On the use of ICESAT‐GLAS measurements for MODIS and SEVIRI cloud‐top height accuracy assessment

This study reports on the first attempt to use cloud boundary and optical depth retrievals from the GLAS lidar to assess the accuracy of cloud‐top heights obtained with MODIS (onboard NASA‐TERRA and AQUA) and SEVIRI (onboard METEOSAT‐8). Over the period from 25 September to 18 November 2003, MODIS‐GLAS coincidences were only found in the Polar Regions, whilst SEVIRI‐GLAS coincidences were available for a larger range of latitudes. For both passive instruments, cloud‐top heights were overestimated by about 300–400 m when clouds were low and opaque. For high and thin clouds, MODIS and SEVIRI cloud‐top heights were underestimated, and the bias increased with decreasing optical depth. For optical depths below 0.3, the number of misdetections increased significantly and the bias in cloud‐top height increased from 1 to 2 km. The bias was found to be larger when lower cloud layers were present.

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