Infrared Imagery of the Karst Terrain of Lancaster County, Southeastern Pennsylvania

Since the inception of the Pennsylvania sinkhole inventory project in 1985, remote sensing techniques have played a large role in helping to define the areal extent of the karstic landscape. These techniques can range in scope and can often provide valuable data for a number of cross-cutting disciplines in statewide and more regional applications. This includes the use of high resolution laser-based imagery such as lidar and multispectral imagery in forest and agricultural studies. It was during a period of drought that an agricultural survey of Lancaster County revealed crop anomalies related to moisture. Color infrared imagery showed more vigorous growth in zones of increased soil moisture availability. This coincided with the surface expression of subsurface structures related to dissolution along bedrock discontinuities. Color infrared imagery is a useful tool in recognizing areas of stressed vegetation. The near infrared (NIR) portion of the spectrum can be used to measure leaf moisture as well as plant health. The near infrared range of 0.8–1.1 μm reflects brightly when a plant has sufficient water and chlorophyll. Thus plants growing in an area with increased soil moisture relative to surrounding areas during a time of drought will have higher reflectance in the NIR and more easily interpreted. An advantage in using the infrared imagery is that it is not dependent on being free of vegetative cover. One can interpret patterns of stressed vs. non-stressed vegetation and not be limited to using leaf-off aerial imagery. In addition, finer resolutions provide a more usable base than a standard 1:24,000 topographic map. Coupled with GIS software, the newer digital photography can be georeferenced and interpreted features can be transferred to the base map without major offsets. This results in a more accurate location of karst surface features during the early phase of a site investigation or in the creation of a karst features map.