CHAPTER 14: Remote Sensing of Soil, Minerals, and Geomorphology REFERENCE: Remote Sensing of the Environment John R. Jensen (2007) Second Edition Pearson Prentice Hall Some Facts about our Planet • 26% of the Earth’s surface is exposed land. • 74% of the Earth’s surface is covered by water. • Almos t all human ity lives on the terrestrial, solid Earth comprised of bedrock and the weathered bedrock called soil. 1 Why Remote Sensing? • It can play a limited role in the identification, inventory, and mapping of surficial soils not covered with dense vegetation. • It 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 iiimaging spectroscopy thitechniques. • It can also be used to extract geologic information including, lithology, structure, drainage patterns, and geomorphology (landforms). 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 surfaceandthebedrockbelowthesurfacetoa 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. 2 Standard Soil Profile (U.S. Department Of Agriculture) Soil Particle Size Scales a. Soil Science Society of America and U.S. Department of Agriculture Soil Particle Size Scale Sand Clay Silt Gravel v. fine fine medium coarse v. coarse 0.002 0.05 0.1 0.25 0.5 1 2 mm 76.2 Particle size relative to a grain of sand Clay Silt 0.15 mm in diameter 0.15 mm Sand b. MIT and British Standards Institute Silt Sand Clay Gravel Stones fine medium coarse fine medium coarse 0.0020.006 0.02 0.06 0.2 0.6 2 mm c. International Society of Soil Science Sand Clay Silt Gravel fine coarse 0.0020.02 0.2 2 mm 3 Soil Texture Triangle 100 90 10 ) % 20 ( 80 y a Cl 70 30 read Clay 60 40 50 50 read silty 40 sandy clay 60 S i l t clay ( clay loam silty clay % 30 70 ) sandy clay loam 20 loam 80 Loam silt loam 10 sandy 90 loamy loam Silt sand Sand 100 100 90 80 70 60 50 40 30 20 10 Sand (%) read Total Upwelling Radiance (Lt))RecordedRecordedby a Remote Sensing System over Exposed Soil is aaFunctionFunctionof Electromagnetic Energy from Several Sources 4 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. In situ Spectroradiometer Reflectance Curves for Dry Silt and Sand Soils 100 90 80 70 Silt 60 50 Sand ercent Reflectance ercent Reflectance 40 P 30 20 10 0 0.5 0.7 0.91.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 Wavelength (μm) 5 specular incident energy Reflectance from Dry reflectance 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 dry absorbed or scattered. Total reflectance soil interstitial specular reflectance from the dry soil is a function of specular a. air space volume reflectance reflectance and the internal volume specular incident energy reflectance reflectance. As soil moisture increases, each soil partic le may be encapsu lat ed with a thi n membrane of capillary water. The interstitial spaces may also fill with water. The greater the amount of water in the wet soil b. soil water soil, the greater the absorption of incident energy and the lower the soil reflectance. Reflectance from 60 Sand 0 – 4% moisture content Moist Sand 50 40 and Clay Soils flectance flectance e 30 5 – 12% 20 22 – 32% Higher moisture content Percent R 10 0 in (a) sandy soil, and (b) 0.5 0.70.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 a. clayey soil results in 60 Clay decreased reflectance 50 2 – 6% throughout the visible tance tance c 40 and near -infrared region , 30 especially in the water- 20 35 – 40% absorption bands at 1.4, Percent Refle 10 0 1.9, and 2.7 μm. 0.5 0.70.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 b. Wavelength (μm) 6 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 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 μm) and a decrease in in near-infrared (0.85 - 0.90 μm) reflectance 7 Remote Sensing of Rock and Minerals Remote Sensing of Soils, Minerals, and Geomorphology Rocks are assemblages of minerals that have interlocking grains or are bound together by various types of cement (usually silica or calcium carbonate). When there is minimal vegetation and soil present and the rock material is visible directly by the remote sensing system, it maybe possible to differentiate between several rock types and obtain information about their characteristics using remote sensing techniques. Most rock surfaces consist of several types of minerals. 