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^a University of lowa.

^b U S. Army Corps of Engineers.

^c NASA Lyndon B. Johnson Space Center.

^d Lockheed Elecronics Company, Inc.

^* Principal Investigator.

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[119] THE APPLICATION OF REMOTE SENSING to geological studies began in the early 1920's through the use of visual analysis of aerial photographs, and their use advanced rapidly after World War II for regional geological mapping and for petroleum and mineral exploration. The use of photogeology reached its peak in the United States by the middle 1950's. The distribution of hand-held-camera photographs taken during the Gemini Program in the mid-1960's and of data from the Apollo, Landsat, and Skylab Programs in late 1960 and the early 1970's increased the interest in the use of space remote-sensing surveys for geological and hydrological studies.

Several types of geological and hydrological studies were conducted by approximately one-third of the Skylab investigators. Geologic studies included regional mapping of structure and lithology; mineral, petroleum, and geothermal exploration; mapping of volcanic phenomena; mapping of fault systems for location of active earthquake zones; and mapping of fracture zones in a coal mining area for mine safety purposes. Water resource studies included analysis of such features as streamflow, effluent discharge, river stage, flooding, snow accumulation and ablation, estuarine circulation, sedimentation, stream erosion, and shoreline retreat.

Hydrological studies were directed to generation of models of ground water movement, detection of trapped ground water along faults, and studies of the relationship of ground water to photolinears. Although the Earth Resources Experiment Package (EREP) investigators studied a wide variety of terrain and geographic areas, domestic investigations were concentrated in the Great Plains area and the Central and Western United States. Three investigators analyzed data of the Appalachian Mountains of the Eastern United States. Investigations were also conducted in Central and South America, Europe, Africa, and Australia.

Results of the Skylab EREP studies show that the most practical and useful space sensor for geological studies is a high-resolution camera. The photographs from the Earth Terrain Camera (S190B) will probably continue to be the data most in demand by geologists. The main advantages of the EREP camera systems are synoptic view, stereoscopy, and resolution. For field geologists, the synoptic view is a particularly important aid in understanding and interpreting the regional geology of an area because it provides an expanded opportunity to look at the total area of interest. Space data in the format of color or color-infrared photographs enable the geologist to map and extend trends for great distances and to perceive anomalous areas that may be indicators of subsurface structures capable of trapping oil or gas or of containing prospective mineral deposits. Fracture systems and rock alteration zones are probably the two most useful indicators of mineralization. These [120] often appear as tonal lineaments and color anomalies on the photographs. Space photographs and images do not provide direct evidence of oil, gas, or mineral deposits; but they can often provide geological clues on where to conduct further exploratory surveys, such as aerial photography, surface mapping, geophysical surveys, and exploratory drilling. They can be useful also in geothermal exploration for mapping major fault trends that may be conduits for magma and hot water moving upward near the surface, where the heat can be tapped economically. In addition, the view from space may serve as a stimulus for new concepts concerning the fundamental geological structure of the Earth and lead to the formulation of new hypotheses to be tested.

Geologists and hydrologists tend to use initially simple, economical methods of analysis. The basic technique consists of photointerpretation of transparencies using a stereoscope or zoom transfer scope. In most areas, only the morphology is directly observable by photointerpretation; and the geology is inferred. For example, sinkholes, sand dunes, alluvial fans, flood plains, glacial features, and volcanic cones were identified on the basis of shape and color. Drainage patterns can aid in the recognition of folds, faults, and areas of bedrock. Drainage anomalies can be seen on many images and photographs and marked for ground checking. Many investigators enhanced the EREP photographs by selective color-additive techniques. However, for most investigations, these techniques did not provide much additional information. The digital Multispectral Scanner (S192) data were converted to images and studied in a similar manner. The results of these analyses indicate that S192 bands 8 (0.98 to 1.08 µm), 10 (1.20 to 1.30 µm), 11 (1.55 to 1.75 µm), and 12 (2.10 to 2.35 µm) provide the best contrast for mapping rocks. This finding may prove to be very important for geological mapping because these infrared bands are not available on film from camera systems.

Studies of the spectral reflectance and radiance of rocks using computer-processed S192 digital tapes were supplemented by spectroradiometric measurements made on the ground during the Skylab overflights. Other investigations included comparisons of the film products of the Multispectral Photographic Camera (S19OA) and the S19OB camera as well as comparisons of the different bands of the S192 scenes.

Verification of observations and interpretations was a necessary part of each investigation. Field checking and correlation with published geological, gravity, and magnetic or earthquake-epicenter maps were conducted by most investigators. To aid in determining the usefulness of EREP data for Earth resources studies, EREP investigators compared photographs from Skylab, U-2 and RB-57 aircraft, and Landsat-1.

The summary results presented in the following subsections represent only a small percentage of the total geologic, hydrologic, and engineering information that will ultimately be derived from the analysis of the data collected during the EREP program. These results, however, are indicative of the wide variety of the use to which such data can be applied for study of the Earth's features and phenomena.

Maps are the fundamental data base of geology; they are used for various applications such as exploration for mineral and water resources, determination of land use, investigation of the environment and potential hazards, and resolution of engineering problems. Maps prepared from EREP data analysis were of two types: (1) general geological maps showing patterns of rock-unit outcrops, faults, and folds; and (2) linear-lineament maps showing the location and orientation of continuous or en echelon linear features.

Geologic maps prepared by EREP investigators were less detailed than the published maps derived from aerial photographs and field investigations because of the lower resolution of the EREP photographs. In addition, the photographic units derived from the EREP data may not correspond to field geologists' stratigraphic units, which are based on fossil content or rock type. Nevertheless, regional structures were defined and several previously unmapped structures were recognized. Quade et al. (ref. 4-1) identified a 19-km-long anticline in Gabbs Valley, Nevada, that is not shown on the State geological map. In several investigators' areas, many more faults were interpreted from photographs than appear on published maps; field checking validated some of these faults but eliminated others. In semiarid regions such as the Southwestern United States, geologists found that the large structures and distinctive rock units or contacts could be mapped with EREP photographs, and the following examples illustrate their use in photogeologic analysis of areas that differ in terrain features.

In the Canyonlands National Park in Utah, Lee et al. (ref. 4-2) used an EREP photograph (fig. 4-1(a)) to map all the sedimentary rock formations ranging in age from Pennsylvanian to Quaternary that appear on the published U.S. Geological Survey 1:250 000-scale map of this region (fig. 4-l(b)). At this scale, EREP photographs made possible some subdivision of formations into members as well as the mapping of stratigraphic pinchouts, intertonguing sedimentary rocks, and lateral facies changes. The photographs and the topographic maps were used to estimate the thickness of major stratigraphic units. Most major geological structures were recognized, and the dip of beds was estimated within 2° of field measurements. During this investiga-....

....-tion, mapping was accomplished at scales of 1:250 000 to 1:62 500. At this latter scale, a geologic map of a portion of the area was prepared that demonstrates the use of space data for detailed photogeologic analysis (fig. 4-1(c)).

Skylab color photographs of the San Rafael Swell, a well-exposed, 116-km-long anticline in Utah, were used to map rock types and structural and linear features (fig. 4-2(a)). The results of this photogeologic mapping are shown in figure 4-2(b). Other regions photogeologically mapped from EREP photographs include Owl Creek Mountains and Bighorn Mountains, Wyoming (figs. 4-3 and 4-4). in the Owl Creek area (ref. 4-4), the Triassic red beds are vividly portrayed and were used as a.....

....marker bed for interpreting the structural features. High-resolution black-and-white photographs of the "Horn" area (ref. 4-5) in the Bighorn Mountains portray the structural setting of the region, which aids in planning detailed geologic analysis.

