Xiuping Yan
IUP
24.06.2005, 13.00 c.t.
Room S3120
SCIAMACHY (SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY) is a remote sensor flying on the ESA (European Space Agency) ENVISAT satellite.
The primary scientific objective of SCIAMACHY is the measurements of atmospheric trace gases in both the troposphere and stratosphere. However clouds residing in the troposphere do interfere with the retrievals from SCIAMACHY measurements by the shielding effect and albedo effect. In order to correct for the effect of clouds, a fast and reliable cloud fraction algorithm is necessary for SCIAMACHY.
The fast SCIAMACHY PMD Cloud Algorithm (SPCA)
is a cloud fraction algorithm using the broad band measurements of the SCIAMACHY
Polarisation Measurement Devices (PMD). The basic principle of the algorithm is
that the cloud albedo is much higher than the earth’s surface albedo. Therefore
a measurement containing clouds will have a higher detector signal than one that
is cloud free. The mathematical principle is a threshold technique. The maximum
threshold represents a cloudy situation while the minimum threshold defines a
cloud free situation. The cloud fraction is calculated by comparing a PMD signal
with the maximum and minimum thresholds. The results of SPCA have been validated
by comparison with other SCIAMACHY retrievals such as HICRU (Heidelberg
Iterative Cloud Retrieval Utilities), FRESCO (Fast Retrieval Scheme for Clouds
from the Oxygen A-band) and OCRA (Optical Cloud Recognition Algorithm), as well
as the cloud climatology from the ISCCP (International Satellite Cloud
Climatology Project). In the talk, the process for developing SPCA and the
results of the comparisons will be presented.