This radiometer, the TRMM Microwave Imager (TMI) is well-calibrated, similar to SSM/I, and contains lower frequency channels required for sea surface temperature retrievals. The entire data set includes sea surface temperatures (SST), surface wind speeds derived using two different radiometer channels, atmospheric water vapor, liquid cloud water and rain rates. TRMM is a joint program between NASA and the National Space Development Agency of Japan (NASDA).
The TMI data are provided as daily maps (separated into ascending and descending orbit segments), 3-day mean maps, weekly mean maps and monthly mean maps. The data are available from December 1997 to the present. All images cover a global region extending from 40S to 40N at a pixel resolution of 0.25 deg (~25 km). Unlike SSM/I on DMSP platforms, the TRMM satellite travels west to east in a semi-equatorial orbit. This produces data collected at changing local times for any given earth location between 40S and 40N. The DMSP platforms are in a near-polar, sun-synchronous orbit. Therefore, the SSM/I instruments collect data daily at the same local time. Due to these orbital differences, we offer morning/evening (local time) maps of SSM/I data and ascending/descending maps of TRMM data.