Variations In Spectral Reflectance Research Articles

Evaluation of visible and near‐infrared and thermal‐infrared reflectance spectra for studying thermal alteration of Pierre Shale, Wolcott, Colorado

Analyses of visible and near‐infrared (0.4–2.5 μm) and thermal‐infrared (2.5–25.0 μm) spectral reflectance of whole rock and kerogen concentrates of dike‐intruded Pierre Shale indicate that the degree of thermal alteration of contained organic matter (OM) can be estimated by use of spectral reflectance. With increasing thermal alteration of the OM, whole rock, and kerogen spectra show the following trends: (1) visible and near‐infrared (VNIR) and thermal‐infrared (TIR) reflectance decreases progressively, with the largest change in the VNIR occurring between 0.90 and 1.50 μm; and (2) the intensities of absorption features in the 3‐ to 5‐μm region, which are related to C‐H stretching vibrations, decrease. The VNIR and TIR spectral reflectance trends are highly correlated with H/C ratios and vitrinite reflectance data. The largest changes in all these parameters occur at a distance that is equivalent to about one‐half the dike thickness, where the temperature range is estimated to have been 240°–350° C. The VNIR and TIR spectral reflectance variations are related to thermally induced composition and structural changes in the OM. Landsat Thematic Mapper channels 3, 4, and 5 should have excellent potential for remote detection of OM maturity. Analysis of in situ VNIR and TIR measurements may provide a rapid method for estimating thermal maturity in the field. In addition, laboratory measurements of TIR spectral reflectance are a more sensitive and convenient means of measuring the maturity of kerogen than the traditional transmittance method. Further work is necessary to examine the effects of variable OM abundance and type, mineralogic composition, grain size, and weathering on spectral reflectance characteristics.

STUDY ON SPECTRAL REFLECTION CHARACTERISTICS OF SNOW, ICE AND WATER OF NORTHWEST CHINA

The spectral reflection characteristics of snow, ice and turbid water within spectral range 380-1200 nm have been analysed. The spectral reflectance of snow decreases with increasing of snow density and its crystal size, and there is good correlation between density and spectral reflectance. The spectral reflactance gradually decreases from 95% to 60% within visible range while snow is metamorphosed to glacier ice. The variation of spectral reflectance of turbid water is determined by the silt content of water; that is, when the silt content is more than 5400 mgl-1 and the wavelengtho f the maximum reflectance is stable (near 820 nm). Based on the test, Mj and Cv , values, the optimum remote sensing bands have been selected respectively, namely, 420-450, 840-910, 950-1110 nm for snow, 670-760 nm for ice and 730-810 nm for turbid water.

Coniferous tree species mapping using LANDSAT data

The identification and mapping of 12 surface-cover types within Crater Lake National Park, Oregon, including seven classes of coniferous tree species, has been accomplished through the use of LANDSAT digital data. The 12 surface-cover types were mapped with an average accuracy of 88.8%, as compared with detailed ground truth. The classification of the LANDSAT data was accomplished through use of the Interactive Digital Image Manipulation System (IDIMS) available at the EROS Data Center in Sioux Falls, South Dakota. The combined effects of a quantity and quality of ground truth, the use of the controlled clustering classification technique, and the prudent placement of Intensive Study Areas (ISA) on the image-processing CRT screen for training statistic collection provided very subtle spectral reflectance differences between coniferous tree species. Slope angle, slope aspect, and surface-cover type variation, and to a lesser degree, crown size, and crown density were the main environmental factors that accounted for spectral reflectance variation of surface-cover types within the park. Through an appreciation of the influence of environmental factors on the reflectance value of surface-cover types, and an appreciation for the placement of training areas to sample the environmental effects on reflectance, one can reduce misclassification or nonclassification possibilities.

Color and Reflectance of Human Flesh

A recent investigation of the variation in spectral reflectance and chromaticity of the flesh tones of various individuals is described. Spectrophotometric reflectance measurements were made on the face, arms and hands of several individuals having different complexions and degrees of sun tan. Spectro-radiometric measurements were made of many phases of daylight. The variations in chromaticity of fleshtones due to daylight variations were calculated. The reflectance of the flesh was computed in terms of the response of an exposure meter to determine the exposure constant for reflected-light readings taken on the human face.