Jason Microwave Radiometer On Orbit Calibration, Validation and Performance

The Jason Microwave Radiometer (JMR) on the Jason-1 altimeter satellite measures radiometric brightness temperature (TB) at 18.7, 23.8, and 34.0 GHz in the nadir direction, from which is estimated the excess path delay (PD) through the atmosphere experienced by the Jason radar altimeter signal due to water vapor and suspended cloud liquid water. JMR is an improved follow-on to the TOPEX Microwave Radiometer (TMR) on the earlier TOPEX/Poseidon altimeter satellite. Early work calibrating JMR and validating its performance during the first six months of the mission will be presented. Placement of Jason-1 into a virtually identical orbit with TOPEX/Poseidon, with approximately 70 s time displacement, has afforded unprecedented accuracy in the intercalibration of two satellite radiometers. The virtual elimination of spatial and temporal decorrelation errors between JMR and TMR TBs and PDs allows intercomparison fine tuning at a much more precise level, and with greatly reduced data averaging requirements, relative to the earlier TMR comparisons with other satellite instruments (SSM/I, ERS-1,2), island radiosondes, GPS, and ground-based water vapor radiometers. Calibration of the JMR TBs has been evaluated at the low end of its on-orbit range by comparing the differences between vicarious cold reference TBs of it and adjacent TMR channels with those predicted by theory. At the high end of the TB range, comparisons are made with TMR TBs over suitable regions of the Sahara desert and Amazon rain forest. Characterization of JMR performance at intermediate TB levels is possible using a variety of statistical intercomparison techniques.