REMOTE SURFACE MAPPING USING ORTHOPHOTOS DRAPED OVER DEMS: APPLICATION TO THE SHEEP MOUNTAIN ANTICLINE, WYOMING

Remote mapping of surface structures can be accomplished by a method involving draping of geologic maps and orthorectified photographs over digital elevation models within a geographic information systems (GIS) database. The method improves the accuracy and efficiency of mapping over traditional approaches using aerial photographs and satellite images. Formation contacts can be more accurately mapped by viewing the images in three-dimensions and removing distortions associated with the use of stereo images. In addition, quantitative measurements of bedding attitude can be obtained using two approaches: (1) slope measurements from dip slopes, and (2) intersections of bedding and topography. Bedding attitudes from dip slopes involves extraction of dip data from the maximum value of slope, and strike data from the trend of the outcrop. Intersections of bedding with the topography can also be used to determine bedding attitude by determining the best-fit median plane for multiple points on the plane.

These methods are applied to the Sheep Mountain anticline, located on the eastern margin of the Bighorn basin in northern Wyoming, to study the correlation between the measurements obtained using remote mapping methods with those obtained by direct field mapping. Mapping in three dimensions provides better control in the placement of formational contacts at topographic V’s formed by an intricate network of bedding-normal drainage in the study area. The structural orientations from the two different methods mentioned above are statistically compared to the field measurements. The results show good positive correlation between the measured and interpreted dips. These observations suggest that this mapping technique can be used as a reconnaissance tool for structural mapping in a relatively short period of time. It can also be used to map relatively inaccessible areas to produce accurate structural maps.