SAR Altimeter Backscattered Waveform Model

Ray, Chris; Martín-Puig, Cristina; Clarizia, Maria Paola; Ruffini, Giulio; Dinardo, Salvatore; Gommenginger, Christine; Benvéniste, Jérôme

doi:10.1109/tgrs.2014.2330423

Cited by 128 publications

(99 citation statements)

References 7 publications

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“…SARvatore data were downloaded from gpod.eo.esa.int in May 2015. SARvatore processes the CS-2 raw data in the SAR boxes using the SAMOSA2 functional form (Ray et al, 2015); the settings suggested for coastal areas are all applied, i.e. Hamming weighting window on the burst data, zero-padding and extended radar receiving window size (for details, see Dinardo and Benveniste (2013)).…”

Section: Altimetry Datasetmentioning

confidence: 99%

Cross-calibrating ALES Envisat and CryoSat-2 Delay–Doppler: A coastal altimetry study in the Indonesian Seas

Passaro

Dinardo

Quartly

et al. 2016

Advances in Space Research

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A regional cross-calibration between the first Delay-Doppler altimetry dataset from Cryosat-2 and a retracked Envisat dataset is here presented, in order to test the benefits of the Delay-Doppler processing and to expand the Envisat time series in the coastal ocean. The Indonesian Seas are chosen for the calibration, since the availability of altimetry data in this region is particularly beneficial due to the lack of in-situ measurements and its importance for global ocean circulation. The Envisat data in the region are retracked with the Adaptive Leading Edge Subwaveform (ALES) Retracker, which has been previously validated and applied successfully to coastal sea level research.The study demonstrates that CryoSat-2 is able to decrease the 1-Hz noise of sea level estimations by 0.3 cm within 50 km of the coast, when compared to the ALES-reprocessed Envisat dataset. It also shows that Envisat can be confidently used for detailed oceanographic research after the orbit change of October 2010. Cross-calibration at the crossover points indicates that in the region of study a sea state bias correction equal to 5% of the significant wave height is an acceptable approximation for Delay-Doppler altimetry.The analysis of the joint sea level time series reveals the geographic extent of the semiannual signal caused by Kelvin waves during the monsoon transitions, the larger amplitudes of the annual signal due to the Java Coastal Current and the impact of the strong La Niña event of 2010 on rising sea level trends.

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Section: Altimetry Datasetmentioning

confidence: 99%

Cross-calibrating ALES Envisat and CryoSat-2 Delay–Doppler: A coastal altimetry study in the Indonesian Seas

Passaro

Dinardo

Quartly

et al. 2016

Advances in Space Research

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“…CryoSat-2 (launched in 2010) is primarily a cryosphere mission and not planned for ocean observations. Yet over the last years, considerable efforts have been made by the ESA SAMOSA project (Ray et al, 2015) and the CNES Cryosat-2 Processing Prototype (CPP) project (Boy et al, 2017) in collaboration with oceanographers to improve the waveform retracking over the ocean and provide adequate corrections for ocean observations. CryoSat-2 is in low-resolution mode over most of the global ocean but has synthetic aperture radar (SAR) mode observations available over a few regions, including the Mediterranean Sea, with improved along-track sampling down to 300 m and reduced noise.…”

Section: Introductionmentioning

confidence: 99%

Observability of fine-scale ocean dynamics in the northwestern Mediterranean Sea

et al. 2017

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Abstract. Technological advances in the recent satellite altimeter missions of Jason-2, SARAL/AltiKa and CryoSat-2 have improved their signal-to-noise ratio, allowing us to observe finer-scale ocean processes with along-track data. Here, we analyse the noise levels and observable ocean scales in the northwestern Mediterranean Sea, using spectral analyses of along-track sea surface height from the three missions. Jason-2 has a higher mean noise level with strong seasonal variations, with higher noise in winter due to the rougher sea state. SARAL/AltiKa has the lowest noise, again with strong seasonal variations. CryoSat-2 is in synthetic aperture radar (SAR) mode in the Mediterranean Sea but with lower-resolution ocean corrections; its statistical noise level is moderate with little seasonal variation. These noise levels impact on the ocean scales we can observe. In winter, when the mixed layers are deepest and the submesoscale is energetic, all of the altimeter missions can observe wavelengths down to 40-50 km (individual feature diameters of 20-25 km). In summer when the submesoscales are weaker, SARAL can detect ocean scales down to 35 km wavelength, whereas the higher noise from Jason-2 and CryoSat-2 blocks the observation of scales less than 50-55 km wavelength.This statistical analysis is completed by individual case studies, where filtered along-track altimeter data are compared with co-located glider and high-frequency (HF) radar data. The glider comparisons work well for larger ocean structures, but observations of the smaller, rapidly moving dynamics are difficult to co-locate in space and time (gliders cover 200 km in a few days, altimetry in 30 s). HF radar surface currents at Toulon measure the meandering Northern Current, and their good temporal sampling shows promising results in comparison to co-located SARAL altimetric currents. Techniques to separate the geostrophic component from the wind-driven ageostrophic flow need further development in this coastal band.

