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Remote Sensing of Soils

Remote Sensing of Soils. Remote Sensing of Soils, Minerals, and Geomorphology. • 26% of the Earth’s surface is exposed land • 74% of the Earth’s surface is covered by water • Almost all humanity lives on the terrestrial, solid Earth

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Remote Sensing of Soils

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  1. Remote Sensing of Soils

  2. Remote Sensing of Soils, Minerals, and Geomorphology • 26% of the Earth’s surface is exposed land • 74% of the Earth’s surface is covered by water • Almost all humanity lives on the terrestrial, solid Earth comprised of bedrock and the weathered bedrock called soil. • Remote sensing can play a limited role in the identification, inventory, and mapping of surficial soils not covered with dense vegetation. • Remote sensing can provide information about the chemical composition of rocks and minerals that are on the Earth’s surface, and not completely covered by dense vegetation. Emphasis is placed on understanding unique absorption bands associated with specific types of rocks and minerals using imaging spectroscopy techniques. • Remote sensing can also be used to extract geologic information including, lithology, structure, drainage patterns, and geomorphology (landforms).

  3. Soil Characteristics •Soil is unconsolidated material at the surface of the Earth that serves as a natural medium for growing plants. Plant roots reside within this material and extract water and nutrients. Soil is the weathered material between the atmosphere at the Earth’s surface and the bedrock below the surface to a maximum depth of approximately 200 cm (USDA, 1998). •Soil is a mixture of inorganic mineral particles and organic matter of varying size and composition. The particles make up about 50 percent of the soil’s volume. Pores containing air and/water occupy the remaining volume.

  4. Soil Taxonomy • We no longer identify a “soil type”. Rather, soil scientists determine the soil taxonomy (Petersen, 1999). “Keys to Soil Taxonomy” have been used by the USDA Natural Resources Conservation Service since 1975 to qualitatively and quantitatively differentiate between soil taxa. The highest category of the U.S. Soil Taxonomy is Soil Order. Each order reflects the dominant soil-forming processes and the degree of soil formation. • There are 12 dominant U.S. Soils Orders: Alfisols (high-nutrient soils), Andisols (volcanic soils), Aridisols (desert soils), Entisols (new soils), Gelisols (tundra soils), Histosols (organic soils), Inceptisols (young soils), Mollisols (prairie soils), Oxisols (tropical soils),Spodosols (forest soils), Ultisols (low-nutrient sols), and Verticols (swelling-clay soils). Scientists use Dichotomous Keys to classify soils into Suborder, Great Groups, Subgroups, Family Level, and Soil Series.

  5. Standard Soil Profile (U.S. Department of Agriculture)

  6. Soil Particle Size Scales

  7. Soil Texture Triangle Clay (%) Silt (%) Sand (%)

  8. Total Upwelling Radiance (Lt) Recorded by a Remote Sensing System over Exposed Soil is a Function of Electromagnetic Energy from Several Sources

  9. Spectral Reflectance Characteristics of Soils Are a Function of Several Important Characteristics • soil texture (percentage of sand, silt, and clay), • soil moisture content (e.g. dry, moist, saturated), • organic matter content, • iron-oxide content, and • surface roughness.

  10. In situ Spectroradiometer Reflectance Curves for Dry Silt and Sand Soils Percent Reflectance Wavelength (mm)

  11. Reflectance from Dry versus Wet Soils Radiant energy may be reflected from the surface of the dry soil, or it penetrates into the soil particles, where it may be absorbed or scattered. Total reflectance from the dry soil is a function of specular reflectance and the internal volume reflectance. As soil moisture increases, each soil particle may be encapsulated with a thin membrane of capillary water. The interstitial spaces may also fill with water. The greater the amount of water in the soil, the greater the absorption of incident energy and the lower the soil reflectance.

  12. Reflectance from Moist Sand and Clay Soils Sand Higher moisture content in (a) sandy soil, and (b) clayey soil results in decreased reflectance throughout the visible and near-infrared region, especially in the water-absorption bands at 1.4, 1.9, and 2.7 mm. Percent Reflectance Clay Percent Reflectance

  13. Organic Matter in a Sandy Soil Generally, the greater the amount of organic content in a soil, the greater the absorption of incident energy and the lower the spectral reflectance

  14. Iron Oxide in a Sandy Loam Soil Iron oxide in a sandy loam soil causes an increase in reflectance in the red portion of the spectrum (0.6 - 0.7 mm) and a decrease in in near-infrared (0.85 - 0.90 mm) reflectance

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