 |
| Titel |
The retrieval of cloud-top pressure of multilayer clouds using combined measurements of MERIS and AATSR onboard ENVISAT |
| VerfasserIn |
R. Lindstrot, R. Preusker, J. Fischer |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250031072
|
|
|
|
|
|
| Zusammenfassung |
| Measurements of the Medium Resolution Imaging Spectrometer (MERIS) within the oxygen
A band at 762nm 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, single-layer clouds. However, problems arise in
presence of multilayered clouds, as the single channel within the oxygen A band does
not allow the identification of multiple cloud layers. The retrieved cloud height
thus represents the effective single layer height, located in-between the true cloud
layers.
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, as both are
nadir viewing, imaging instruments with a similar spatial resolution of ~1km. The synergetic
measurements can be used for the retrieval of the height of two cloud layers in case the upper
layer is optically thin (Ï -¤ 5).
The retrieval algorithm is based on the Optimal Estimation technique using radiative
transfer simulations of the Matrix Operator Model (MOMO). |
|
|
|
|
|
|