Jet Contrail Identification Using the AVI-IRR Infrared Split Window

Abstract

Advanced Very High Resolution Radiometer channels 4 (11 ?m) and 5 (12 ?m) are used together to produce images which greatly enhance contrails. Four steps are required: 1) select coregistered digital data sets from the two channels; 2) convert each raw grayshade to a calibrated brightness temperature; 3) substract corresponding channel 5 temperatures from channel 4 temperatures, creating a field of temperature differences; and 4) display these differences as an image. On the image, the earth's surface and all but thin ice clouds are associated WM small temperature differences (of about ?1 to +2 K in the midlatitudes) and appear dark. Newly formed contrails and other thin ice clouds, which are associated with larger temperature differences (of about +2 to +6 K in the midlatitudes), appear bright and stand out well against a dark background.