The Alice Springs area in the arid central part of Australia was mapped by Lambert et al. (ref. 4-6) from EREP photographs, and the results were verified by field studies. These analyses showed that the strike of outcropping units was mapped accurately, that known folds were identified, and that areas of metamorphic and younger sedimentary rocks and Tertiary surficial deposits were delineated. Circular features detected on the photographs were found by field studies to be a ring dike, a granite intrusive, and a landslide.

In contrast to the application of color photographs in photogeologic analysis of semiarid regions, color-infrared and black-and-white infrared photographs are most useful in heavily vegetated regions. Structure can be revealed by landforms as in the Appalachian Mountains, where long, vegetated ridges are caused by resistant sandstones that resulted from the folding that occurred in this region. In the Black Hills of South Dakota, the Precambrian metamorphic and granitic rocks and the Paleozoic sedimentary sequences are tree covered and appear dark in the infrared photographs (figs. 4-5(a) and 4-5(b)). The color-infrared photograph (fig. 4-5(b)) shows the distribution of the Triassic red bed that outlines the regional extent of the Black Hills uplift. The lineament map (fig. 4-5(c) ) derived from the photographs suggests a variation in pattern in the Paleozoic and Precambrian rocks that is an aid in delineating the contact.

In the areas of limited geological information, such as Central America, Skylab photographs have aided in the compilation of new information that can form the basis for further specialized mapping. Good examples are in Central America (ref. 4-7) and northeastern Spain (ref. 4-8). The usefulness of the photographs from spacecraft sensors varies with regional setting and environmental conditions at the site; table 4-1 provides a comparison of the information content of the data acquired over the Great Plains area, which has subdued topography, heavy soil and vegetation cover, and a large amount of manmade disturbance (ref. 4-9).

Linear and lineament maps are common products of photographic analysis. A lineament is defined as any unidimensional straight or continuously curved combination of picture elements that appears on photographs or images and that is thought to have geologic significance (ref. 4-2). Straight or linear features on photographs have many possible causes. They may appear as alined sags and depressions, ridge gaps, tonal differences, alined springs, vegetational trends and types, straight drainage segments, ridges, textural differences, and cultural features. Many linears are faults or fracture traces, but unequivocal identification of all linears cannot be made from photographs; sometimes, identification cannot even be made after field checking.

Olson (ref. 4-10) found many topographic linears in South Carolina and northern Georgia to be parallel to....

....zones of crushed rocks or to coincide with previously mapped regional fracture trends. Because linear patterns are often parallel to fracture and/or fault patterns as determined on the ground, linear diagrams are commonly considered to be reasonable approximations of fracture trends. In the Black Hills of South Dakota, Hoppin et al. (ref. 4-4) noted a strong north-northwest linear trend in the Precambrian core that parallels a widespread, closely spaced fracture system common throughout the region.

A major goal of the geology studies was to determine the scale, the resolution, and the spectral bands best suited for interpretation. Many investigators compared the number and length of linears observed on Landsat....

....imagery, Skylab S19OA and S19OB photographs, and aircraft photographs. In general, more linears were found on Skylab photographs than on Landsat images. Longer linears were noted on Landsat images and shorter ones on aircraft photographs. The actual number observed can be a function of the season of the year in which the imagery is obtained. Cassinis et al. (ref. 4-11) noted that linear detection on the Skylab photographs acquired over Italy in September 1973 was not as good as on the Landsat imagery, because of the low contrast caused by uniform reflectance from vegetation. From geologic study of western Colorado, Lee et al. (ref. 4-2) showed that linears are selectively enhanced as a function of Sun elevation, Sun azimuth, and linear....

a Numerical rating system: 0 = very poor, 1 = poor, 2 = fair, 3 = good, and 4 = excellent.

b Better quality unenlarged third-generation transparencies of the project region.

c Black and white.

d Based on three snow-covered scenes from the Skylab 4 mission, groundtracks 1 and 58.

e Better quality photographic images (70-mm and/or 1:1 000 000-scale formats) of the project region.

[136] ....orientation. Fractures as short as 1 km can be recognized on S19OB photographs and joint spacing less than 200 m can be resolved.

Lambert et al. (ref. 4-6) compared the number of faults shown on a 1:250 000-scale geological map and the number of faults detected by interpretation of satellite images for the Alice Springs, Australia, area. The results, shown in table 4-II, include the following observations.

1. Many more faults were interpreted from S19OB photographs than from any other type of image.

2. When faults shorter than 10 km are excluded from computation, the number of faults interpreted....

....from each type of satellite image is greater than that shown on the geological map.

3. Approximately the same number of known faults was detected on S19OA and S19OB photographs. Many more new faults were interpreted on S19OB than S19OA photographs, probably because the high resolution of the S19OB camera makes it easier to discriminate faults from other linear features. Approximately 50 percent of the faults detected on S19OB photographs are shorter than 10 km.

4. Almost 70 percent of the faults detected by analysis of Landsat-l imagery were also interpreted on S19OB photographs. However, the total number of faults detected on S19OB photographs is twice that detected on Landsat imagery.

Merifield and Lamar (ref. 4-12) conducted extensive field studies in am effort to determine the origin of the linears they mapped from Skylab photographs of southern California. Although unable to assign a cause to all linears, they did correlate many linears with faults, foliation, and closely spaced fracture sets. Faults were indicated by topographic scarps; offset drainage or ridges; linear valleys and mountain fronts; contrasting tone, color, and texture; and vegetational differences caused by ground water blockage.

Structural and Tectonic Synthesis¹

Results of photogeologic analysis have shown that Skylab photographs are valuable for preparation of regional structural maps. From such maps, geologists can select areas for detailed ground studies, leading to definition of targets for further exploration of potential mineral resources or suspected geological hazards.

New maps based on EREP data of areas that have been studied previously can lead to reinterpretations of the geology and new hypotheses of regional structure. During a structural analysis of the Anadarko Basin (Oklahoma-Texas), Collins et al. (ref. 4-13) found a substantial correspondence between lineaments interpreted from the photographs and faults indicated by seismic data. This correspondence suggests a greater [137] amount of normal faulting on the northern side of the basin than has been recognized. The lineaments and faults could have associated structural closures, which might contain hydrocarbon accumulations. Further exploration to test the hypothesis appears to be warranted.

Whether or not a particular fracture originated by tension or by shear is much debated. Determining which model is applicable to the rocks in an area is an important step toward determining the orientation of the stresses that were responsible for the deformation of the rocks. McMurtry and Petersen (ref. 4-14) stated that lineaments, fracture traces, and joints mapped on Skylab photographs are coincident in direction in an area of the Allegheny Plateau. They postulate that the relationship is more consistent with a tensional than a shear model of origin.

The EREP photographs provided synoptic views of mapped lineaments (complex, long, rectilinear fracture zones). Geologists believe these structures are important to understanding the global tectonic systems, but their nature and origin are not yet well established. Lee et al. (ref. 4-2) noted that lineaments cut across young structural trends in the Colorado Front Range. The origins of these lineaments are not known, but they probably result from recurrent movement along old fracture systems.

In areas where linears and lineaments can be shown by field studies to be faults, the kind and amount of displacement along them may still be a matter of conjecture. When considering several tectonic hypotheses, it is necessary to determine not only the sense of displacement (horizontal or vertical movement) but also the length. Direct evidence of the sense of horizontal displacement along faults could seldom be obtained from Skylab photographs. In the Peninsular Ranges, southwestern California, Merifield and Lamar (ref. 4-12) wed Skylab photographs and Landsat images to discover four faults in the basement rocks and to determine from fieldwork the direction of displacement (fig. 4-6). They noted a regional alinement of features possibly revealing unrecognized segments of the San Andreas Fault system southeast of the Salton Sea along which predominant right-horizontal slip is known to occur.