8 Remote Sensing of Rocks and Minerals Clark (1999) suggests that it is possible to model the reflectance fdkitiflililfrom an exposed rock consisting of several minerals or a single mineral based on Hapke’s (1993) equation: -1 rλ = [[(w’/4π) x (μ / μ + μ o)] x [(1+Bg)Pg + H μ H μ o ] Where rλ is the reflectance at wavelength λ, w’ is the average single scattering albedo from the rock or mineral of interest, μ is the cosine of the angle of emitted light, uo is the cosine of the angle of incident light onto the rock or mineral of interest, g is the phase angle, Bg is a back-scattering function, Pg is the average single particle phase function, and H is a function for isotropic scatterers. Remote Sensing of Rocks and Minerals Using Spectroradiometers There are a number of processes that determine how a mineral will absorb or scatter the incident energy. Also, the processes absorb and scatter light differently depending on the wavelength (λ) of light being investigated. The variety of absorption processes (e.g., electronic and vibrational) and their wavelength dependence allow us to derive information about the chemistry of a mineral from its reflected or emitted energy. The ideal sensor to use is the imaging spectrometer because it can record much of the absorption information, much like using an in situ spectroradiometer. All materials have a complex index of refraction. If we illuminate a plane surface with photons of light from directly overhead, the light ( R), will be reflected from the surface according to the Fresnel equation: R = [(n -1)2 + K2]/ [(n + 1)2 + K2] where n is the index of refraction, and K is the extinction coefficient. 9 Spectra of Three Minerals Derived from NASA’s Airborne Visible Infrared Imaging Spectrometer (AVIRIS) and as Measured Using A Laboratory Spectroradiometer (after Van der Meer, 1994) Alunite Laboratory Spectra, Simulated Landsat Thematic Mapper Spectra, and Spectra from a 6363-- Channel GERIS Instrument over CupriteCuprite,, Nevada 90 Laboratory ty) ) Spectra Alunite 80 70 60 1 23 4 5 50 Landsat Thematic Mapper 30 40 23 29 31 t Reflectance (offset for clarity t Reflectance (offset ectance (offset for clari n l 30 7 Perce 28 20 GERIS 32 10 hyperspectral Percent Ref 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 Wavelength, μm 10 6 Quartz Optical Constants n, index of refraction K, extinction coefficient Index of refraction 4 K and extinction n dex of Refraction or exRefraction of or xtinction Coefficient tinction Coefficient tinction coefficient of quartz n d I E 2 n In Ex n for the wavelength n K K 0 interval 81012 14 16 Wavelength,μ m 6-16 mm Spectral reflectance ctance ctance Quartz (powdered) e e characteristics of powdered quartz obtained using a Relative Refl Relative Relative Refl spectroradiometer 0 (after Clark, 1999) 810121416 Wavelength,μ m Mineral Maps of Cuprite, NV, Derived from Low Altitude (3.9 km AGL) and High Altitude (20 km AGL) AVIRIS Data obtained on October 11 and June 18, 1998 Hyperspectral data were analyzed using the USGS Tetracorder program. 11 RtRemote SiSensing of Geology and Geomorphology Geologists often use remote sensing in conjunction with in situ observation to identify the lithology of a rock type, i.e., itsso orig in. The ed diffe re nt r ock types ypesa ar e formed by one of three processes; • igneous rocks are formed from moulten material; • sedimentary rocks are formed from the deposition of ppparticles of pre-existinggp rocks and plant and animal remains; or • metamorphic rocks are formed by applying heat and pressure to previously existing rock. 12 Rock Structure: Folding and Faulting The type of rock determines how much differential stress (or compression) it can withstand. When a rock is subjected to compression, it may experience: 1) elastic deformation in which case it may return to its original shape and size after the stress is removed, 2) plastic deformation of rock called folding, which is irreversible ((,i.e., the comp ressional stress is bey ond the elastic limit, and/or 3) fracturing where the plastic limit is exceeded and the rock breaks into pieces (the pieces can be extremely large!).