Abstract
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)
Highlights
The principal objective of this work is to provide an independent assessment of satellite-based, cloud-top pressure/height products that are produced operationally for the Moderate resolution Imaging Spectrometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) instruments
We initially found 82 cases at Southern Great Plains (SGP) and 71 cases at Chilbolton Facility for Atmospheric and Radio Research (CFARR), with clouds detected by both radar and MODIS
At SGP, 22 cases retrieved with CO2-slicing showed that MODIS cloud-top heights were lower than radar cloud-top heights by an average difference of −1.2±1.0 km
Summary
The principal objective of this work is to provide an independent assessment of satellite-based, cloud-top pressure/height products that are produced operationally for the Moderate resolution Imaging Spectrometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) instruments. Both instruments are on NASA’s Earth Observing System (EOS) Terra platform that was launched on 18 December 1999. As will be discussed further throughout this article, each method has strengths and weaknesses that can be evaluated through comparison with independent cloud boundary assessments derived from ground-based radar The focus of this investigation is to compare the Terra platform cloud-top pressure/height product from both MODIS and MISR to ground-based cloud observations from two surface sites
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