Technical note: A new day- and night-time Meteosat Second Generation Cirrus Detection Algorithm MeCiDA W. Krebs, H. Mannstein, L. Bugliaro, and B. Mayer Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Abstract. A new cirrus detection algorithm for the Spinning Enhanced Visible
and Infra-Red Imager (SEVIRI) aboard the geostationary
Meteosat Second Generation (MSG), MeCiDA, is presented.
The algorithm uses the seven infrared
channels of SEVIRI and thus provides a consistent scheme for cirrus
detection at day and night. MeCiDA combines morphological
and multi-spectral threshold tests and detects optically thick and thin
ice clouds. The thresholds were determined by a comprehensive theoretical
study using radiative transfer simulations for various atmospheric
situations as well as by manually evaluating actual satellite
observations. The cirrus detection has been optimized for mid- and high
latitudes but it could be adapted to other regions as well.
The retrieved cirrus masks have been validated by comparison with the
Moderate Resolution Imaging Spectroradiometer (MODIS) Cirrus Reflection
Flag. To study possible seasonal variations in the performance of the
algorithm, one scene per month of the year 2004 was randomly selected and
compared with the MODIS flag. 81% of the pixels were
classified identically by both algorithms. In a comparison of monthly mean values
for Europe and the North-Atlantic MeCiDA detected 29.3% cirrus coverage, while
the MODIS SWIR cirrus coverage was 38.1%. A lower detection efficiency is to be expected for
MeCiDA, as the spatial resolution of MODIS is considerably better and
as we used only the thermal infrared channels in contrast to the
MODIS algorithm which uses infrared and visible radiances. The advantage
of MeCiDA compared to retrievals for polar orbiting instruments or
previous geostationary satellites is that it permits the derivation of quantitative
data every 15 min, 24 h a day. This high temporal resolution allows
the study of diurnal variations and life cycle aspects. MeCiDA is fast enough for
near real-time applications.
Citation: Krebs, W., Mannstein, H., Bugliaro, L., and Mayer, B.: Technical note: A new day- and night-time Meteosat Second Generation Cirrus Detection Algorithm MeCiDA, Atmos. Chem. Phys., 7, 6145-6159, doi:10.5194/acp-7-6145-2007, 2007.