Quantitative assessment on the value of 1.38-um imagery for the automated analysis of optically thin cirrus in daytime imagery

Abstract

While considerable effort has been expended on research into the analysis of optically-thin cirrus clouds, the global detection and accurate identification of these clouds remains inadequate, especially in daytime meteorological satellite imagery collected over land surfaces. Recently, 1.38 micron imagery was recommended for the improved detection of thin cirrus clouds. Since this channel is centered on a strong water vapor absorption band and watervapor is concentrated in the lower atmosphere, solar energy normally reflected by the Earth's surface is absorbed in the 1.38 micron spectral band. Thus, any energy measured by an airborne (or spaceborne) radiometer should originate from scattering off of mid-level water and high-level ice clouds, making even thin cirrus readily detectable. While initial results have been encouraging, quantitative analyses are needed to assess the value of 1.38 micron imagery as a candidate for the next generation of meteorological satellite sensors. Thus, this project investigates the potential for improved thin cirrus detection in daytime imagery using scenes of nearly coincident Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) sensor data, which collects 1.38 micron imagery, and imagery collected by the operational NOAA AVHRR sensors. Automated cloud analyses from these data are compared against manual (ground truth) cloud analyses for each data type. Initial results show that 1.38 micron imagery is valuable for improved thin cirrus detection over land surfaces.