Abdel-Gawad and Tubbesing (ref. 4-15) analyzed Landsat imagery and Skylab photographs for a large area of the Southwestern United States and northwestern Mexico (fig. 4-7). Linears interpreted as faults were used to develop a tectonic model relating major fault zones to fragmentation and rotation of crustal blocks. The model supports the interpretation that the Texas shear zone is one of three elements in a broad zone of deformation 2000 km long and 250 km wide that trends northwest from the Gulf of Mexico to the Transverse Ranges in California. The zone is postulated to have a left-lateral offset of 500 km. The investigators suggest that the Mojave block and the Sierra block may have rotated 25° counterclockwise and the Colorado Plateau, 15° clockwise.

Lineaments have been extended speculatively by some authors for considerable distances beyond their known limits. Hoppin et al. (ref. 4-4) used EREP photographs to test some of these predictions. No evidence of an extension of the Nye-Bowler lineament east of its presently mapped limit in the Pryor Mountains could be found on an S190B color scene of the northern Bighorn Mountains in Wyoming. Other lineaments in this region also appear to be limited in length. Extending lineaments to great distances on the basis of analysis of space photographs may be unwarranted.

The nature of geologic structures is a key to understanding the location and types of past movements that are now inactive. There are, however, geologic structures actively forming that are evidence of crustal movement. (See the subsection on earthquake hazards.) Surface displacement not related to known faults can be inferred from the distribution and occurrence of youthful landforms. In Utah, Jensen and Laylander (ref. 4-16) noted that recent alluvial fans cover old Lake Bonneville terraces and are interpreted as indicative of recent regional uplift of the Wasatch Range. Such information may lead to a better understanding of Earth dynamics.

Photolinear maps of southwestern Guatemala and Chiapas document the structural complexity of the junction of the Cocos, Americas, and Caribbean plates and show the structural relationships to volcanic regions. Stoiber and Rose (ref. 4-7) found that the photolinear patterns within the Central American volcanic chain support their segmented model of the Benioff zone by showing a concentration of transverse, northeast-trending linears in the predicted locations.

Tectonic synthesis, one of the final goals of structural analysis, begins with mapping on the best Skylab photographs followed by field checking, detailed mapping of key areas, interpretation, and verification of hypotheses. The resulting regional geological maps are excellent for such a synthesis.

[140] Rock Types

A major effort in remote sensing has been directed toward the identification and discrimination of rocks and minerals. Discrimination is the separation of one rock type from another; identification is the classification of a specific rock or mineral according to unique physical properties. The results of this effort show that detailed information is needed for the discrimination and identification of rock types. Most attempts at rock discrimination are made for regional mapping inventories, whereas most mineral identification is made for exploration for a single type of material.

As described by Morrison et al. (ref. 4- 9) in the Great Plains States, by Morrison² in Arizona, and by Lee et al. (ref. 4-2) in Colorado, most regional mapping is conducted at the State government level or by private exploration companies. The distribution of all surface materials in the area is examined. Specialized rock-type or surface-type maps are prepared for specific purposes, such as selecting sites suitable for locating public utilities, providing construction materials, or routing new highways.

The work of Jensen and Laylander (ref. 4-16) and Bechtold et al. (ref. 4-17) illustrates the efforts of private interests in locating deposits of minerals that may have potential value. Using their approach, an investigator searches for areas where geological events altered the composition or structure of the rock in such a way that it serves as a host rock for the ore minerals or hydrocarbons. When an area of potential interest has been located, intensive geophysical and field surveys are initiated to provide more detailed information on which to base development plans.

Skylab investigators used the characteristics of sunlight reflected from surface materials as a means of identifying and mapping rock and mineral types. This process has been used for many years in field identification and aircraft reconnaissance to determine the color, brightness, texture, and geographical position of the material. A preliminary identification can be made from this information by an experienced geologist. However, many more field and laboratory tests are required to make a positive identification after an area of specific interest has been defined.

The discrimination factors examined by most Skylab investigators were those of visible color and brightness. Color and brightness of the remotely sensed surface were compared with the characteristics of a known standard. Identification was then made on the basis of the degree of similarity between the test material and the standard. The work of Lambert et al. (ref. 4- 6) in Australia and the examination of Nevada surface materials by Quade et al. (ref. 4-1) exemplify this technique. Color photographs from the S19OA and S19OB camera systems were compared with aircraft color photographs and with field photographs and samples of materials. Although primary color comparisons were possible, atmospheric dispersion of light and laboratory processing of the photographs modified the Skylab photograph color, color balance, and brightness to such an extent that the photographs could not be used as accurate indicators of the sampled ground color. Laboratory modification of the Skylab photograph colors was made to match the colors visible in field examination. It was found that, when one specific sample area was color-corrected to match the ground sample, other sample areas might be degraded in color representation. High-quality photographic processing was considered to be essential to the interpretation. Quade et al. (ref. 4-1) stressed that differences in photograph colors enhance an interpreter's ability to separate one surface unit from another, even though the colors may not exactly match ground color (figs. 4-2 and 4-8).

To emphasize specific types of rocks and to enhance the contrast between different materials, a variety of color combinations and single-bandwidth spectral regions was used. Multiband photographs in the visible and near-infrared spectral regions were used in combination and separately by Lee et al. (ref. 4-2), Houston et al. (ref. 4-5), Bechtold et al. (ref. 4-17), Goetz et al. (ref. 4-18), Lee and Raines (ref. 4-9), and others to produce photographs that enhanced the differences between adjacent surfaces for visual interpretation. As an example, an improvement in discrimination of alluvium-covered and hydrothermally altered areas was evident in some false-color-composite photographs formed from the black-and-white S19OA photographs. This technique enabled the interpreter to vary the emphasis within the four spectral regions to accentuate the desired color balance. Particular value was noted for the S19OA photographs in the 0.6- to 0.7-µm bandwidth. Discrimination of red beds was improved using the infrared spectral regions because of the distinctive reflectance of these rocks.

[142] Skylab experiments have demonstrated that it is possible, from orbital altitudes, to discriminate effectively among general types of surface materials on a regional scale. Experience using EREP data for identification of specific rock and mineral types indicates that only a few of the many component materials of rocks and minerals exhibit a distinctive reflectance response pattern within the spectral regions sampled by EREP sensors. Two common rock components, water and carbonate materials, exhibit characteristic responses within the EREP infrared spectral regions at 1.4,1.9, 2.2, and 2.35 µm. These materials are also present in many other forms on the Earth's surface as well as in the atmosphere. The result is that differences in reflected energy in these spectral regions are often greatly obscured by surface moisture, organic compounds in surface vegetation, and atmospheric effects.

Compounds of iron are found in many surface materials and exhibit characteristic reflectance features in the wavelength areas of O.55, 0.75,1.0,1.6, and 2.0 µm. The response features are rather broad and occur at slightly higher or lower wavelengths in different....

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[143] ...minerals. A very small percentage of iron may dominate the reflectance response measured at the spacecraft, as exemplified by figure 4-9.

The EREP investigations of atmospheric effects by Thomson (ref. 4-20), Chang and Isaacs (ref. 4-21), and others illustrate the influence of atmospheric absorption and scattering on spectral reflectance data (fig. 4-10). Many major atmospheric effects coincide with the spectral bands required for accurate identification of rocks, which suggests that future progress in rock-type classification from orbital altitudes should be linked closely to atmospheric-correction models based on surface altitude and aerosol absorption.

