Satellite Infrared/Other Climate Rainfall Products

Satellite infrared window channel measurements around the 11 to 12 micron band have long been used to estimate precipitation over the tropics. The availability of IR window channels on board geostationary satellites, which see through to the surface except when clouds are present, provides high temporal sampling (3-hourly or better) from space. Since clouds are opaque at IR frequencies, the resulting brightness temperatures over cloudy regions corresponds to the temperature of the cloud top, providing a measure of the cloud-top height. In the tropics where deep convection is prevalent, high-level cloudiness is reasonably well correlated with precipitation, at least when averaged over large space and time scales. Unfortunately the relationship between cloud-top height and precipitation changes with latitude and over land as well as over regions with significant amounts of non-precipitating cirrus or other clouds. As a result, IR only techniques suffer from significant regional and time dependent biases, which is why the merged techniques use passive microwave rain estimates to "adjust" the IR estimates.

GPI [More information] [Plot Intercomparison]
The GPI or Global Precipitation Index computes rainfall using a simple cloud-top temperature treshold technique from geostationary IR window channel data. This product is one of the component satellite products used in the GPCP merged satellite/gauge dataset and covers the period from January 1986 through the present.
Adjusted GPI [More information] [Plot Intercomparison]
Monthly GPI rain estimates are adjusted based on monthly accumulations of passive microwave rain estimates from SSM/I. This product is one of the component satellite products used in the GPCP merged satellite/gauge dataset and covers the period from January 1986 through the present.
GPCP OPI [More information] [Plot Intercomparison]
The OPI or Outgoing Longwave Radiation (OLR) Precipitation Index uses the merged satellite gauge CMAP dataset to calibrate OLR observations from NOAA's polar-orbiting satellites. This product is of the component satellite products used in the GPCP merged satellite/gauge dataset and covers the period from July 1987 through December 1987.
NCEP OPI [More information] [Plot Intercomparison]
The OPI or Outgoing Longwave Radiation (OLR) Precipitation Index uses the merged satellite gauge CMAP dataset to calibrate OLR observations from NOAA's polar-orbiting satellites. This product is produced by NCEP and it is used in the merged CAMS-OPI dataset. It covers the period from January 1979 through the present.
TOVS [More information] [Plot Intercomparison]
Infrared sounding observations from the TIROS Operational Vertical Sounder (TOVS) on board NOAA's polar-orbiting satellites is used to infer precipitation from deep, extensive clouds. This product is one of the component satellite products used in the GPCP merged satellite/gauge dataset and covers the period from July 1987 through the present.