1. Remote Sensing for Geologic Applications Soil Properties Mineral and Rock Identification Geomorphology (landforms) Volcanology Coastal Processes Fluvial Processes Desertification

2. Remote Sensing of Soils A mature, fertile soil is the product of centuries of physical and chemical weathering of rock, combined with the addition of decaying plants and organic matter. Soil is a mixture of inorganic mineral particles, organic matter, and pores containing air or water. Horizontal layers are called horizons: O,A,E,B,C. In remote sensing, we see only the upper layer that is present (not always an “O”). EMR in the visible and near-IR only penetrates about ½ of the wavelength of the radiation. Longer wavelength microwave energy can penetrate dry, very sandy soils do depths of up to several meters.

3. Soil Grain Size

4. Spectral Reflectance of Soils Spectral Reflectance of Soils controlled by: –Soil moisture: Percentage of sand, silt, and clay –Moisture content –Organic matter –Mineral contents, including Iron oxide and carbonates –Surface roughness

5. Soil Grain Size Different size particles play different roles in soil: –Sand (0.05 to 2.0 mm): large air spaces, rapid drainage of water –Silt (0.002 to 0.05 mm): enhance movement and retention of soil capillary water –Clay (< 0.002 mm): enhance movement and retention of soil capillary water; carry electrical charges which hold ions of dissolved minerals (e.g. potassium and calcium)

6. Spectral Reflectance from Soils

7. Soil Texture and Moisture Content The void space between soil particles, called interstitial air space, can hold water from precipitation. A layer of water can also form around the particles, called capillary water As soil moisture increases, overall reflectance decreases and water absorption features develop at 1.4, 1.9, 2.7 microns Microwave reflectance increases with increasing soil moisture Sandy soils drain faster and dry by evaporation faster than clay soils.

8. The effect of increasing soil moisture content on spectral reflectance Clay mineral hydroxyl absorption band at 2.2 microns Soils with a large amount of clay exhibit hydroxyl Absorption bands at 1.4 and 2.2 microns. 2.2 microns is more useful since it doesn’t overlap the water absorption feature.

9. Soil Moisture from Thermal Sensors Water has a higher thermal capacity than soil and rock. Moist soils will change in temperature more slowly than dry soils.

10. Soil Moisture and Texture -Clays hold more water more ‘tightly’ than sand. -Thus, clay spectra display more prominent water absorption bands than sand spectra. -AVIRIS can be useful for quantifying these absorption features.

11. Effects of Organic Matter in Soils Organic matter is a strong absorber of EMR, so more organic matter leads to darker soils (lower reflectance curves).

12. Soil Organic Matter Organic matter content in the Santa Monica mountains mapped using AVIRIS

13. Effect of Fe-oxide: Increase in the 600 – 700 nm reflectance, decrease in 400 – 600 nm reflectance, decrease in near- IR (absorption feature at ~875 nm)

14. Iron Oxide Iron content in the Santa Monica mountains mapped using AVIRIS

15. Surface Roughness If a surface is smooth (particles smaller than wavelength), specular reflection is important. No return – surface dark – unless sensor correctly positioned and pointed in specular direction. Smooth soil surfaces tend to be clayey or silty, often are moist and may contain strong absorbers such as organic content and iron oxide. Conversely, a rough surface scatters EMR and thus appears bright. But paradoxically, microwave data of well drained sands are often very bright, regardless of angle.

16. Surface Roughness and SAR