EXPLORATION FOR MINERAL AND ENERGY RESOURCES

Exploration for economically useful mineral resources involves surveys or reconnaissance studies of large regions to locate the much smaller areas that may be worth the expense of detailed study. Geologists routinely use surface traverses, geophysical surveys, and interpretation of aerial photographs for reconnaissance. Photographs of the Earth obtained from spacecraft are useful because they can provide views of large areas under uniform lighting conditions with spatial resolution adequate for photointerpretation. The EREP investigators studied different types of data to determine the most useful spatial resolution, spectral resolution, scale, and format for resource exploration. Their results indicate that color or color-infrared, synoptic, stereoscopic photographs with approximately 10m ground resolution are the best tools for photointerpretation. Positive transparencies are best for laboratory study, 23- by 23-cm positive paper prints are most useful for field checks, and larger paper prints are best for compiling information.

Mineral Exploration

Fracture systems (i.e., combinations of faults and joints) provide pathways for ore-bearing fluids and tend to localize deposition of ore minerals. Fractures may be expressed at the Earth's surface as straight valleys if the material along the fracture is crushed or altered, or as straight ridges if the fracture is filled with resistant vein deposits. Straight topographic features such as these are visible on EREP photographs as linears that can be mapped, and their significance can be determined by field check. For example, Stoiber and Rose (ref. 4-17) found that trends of linear features mapped on S190A and S190B photographs agreed with previously mapped trends of lead-zinc, gold-silver-mercury-tin, and copper veins in Central America. Prost (in ref. 4-12) found a general correspondence between density of linears and location of mineral districts in Colorado. He and other investigators emphasize the necessity of careful field checking to eliminate linear features that do not represent the surface expression of geological fractures or rock-body contacts.

Bechtold et al. (ref. 4-17) studied S190A and S190B photographs and S192 imagery of California, Nevada, and Arizona to define combinations of linear and curvilinear features that might be correlated with mineral deposits. As an example, they described a nearly circular topographic feature near Hunter Mountain (fig. 4-11) in the Panamint Range, California. Similar circular features mark the location of bodies of intrusive igneous rocks in the Southwestern United States; many of these rock bodies are permeated with low-grade (0.5 to 3.0 percent) copper sulfide and/or molybdenum sulfide. The circular topographic features are caused by erosion of fractured rock. Some fractures are lined by soft, altered material; others are filled with resistance quartz. The net result is a dense network of short, straight, and curvilinear valleys and ridges that outline the potential ore body. The Hunter Mountain feature is not differentiated from other granitic bodies in the area (fig. 4-11(d)), although it is easily distinguished on the Skylab photographs. Field checks showed that copper and iron sulfides and their alteration products occur most of the way around the periphery of the circular body. Features such as these are targets for more detailed investigation because they may represent large, hidden ore bodies.

Another useful indication of possible large, low-grade ore deposits is an area of altered material at the surface (ref. 4-22). The alteration is caused by chemical solutions in heated water that spread from the source of mineralization into surrounding rocks. Surface indications of alteration zones range from brightly colored in shades of red and yellow due to oxidation of iron minerals, to white resulting from bleaching of the rocks and deposition of clay minerals. In reference 4-23, Levandowski and Borger report that computer-aided analysis of S192 data from the San Juan Mountains,....

....Colorado, allowed the delineation of alteration zones associated with vein mineralization, provided adequate field studies and ground-training samples were available. Investigators who studied Skylab imagery for color clues to possible mineral deposits include Quade et al. (Nevada; ref. 4-1), Lee et al. (Colorado; ref 4-2), Houston et al. (Wyoming; ref. 4-5), Lambert et al. (Australia; ref. 4-6), Jensen and Laylander (Utah and Nevada; ref. 4-16), Bechtold et al. (Arizona, Nevada, and California; ref. 4-17), and Watson et al. (Nevada; ref. 4-24). Figure 4-12 illustrates the altered zone associated with the mineralized area in Goldfield, Nevada, in comparison with previous mapping. It should be emphasized that color, as do fracture patterns, forms only one piece of evidence in a long chain of logic that may lead to the discovery of mineral deposits.

Jensen and Laylander (ref. 4-16) reported that study of S190A color photographs from the Skylab 2 mission suggested that portions of an area in the northern Egan Range in Nevada are underlain by light-colored carbonate rocks rather than by dark-colored volcanic rocks as previously mapped. This observation is significant because a large magnetic anomaly in the area coincides approximately with the extent of volcanic rocks (ref. 4-25). Jensen suggested that the magnetic anomaly might be caused, in part, by a body of igneous rock that intruded the carbonate rocks. If so, mineralization similar to that at Ely, Nevada (25 km to the south), might be present. Geologists from universities, industry, and governmental agencies promptly investigated the area. For example, Quade (ref. 4-1) enlarged the S190A photographs to the scale of published maps (ref. 4-26), compared them with aerial photographs, and performed a field check. He decided that the geology had been mapped correctly by Carlson and Mabey (ref. 4-25), that the magnetic anomaly is coincident with outcrops of volcanic rocks, and that no mineralization could be found in the outcropping carbonate rocks. Explorative work is being continued in the area.

Prost (in ref. 4-2) investigated the hypothesis that anomalous reddish or pinkish areas that are caused by a concentration of iron oxide and that occur in regions marked by dense fracture networks might be indicators of potentially economical ore minerals in central Colorado. Anomalous reddish areas were observed on EREP color photographs of two test sites (Cripple Creek and Weston Pass). Field checks showed that one such area was caused by iron oxide derived from weathering of sulfide minerals, one by iron oxide and feldspar, and two by feldspar alone. Anomalous tannish....

...areas in this region were attributed to quartz-rich pegmatites and light-colored sedimentary rocks and altered intrusives.

No mineral finds based on the study of EREP data have been reported. The three examples just described illustrate the use of space data in developing testable hypotheses of potential mineral occurrences. Exploration programs are usually of 5 to 10 years duration, and it is anticipated that use of the EREP data will lead to some significant discoveries over the next decade.

Petroleum Exploration

Although hydrocarbon accumulations cannot be directly detected, the interpretation of EREP data can provide information on regional lithologic and structural relationships and quickly draw attention to anomalous features and areas that are of the greatest interest in petroleum exploration. To be useful, EREP information must be integrated effectively with a wide variety of other types of data (geophysical, subsurface geology, and production history) and included within the structure of a rational exploration strategy. The advantages of Skylab data can be obtained with little additional cost to a conventional exploration program (ref. 4-13). Cost-saving benefits accrue from decreases in reconnaissance time, in seismic exploration, and in lease-acquisition expenses. The cost savings have been estimated to be as great as 40 percent in an exploration program (table 4-III).

In the study of the Anadarko Basin in Oklahoma, Collins et al. (ref. 4-13) found the S19OA and S19OB photographs to be exceedingly valuable for obtaining a rapid geological assessment of large areas and for conducting a relatively detailed study of specific areas of interest. Linears interpreted from Skylab data and Landsat imagery relate well to joints and subsurface faults. Some known surface faults were mapped and several unknown faults were inferred from Skylab data by Collins et al. (fig. 4-13). Field studies show that many long linears coincide with disturbed zones in surface rock exposures; these may represent major faults at depth. Tonal and drainage anomalies were detected in many photographs. Circular drainage patterns and tonal anomalies show the highest correlation with known hydrocarbon occurrences. Collins et al. (ref. 4-13) stated that lithologic interpretations from the EREP data are generally accurate but do not always match published interpretations. These interpretations indicate areas where remapping is desirable to verify new ideas derived from the reevaluation of supposedly well-known petroleum provinces (ref. 4 27).

