Relating Nimbus-7 37 GHz data to global land-surface evaporation, primary productivity and the atmospheric CO2concentration

Abstract

Global observations at 37 GHz frequency by the scanning multichannel microwave radiometer (SMMR) on board the Nimbus-7 satellite are related to zonal variations of land surface evaporation and primary productivity, and to temporal variation of atmospheric CO₂ concentration. The ground resolution of the 37 GHz data used in this study is 0·25° × 0·25° (latitude × longitude) and is composited monthly from January 1979 to December 1985. The annual actual evaporation and primary productivity data are extracted from the literature and correspond to averages for 5° latitude bands from 75° N to 55°S, while the CO₂ data are monthly observations at 20 globally distributed monitoring stations from August 1981 to July 1983. The satellite sensor data have been averaged for 7 years and then averaged zonally in 5° latitude bands to relate to evaporation and primary productivity, while the monthly satellite sensor data have been averaged from 75° N to 55° S to relate to the CO₂ data. The temporal variation of CO₂ concentration and the zonal variations of evaporation and primary productivity are shown to be highly correlated with the satellite sensor data. Evaporation and primary productivity for latitude bands in the Sahel zone of Africa appear anamolous when compared with the satellite sensor data, perhaps because the estimated evaporation and primary productivity values do not represent the recent drought conditions over the Sahel zone. Potential usefulness of the 37 GHz data for global biospheric and climate studies are suggested.