Classification of depressions in landfill covers using uncalibrated thermal-infrared imagery

A two-step analysis was used to classify depressions developed in covers of two landfills: (1) manual delineation of depressions by stereoscopic, aerial photographic interpretation, followed by (2) classification of depressions according to infiltration characteristics using uncalibrated, nighttime, air-borne, thermal IR imagery. Depressions were delineated as landforms according to their topographic expression using color infrared aerial photography. Classification of depressions into Type I or Type II was made by comparison of mean values of the digital numbers (exitance) inside and outside of a depression (interdepressional area). Samples are taken along a single scan line in order to eliminate variations caused by the gain adjustment of the scanner