Remote Sensing of the Lithosphere

1. Remote Sensing of the Lithosphere

2. Objectives • Review fundamental concepts pertaining to soils, minerals and rocks, geologic structures, drainage patterns, and landforms • Discuss spectral characteristics of soils, rocks, and minerals • Discuss, in general, how geological and geomorphological information can be extracted from remotely sensed data

3. Introduction • Terrestrial surfaces only make up 26 % of Earth’s total surface • Most people live and depend on terrestrial surfaces • Identification, inventory, mapping, and monitoring of soils, rocks, etc. is crucial! • Soil in particular is essential to the Earth’s life-support system

4. Soils • General Characteristics • SOIL IS NOT DIRT!!! • Nurtures life … • Four components: • Mineral matter • Organic matter • Water • Air • Mineral and organic matter constitute the soil matrix • Air and water are contained in pores or interstitial air spaces, the open spaces in the soil matrix

5. Solum Soils • Vertical Cross Section: Surface to Bedrock • Bedrock • Regolith • Soil • Solum (true soil)

6. Soils • Five Soil-Forming Factors • Geology, Climate, Topography, Biology, Chronology • Pedogenesis (soil formation): slow; involves complex interaction of physical, chemical, and biological processes

7. Soils • Four Soil-Forming Processes • Addition, Loss, Trans-location, Transformation • Rate at which soil-forming processes occur is determined by soil-forming factors

8. Soils • Soil Properties • Soil Physical Properties • Color • Texture • Structure • Consistence • Porosity • Soil Chemical Properties • Colloids • Cation Exchange Capacity • Acidity & Alkalinity

9. Soils • Soil Color • Largely determined by the presence/absence of organic matter and oxides (iron, silica, aluminum, etc.) in a soil • Suggests composition and chemical makeup of soils • Munsell Color Chart

10. Soils • Soil Texture • Particle size distribution • Relative proportion of different particle sizes • Particle size classes: • Gravel: > 2mm (not considered soil) • Sand: 0.05-2 mm (beach – gritty) • Very coarse: 1-2 mm • Coarse: 0.5-1 mm • Medium: 0.25-0.5 mm • Fine: 0.1-0.25 mm • Very fine: 0.05-0.1 • Silt: 0.002-0.05 mm (flour – silky) • Coarse: 0.02-0.05 mm • Medium: 0.006-0.02 mm • Fine: 0.002-0.006 mm • Clay: < 0.002 mm (pottery – sticky)

11. Soils • Particle size classes

12. Soils • Soil Texture Triangle • 12 soil textural classes • Texture classes based on the relative amounts of sand, silt, and clay in a soil sample • Best soils for plant growth: medium-textured soils

13. Soils • Soil Structure • Arrangement of soil separates (sand, silt, clay) into peds (clumps or aggregates of particles) • Peds differ in: • Size • Shape • Stability

14. Porous Non-porous Soils • Soil Porosity • Total volume of available pore spaces in soil • Function of soil texture and structure • Important porosity factors: pore size, pore continuity, pore shape, pore orientation, pore location • Permeability – ability of water to flow through soil

15. Soils • Soil Moisture: Forms of Soil Moisture • Hygroscopic, Capillary, Gravitational • Adhesion – attraction of soil water to soil particles • Cohesion – attraction of water molecules to each other

16. Soils • Soil Moisture: Plant Available Moisture • Field Capacity • Wilting Point

17. Soils • Soil Moisture: Soil Water Budget • Precipitation (P) • Potential evapotransp. (PE) • Actual evapotransp. (AE) • Moisture surplus • (P > PE) • Soil moisture utilization • (AE > P) • Moisture deficit • (PE > AE) • Soil moisture recharge • (P > PE) after a period of deficit

18. Cations Anions Cations Soils • Soil Chemistry • Soil solution • Ions • Anions (-) • Cations (+) • Soil colloids

19. Soils • Soil Acidity/Alkalinity • pH scale ranges from 0 to 14 • Acid soils (lower pH) vs. Alkaline soils (higher pH) • Neutral (= 7)

