Infra-red atmospheric temperature sounding from satellites

On 8th April 1970 the Selective Chopper Radiometer (S.C.R.) was launched into a polar orbit on the Nimbus 4 meteorological spacecraft. Since that date the instrument has produced nearly four million temperature profiles of the Earth´s atmosphere, from the ground up to 50 km, in most cases to an accuracy of 1 or 2K. This has therefore made it possible for the first time to study the temperature parameters of the atmosphere daily on a global basis. Results from the S.C.R. and future experiments will therefore have a marked effect on meteorology, which in the past has had to rely on rather sparsely distributed radio and rocket sondes. The principle of operation of the experiment is the measurement of infra-red energy in the 15 ¿m band originating from atmospheric carbon dioxide, but within the band, precise wavelength selection is obtained by combination of interference filters and selective chopping by carbon dioxide cells. This enables the six channels to be tuned to regions of different absorption coefficient in the 15 ¿m wavelength band, and hence to receive radiation from different heights within the atmosphere.