Correction of time-varying radiometric biases in the TRMM Microwave Imager

This paper describes an empirical correction for a time-varying radiometric calibration error present in the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The Tb error is modeled as a function of the spacecraft orbit position and solar angles based on observed systematic differences between the TMI 10 GHz vertically polarized (10V) channel oceanic Tb´s as compared to a radiative transfer model with collocated numerical weather model environmental parameters. This correction technique will be implemented in Version 7 of the TRMM 1B11 data product, which is scheduled to be released in 2010. Available spacecraft in-flight thermal measurements that have relevence to the instrument performance are discussed. Results from thermal modeling of the spacecraft and instrument provide support for the emissive reflector model as the primary cause for the empirical Tb bias estimates. Residual differences between the thermal model and the bias estimates may provide evidence of smaller secondary effects from solar array shadowing of the instrument.