IMPROVEMENT OF THE TOPEX/POSEIDON ALTIMETRIC DATA PROCESSING FOR HYDROLOGICAL PURPOSES (CASH PROJECT)

摘要

Over non-ocean surfaces (wet or dry), the accuracy of the altimetric measurements is degraded to several cm or tens of cm, mainly because of the heterogeneity of the reflecting surface (a mix of water and emerged lands). Another important source of error lies in the propagation of the signal through the atmosphere. This study focuses on these 2 issues. In the framework of the CASH project (Contribution de l'Altimétrie Satellitaire à l'Hydrologie) founded by the French Ministry of Research, it has been decided to initiate a global re-processing of the Topex/Poseidon data (1992-2005) that is dedicated to the constitution of an hydrology-oriented altimetric data base. We applied to the Topex waveforms the same 4 retracking algorithms that are routinely applied to the ENVISAT measurements. Consequently, Topex/Poseidon products become coherent with ENVISAT GDR. Simultaneously, we investigated the so-called wet and dry corrections of the propagation delay through the troposphere. We propose a new computation algorithm where the effective thickness of the atmosphere column is deduced from the altimetric measurement itself.