THE VERTICAL RESOLUTION OF SATELLITE-BORNE RADIOMETERS FOR ATMOSPHERIC MEASUREMENTS

Temperature and composition profiles of the earth's atmosphere may be deduced from measurements of emitted thermal radiation made by satelli te borne instruments. Such measurements have the advantage of continuo us global coverage, but have poor vertical resolution compared with ra dio- and rocket-sondes. The measured signals depend on weighted averag es of the profiles over height so that the measurements are insensitiv e to fine scale structure. Conversely, fine scale structure in a profi le retrieved from the radiances depends critically on the values of th e measured radiances, which include an element of random noise; a bala nce has to be made between resolution and precision of the retrieved p rofile. In this paper, linear system theory is applied to radiometers for atmospheric remote sensing. Fourier transform methods, commonly us ed in the analysis of time dependent or spatial signal processing syst ems, provide a quantitative relationship between vertical resolution a nd precision through the spatial wavenumber response function. Simplif ied atmospheric and spectroscopic models are used to determine the res ponse functions for several types of nadir and limb sounding radiomete rs.