Using S19OA photographs, Rivereau, of the institute Francais du Petrole (in ref. 4-28), reinterpreted the geology of a Permian basin on the southwestern border of the French central massif. In the central southern part of the basin, a relatively thinly bedded unit (unit A, fig. 4-14) composed of fine sediments (siltstone and clayey sandstone) is surrounded by thickly bedded sandstone to the west and north (unit B) and conglomerates to the south (unit C). Unit A was considered by field geologists to represent lateral lithological changes with only the western boundary being structurally controlled by a northwest-trending fault (Fl). A conventional photogeological map of the area showed that unit A was very homogeneous and that it was crossed by numerous faults having a northwest trend, thereby causing small displacements of bedding. However, because of the strike of bedding in units A and B and the same dislocation of bedding caused by the northwesterly trending faults, nothing else was suspected about the relationship between units A and B. The synoptic view of the Skylab photographs (and, to a lesser degree, of the Landsat imagery) showed the distinct regular pattern of unit A, which is bounded on all sides by straight lines. From these photographs, it was obvious to the investigator that the distribution of unit A is structurally controlled by faulting. It is currently believed that unit A occupies a collapsed part of the basin in which the top sediments of the trough have been preserved from erosion. Therefore, unit A should no longer be chronologically correlated with unit B; that is, unit A no longer appears as a local lithological variation of unit B. It is probable that unit A is younger than unit B and has been removed from the top of unit B in other parts of the area and only preserved in the collapsed area. Rivereau emphasized that, even though the....

[156]....feature is visible on Landsat images, it is prominent in the Skylab photographs only because of the well-defined spectral contrast in S19OA color film. The appearance of the feature was enhanced by making false-color composites using various combinations of the S19OA black-and-white photographs. Drilling and geophysical surveys are now underway in the area, and confirmation or non-confirmation of this hypothesis will be determined from the results.

Anticlinal folds often provide structural traps for hydrocarbons. Numerous examples of folds mapped on Skylab photographs can be found in EREP reports (e.g., refs. 4-4 and 4-5). Vargas (ref. 4-29) reports the detection of lineaments and drainage anomalies that may indicate subsurface faults and anticlines in north-central Bolivia, an area undergoing active exploration for oil and gas. These investigators believe that the EREP photographs will be of direct help in locating prospective structures.

Exploration for Geothermal Energy

The indirect methods used to search for minerals and petroleum are also used to search for geothermal energy. In addition, investigators are attempting to use the direct method of mapping hot ground using thermal scanners. An example of indirect methods is provided by Bechtold et al. (ref. 4-17) for the Coso Hot Springs area in California (fig. 4-15). This is a well-known thermal area that has been studied thoroughly (refs. 4-30 and 4-31). Evidence of recent volcanism in the area includes lava flows, vents, cones, hot springs, and areas of steaming ground. Fracturing of the rocks is intense, and patches of hydrothermally altered material occur. The Coso Hot Springs area is a potential source of geothermal power. Study of S19OA and S19OB photographs by Bechtold et al. indicated that, 70 km south of Coso Hot Springs, in the Lava Mountains, there is a similar (though smaller) area of repeated volcanism, intense fracturing, and hydrothermally altered material (fig. 4-15). A well drilled in the 1920's revealed hot rock and steam at 120 m (ref. 4-32), but the resource was never commercially developed. Study of Skylab photographs, together with brief field checking, suggests that an area of approximately 15 km² may be potentially exploitable for geothermal power.

McMurtry and Petersen (ref. 4-14) analyzed S19OA photographs of the Susquehanna River basin in Pennsylvania to determine the relationship of a warm spring, a large circular feature, and a major lineament; and to establish the regional geologic structure for use in detailed studies. Aerial thermal surveys and fieldwork are continuing to determine the size and significance of the thermal feature.

During the Skylab missions, particularly Skylab 4, some predawn thermal imagery was obtained (fig. 4-16) that demonstrates the sufficiency of the S192 spatial and thermal resolutions for discrimination of different types of material on the Earth's surface. Daytime thermal imagery was obtained over the Geysers geothermal power field in California. Analysis of this imagery by Siegal et al. (ref. 4-33) demonstrated that spots approximately 1 K warmer than the surrounding areas can be distinguished (fig. 4-17). Comparison with S19OB photographs, aerial photographs, and previous field mapping showed that many of the warm spots coincide with sites of geothermal wells and steaming ground. However, these known warm sites also are bare of vegetation and, coincidentally, tend to occur on southfacing slopes where solar heating is at a maximum. Calculations indicate that solar heating can account for the effects recorded by the S192 scanner. The results are encouraging because they suggest that similar, perhaps more sensitive, predawn images might provide useful clues to sites for geothermal exploration. Such factors as slope direction (aspect), slope angle, previous weather (temperature history at the site, rainfall), and vegetation will have to be considered when using such thermal Imagery.

ENVIRONMENTAL GEOLOGY

The use of EREP data to identify and study geological hazards and the testing of those data in engineering and environmental-geology applications are described in this subsection. Geological hazards studied include....

....earthquake zones, landslides, and volcanoes, Engineering-geology applications include, from a disciplinary standpoint, assessment of the previously mentioned hazards, studies of tunnel sites, and inventories of construction materials. Finally, environmental geology includes the preparation and assessment of "erosion susceptibility/ease of excavation" maps and "analytic landform" maps. These maps show surficial materials and conditions important in environmental, land use, and geological applications.

Geological Hazards

The geological hazards discussed are earthquakes, landslides, and volcanoes.

Earthquakes.-Several investigators used EREP photographs to map linear features and to investigate the relationship of these features to faults with historical earthquake activity. For example, Olson (ref. 4-10), using S190B transparencies, stated that the most significant finding of his investigation was the detection of [163] fracture traces and related lineaments crossing the Clark Hill Reservoir on the Savannah River, north of Augusta, Georgia. He noted that epicenters of some earthquakes (maximum magnitude of 4.5 on the Richter scale) that occurred in 1974 were plotted in the same area. The EREP data were being used to develop field evidence for assessing the causes of the earthquakes.

Abdel-Gawad and Tubbesing (ref. 4-15) identified segments of faults in the western Mojave Desert adjacent to the San Bernardino and San Gabriel Mountains and the San Andreas Fault zone. They produced maps delineating specific areas of seismic risks based on geomorphic evidence of recent faulting (visible breaks in the surficial alluvium and surface rocks, stream offsets, etc.). Merifield and Lamar (ref. 4-12) mapped faults in the Peninsular Ranges of southwestern California and conducted extensive field investigations to determine their potential for seismicity. Using Skylab photographs, they found two previously unmapped faults but determined, through field studies that revealed no signs of recent movement, that the faults posed little threat for generating earthquakes. Quade et al. (ref. 4-1) mapped lineaments in the Mina region of Nevada and then compared the map with a plot of earthquake epicenters for 1971-73. They found a correspondence between the epicenter locations and the east-northeast-trending faults west and southwest of Mina.

Landslides.-Although EREP photographs generally lack the necessary spatial resolution and vertical exaggeration (for stereo-viewing) required to study small landslides, some positive results were reported. Large landslides were recognized and mapped by Quade et al. (ref. 4-1), Hoppin et al. (ref. 4-4), Houston et al. (ref. 4-5), Lambert et al. (ref. 4-6), and Lee and Raines (ref. 4-19). McMurtry and Petersen (ref. 4-14) noted a good correlation between lineaments observed on Skylab photographs and Landsat imagery and a zone of fractured material that was collecting and channeling ground water. This zone appeared to be the cause of landslides on slopes along a major highway in Pennsylvania. This example again demonstrates the usefulness of identifying linear features in relation to specific geological hazards.

