Tropospheric water vapor retrieval from a nadir THz/FIR sounder

摘要

This work presents clear-sky simulations to study water vapor (H_2O ) retrieval from a nadir sounder operating in the TeraHertz (THz) and Far-Infrared (FIR) spectral domains (100-500 cm~(-1)). The THz/FIR retrieval is compared with retrieval from the mid-InfraRed (IR) 7pm H_2O band (1200-2000 cm~(-1)). The THz/FIR observations are more sensitive in the upper troposphere and lower stratosphere than the IR measurements. On the other hand, the IR sounder has better performance in the lower troposphere. The retrieval error due to uncertainties on the temperature profile are of the same order of magnitude in the THz/FIR and IR bands. No significant retrieval errors from contaminating species have been found. The calculations for several atmospheric scenarios show that retrieval performances are not only dependent on the H 2 0 abundance but also on the temperature gradient. Hence, sensitivity in the UT/LS layer, with a low temperature gradient, is poor. The combination of FIR and IR merges the advantages of both bands, and allows to slightly decorrelate temperature and H20 VMR.