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

Pascal Bonnefond,Sylvie Labroue,Pierre Exertier,François Boy,Nicolas Picot,Matthias Raynal,Salvatore Dinardo,Pierre Féménias,Craig Donlon,Thierry Guinle,Tommaso Parrinello,Olivier Laurain

doi:10.3390/rs10010092

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.

Highlights

The Corsica geodetic facilities that are located both at Senetosa Cape for the TOPEX/Poseidon (T/P) and Jason satellite ground tracks and near Ajaccio for the Envisat satellite ground tracks have been developed to calibrate successive satellite altimeters in an absolute sense
Our results confirm previous results that were obtained from SARAL/AltiKa together with GPS-based sea level measurements [3]
Differences still exist at the millimeter level between the sea surface height (SSH) bias obtained at the Senetosa and Ajaccio sites for Sentinel-3A and CryoSat-2

Summary

Introduction

The Corsica geodetic facilities that are located both at Senetosa Cape for the TOPEX/Poseidon (T/P) and Jason satellite ground tracks and near Ajaccio for the Envisat satellite ground tracks have been developed to calibrate successive satellite altimeters in an absolute sense. Since 1998, the successful calibration process used to calibrate many oceanographic satellite altimeter missions has been regularly updated, see details in [1,2,3]. Taking into account the geoid slope (of several cm/km) over of the issues inbetween comparing offshore altimetric surface height distancesOne of tens ofmain kilometers both locations. Othermeasurements factors including together with in-situ tide gauge data is taking into account the geoid slope (of several cm/km) over ocean dynamics and tidal differences, impact the comparisons with independent coastal in situ distances of tens of kilometers between both locations. As discussed in [4], other factors including measurements, but are negligible in such areas and within the short distance in our study A specific Global Positioning System (GPS) campaign was conducted in 1999 in order to measurements, but are negligible in such areas and within the short distance in our study

Objectives

Methods

Results

Conclusion