High-Resolution Image

To estimate rainfall over tropical land and oceans, a multichannel passive microwave radiometer (TMI) and a precipitation radar were flown onboard the TRMM satellite. The radar areal coverage is limited to a swath width of 220 km while the TMI covers a much larger area with a 760km conical swath. The TMI, being a passive sensor of rain, requires calibration from the onboard radar. The Figure shows a map of the brightness temperature measured by the TMI over southeast United States. (The inset map in the figure indicates rain area). By comparing this map with the radar rain rate map we find the TMI map depicts only qualitatively the spatial distribution of rain rate. In order to estimate rain rate quantitatively from the wider TMI area it is necessary to discriminate convective rain from stratiform rain. This can be done crudely with the help of local minima observed in the TMI map. Such minima identify thunderstorms. This information along with the multichannel measurements of TMI can help to improve rainrate estimation.
(submitted by Prabhakara Cuddapah)