Comparing SMMR and AVHRR data for drought monitoring

Coincident Scanning Microwave Multi-channel Radiometer 37 GHz and Advanced Very High Resolution Radiometer normalized difference vegetation index satellite data have been compared from drought-affected regions of sub-Saharan Africa and northeastern Brazil for the time period of 1980–1985. Although the two satellite data types can be highly correlated, differences between them were found for the Sahel zone in 1985 and for northeastern Brazil from 1984–1985. These findings suggest that scattering or surface roughness contributions may be greater than previously assumed for the 37 GHz microwave data. A programme of field measurements should be undertaken to increase our understanding of natural vegetation at 37 GHz and higher microwave frequencies.