An operational processing system is described for the automated retrieval of\udcloud-top heights (CTHs) and amounts from the Gridded Brightness\udTemperature (GBT) 1 km product derived from the dual view of the Along\udTrack Scanning Radiometer (ATSR-2) instrument onboard the ESA ERS-2\udsatellite. A new stereo matching algorithm, called M4 is described together with\udthe overall processing chain for retrieving cloud-top heights and amounts. M4 is\udbased on the successful stereo matchers, M2 and M3 which have been in\udoperation with the NASA MISR sensor since March 2000 and which have also\udbeen applied to mapping cloud fraction in the polar region using ATSR-2\ud(Cawkwell and Bamber 2002, Cawkwell et al. 2001). Results in companion\udpapers (Naud et al., Denis et al. 2007) describe the accuracy achieved using this\udalgorithm and detailed scene-by-scene results are available from http://\udcloudmap.org under results-.UCL-.ATSR-2 Validation. We assess the impact\udof cloud-top winds on the accuracy of the retrieved cloud-top heights and\udconclude that for most middle and lower tropospheric clouds, cloud-top winds\udwill have little, if any, noticeable impact. We show how ATSR-2 cloud-top\udheights at the different wavelengths (particularly visible compared with thermal\udIR) can sometimes yield information on multi-layer clouds which is unique to\udATSR-2. The processing system has recently been applied to three years of\udASTR-2 GBT data and results are shown. These results are available from the\udBritish Atmospheric Data Centre (http://badc.nerc.ac.uk/data/list_all_datasets.\udhtml?source5data).
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