Detection of multilayer cirrus cloud systems using AVHRR data: Verification based on FIRE II IFO composite measurements

Abstract

A numerical scheme has been developed to identify multilayer cirrus cloud systems using Advanced Very High Resolution Radiometer (AVHRR) data. It is based on the physical properties of the AVHRR channels 1-2 reflectance ratios, the brightness temperature differences between channel 4 and 5, and the channel 4 brightness temperature. In this scheme, clear pixels are fist separated from cloudy pixels, which are then classified into three types: cirrus, cirrus/low cloud, and low clouds. The authors have applied this scheme to the satellite data collected over the FIRE II IFO [First ISCCP (International Satellite Cloud Climatologly Project) Regional Experiment II intensive field observation] area during nine overpasses within seven observation dates. Determination of the threshold values used in the detection scheme are based on statistical analyses of these satellite data. The authors have validated the detection results against the cloudy conditions inferred from the collocated and coincident ground-based lidar and radar images, balloonborne replicator data, and National Center for Atmospheric Research CLASS (Cross-chain Loran Atmospheric Sounding System) humidity soundings on a case-by-case basis. In every case, the satellite detection results are consistent with the cloudy conditions infered from these independent and complementary measurements. The present scheme is well suited for the detection of midlatitude, multilayer cirrus cloud systems and tropical anvils.