.81 for a SWH = 36 cm and 0.34, 0.74, and 0.72 for a SWH = 64 cm, respectively, for transmitter elevation angles of θ e = 60°, 75° and 86°, respectively. Finally, the rms phase of the received signal before the retracking processing is used to estimate the effective rms surface height of the 'facets', where the waves get scattered. It is found to be between 2.5-and 4.1-times smaller than the theoretical values corresponding to the half of the coherent reflectivity decaying factor.

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“…Over the last twenty years, this technique has been used to retrieve accurate sea surface heights from various ground-based and airborne platforms using an upward Right-Handed Circular Polarization (RHCP) antenna, a downward Left-Handed Circular Polarization (LHCP) antenna and a specialized receiver [9][10][11][12][13][14]. Space-borne GNSS-R altimetry has been used to retrieve sea surface height (SSH) data with an accuracy of~7.0 m using data from the British TechDemoSat-1 (TDS-1) satellite [15].…”

Section: Introductionmentioning

confidence: 99%

Sea Level Estimation Based on GNSS Dual-Frequency Carrier Phase Linear Combinations and SNR

Wang

Gao

et al. 2018

Remote Sensing

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Abstract:Ground-based GNSS-R (global navigation satellite system reflectometry) can provide the absolute vertical distance from a GNSS antenna to the reflective surface of the ocean in a common height reference frame, given that vertical crustal motion at a GNSS station can be determined using direct GNSS signals. This technique offers the advantage of enabling ground-based sea level measurements to be more accurately determined compared with traditional tide gauges. Sea level changes can be retrieved from multipath effects on GNSS, which is caused by interference of the GNSS L-band microwave signals (directly from satellites) with reflections from the environment that occur before reaching the antenna. Most of the GNSS observation types, such as pseudo-range, carrier-phase and signal-to-noise ratio (SNR), suffer from this multipath effect. In this paper, sea level altimetry determinations are presented for the first time based on geometry-free linear combinations of the carrier phase at low elevation angles from a fixed global positioning system (GPS) station. The precision of the altimetry solutions are similar to those derived from GNSS SNR data. There are different types of observation and reflector height retrieval methods used in the data processing, and to analyze the performance of the different methods, five sea level determination strategies are adopted. The solutions from the five strategies are compared with tide gauge measurements near the GPS station, and the results show that sea level changes determined from GPS SNR and carrier phase combinations for the five strategies show good agreement (correlation coefficient of 0.97-0.98 and root-mean-square error values of <0.2 m).

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5‐cm‐Precision aircraft ocean altimetry using GPS reflections

Cited by 185 publications

References 12 publications

Improving Jason-2 Sea Surface Heights within 10 km Offshore by Retracking Decontaminated Waveforms

Improving Jason-2 Sea Surface Heights within 10 km Offshore by Retracking Decontaminated Waveforms

Empirical Results of a Surface-Level GNSS-R Experiment in a Wave Channel

Sea Level Estimation Based on GNSS Dual-Frequency Carrier Phase Linear Combinations and SNR

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