Search

Satellite altimetry has demonstrated a strong potential for the continuous monitoring of ocean, ice sheets and land surfaces over the last 25 years. While instrument processing and retracking techniques of the radar echoes improved over the years for ocean applications to produce homogeneous products for all satellite altimetry missions, less effort has been devoted to applications over land. European Space Agency (ESA) continues improving the quality of ENVISAT data over all type of surfaces through frequent reprocessing of altimeter corrections. No similar effort was performed for the ERS missions until recently with the release of the ESA ERS REAPER product mostly devoted to ocean applications. In parallel, Centre de Topographie des Océans et de l'Hydrosphère (CTOH) processed the ERS-2 waveforms (WAP data) with a new implementation of the Ice-2 retracker algorithm, adding improvements and corrections to make ERS-2 data compatible and homogenous with the ENVISAT mission for continuity and long-term altimetry data analysis over land and ice sheets. The resulting product is evaluated against ENVISAT data during the tandem phase when they flew 30 min apart on the same orbit during 10 cycles of the two missions from June 2002 to July 2003. Maps of along-track differences averaged over the 10 cycles of the tandem phase and associated RMSE are presented over ocean, both Antarctica and Greenland ice sheets and land along with time series of altimetry backscattering coefficients and altimetry-based water levels. Similar comparisons were performed between ENVISAT and ERS-2 REAPER data. Low bias and RMSE values for altimeter heights and backscattering were found between ENVISAT and ERS-2 over ocean and flat areas over land and ice sheets with generally better results obtained using CTOH data. Comparisons with in situ water stages also show good agreement for Ice-2 and especially Ice-1 retrackers derived water levels (R > 0.95). [ABSTRACT FROM AUTHOR]

In the coastal ocean zones, satellite altimetry data processing and interpretation poses specific difficulties, due to the interaction of the radar signal with land topography, inaccuracies in some of the geophysical corrections and to the fast changes in the sea level. In order to optimize the completeness and the accuracy of the sea surface height information derived from satellite altimetry in coastal ocean areas, a dedicated post-processing software, called X-TRACK, has been developed by the Center of Topography of the Ocean and Hydrosphere in Toulouse. It is tailored for extending the use of altimetry data to coastal ocean applications and provides freely available along-track Sea Level Anomaly time series that cover today all the coastal oceans. Here, we present the improvements made in version 2016 of X-TRACK and show the gain in near-coastal data accuracy using in situ tide gauge observations. The correlations between altimeter and tide gauge sea level anomalies are higher (by 15% in average) compared with the previous version of X-TRACK. Three examples of applications are shown. The recent evolutions done in the X-TRACK processing result in an improved observation of the seasonal variations of the boundary circulation in the Bay of Biscay. Along Western Africa, sea-level variations derived from X-TRACK data are observed closer to land (5 km) compared to AVISO (10 km), and the sea-level statistics are more robust due to the larger and more stable data availability. Along-track empirical tidal constants derived from X-TRACK Sea Level Anomaly time series are also used to validate tidal models. By improving the altimetric data accuracy in coastal areas, we extend the field of marine applications. [ABSTRACT FROM AUTHOR]