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“…SAMOSA2 retracker (default): The SAMOSA (SAR Altimetry MOde Studies and Applications) model [11] has been implemented in its first-order formulation (SAMOSA2) in a retracker as in [12]. This retracker uses a look-up table to mitigate the effect of the model's approximation of the squared PTR (point target response) with a Gaussian curve, it implements a stack masking for the Doppler beams padded to zero and has in principle no enhancement in the coastal zone.…”

Section: Sentinel-3amentioning

confidence: 99%

“…This retracker uses a look-up table to mitigate the effect of the model's approximation of the squared PTR (point target response) with a Gaussian curve, it implements a stack masking for the Doppler beams padded to zero and has in principle no enhancement in the coastal zone. SAMOSA+ retracker (the SAMOSA2 model tailored for inland water, sea ice and the coastal zone domain): in the case of SAMOSA+, the open ocean SAMOSA [11] model and retracker [13] has been implemented in the retracking scheme with two significant additions [12]: The first one concerns the selection of the first-guess epoch. This is not selected as the position of the waveform peak but as the position of the moving correlation peak in 20 consecutive waveforms (after aligning them for tracker shift).…”

Section: Sentinel-3amentioning

confidence: 99%

“…G-POD uses the SAMOSA2 retracker as default. However, another retracking approach tailored for coastal zones [11,12] was also available (SAMOSA+, SAR altimetry mode studies and applications) and we generated a separate set of data using this option. The different processing schemes were then used to analyze their impact on the SSH bias: SAMOSA2 for one set and SAMOSA+ for the other.…”

Section: Cryosat-2 Ssh Calibrationmentioning

confidence: 99%

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Calibrating the SAR SSH of Sentinel-3A and CryoSat-2 over the Corsica Facilities

et al. 2018

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Initially developed to monitor the performance of TOPEX/Poseidon and to follow the Jason legacy satellite altimeters at Senetosa Cape, Corsica, this calibration/validation site has been extended to include a new location at Ajaccio. This addition enables the site to monitor Envisat and ERS missions, CryoSat-2 and, more recently, the SARAL/AltiKa mission and Sentinel-3A satellites. Sentinel-3A and CryoSat-2 carry altimeters that use a synthetic aperture radar (SAR) mode that is different to the conventional pulse-bandwidth limited altimeters often termed "low resolution mode" (LRM). The aim of this study is to characterize the sea surface height (SSH) bias of the new SAR altimeter instruments and to demonstrate the improvement of data quality close to the coast. Moreover, some passes of Sentinel-3A and CryoSat-2 overfly both Senetosa and Ajaccio with only a few seconds time difference, allowing us to evaluate the reliability and homogeneity of both ground sites in term of geodetic datum. The Sentinel-3A and CryoSat-2 SSH biases for the SAR mode are respectively +22 ± 7 mm and −73 ± 5 mm (for CryoSat-2 baseline C products). The results show that the stability of the SAR SSH bias time series is better than standard LRM altimetry. Moreover, compared to standard LRM data, for which the measurements closer than~10 km from the coast were generally unusable, SAR mode altimeters provide measurements that are reliable at less than few hundred meters from the coast.

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SAR Altimeter Backscattered Waveform Model

Cited by 128 publications

References 7 publications

Cross-calibrating ALES Envisat and CryoSat-2 Delay–Doppler: A coastal altimetry study in the Indonesian Seas

Cross-calibrating ALES Envisat and CryoSat-2 Delay–Doppler: A coastal altimetry study in the Indonesian Seas

Observability of fine-scale ocean dynamics in the northwestern Mediterranean Sea

Calibrating the SAR SSH of Sentinel-3A and CryoSat-2 over the Corsica Facilities

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