20. Soils • Soil Profile and Soil Horizons • Distinct horizontal layers within the upper 200 cm or so of soils --- result of soil-forming processes • Horizon forming at/near the surface = epipedon

21. Soils • Soil Profile and Soil Horizons Eluviationhorizon Illuviationhorizon

22. Soils • Soil Catena • Variation of soil horizons/soil profiles along transects

23. Soils • Classification of Soils • Linkages between soils, climate, vegetation, and parent material • Provides information on the “quality’ of the environment • The Mapping Question: matter of scale … • The U.S. Soil Taxonomy • NRCS • Hierarchical system: soil orders (12) , soil suborders (48), soil great groups (230), soil subgroups (~ 1,2000), soil series (~ 15,000)

24. Soils • Soils of the World

25. Soils • Soils in the United States

26. Soils • Soil Erosion

27. Soils • Desertification U.S.-Mexican border

28. Remote Sensing of Soils Properties • RS alone is not sufficient to identify all crucial facts about soils (e.g., to map soil taxa) • In situ collection of soils data is indispensable • RS of soils can only be performed under certain conditions • Problems: e.g., obliteration of soils by dense vegetation • However: • RS can aid in the soil mapping process • RS can provide information about a number of specific soil surface characteristics and their changes

29. Remote Sensing of Soils Properties • Total upwelling radiance from exposed soil recorded by a sensor, Lt, is a function of: • Atmospheric scattering (Lp) • Specular boundary layer reflectance: reflected or scattered radiance from the soil surface (~ ½ wavelength deep) (Ls) • Volumetric scattering: radiance from subsequent soil/rock substrate (Lv)

30. Remote Sensing of Soils Properties • Spectral reflectance indirectly depends on characteristics of soil profile: Very long active microwaves may penetrate farther into the soil (Lv) as hasbeen demonstrated in the Sahara

31. Remote Sensing of Soils Properties • Spectral reflectance characteristics of soils are: • typically reported as combined surface (Ls) and subsurface (Lv) radiance • Atmospheric attenuation (Lp) can be removed • Individual contribution of Ls and Lv difficult to disentangle • a function of: • Soil texture • Soil moisture content • Organic matter content • Iron oxide content, salinity content, etc. • Surface roughness

32. Remote Sensing of Soils Properties • In situ spectroradiometer reflectance curves of soils that contain (a) no moisture and (b) very little organic matter • Increasing reflectance with increasing wavelength • Especially in the visible, near- and mid-infrared portions of the EM spectrum

33. Remote Sensing of Soils Properties • Soil Texture and Moisture Content • Soil particles may: • Reflect incident radiant flux (specular reflectance) • Absorb, transmit, and/or scatter incident radiant flux —internal scattering (volume reflectance) • Total reflectance per wavelength for soils without moisture, organic matter, and iron oxides = Function of: • Soil specular reflectance • Soil volume reflectance

34. Remote Sensing of Soils Properties • Soil Texture and Moisture Content • Both influence reflectance • Fine-textured soils have a greater soil moisture retention capacity than coarse-textured soils • The greater the soil moisture content, • the smaller the amount of reflectance • the greater the amount of absorption

35. Remote Sensing of Soils Properties • Soil Texture and Moisture Content • Absorption increases as soil moisture content increases, especially in the water absorption bands at: • 1.4, 1.9, and 2.7 mm • Water absorption more extreme in fine-textured soils • Moist soils appear darker in RS imagery

36. Remote Sensing of Soils Properties • Soil Organic Matter • Amount has significant impact on spectral reflectance characteristics of soils • The greater the amount of organic matter in the surface soil, the greater the absorption of incident energy and the lower the spectral reflectance

