Application of AVHRR/3 Imagery for the Improved Detection of Thin Cirrus Clouds and Specification of Cloud-Top Phase

Abstract

A multisensor, data fusion technique has been developed that merges the spectral signatures of ice and water clouds in Advanced Very High Resolution Radiometer (AVHRR) imagery with cloud-top pressure analyses derived from the High-Resolution Infrared Sounder (HIRS) to retrieve cloud-top phase and then cloud-top temperatures. While the performance of this algorithm has been encouraging, the specification of cloud-top phase is impacted by the absence of a unique spectral signature for either ice particles or water droplets in AVHRR/2 imagery and the inability to successfully identify very thin cirrus clouds, especially in daytime imagery, with automated cloud detection procedures. With the launch of the AVHRR/3 sensor, new spectral imagery in the 1.6-?m band will ultimately become available, which could help resolve these inadequacies. Thus, the utility of data in the 1.6-?m band is examined for improving the specification of cloud-top phase, while a derived 3.7-?m albedo channel is evaluated for enhancing the automated detection of very thin cirrus clouds in daytime imagery collected over a variety of surfaces. It is concluded that optimal performance of the cloud-top phase algorithm requires the use of both the 1.6- and 3.7-?m bands along with other AVHRR/2 channels. Unfortunately, since these data are not scheduled for simultaneous transmission in the Television Infrared Oberservational Satellite data stream, different implementation strategies are recommended for use with the transmission of the 3.7-?m channel, the 1.6-?m data, and both should they become available in the future.