Information content and optimisation of high spectral resolution remote measurements

Remote measurements of the atmosphere with high spectral resolution from the ground or from space. are being or will be made from a new generation of instruments such as the Fourier transform or grating spectrometers AIRS, MIPAS, TES or IASI. Such measurements would appear to contain a large amount. of information about the atmosphere, but it is not immediately obvious how to quantify it or to use it efficiently or effectively. The somewhat neglected concepts of 'information content' and 'degrees of freedom for signal' provide single parameters which can be used in the automated optimisation of, for example, instrument design parameters, the selection of microwindows or subsets of channels for retrieval: the optimisation of retrieval strategy, and the understanding of the information content of a spectrum. Some such applications are illustrated by means of simulated spectra for the AIRS instrument. (C) 1998 COSPAR. Published by Elsevier Science Ltd.