37. Remote Sensing of Soils Properties • Biological Soil Crusts • Communities of mosses, lichens, liverworts, algae, fungi, cyanobacteria, bacteria (primarily in deserts) • Survive dessication and high temperatures, pH, and salinity • Crucial for soil stability, fertility, erosion control, fermentation, etc. • Biological soil crust index (BSCI) for TM data (Chen 2005)

38. Remote Sensing of Soils Properties • Iron Oxide • Amount has significant impact on spectral reflectance characteristics of soils • Iron oxides in soils generally cause: • increased reflectance in the red portion of the EM spectrum • decreased reflectance in the blue and green portions of the EMS • absorption in the 0.85 to 0.90 mm region

39. Remote Sensing of Soils Properties • Soil Salinity • Major environmental hazard, especially in arid and irrigated areas • Increasing surface soil salt concentrations generally cause increased reflectance, especially in the visible and NIR

40. Remote Sensing of Soils Properties • Soil Salinity • Reflectance increases with increasing soil salt concentration

41. Remote Sensing of Soils Properties • Surface Roughness • The smaller the surface roughness relative to the size of the incident radiation, the greater the specular reflectance • In the absence of organic matter, moisture, and iron oxides, fine-textured soils would have higher spectral response throughout visible and near-infrared regions due to near-specular reflection • In the presence of organic matter, moisture, and iron oxides, coarse-textured soils have a relatively higher spectral response in the visible and near-infrared regions due to effective diffusive scattering of incident wavelengths • Relationships above may cause interpretation problems

42. Rocks & Minerals • Minerals • must be found in nature • must be made up totally of inorganic substances • must have the same chemical composition wherever found • must contain atoms arranged in a regular pattern and forming solid units called crystals • Rock • Solid material composed of aggregated mineral particles • Found at or near Earth’s surface • Outcrop – surface exposure of bedrock • Bedrock – rock buried by a layer of soil and/or regolith

43. Rocks & Minerals • Three Major Rock Classes • Igneous • Intrusive • Extrusive • Sedimentary • Clastic • Chemically precipitated • Organic • Metamorphic • Various parent rocks

44. Rocks & Minerals • Igneous Rocks – Some Examples Rhyolite - extrusive Granite - intrusive

45. Rocks & Minerals • Sedimentary Rocks – Some Examples Gypsum – Chem. prec. Coal – Organic Silstone – Clastic

46. Rocks & Minerals • Metamorphic Rocks – Some Examples Gneiss (from granite) Marble (from limestone)

47. Remote Sensing of Rocks & Minerals • RS allows for differentiation between rock types and identification of various rock characteristics • Model of reflectance for exposed rock consisting of a single or several minerals: • rl = reflectance at wavelength l • mo = cosine of the angle of incident light onto the rock or mineral of interest • m = cosine of the angle of emitted light • g = phase angle • w’ = average single scattering albedo from the rock or mineral of interest • Bg = backscatter function • Pg = average single particle phase function • H = function for isotropic scatterers

48. Remote Sensing of Rocks & Minerals • Knowing advanced reflectance theory and optical constants of the minerals involved, theoretical reflectance spectra an be computed for: • pure minerals that have a single grain size • a pure mineral with a variety of grain sizes • mineral mixtures with varying grain sizes • Key for imaging spectroscopy: • Reflectance curves of specific types of minerals or rocks can be predicted!

49. Imaging Spectroscopy of Rocks/Minerals • Energy Matter Interactions: Reflection & Absorption • Photons of light incident on a mineral or rock may be: • reflected from grain surfaces onto other grain surfaces • passed through the grain onto other grains • absorbed within a grain • (emitted from a grain) • Minerals absorb or scatter incident energy in (a) different ways and (b) at different wavelengths • High-spectral-resolution data can provide info about mineral chemistry

50. Imaging Spectroscopy of Rocks/Minerals • Energy Matter Interactions: Reflection & Absorption • Alunite spectra provided by three different sensors