Volcanoes.-Cassinis et al. (ref. 4-11) noted that am S19OB color-infrared photograph (fig. 4-18) taken over Sicily showed an anomalously low infrared reflectance in an area of Mount Etna that later erupted. The investigators postulated that this type of anomaly might be caused by stressed vegetation resulting from small but continuous amounts of volcanic gases filtering through the soil. They analyzed 17 anomalies and found that most were caused by different vegetation assemblages rather than by stressed members of the same type. In an attempt to correlate lineations and eruptions, they mapped and analyzed lineations on the western flank of Mount Etna. It was found that (1) the maximum density occurred in the eruption zone, (2) the first effusive opening of the February 1974 eruption occurred at the intersection of four linears that were 0.5 to 2.5 km in length, and (3) the vegetative anomalies correlated well with the geometry of the lineations. From these results, the investigators concluded that their hypothesis, which suggested volcanic gases could stress vegetation and result in reflectance anomalies, might be valid, even though they were not able to verify it in this investigation of Mount Etna. They did determine that the relationship between lineations and eruption features was significant.

Stoiber and Rose (ref.4-7), using EREP photographs of the Guatemalan highlands, mapped circular and arcuate features that correlated with distributions of early Quaternary and Tertiary volcanoes.

Engineering Geology

This discussion of engineering geology includes tunnel-site studies and construction materials inventory.

Tunnel-site studies.-Lambert et al. (ref. 4-6) used Skylab photographs of the Snowy Mountains area of Australia to prepare structural maps for comparison with detailed structural information obtained in the construction of long tunnels. The tunnels, built for irrigation and hydroelectric purposes, are am average of 247 m below the surface. The comparison enabled the investigators to determine directly the value of remote sensing in identifying fractures of concern in tunnel-site studies. They concluded that "The combination of three [164] factors: (1) means of measuring and achieving acceptable standards of data quality, (2) empirical evidence that approximately 50 percent of surface features will be detected underground, and (3) sufficient resolution to identify the location of these features indicates a potential operational role in 1:100 000 survey mapping and in engineering and mining investigations."

Construction materials inventory.-Several investigators used Skylab photographs to study and map surficial materials containing sand and gravel, but very few used the photographs specifically to locate new sources of these deposits. Three investigators who spent considerable time on this last objective reported worthwhile results. Woodman (ref. 4-34) used the photographs of Maine to map moraines and eskers, which are the State's major sources of sand and gravel for road construction. Cassinis et al. (ref. 4-11) used multispectral analysis of S19OA photographs to identify and map the locations of ancient river channels in the Venetian Plain of Italy. As is the glacial material in Maine, these old riverbeds are sources of sand and gravel for construction and freshwater. Cassinis stated that he determined for the first time the regional extent of these resources. Furthermore, he estimated a cost saving of 90 percent in locating the buried channels with Skylab photographs as compared to locating them with electrical resistivity surveys. While working in Puerto Rico, Trumbull (ref. 4-35) was able to locate coral reefs, offshore sand arid gravel deposits (potentially a valuable resource), and areas of coastal erosion, and to identify patterns of sediment transport.

Geoenvironmental Mapping

The EREP photographs were used with varying degrees of success in several geology studies in which surface geological features of environmental interest were examined. Among the most significant results are those reported by Morrison (ref. 4-9). He used EREP photographs in constructing erosion-susceptibility maps of areas of southeastern Arizona ² and, in conjunction with associates from six Great Plains and Midwestern States, in preparing analytical-geomorphology maps of areas within the six States (ref. 4-9).

The maps of Arizona combine information on soil types, surficial deposits (including particle size and character of the deposits for several meters below the soil profile), and occurrences of exposed bedrock. The maps also provide background data on the susceptibility of various types of surface materials to erosion and, hence, on the potential magnitude of the modern accelerated-erosion problem in southeastern Arizona. Additionally, the maps indicate the ease of excavating near-surface materials for construction. The maps were prepared by direct photo-interpretation of 1:250 000-scale Skylab photographs using a stereoplotter and without supplemental ground control. Published geologic reports and maps were then used for constructing detailed descriptions of the mapped units. These maps offer the land use planner or manager a low-cost tool because they can be prepared in a portion of the time required by standard field studies and map-preparation procedures. An example of one of these maps is shown in figure 4-19; the explanation of the map units is contained in table 4-lV.

The maps prepared for areas of the Great Plains and Midwestern States (e.g., fig. 4-20) show surficial features and contain rating systems (table 4-V) for each map unit in terms of limitations or advantages of topography, availability of shallow ground water, availability and quality of gravel and rock, slope stability, foundation conditions, ease of excavation, road construction, surface drainage, and soil (internal drainage, erodibility of soils, and sites for sanitary landfills, sewage lagoons, and septic tanks). The maps were prepared without field studies by using ancillary information such as topographic maps, geological and soil maps, reports, and high-altitude aerial photographs in conjunction with the EREP photographs. They contain information that should become increasingly useful as regions develop and detailed plans and environmental assessments are needed.

[169] WATER RESOURCES

Surface-Water Management

One of the most striking differentiations possible from multispectral aerial and EREP satellite imagery is the identification and delineation of surface-water bodies. Accurate delineation of regional drainage networks has been made possible by space photographs as demonstrated by Stoeckeler et al. (ref. 4-34), Colwell et al. (ref. 4-36), and Baker et al. (ref. 4-37). In instances in which overlap of the photographs enabled stereoscopic viewing, investigators were better able to detect and compare topographic relief. This capability enabled the accurate delineation of watershed boundaries by locating the ridge lines that circumscribe individual surface-water drainage systems. For this purpose, the S19OB photographs were nearly equal to the best high-altitude-aircraft photographs available to the investigator (from an RC-10 camera at 18 300 m). This conclusion is important because frequent high and low-altitude-aircraft coverage is expensive. The demonstration of the capability of the Skylab camera systems to provide accurate resolution of drainage basins and surface-water bodies offers the possibility of significant cost savings when applied on a nationwide or worldwide basis.

The Skylab multispectral photographic system provided coverage of the spectrum from the visible through the near-infrared. Piech et al. (ref. 4-38) used these photographs to assess the value of remote sensing from space for determining the eutrophication of lakes. Comparisons were made between conventional water quality indices and relative values of reflectance in the blue and green portions of the visible spectrum at various locations in Lake Erie, Lake Ontario, and Conesus Lake, New York. Reflectances measured from the S19OA color photographs were in excellent agreement with those determined from simultaneous aircraft flights. Changes in the balance acquired on organic compound concentrations of the surface waters caused variations in the blue-to-green reflectance ratios. The ratio of blue-to-green reflectance in Lake Ontario is shown in figure 4-21. Similar results were reported by Hannah et al. (ref. 4-39) using data acquired over lakes in Florida. Because the atmosphere can reduce the measured reflectance by as much as 60 percent, it was necessary to correct for this effect. Correction made by reference to reflectance standards was used by Piech et al. (ref. 4-38) in this successful application. It was predicted that an additional advance in resolution would permit use of the shadow-calibration procedure now used in the measurement of eutrophication indices by low-flying aircraft. The synoptic view provided by satellite imaging systems with repetitive coverage would enable the monitoring of natural and artificial lakes for the onset or amelioration of eutrophication. The resolution of the Skylab camera systems also greatly facilitated this application.

Yarger and McCauley (ref. 4-40) achieved good results by applying the band-ratioing technique to the problem of detecting the presence of suspended solids in reservoirs. They found that reflectance values in both S19OA and S19OB photographs correlated well with suspended (mostly inorganic) sediment. Band ratios of blue-green to red reflectances provided quantitative correlation at concentrations greater than 200 p/m in three small reservoirs in Kansas. Repetitive coverage provided by satellites could improve the regulation and management of lakes and reservoirs with respect to this water-quality parameter.

