RETRIEVAL OF ATMOSPHERIC TEMPERATURE FROM AIRBORNE MICROWAVE RADIOMETER OBSERVATIONS

摘要

Atmospheric temperature is a key geophysical parameterrnassociated with fields such as meteorology, climatology,rnor photochemistry. There exist several techniques to measurerntemperature profiles. In the case of microwave remoternsensing, the vertical temperature profile can be estimatedrnfrom thermal emission lines of molecular oxygen.rnThe MTP (Microwave Temperature Profiler) instrumentrnis an airborne radiometer developed at the Jet PropulsionrnLaboratory (JPL), United States. The instrument passivelyrnmeasures natural thermal emission from oxygenrnlines at 3 frequencies and at a selection of 10 viewingrnangles (from near zenith to near nadir). MTP has participatedrnin hundreds of flights, including on DLR’s Falconrnand HALO aircrafts. These flights have provided data ofrnthe vertical temperature distribution from the tropospherernto the lower stratosphere with a good temporal and spatialrnresolution. In this work, we present temperature retrievalsrnbased on the Tikhonov-type regularized nonlinearrnleast squares fitting method. In particular, Jacobians (i.e.rntemperature derivatives) are evaluated by means of automaticrndifferentiation. The retrieval performance fromrnthe MTP measurements is analyzed by using syntheticrndata. Besides, the vertical sensitivity of the temperaturernretrieval is studied by weighting functions characterizingrnthe sensitivity of the transmission at different frequenciesrnwith respect to changes of altitude levels.