Thermal IR for Geology

FIG. 1. Index (nap showing major physiographic features and approximate location of areas described and illustrated in this report. EDWARDW. WOLFE* U.S. Geological Survey Flagstaff, Ariz. 86001 Thermal IR for Geology An evaluation for Caliente and Temblor Ranges in Southern California compares pre-dawn and post-dawn imagery and a conventional photograph. (Abstract on next page) in the Caliente Range, and unpublished maps by both T. W. Dibblee and G. Vedder HERMAL INFRARED IMAGERY, recording J. radiation from 8 to 13 micrometers in were used to evaluate the imagery in the T Temblor Range. wavelength, was flown by NASA on June 18, 1965, in the Carrizo Plain of southern Calif- Figure 2 is a generalized geologic map of ornia. A line approximately normal to the re- the area in which imagery was studied in gional geologic structure was selected for detail. The stratigraphic nomenclature used detailed analysis and is shown in Figure 1. A on the map and in this report is that of preliminary report on imagery from the Car- Dibblee (1962). Its use herein does not consti- rizo Plain was made by Wallace and Moxham tute adoption of the names by the U.S. (1966). A published geologic map by Vedder Geological Survey. and Repenning (1965) was extensively used In the image area the Caliente and Temblor Ranges are underlain by steeply dipping * Publication authorized by the Director, U.S. clastic rocks of late Tertiary age. In addi- Geological Survey. tion, three basalt flows occur within the Caliente Range sequence. The Caliente and Figure 5, an aerial photograph of the north- Temblor Ranges in the image area are largely eastern part of the imaged strip, was taken mantled by debris derived from the under- from about 35,000 feet on a midsummer day. lying strata, and extensive outcrops of bare In order to facilitate comparison and dis- bedrock are rare. Generally references to cussion, observation points are numbered on geologic units such as Morales Formation or the pre-dawn and post-sunrise images (Fig- Bitterwater Creek Shale apply to the debris ures 3 and 4) and on the aerial photograph that represents the units at the ground sur- (Figure 5). The annotations tabulated below face. are numbered to correspond to the numbers on Figures 3, 4, and 5. Unless specifically noted ACKNOWLEDGMENTS otherwise, the annotations refer to the pre- Extensive discussion with Malcolm M. dawn image (Figure 3). Clark and critical reviews by R. J. P. Lyon, 1. Subparallel white lines coincide at least in F. F. Sabins, J. G. Vedder, and R. E. Wal- part with local strike ridges on which bare sand- ABSTRACT:Thermal infrared (8 to 13 micrometers) imagery was obtained in the Caliente and Temblor Ranges and Carrizo Plain, southern Calijornia, in the predawn and post-sunrise hours of June 18, 1965. Field observations, measure- ments of moisture and specific gravity of the regolith, and rad:ation temper- atures, and comparison with geologic maps and aerial photographs lead to the following conclusions: (1) The specific gravities of sztrficial materials (usually not bedrock) influence tonal densities in the pre-dawn imagery. Hence areas underlain by sandy alluvium, sandstone, or conglomerate (highspecific gravity) tend to be brighter in pre-dawn imagery than areas underlain by shale, mudstone, or diatomite (low specific gravity). (2) Geologic interpretation of tonal density patterns is complicated by topographic, atmospheric, and vegetative effects on pre-dawn radiation. (3) Geologic features such as outcrop patterns and some faults are recognizable in the infrared imagery as well as in aerial photographs. -(4) post-sunrise imagery is dominated by the preferential warming of slopes exposed to the early morning sun and resembles low-sun-angle photographs. lace led to significant improvements in the stone beds and basalt flows are exposed. Pebbly texture is chapparal. manuscript. Illustrations were drafted by 2. White line coincides with sharp break in Mrs. Gertrude Edmondston. slope at the outer edge of a terrace mantled by old alluvium. 3. Flat to slightly concave remnants of an old alluviated surface appear dark, as do portions of The infrared images (Figures 3 and 4) are nearby stream canyons. line-scan displays of the areal distribution of 4. White line coincides with strike ridge on radiation intensities in the 8- to 13-microm- which the uppermost of three basalt flows forms eter wavelength band. Areas of intense a bold outcrop of bare rock. 5. Same strike ridge as 4, but here, where the radiation are relatively light in tone; those of white line is indistinct, the basalt is mantled by relatively weak radiation are dark in tone in soil and rubble. the images. Radiation intensity ,varies di- 6. White line corresponds to bare outcrop of rectly with emissivity and with the fourth hard. light-colored mudstone to sandy mudstone. Adjacent bedrock mantled by soil. power of absolute surface temperature. Cur- 7. Dark band corresponds to the outcrop of vature near the image margins is a distortion the Quatal Formation, a mudstone consisting inherent in the scanning technique. largely of expanding clay in contact with sand- Figure 3 is an image made shortly before stones of the Caliente and Morales Formations. 