Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments
Current algorithms for the determination of cloud top height and cloud fraction in Polar Regions tend to provide unreliable results, particularly in the presence of isothermal conditions within the atmosphere. Alternative methods to determine cloud top heights in such regions effectively, from space...
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ftucl:oai:eprints.ucl.ac.uk.OAI2:1420871 2023-05-15T16:28:20+02:00 Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments Fisher, D Muller, J-P 2012 http://discovery.ucl.ac.uk/1420871/ unknown In: International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives. (pp. 109 - 113). (2012) Proceedings paper 2012 ftucl 2015-03-26T23:11:28Z Current algorithms for the determination of cloud top height and cloud fraction in Polar Regions tend to provide unreliable results, particularly in the presence of isothermal conditions within the atmosphere. Alternative methods to determine cloud top heights in such regions effectively, from space borne sensors, are currently limited to stereo-photogrammetry and active sensing methods, such as LiDAR. Here we apply the modified census transform to one month of AATSR stereo data from June 2008. AATSR is unique in that it is the only space borne stereo capable instrument providing data continuously in both the visible, near infrared and thermal channels. This allows for year round imaging of the poles and therefore year round cloud top height and cloud fraction estimation. We attempt a preliminary validation of the stereo retrieved cloud top height measurements from AATSR against collocated cloud height measurements from the CALIOP LiDAR instrument. CALIOP provides an excellent validation tool due to its excellent height resolution of between 30-60 meters. In this validation, a pair of collocated swaths is assessed with a total of 154 inter-comparisons; the results show that AATSR correlates well with CALIOP cloud base layers with an R score of 0.71. However, in all cases AATSR appears to be underestimating the cloud top height compared to CALIOP, the causes for this are currently not fully understood and more extensive inter-comparisons are required. Once validation is completed a processing chain is in place to process the entire ATSR time-series data generating a 20 year cloud top height dataset for Greenland. Report Greenland University College London: UCL Discovery Greenland |
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University College London: UCL Discovery |
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ftucl |
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description |
Current algorithms for the determination of cloud top height and cloud fraction in Polar Regions tend to provide unreliable results, particularly in the presence of isothermal conditions within the atmosphere. Alternative methods to determine cloud top heights in such regions effectively, from space borne sensors, are currently limited to stereo-photogrammetry and active sensing methods, such as LiDAR. Here we apply the modified census transform to one month of AATSR stereo data from June 2008. AATSR is unique in that it is the only space borne stereo capable instrument providing data continuously in both the visible, near infrared and thermal channels. This allows for year round imaging of the poles and therefore year round cloud top height and cloud fraction estimation. We attempt a preliminary validation of the stereo retrieved cloud top height measurements from AATSR against collocated cloud height measurements from the CALIOP LiDAR instrument. CALIOP provides an excellent validation tool due to its excellent height resolution of between 30-60 meters. In this validation, a pair of collocated swaths is assessed with a total of 154 inter-comparisons; the results show that AATSR correlates well with CALIOP cloud base layers with an R score of 0.71. However, in all cases AATSR appears to be underestimating the cloud top height compared to CALIOP, the causes for this are currently not fully understood and more extensive inter-comparisons are required. Once validation is completed a processing chain is in place to process the entire ATSR time-series data generating a 20 year cloud top height dataset for Greenland. |
format |
Report |
author |
Fisher, D Muller, J-P |
spellingShingle |
Fisher, D Muller, J-P Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
author_facet |
Fisher, D Muller, J-P |
author_sort |
Fisher, D |
title |
Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
title_short |
Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
title_full |
Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
title_fullStr |
Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
title_full_unstemmed |
Stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (ATSR) instruments |
title_sort |
stereo derived cloud top height climatology over greenland from 20 years of the along track scanning radiometer (atsr) instruments |
publishDate |
2012 |
url |
http://discovery.ucl.ac.uk/1420871/ |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Greenland |
genre_facet |
Greenland |
op_source |
In: International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives. (pp. 109 - 113). (2012) |
_version_ |
1766017982309335040 |