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Ann. Geophys., 23, 2415-2424, 2005
www.ann-geophys.net/23/2415/2005/
© European Geosciences Union 2005
Intercomparison of multiple years of MODIS, MISR and radar cloud-top heights
C. M. Naud1,*, J.-P. Muller1, E. E. Clothiaux2, B. A. Baum3, and W. P. Menzel4
1University College London, Department of Geomatic Engineering, Gower Street, London WC1E 6BT, UK
2The Pennsylvania State University, Dept. of Meteorology, 603 Walker Building, University Park, PA 16802, USA
3NASA/Langley Research Center, Hampton, VA 23681, USA
4NOAA/NESDIS, 1225 W. Dayton St., Madison, WI 53706, USA
*now at: Columbia University, 2880 Broadway, New York, NY 10025, USA
Abstract. Radar cloud-top heights were retrieved at both the Chilbolton Facility for
Atmospheric and Radio Research, UK (CFARR) and the ARM Southern Great Plain
site, USA (SGP), using millimetre wave cloud radars and identical algorithms.
The resulting cloud-top heights were used for comparison with MODIS and MISR
retrieved cloud-top heights, from March 2000 to October 2003. Both imaging
instruments reside on the NASA Earth Observing System (EOS) Terra platform
launched in 1999. MODIS and MISR cloud-top products were from the recent
collections (4 and 3, respectively) that cover the entire mission. The cloud
characteristics are different at each ground site, with clouds generally
residing at higher altitudes at SGP, but with a greater occurrence of broken
or multilayered clouds at CFARR. A method is presented to automatically
eliminate scenes where clouds are of a broken nature, since it is difficult in
these conditions to ensure that ground-based and satellite measurements
refer to the same cloud deck. The intercomparison between MODIS and radar
cloud-top heights reveals that MODIS cloud-top heights agree with radar
within about 1km for mid- and high-level clouds. However, this accuracy is
degraded to nearly 3 km for low-level clouds. MISR cloud-top heights are
found to agree with radar cloud-top heights to within 0.6 km, which is in
line with theoretical expectations. In single-level cloud situations MODIS
and MISR cloud-top heights tend to agree within 1 km. This comparison also
reveals that the loss of radar sensitivity during 2001 resulted in the CFARR
instrument being less accurate for high-level cloud-top height measurements.
Keywords. Atmospheric composition and structure (Instruments
and techniques)
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