8. Small dark patches oorrespond to outcrops dawn (0506-0510 PDT), and the effects of of reddish-brown expanding clay in the Morales differential solar heating related to slope Formation. The bordering materials giving orientation are therefore minimized. Figure 4 brighter tones are sandy soils developed on the is an image made shortly after sunrise Morales Formation and deposits of sandy and gravelly alluvium that veneer all but the small (0635-0638). In this image, surfaces warmed areas represented by the dark spots. by the sun appear relatively bright, much as 9. Low hill underlain by claystone, sandstone, they would in early morning photographs. and conglomerate of the Morales Formation; THERMAL IR FOR GEOLOGY 45 EXPLANATION 4 FOIMATlOlS llS1 OF SAW Al01tAS FAULT -Conlac, -Fa",, q5s,r,*s and dl. 01 Oeldlns 11111. and dl0 01 70x .".ltYl".l l.OOl"l o I 2 4 a MIL~S -1 FIG.2. Generalized geologic map of study area. See Figure 1 for location. bounded by broad alluviated areas. In the post- water Creek Shale project through the alluvial sunrise imagery the hill is more distinctly out- apron that underlies the Elkhorn Plain at the lined because of preferential heating of slopes foot of the Temblor Range. Bitterwater Creek exposed to the sun. Shale dark in both pre-dawn and post-sunrise 10. Small hill, a few feet high, relatively imagery but bright in aerial photograph. bright, lies within a dark region that corre- 15. Bitterwater Creek Shale in contact to sponds approximately with the ibwest part of the northeast with very coarse conglomerate of the Carrizo Plain in the image area. Iinages show Santa Margarita Formation. Conglomerate and agricultural field patterns and fan patterns where alluvial apron that bounds it on the southwest intermittent streams debouch onto the broad are bright and contrast sharply with darkly alluviated Carrizo Plain. Because the Carrizo imaged Bitterwater Creek Shale. Note that in Plain is nearly flat, almost no preferential solar the aerial photograph the contact between Santa heating occurs, and the post-sunrise image Margarita conglomerate and alluvium is readily closely resembles the pre-dawn image. apparent because the two units differ in topo- 11. Dark spots represent accumulations of tumbleweed against a fence at the northeast graphic expression. edge of the Carrizo Plain. 15. Outcrops of downfolded Bitterwater Creek 12. Northwest-trending trench along recently Shale dark; bright in aerial photograph. Geo- active trace of San Andreas fault. Well-drained logic map (Figure 2) portrays distribution of gully bottoms, including the trench along the sandstone and shale mapped together as Bitter- fault and the fine gullies forming a filigree pat- water Creek Shale. Imagery and aerial photo- tern on low ridge southwest of the fault, appear graph, on the other hand, display shale facies in bright. sharp contrast to surrounding rocks whether 13. Two elongate hills underlain by Bitter- they be Santa Margarita Formation, a sand- 46 PHOTOGRAMMETRIC ENGINEERING, 197 1 FIG. 3a. Pre-dawn infrared image-Caliente FIG. 4a. Post-sunrise infrared image-Caliente Range and Carrizo Plain. See Figure 1 for location. Range and Carrizo Plain. See Figure 1 for location. For key to numbers, see text. For key to numbers, see text. with rare granitic or metamorphic boulders. stone facies of the Bitterwater Creek, or the Conglomerate facies darker in aerial photograph alluvium of the Elkhorn Plain. than sandstone facies. 16. Sharp radiation contact coincides with a 20. Sharp radiation boundary coincides with fault separating Monterey Shale to the north- crest of Temblor Range. Immediately northeast east from Santa Margarita conglomerate and a of the range crest, Santa Margarita conglomer- sandstone mapped with the Bittenvater Creek ate, Media Shale, and the Temblor or Vaqueros Shale. The conglomerate and the Bitterwater Formations all appear bright. Most of the slope Creek sandstone, inseparable in the imagery as for about a mile and a half northeast of the range well as in the aerial photograph, contrast crest in the image area is underlain by grass- sharply with the Monterey Shale, which is dark covered Monterey Shale colluvium that appears in the pre-dawn image and light in the aerial relatively bright. photograph. 21. Dark band coincides with prominent, 17. Broad dark band occurs in an area under- steep, southwest-facing slope nearly devoid of lain by Monterey Shale, shale and sandstone of vegetation. It is underlain in part by diatomite the Temblor or Vaqueros Formations, and a mapped by Dibblee (1962) as the Reef Ridge sandstone unit at the base of the Santa Mar- Formation (Fig.

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