X-TRACK L2P : SEA LEVEL ANOMALIES DEDICATED TO COASTAL APPLICATIONS - Regional

Along-track Sea Level Anomalies projected onto the reference tracks with a spatial interval of about 6-7 km between points (1 second). The Sea Level Anomaly time series have been computed with the X-TRACK processing system (developed at CTOH/LEGOS) starting from the Level 2 Plus (L2P) products distributed by CDS-AVISO.

The CTOH computes and distributes specific, coastal along-track sea level anomalies (SLA) using its X-TRACK processor over 29 regions, for all precise altimeter missions : Topex/Jason-1/Jason-2/Jason-3 (+ interleaved orbits for Topex, Jason-1, Jason-2, Jason-3), ERS-1, ERS-2, Envisat, SARAL/AltiKa, Geosat Follow On, HaiYang-2A, HaiYang-2B, Sentinel-3A, Sentinel-3B and Sentinel-6A..

The X-TRACK L2P product is also more complete since in addition to the sea surface height anomalies, it contains the significant wave height and the backscatter coefficient. The applied altimetry corrections are also provided in this product. This tool is based on:

• The use of new measurement correction algorithms to eliminate or reduce the effects due to the presence of the land on the measurement and corrections, with in particular, a procedure of selection, reconstruction and smoothing of corrections. This procedure consists in defining an "editing criterion" (i.e. the set of min and/or max values that guarantee the elimination of most of the outliers) more restrictive than the standard criterion. In a second step, a statistical quality control procedure allows the elimination of residual outliers. In parallel, a method of reconstruction/smoothing of erroneous corrections, by Bézier polynomials, is performed.

This approach allows to recover a significant number of altimetric measurements close to the coast.

The contribution compared to standard treatments is:

• A decrease in the rate of erroneous measurements,

• An increase of the coverage in coastal areas.