Cirrus cloud shape detection by tomographic extinction retrievals from infrared limb emission sounder measurements

Abstract. An improved cloud index-based method for the detection of clouds in limb sounder data is presented that exploits the spatial overlap of measurements to more precisely detect the location of (optically thin) clouds. A second method based on a tomographic extinction retrieval is also presented. Using CALIPSO data and a generic advanced infrared limb imaging instrument as example for a synthetic study, the new cloud index method is better in detecting the horizontal cloud extent in comparison to the traditional cloud index and has a reduction of false positive cloud detection events by about 30 %. The results for the extinction retrieval show even an improvement of 60 %. In a second step, the extinction retrieval is applied to real 3-D measurements of the air-borne limb sounder GLORIA taken during the Wave-driven ISentropic Exchange (WISE) campaign to retrieve small-scale cirrus clouds with high spatial accuracy.