The information content of data from satellite sounding systems: A simulation study

The potential of the TIROS Operational Vertical Sounder (TOVS) and the Advanced TOYS (ATOVS) for providing information on the vertical profiles of atmospheric temperature and humidity is investigated. the theoretical performances of these systems are examined primarily in terms of their ability to contribute information to a numerical weather prediction (NWP) system. the covariance of retrieval error expected from an optimal nonlinear inversion scheme, which retrieves simultaneously all the atmospheric and surface variables which significantly affect the measured radiances, is calculated theoretically and compared with the covariance of error assumed in the prior information which constrains the inversion. Performance is assessed for different combinations of radiometers, corresponding to present and future operational systems, and for different sets of assumed conditions: in the atmospheric profile, the cloud conditions, the surface characteristics and the assumed prior knowledge of these variables. The potential performance of ATOVS is shown to be a considerable improvement on the present TOVS in many respects. the value of retaining a combined infrared and microwave system is confirmed. It is demonstrated that, although the ability of these sounding systems to improve on an NWP model's analyses of temperature and humidity is rather limited, the potential for improving on the analysis of layer quantities is much greater. Some new ideas are presented for extending current retrieval methods to accommodate the additional problems presented by ATOVS data. Methods are proposed for treating the effects of microwave surface emissivity and cloud liquid water in a simultaneous inversion.