Surface moisture and satellite microwave observations in semiarid southern Africa

Nimbus 7 scanning multichannel microwave radiometer 6.6‐GHz passive microwave data were studied in relation to large‐scale soil moisture estimates over a 3‐year period in southeastern Botswana. An extensive data base of weekly surface soil moisture measurements was used with meteorological data to estimate pixel average soil moisture on a daily basis. The influence of the vegetation canopy on the surface emissivity was studied by partitioning the data set into classes on the basis of the normalized difference vegetation index. After correcting for the vegetation optical depth, a correlation of r = 0.84 was established between the normalized brightness temperature observations and surface soil moisture for the 3‐year period.