Snow Cover

An ever-increasing need in agricultural, industrial, and metropolitan areas for reliable sources of water makes efficient management of water resources a continuing concern. In many areas, winter storage of water in the form of mountain snow, together with its runoff regime, governs the availability of water during the periods of greatest need. Because of the general inaccessibility of high-mountain snowpacks and their relatively inhomogeneous distribution and irregular boundaries, estimation of total water content in them....

....has been difficult. Hoffer (ref. 4-23) demonstrated that photographs from the S190A camera and imagery from the S192 scanner have potential use in delineating snow cover (fig. 4-22). A simple delineation of snow-covered areas usually is not possible because of obscuration by clouds, vegetation canopies, or shadows of clouds. However, digital processing of the S192 imagery data enabled recognition of five spectral classes of snow-covered areas (table 4-VI) according to differences in the proportion of the forest or vegetation canopy constituting each picture element (pixel) of the scanner data. Computer processing of the data permitted the digital overlay of 13 bands of EREP data, 4 bands of Landsat multispectral imagery, and topographic data (including elevation, slope, and aspect). The capability of comparing multiple data sets provides an effective means for rapidly generating accurate snow-cover maps using the repetitive coverage that will be provided by future satellites.

According to Barnes et al. (ref. 4-41), the differentiation of cloud cover from snow cover can be accomplished by selective use and analysis of S192 imagery data. Snow reflectance is high in the visible part of the electromagnetic spectrum but drops to comparatively low levels in the 1.55- to 1.75-µm and 2.10- to 2.35-µm bands. In the imagery covering this range (S192 bands 11 and 12), snow appears to be nearly black regardless of age and condition, but water and cloud-top reflectances are uniformly high throughout the range. Through computer processing of the data, a clear distinction can be made between cloud tops and snow cover. An area showing a high reflectance in the visible range but a low reflectance in the near-infrared range (S192 band 11 or 12) can be recognized as snow; an area showing high reflectance in both spectral regions can be recognized as water or clouds. Most snow-free areas exhibit relatively low reflectances in the visible range and medium reflectance in the near-infrared range (fig. 4-23). Exploitation of this technique for automatic snow-cover recognition and mapping was shown to be possible; when fully developed, it may aid in better management of large watersheds for flood protection and maximum water storage and utilization.

Hydrological Factors

The hydrological factors discussed are flood prediction, watershed management, and ancient water systems.

Flood. prediction.-Flood-hazard indices are often used by insurance companies, banks, and others concerned with evaluating investment risk. Multispectral photographs are useful in defining relationships between the local geomorphology and land use within a given watershed. For example, in central Texas, where the orographic influence of the Balcones Escarpment tends to localize thunderstorms, it has been suggested by Baker et al. (ref. 4-37) that local geomorphology of the several drainage basins governs the conversion of storm precipitation to floods. A test of this idea and the beginning of the development of a quantitative hydrogeomorphic model to describe the floods are made possible by the availability of repetitive satellite imagery. A similar application was made by Colwell et al. (ref. 4-36) in defining patterns of runoff and alluviation in the San Bernardino Mountains. Geohydrological units within drainage basins were easily recognized and delineated by ridge lines, drainage divides, faults, and contact between different lithological units. A generalized model of ground water movement was constructed that includes a prediction of flood hazards in the south-central Mojave Desert. This model can be very useful in planning for the orderly growth and development of rapidly expanding communities in this region. The S1 90B photographs bridged the gap between high-altitude aerial photographs and relatively low-resolution multispectral imagery. Similar results were obtained at study sites in Illinois, lowa, Kansas, Missouri, Nebraska, and South Dakota (ref. 4-9).

Watershed management.-A detailed comparison of Skylab S190A and S190B photographs and high-altitude-aircraft photographs of the New England area was made by Cooper et al. (ref. 4-42) to provide hydrological information needed for reservoir management. The relationship between the land use within a watershed and its hydrological characteristics is generally believed to be fundamental to an understanding of watershed functioning. The EREP S19OB photographs made possible the identification and delineation of all 6 Level I classification units (ref. 4-43),17 Level II units, and I Level III unit. (See table 2-1 in sec. 2.) These results are almost as good as those obtained with the best high-altitude-aircraft photographs (6 Level I, 21 Level II, and 5 Level III units); at Level II, they are practically equal in utility. The S190B photographs meet the remote-sensing requirements for regional land use mapping and for evaluation of runoff potentials in situations requiring regional hydrological surveys for urban planning or....

....resource development. Similar results were reported by Stoeckeler et al. (ref. 4-34).

Ancient water systems.-Skylab photographs enabled Gumerman et al. (ref. 4-44) to study the hydrology of prehistoric farming systems within a large and environmentally diverse area of central Arizona. Hydrologists, geologists, biologists, and archeologists evaluated the adaptation of prehistoric man to the semiarid desert of central Arizona and his creation of land management and water control systems. Ecologically significant subareas, or drainage basins, were selected on the basis of basin area, stream length and order, slopes, bedrock type, and rainfall distribution. Table 4-VII illustrates the usefulness of S190A and S19OB photographs for defining environmental parameters. Estimates of available water were established from these parameters and from vegetation communities, and an evaluation of types of prehistoric water management systems was based on these data.

Ground Water

The location of reliable sources and supplies of ground water is of growing social and economic importance in nearly all parts of the world. It has become obvious that ground water exists in limited quantities and that the continued existence of these quantities ultimately depends on the rate of replenishment. For rational resource management, it is important to have the means available for locating ground water reserves.

Although aerial and satellite imagery can provide only indirect evidence of ground water reserves, this evidence can be accurate and definitive under some circumstances.

Skylab photographs and imagery are useful for the assessment of ground water resources, both in terms of spatial distribution and of functioning According to Colwell et al. (ref. 4-36), arid lands such as the south-central Mojave Desert are most amenable to analysis by photo-interpretative techniques, and the information....

....generated could be of immediate utility in managing the water resources of these regions. Geohydrological units are delineated by noting such flow barriers as drainage divides, faults, and lithological contacts, which are easily discernible on photographs (figs. 4-24 and 4-25). Lithological units are distinguishable and their permeability may be deduced from lithology. From study of EREP photographs, a generalized model for ground water movement within the south-central Mojave Desert was postulated by outlining the drainage basins, delineating the individual geohydrological and lithological units, and deducing the hydrological characteristics of the lithological units.

Water-well siting on lineaments.-in central Tennessee, ground water occurs mostly in a network of solution cavities. It seemed reasonable that the lineaments visible in the Skylab photographs might show the existence and location of a major structural system of...

...joints that interconnects this system of cavities and governs the rate at which this ground water can be removed. Accordingly, Moore (ref. 4-45) studied the lineament types revealed by the view from space. He then compiled data on water yields from wells in this area and separated the values of those located on lineaments visible in the Skylab photographs from all the others. He found that the yield of water wells located on these lineaments was approximately six times that of randomly located wells (table 4-VIII). it was concluded that when water-well yields of 1.6 x 10^-3 m³/sec (25 gal/min) are required, large savings in time and money can be achieved by locating the wells on lineaments mapped by stereoscopic viewing of Skylab photographs. For wells having yields larger than 6.3 x 10^-3 m³/sec (100 gal/min), the potential cost saving between wells randomly located and those on or near stereoscopic and projection linears is approximately $18 000.

Near-surface ground water. In some areas, the presence of near-surface ground water is clearly, although indirectly, indicated by tonal or textural variations in space photographs. These variations may be caused by differences in surface vegetation, soil composition, or some similar factor (ref. 4-2). Near-surface ground water may represent an important untapped ground water resource in some places or an undesirable buildup of the water table as a consequence of excessive irrigation or poor drainage in others. When combined with a program of ground-based measurements, analysis of the S19OB-quality photographs permits the identification and delineation of some types of near-surface ground water with a degree of precision far greater than that possible from conventional ground-survey methods alone (Bannert et al., ref. 4-46; fig. 4-26).

