MIPAS USED AS A NONLOCAL THERMODYNAMIC-EQUILIBRIUM SOUNDER FOR NO 5.3MU-M BAND

The spaceborne MIPAS experiment has been numerically simulated in the 5.3 mu m spectral domain, and the possible nonlocal thermodynamic equi librium (non-LTE) emissions from NO have been investigated. The interf ering non-LTE contributions from H2O, CO2, and O-3 to atmospheric limb radiances have been estimated. The results have shown a negligibly sm all non-LTE interference from H2O, CO2, and O-3 but a considerable non LTE effect from NO in the stratosphere. The inverse problem has been formulated for the retrieval of the NO vertical profile and the vibrat ional temperatures of the NO lower vibrational states. The optimal est imation technique has been selected as a tool for the evaluation of th e retrieval accuracy of NO number density and vibrational temperature vertical profiles, The error matrix calculations have shown that the r etrieval accuracy for NO concentration is 30-40% in the altitude regio n 10-50 km in case of simultaneous retrieval of NO and vibrational tem perature vertical profiles but can be improved by 10% if averaging of spectra is performed to achieve low noise. The retrieval accuracy for the vibrational temperatures of the X1/2-1 and X3/2-1 states was estim ated to be better than 10 K in the stratosphere, but for the states X1 /2-2 and X3/2-2, it appeared to be rather poor. The problem of NO vert ical profile retrieval in the non-LTE atmosphere is discussed. It was shown that in order to obtain a reasonable accuracy of NO retrieval of 20% up to 50 km altitude, it is necessary that the a priori uncertain ty of the vibrational temperature df the state X1/2-1 is not higher th an 5 K.