An Evaluation of Direct Readout Infrared Data

Abstract

The appearance of clouds in the video and the 11.5- and 6.7-µm infrared satellite bands is compared with contemporary observations taken aboard a jet reconnaissance aircraft. Attempts are made to extract temperatures from satellite infrared imagery by comparing the brightness of the target with the calibration step wedge transmitted by the satellite. In the presence of the type of cirrus clouds observed on the flights, satellite-measured cloud-top temperatures are misleading due to the transmissivity of cirrus. However, most cirrus are easily recognized in the facsimile presentation by their appearance and organisation. Some cirrus observable from the air cannot be seen either from the ground or in the video and 11.5-µm satellite bands. This so-called ?invisible? cirrus presents no weather or flight hazard; but according to earlier investigators, this could cause errors in the interpretation of temperature data. The 6.7-µm channel offers hope of identifying areas of invisible cirrus and thus the possibility of correcting for its effects.