PEACHI : A Way of Considering SARAL/AltiKa Altimeter Data for Coastal Hydrology
Valladeau, Guillaume1; Thibaut, Pierre1; Picot, Nicolas2; Guillot, Amandine2

SARAL/AltiKa ground processing and associated user products are directly derived from the Jason-2 ground processing chains (GDR-D standards). Even if this standard is state of the art for current altimeter systems in orbits and for deep ocean applications, the processing of the innovative Ka-band altimeter (40 Hz variable PRF system and mono-frequency) coupled with dual frequency radiometer slightly differs from the Jason-2 one (typically their frequencies and associated bandwidths). As an example, one major drawback of the use of a Ka-band is that the attenuation of the signal due to liquid water (rain and clouds which are often dense and frequent in the Tropics) is high. Consequently, to account for such behaviors, the ground processing has to be enhanced to provide to the altimeter community the most reliable and relevant data for scientific studies and applications.

In particular, the reliability of AltiKa measurements for coastal hydrology is of main interest in the frame of the PEACHI project (Prototype for Expertise on AltiKa for Coastal Hydrology and Ice). This project is a CNES (Centre National d’Etudes Spatiales) initiative to provide end-users reliable Ka altimeter measurements over coastal areas and in open ocean but also in continental and sea ice domains, and also linked to the CNES PISTACH and ESA Coastalt projects.

The PEACHI prototype developed first aims at improving the reliability and the accuracy of the geophysical parameters (impact of the rain flag on Ka measurements, Sea Wave Height, Sea State Bias, new radiometer corrections …) thanks to new or improved algorithms. Additional flags can also be provided to allow an improved editing of the data before their use.

Preliminary results of the improvements performed on the main altimeter corrections applied to SARAL/AltiKa measurements in the frame of the PEACHI project are presented here and especially focus on coastal areas. The data quality obtained with SARAL mission is compared with previous (ESA ENVISAT) and/or current missions like Jason-2 and the ESA CryoSat mission. These developments intend to demonstrate the advantage of the innovative Ka band for scientific studies.