Derivation of temperature and pressure from submillimetric limb observations

We demonstrate the feasibility of retrieval of temperature and pressure pro files from spaceborne limb-sounding spectroscopic measurements in the submi llimetric region. Whether these profiles can be retrieved determines whethe r a submillimetric instrument can be self-sufficient as far as the atmosphe ric model is concerned or whether complementary sensors in other spectral r egions, dedicated to temperature and pressure measurements, are needed. Mol ecular-oxygen transitions are selected for the purpose of temperature and p ressure retrieval on the basis of realistic observational parameters. We us e a mathematical model of the retrieval process to evaluate the information content of the spectral features and to study the trade-off between the un certainty of the retrieved profiles and their vertical resolution. It is sh own that, using only one oxygen transition and without any constraint, one can achieve uncertainties of 5% for both temperature and pressure from 10 t o similar to 40 km of altitude with a vertical resolution of 3 km; above 40 km the vertical resolution needs to be degraded to limit the uncertainties . The possibility of exploiting a priori information is discussed, as well as the effects of external constraints that can be used to improve the qual ity of the retrieved profiles. The sources of systematic error that need to be considered for the compilation of the total error budget are also evalu ated. (C) 1999 Optical Society of America.