RALPH N. BAKER General Electric Company-Space Division Beltsville, MD 20705 LANDSAT Data: A New Perspective for Geology A review of the utilization of LANDSAT imagery for geological interpretation. HE LANDSAT (formerly ERTS) satellite geologic mapping, mineral and petroleum T program has been in existence for just exploration, and natural hazards surveys. The over two years, and in this brief time has categories are arbitrary, and results of inves­ added a whole new dimension to the study of tigations might fit equally well into more our Earth. Scientists from all over the world than one of these. have used data measured by LANDSAT's sensors (telemetered down from a REGIONAL STRUCTURAL STUDIES 580-mile-high vantage point in space) to Several investigators studied regional monitor pollution and crop growth, explore structures and their relationships in LAND­ for minerals and petroleum, and conduct a SAT imagery, availing themselves of a per­ host of other investigations ranging from spective previously impossible to achieve. ABSTRACT: The LANDSAT (formerly ERTS) program, while con­ ceived and implemented as a research and development project, has been used as an operational orbital remote sensing system providing data of considerable value to various branches of geology. Areas in which the satellite imagery has been found most useful include re­ gional interpretations ofgeologic structure,lupdating and verifying of geologic maps, mineral and petroleum exploration, and the monitor­ ing of natural hazards such as large-scale erosion and seismicity. Investigations in these areas of application demonstrate the wide variety of uses presently undertaken or envisioned for the future. Many benefits have already been felt; others will be seen in the near future where the promise ofmineral or petroleum concentration will be realized through conventional ground based and satellite explora­ tion techniques. LANDSAT will aid considerably in pinpointing the likely site; "hands on" geology will do the rest. animal migration patterns to iceberg monitor­ Y. Isachsen of New York State's Geological ing. The mission, originally designed for re­ Survey used the IOO-by-IOO-mile images to search and development, has for all practical construct a mosaic of the State and neigh­ purposes been considered "operational" boring regions. This mosaic shows, at a from the user's point of view. glance, geologic relationships of New York To geologists, the regional overview and State's diverse terrain, major rock units, gla­ repetitive coverage of LANDSAT data has cial features, large scale lineaments, and cir­ been particularly useful, enabling them to cular structures (Figure I). Isachsen went take advantage of vegetation and sun angle into the field to verify the existence of many changes in theirattempts to unravel the phys­ of these features discovered in the LAND­ ical history and setting ofthe Earth. Success­ SAT mosaic, and demonstrated how one ful LANDSAT investigations in geology can could use satellite imagery to discern fea­ be grouped for convenience into four general tures unsuspected at a larger scale. categories: regional structural studies, Houston and Marrs, LANDSAT inves- PHOTOGRAMMETRIC ENGINEERING AND REMOTE SENSING, 1233 Vol. 41, No. 10, October 1975, pp. 1233-1239. 1234 PHOTOGRAMMETRIC E GINEERING & REMOTE SENSING, 1975 FIG. 1. LANDSAT mosaic and lineament map of eastern New York State (after Isachsen, 1973). tigators from the University of Wyoming, between surface and sensor, investigators studied geologic structures in Wyoming by have shown that much geological informa­ using a LANDSAT mosaic, and reported that tion can be derived from imagery where the their interpretations compared favorably ground is obscured by vegetation. with known ground truth ofthe region. While this region had been reasonably well mapped GEOLOGIC MAPPI G by conventional field surveys, the The LANDSAT overview and coverage Houston-Marrs study points out the possibil­ cycle makes map correction and verification a ity of interpreting poorly mapped regions natural application to geology. Investigators with a minimum of ground truth, time, and H. Blodget and A. Anderson of NASA's God­ cost with some measure of confidence. dard Space Flight Center constructed a In the East where climate is generally less three-image mosaic of southern Morocco arid than in some Western States, LANDSAT from which they were able to verify and mod­ investigators have still been able to collect ify previously mapped lithologic boundaries, valuable geologic information despite the and investigate relationships between struc­ heavier vegetation cover. For example, re­ tural character and mineral emplacement gional lineaments were discovered and map­ from a regional perspective. A