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

Abstract

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.

The Benefits of the Ka-Band as Evidenced from the SARAL/AltiKa Altimetric Mission: Quality Assessment and Unique Characteristics of AltiKa Data

“…This problem was identified in [11] and has been solved recently. This is discussed in [12] in which we have performed the Sentinel-3A calibration over both Senetosa and Ajaccio sites in a configuration close to the one encountered with SARAL/AltiKa for cycle 104 and pass 677 (see Figure 5). …”

Requirements for a Coastal Hazards Observing System

“…Similarly, the standard deviation of SSHa, which increases near coast, is the smallest for DDA data processed with SAMOSA+ and within the expected range until 2-3 km from the coast. Standard deviation of differences and absolute biases between the SSHa and tide-gauge data are on the order of few centimeters (Bonnefond et al, 2018a;Fenoglio et al, 2019). Best results come from CryoSat-2 and Sentinel-3A SAR altimetry processed with SAMOSA+ at the Grid Processing On Demand (GPOD) service at ESRIN 1 .…”

“…Several studies compared these data sets with independent measurements (e.g., Gómez-Enri et al, 2016;Vu et al, 2018;Xu et al, 2018). Quality assessments for Sentinel-3A and CryoSat-2 (Bonnefond et al, 2018a;Fenoglio et al, 2019) and AltiKa data (Bonnefond et al, 2018b) have also been performed.…”

The Analysis of the Basic Trends in Satellite Altimeters Development: “Disruptive” or Evolutional Technologies?

“…За последние несколько десятилетий направление спутниковой альтиметрии шагнуло далеко вперед: от приборов и космических аппаратов, пригодных для выполнения исключительно геодезических миссий (для которых характерны невысокие требования к точности измерений высоты морской поверхности) до сложнейших космических комплексов, использующихся в интересах решения задач фундаментальной климатологии, промысловой океанологии и пр., предоставляющих измерения высоты морской поверхности с точностью до нескольких сантиметров [1][2][3].…”