SARAL/AltiKa Wet Tropospheric Correction: In-Flight Calibration, Retrieval Strategies and Performances

摘要

The SARAL/AltiKa mission is a complement of the Jason altimeter series. A twochannels ( 23.8 GHz and 37 GHz) microwave radiometer ( MWR) is combined to the altimeter in order to correct the altimeter range for the excess path delay ( referred as WTC for wet tropospheric correction. First, the in- flight calibration of AltiKa MWR is assessed from a systematic comparison to other radiometers using a complete set of metrics ( comparison to simulations and over geophysical targets). Then the "mixed" empirical approach successfully used for Envisat shows nonoptimal performances for the WTC retrieval. In order to find the potential sources of issues, this method is compared to a purely empirical relationship established between measured brightness temperatures ( TB) and altimeter backscattering coefficient ( sigma 0) on one hand and modeled WTC on the other hand. Various retrieval configurations for both AltiKa MWR and advanced microwave radiometer ( AMR) on Jason-2, are for the first time systematically compared with respect to their performances against the variance of sea surface height differences at crossovers. Finally, the issues on the "mixed" approach are attributed to the differences between simulated and measured s0 at Ka-band. Now, a configuration of the empirical approach proved to have performances closed to what is initially expected with the "mixed" approach.