common pro­ ped by Gold and co-investigators at Penn cedure among LANDSAT investigators has State, using LANDSAT imagery of the been to use the imagery as base maps upon thickly forested Pennsylvania Appalachians. which geologic interpretations of structure, A private consulting firm has applied lithology, and lineament patterns are computer-aided enhancementtechniques (in superimposed. Another team of inves­ this case General Electric Company's tigators, M. Abdel-Gawad and J. Silverstein IMAGE 100 multispectral image processing of Rockwell International, discovered that and display system) to imagery ofother areas LANDSAT images of Baja and the Gulf of in eastern Pennsylvania, with success in dis­ California showed several small islands to tinguishing rock outcrops oflimited areal ex­ have been misplaced on conventional maps, tent. Thus, while imagery ofarid regions has both in geographic location and in topo­ the obvious advantage of little interference graphic detail. LANDSAT DATA: A NEW PERSPECTIVE FOR GEOLOGY 1235 M. Viljoen ofSouth Africa used LANDSAT from LANDSAT has been accomplished imagery to unravel the geologic relationships using the following well-known geologic ofthe South African shield. This investigator principles: was able to distinguish between the granite­ • Mineralizing fluids from within the Earth gneiss craton, adjacent metomorphic mobile may follow the paths of least resistance to belts, and major "greenstone" intrusions. the surface; these paths are zones of weak­ The nature of these intrusions and their ness through the Earth's crust and occur characteristic relationship to the overall where the solid rock has been fractured and geologic setting was recognized by Viljoen to faulted. Thus, a concentration of "linea­ be similar to that found in metallic mineral ments", many ofwhich can be discerned in LANDSAT imagery, may well indicate mining districts in Canada (e.g., Sudbury, where the crust is weakest and, therefore, Ontario) and Western Australia, and suggests most likely to be mineralized. that the South African regions might contain • Some rock types discernible from orbital useful concentrations of minerals as well. In altitudes are characteristically associated this example, the roughly 34,OOO-square­ with certain types of minerals because they kilometer region surveyed in a single indicate similar formative conditions or alt­ LANDSAT frame could be broken down into eration through time. mineralization potential maps with consid­ • Mineralization may alter surface tones by secondary enrichment, vegetation stress erable savings in time and cost to mineral andJor chemical changes in the vicinity of exploration interests. On a larger scale, the ore body, all of which can indicate that perhaps the most impressive display of significant mineral concentration has taken LANDSAT's map~making capability can be place. seen in the mosaic of the 48 conterminous Using these and other, more subtle clues, United States, produced by the Soil Conser­ geologists using LANDSAT imagery have vation Service ofthe U. S. Department ofAg­ reported varying degrees of success in min­ riculture, and available to the public (Figure erai and petroleum exploration studies. Some 2). of these investigators have related LANDSAT-discovered Iineaments to known MINERAL AND PETROLEUM EXPLORATION mineral concentrations; many of these The majority of LANDSAT geology inves­ studies have been undertaken in the arid re­ tigations fall into this category primarily be­ gions ofWestern North America. E. Lathram cause ofthe direct impact on current and pro­ and other geologists of the U. S. Geological jected national needs. Mineral exploration Survey discovered a series ofintersecting re- FIG. 2. Mosaic of continental United States compiled from LANDSAT imagery by USDA. 1236 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1975 gional lineaments in a rare cloud-free NIM­ and of little value as ore guides. With the BUS image ofAlaska. These lineaments were relationship demonstrated by these inves­ verified in LANDSAT imagery and enabled tigators, future exploration efforts should be the investigators to propose a radically dif­ simplified markedly (Figure 4). Another ferent picture of mineral emplacement in Californian, 1. Bechtold, demonstrated a Alaska. Earlier speculation suggested that similar correlation between tensional fis­ mineral deposits in Alaska were related to sures in the Lake Mead area (resulting from fold belts of the Canadian Cordillera. Based east-west crustal extension) and concentra­ on the occurrence of the newly discovered tions of gold, silver and other metallic ore regional fractures, Lathram and his cowork­ deposits. ers suggested that mineral emplacement An interesting multilevel geochemical ex­ might