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 satellite borne instruments. Such measurements have the advantage of continuous global coverage, but have poor vertical resolution compared with radio- and rocketsondes. The measured signals depend on weighted averages of the profiles over height so that the measurements are insensitive to fine scale structure. Conversely, fine scale structure in a profile retrieved from the radiances depends critically on the values of the measured radiances, which include an element of random noise; a balance has to be made between resolution and precision of the retrieved prolile. In this paper, linear system theory is applied to radiometers for atmospheric remote sensing. Fourier transform methods, commonly used in the analysis of time dependent or spatial signal processing systems, provide a quantitative relationship between vertical resolution and precision through the spatial wavenumber response function. Simplified atmospheric and spectroscopic models are used to determine the response functions for several types of nadir and limb sounding radiometers.