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The retrieval of cloud-top pressure using combined measurements of MERIS and AATSR

Rasmus Lindstrot(1), Rene Preusker(1) and J├╝rgen Fischer(1)

(1) Freie Universit├Ąt Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany


Measurements of the Medium Resolution Imaging Spectrometer (MERIS) within the oxygen A band at 761nm are operationally used for the retrieval of cloud-top pressure. A validation with airborne lidar measurements revealed a high accuracy (~25hPa) of the cloud-top pressure product in case of low, singlelayer clouds. However, the sensitivity of MERIS measurements to high clouds is weak, due to the narrow absorption lines at low pressure. The errors for high clouds are therefore large, especially in case of underlying low-level clouds. This problem can be resolved by combining MERIS observations with measurements in the thermal infrared spectral range. Since clouds are strongly absorbing at infrared wavelengths, the cloud-top temperature of even optically thin clouds can be determined and related to cloud-top pressure using the respective temperature profile. The Advanced Along Track Scanning Radiometer (AATSR) onboard ENVISAT provides radiance measurements in the thermal infrared region that can easily be combined with MERIS observations, since both are nadir viewing, imaging instruments with a similar spatial resolution of ~1km. The synergetic use of MERIS and AATSR improves the accuracy and reliablility of the retrieval of cloud-top pressure. Additionally, the height of multiple cloud layers can be estimated, using large differences of retrieved cloud-top pressure of MERIS and AATSR as an indicator for multilayer clouds. The retrieval is based on the Optimal Estimation technique using radiative transfer simulations of the Matrix Operator Model (MOMO).


Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry