Combining all flying microwave radiometers to compute the water vapor path delay for altimeter missions

Abstract

An objective analysis (OA) method is implemented, to compute the altimeter path delay (PD) induced by atmospheric water vapor. Input PD observations are derived from total precipitable water measurements from all currently flying scanning microwave radiometers (AMSU-A, AMSR-E, TMI and SSMI). ECMWF model derived PD is used as first-guess field. Calculation of the statistical variables required by the OA are presented : these include the variance and correlation function of the radiometer path delay minus its first-guess, as well as the observations error variance. The performance of the OA-derived water vapor path delay is assessed, using 4 months of Jason-1 altimeter data. It is shown that the OA-derived PD estimate is more accurate than the ECMWF model derived one, but remains less accurate than the one derived from the Jason microwave radiometer.