SUMMARY

Skylab EREP data provide the geologist with an ideal combination of stereoscopic synoptic view and multispectral coverage of his area of interest. This broad view can reveal regional patterns of geology, landforms, and drainage that are not as obvious on large-scale photographs. The availability of a variety of images for a given area allows an investigator to find the best image or combination of images for study of his particular region. Although S190B color photographs with stereoscopic coverage and high resolution proved to be the most preferred product, all products were found to be useful to some extent, depending on geology, vegetation, topography, and season. Analysis of the EREP data led to a number of geologically significant results.

1. Photogeological reconnaissance and regional maps as good as or better than published small-scale maps can be rapidly prepared.

 

2. Detailed geological maps were made for arid or semiarid regions for use in conjunction with published data and ground checking.

 

3. In more heavily vegetated areas, the general structure, particularly lineaments and large folds, was inferred through topographic and drainage analysis.

 

4. Many previously unknown structures were discovered that were verified by field checking.

 

5. Active faults and other evidence of recent ground movement were located.

 

6. Areas were targeted for specialized large-scale ground surveys of various kinds. For example, maps of linear patterns and intensity, where related to rock fracturing, have significance in mineral resource, ground water, and engineering applications.

 

7. Surface-water and snow-cover inventories were shown to be feasible.

 

8. Considerable reduction in costs of exploration was documented.

The EREP studies led to the development of new models or hypotheses, or to refinements or rejection of older ideas, which in turn led to a reappraisal of areas formerly considered devoid of economic mineral deposits. The geological investigations and applications described in this section are the beginning of the use of EREP data. Researchers associated with the experiments will extend their applications to other geographical areas, and new users will have the opportunity to use EREP data in their particular areas of interest. As future space platforms are designed and become operational, the lessons learned and the methods tested during the EREP program will contribute to a better understanding of the distribution of the Earth's resources.

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4-20. Thomson, F.: Machine Processing of 5-192 and Supporting Aircraft Data: Studies of Atmospheric Effects Agricultural Classifications, and Land Resource Mapping. NASA CR-144503, 1975.

4-21. Chang, David T.; and Isaacs, Ronald G.: Experimental Evaluation of Atmospheric Effects on Radiometric Measurements Using the EREP of Skylab. NASA CR-144500, 1975.

4-22. Jerome, J. E.: Some Features Pertinent in Exploration of Porphyry Copper Deposits. Geology of the Porphyry Copper Deposits, Southwestern North America, S. R. Titley and C. L. Hicks, eds., Univ. Arkona Press, 1966, pp. 75-85.

4-23. Hoffer, Roger M.: Computer-Aided Analysis of Skylab Multispectral Scanner Data in Mountainous Terrain for Land Use, Forestry, Water Resource, and Geologic Applications. NASA CR-147473, 1975.

4-24. Watson, K.; O'Leary, D. W.; and Pohn, H. A.: A Photogeologic Comparison of Skylab and Landsat images of Southwestern Nevada and Southeastern California. NASA CR-144642, 1975.

4-25. Carlson, J. E.; and Mabey, D. R.: Gravity and Aeromagnetic Maps of the Ely Area, White Pine County, Nevada. U.S. Geol. Surv. Geophys. Inv. Map GP-392, 1963.

4-26. Hose, R. K.; and Blake, C., Jr.: Preliminary Geologic Map of White Pine County, Nevada. U.S. Geol. Surv., 1970.

[188] 4-27. Amsbury, David L.; Clanton, Uel S.; and Frierson, Von R.: Smallscale imagery: A Useful Tool for Mapping Geological Features in the Texas Gulf Coastal Plain. NASA Earth Resources Survey Symposium, NASA TM X-58168, vol. IB, 1975, pp. 833-849.

4-28. Guillemot, J.: Project Pyralp: Tectonic Relationship Between Pyrenees and Alps (Southern France). NASA CR-140127, 1974.

4-29. Vargas F., Carlos: Interpretacion Geologico-Fisiografica de Una Fotografica Skylab Correspondiente al Area: Santa CruzMontero-Buena Vista. Yacimientos Petroleferos Fiscales Bolivianos, Special Report, 1975.

4-30. Austin, C. F.; Austin, W. H., Jr.; and Leonard, G. W.: Geothermal Science and Technology-A National Program. U.S. Naval Weapons Center Tech. Ser. 45-029-72,1971.

4-31. Duffield, W. A.: Late Cenozoic Ring Faulting and Volcanism in the Coso Range Area of California. Geology, vol. 3, no. 6,1975, pp 335-338.

4-32. Anderson, D. H.; and Hall, R. A.; eds.: Geothermal Exploration in the First Quarter-Century. Geothermal Resources Council Special Report No. 3,1973, pp. 117-144.

4-33. Siegal, Barry S.; Kahle, Anne B.; et al.: The Detection of Geothermal Areas From Skylab Thermal Data. NASA CR-143133, 1975.

4-34. Stoeckeler, E. G.; Woodman, Raymond G.; and Farrell, Robert S.: Multidisciplinary Analysis of Skylab Photography for Highway Engineering Purposes. NASA CR-141942, 1975.

4-35. Trumbull, J. V. A.: The Utility of Skylab Photointerpreted Earth Resources Data in Studies of Marine Geology and Coastal Processes in Puerto Rico and the Virgin islands. NASA CR-147437, 1975.

4-36. Colwell, Robert N.; Bowden, Leonard W.; et al.: Use of Skylab imagery to Assess and Monitor Changes in the Southern California Environment. NASA CR-147561, 1974.

4-37. Baker, Victor R.; Holz, Robert K.; et al.: Stream Network Analysis and Geomorphic FIood Plain Mapping From Orbital and Suborbital Remote Sensing imagery Application to FIood Hazard Studies in Central Texas. NASA CR-144354, 1975.

4-38. Piech, Kenneth R.; Schott, John R.; and Stewart, Kenton M.: S190 interpretation Techniques Development and Application to New York State Water Resources. NASA CR-144499, 1976.

4-39. Hannah, John W.; Thomas, Garland L.; et al.: Planning Ap-plications in East Central Florida. NASA CR-145415, 1975.

4-40. Yarger Harold L. and McCauley, James R.: Skylab Study of Water Quality. NASA CR-144505, 1975.

4-41. Barnes, J. C.; Smallwood, M. D.; and Cogan, J. L.: Study to Develop improved Spacecraft Snow Survey Methods Using Skylab/EREP Data. NASA CR-144338, 1975.

4-42. Cooper, Saul; Anderson, Duwayne; et al.: Skylab imagery: Application to Reservoir Management in New England. NASA CR-144514, 1975.

4-43. Anderson, J. R.; Hardy, E. E.; and Roach, J. T.: A Land-Use Classification System for Use With Remote Sensor Data. U.S. Geol. Surv. Circ. 671,1972.

4-44. Gumerman, George J.; Hanson, John A.; et al.: The Hydrology of Prehistoric Farming Systems in a Central Arizona Ecotone. NASA CR-144492, 1975.

4-45. Moore, G. K.: Hydrologic Significance of Skylab Lineaments in Central Tennessee. NASA CR-1+4490, 1976.

4-46. Bannert, Dieter; Bender, H.; et al.: Hydrogeological investigations in the Pampa of Argentina. NASA CR-1+4438, 1975.

² R. B. Morrison, "Application of Skylab EREP Photographs to Study of the Modern Episode of Accelerated Erosion in Southern Arizona" unpublished Final Report, NASA-USGS Agreement T-4113-B, 1975.

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