USE OF CIR IMAGERY IN TIME OF DROUGHT FOR GEOLOGIC MAPPING IN CROP-COVERED TERRAIN

During the 1999 drought in Lancaster County, Pennsylvania, crops under water stress were useful in delineating previously unknown geologic structure. One meter color infrared (CIR) aerial photography was converted into digital orthos. The spatially correct imagery allowed researchers to locate features within 1-2 meters.

Differential availability of water in the subsoil appears to be the controlling factor in vegetative health: bedding was visible because of the varying water-holding capacity of the parent material. Because the effect was of a differential nature, bedding or fractures are evident in a variety of lithologies including schist, limestone, shale, etc.

Shallow-rooted vegetation, such as may be found in a lawn, did not show underlying structure, nor did it matter if the near surface had been disturbed. Crops such as soybeans, corn or alfalfa, were essential in providing a uniform base to display small differences in vigor related to water stress.