Geologic evaluation of 3-5 micrometer infrared imagery and color photography in southern Utah

Abstract

A comparison of 3-5 micrometer, afternoon and midnight infrared (IR) imagery and color photography with conventional aerial photography shows that IR imagery and color photography have some unique capabilities. In general, the IR imagery provides in shades of gray a record of the relative ground temperature at the time the image was taken. It has day or night capabilities for imaging large areas of terrain. In sparsely vegetated areas, midnight IR imagery shows some tonal variations that may be relate to specific rock type based on temperature differences. In heavily vegetated areas, any temperature difference that might exist between rock units is masked by the temperature difference associated with different vegetation communities; although, isolated outcrops in such areas are generally apparent because they are brighter (warmer) on the afternoon IR. On the midnight IR they may or may not be brighter according to their differences in thermal inertia. The afternoon IR image showed one fault that was not visible on the aerial photographs. In contrast, only some of the faults visible in the stereoscopic model were recognized on the IR imagery. The interpreter using IR imagery must be aware of changes in heat patterns resulting from modification of the land by man and from the effect of cloud shadows. Apparent anomalies on IR image resulting from such factors might be misinterpreted. Compared to conventional photography with the added ability of stereoscopic viewing the day and night IR provided less geologic information in the area of study. IR imagery may be useful in hydrologic studies such as the relative temperatures of alpine lakes, ponds, and marshes during the night. and day. It should prove valuable in ecological studies involving the relative temperatures of different plant communities. Roads in heavily wooded areas are easier to see on the IR image, than on conventional photography because of their temperature differences. Color photography, as might be expected, shows the terrain in a close approximation to its natural color, and delineates some stratigraphic units and rock alterations that are indistinguishable on black and white photography.