Operational rain-rate algorithms utilize a combination of emission and scattering indices to characterize observed brightness temperatures as related to either cloud water or cloud ice content. Since signatures relating to ice are easily detectable over both land and ocean, a scattering index approach is applied to rainfall estimation for all areas. Since emissions related directly to rain can be detected over oceans, an emission component to rain is included over the ocean. This technique includes identification of rain/no-rain using a threshold where CLW amounts above about 0.2 mm are indicative of rain.

Rain rates are determined using empirical relationships developed with co-incident radar data. Studies indicate that microwave observations using these techniques are capable of detecting a minimum rain rate over land of about 0.5 mm/h while over ocean it is about 0.2 mm/h. Accuracy of the POES rain-rate estimates has been shown to be within about 2 mm/h RMS when compared to radar observations. The reliability of radar rain rates used for this type of verification has been noted by various researchers.

Melting snow and sea ice can create false rain rate signatures. Melting snow is a problem particularly over the Great Plains of the U.S. Coastlines provide another source of contamination due to FOVs that contain a mix of ocean and land effects. Algorithms employ careful screening techniques to help filter out various potential sources for contamination.