Using Objective Analysis of Scanning Radiometer Measurements to Compute the Water Vapor Path Delay for Altimetry

Abstract

An objective analysis (OA) method is implemented to compute the water vapor path delay (PD) correction of the altimeter range using total precipitable water measurements from scanning microwave radiometers (Advanced Microwave Sounding Unit A, Advanced Microwave Scanning Radiometer-Earth Observing System, Tropical Rain Measuring Mission Microwave Imager, and Special Sensor Microwave Imager). The European Centre for Medium Range Weather Forecasts (ECMWF) model-derived water vapor PD correction given in the altimeter products is used as the first-guess field. The calculation of the statistical variables required by the OA is presented: These include the variance and correlation function of the radiometer observations minus its first guess, as well as the observation error variance. The performance of the OA-derived water vapor PD correction is assessed, using four months of Jason-1 altimeter data. It is shown that the OA-derived correction is more accurate than the ECMWF-derived correction but remains less accurate than the one derived from the Jason microwave radiometer.