Three techniques for detecting and mapping sulfur dioxide (SO sub 2 ) effects on the foliage of sensitive crops and trees near large, coal-fired power plants were tested and evaluated. These techniques were spectroradiometry, photometric analysis of aerial photographs, and computer analysis of airborne multispectral scanner data. Spectroradiometry is a useful, ground-based technique for measuring the changes in reflectance that accompany exposure of sensitive crops to SO sub 2 . Photometric analysis of aerial color-infrared photographs has some practical advantages for measuring the reflectances of forest species or for synoptic point-sampling of extensive areas; these tasks cannot be done effectively by field crews. The relationships among reflectance, foliar injury, and yield of crops are complex and are affected by many extraneous variables such as canopy density. The SO sub 2 effects are easier to detect on winter wheat than on soybeans, but in either case they cannot be consistently detected by airborne remote sensors except under near-ideal conditions when the injury is moderate to severe. Airborne multispectral scanner data covering affected soybean fields were analyzed using three computer-assisted procedures: unsupervised, supervised, and pseudosupervised; the last method provided the best results. Landsat imagery was also investigated, but the foliar effects of SO sub 2 were too subtle to detect from orbit. (ERA citation 07:005660)