Soils and Minerals Flashcards
Why is RS limited for soils?
- Dense vegetation often on top of soil
- Needs exposed soils and minerals
- Visual good for drainage basins and Earth structures
Geobotany
- Infer mineralogical or soil type based on overlying vegetation
- Vegetation as proxy
What is the greatest enemy to measuring soils radiance?
Vegetation
Ltotal = ?
Lp plus Ls plus Lv
- Ls and Lv of interest for bare soil
How deep into soil does Ls go?
- 1/2 of lambda deep
- ex. 0.55micrometers = 0.27micrometers depth of penetration (hair is 100micrometers for comparison)
- O horizon
How deep into soil does Lv go?
- A few cm
- O and A horizons
Ls and Lv are a function of?
- Soil texture (grain size/roughness)
- Soil moisture
- Organic matter content
What happens to penetration with depth of Organic layer horizon?
- Deep O layer = fully attenuates and will not penetrate deeper soil
- Thin O layer = more light penetration and better Lv radiance
Soil texture
- Percent sand, silt, clay in soil
Sand soil
- 2mm
- water can percolate easily in large air spaces
Silt and clay soil
- Clay 0.002mm
- Silt 0.05mm
- Retention of soil capillary water = more water
What happens as grain size increases?
- Probability of photon absorption increases
- Due to larger internal path of grain
- Smaller grain has more surface (reflection) than volume (absorption)
Graph of dry bare silt vs. sand
- Reflectance increases with increasing wavelengths throughout Vis, NIR, and MIR
- Sand less reflection than silt b/c of more volume in larger grain absorbing
Dry soil
- Ls specular reflection
- Increase scatter btwn grains
- Lv volume reflectance penetrates into particle and can be absorbed
Wet soil
- Specular reflection
- Volume reflectance
- Absorption by water in interstitial space and capillary water at familiar peaks (0.76, 0.97, 1.1, 1.4, 1.9, 2.7)
- Darker appearance b/c water absorbs IR and lowers reflectance
What is the amount of moisture held in a soil layer a function of?
- Function of Soil texture (grain size)
- Smaller particle = greater ability to hold more moisture for longer b/c of capillary water
- Sand drains rapidly
What effect does increased moisture have on reflectance?
- More valleys in reflectance from water absorption
- Soil will appear darker
- Reflectance will decrease, absorption increase
Where are the ‘valleys’ of absorption in sand and what happens as moisture increases?
- Dry soil has negligible valleys
- Increase moisture and reflectance decreases
- Valleys appear at 1.4, 1.9, 2.7, the typical water absorption locations
Where are the ‘valleys of absorption in clay and what happens with increasing moisture?
- Dry clay has valleys at 1.4 and 2.2 regardless of moisture content
- 2.2 micrometers is unique to clay b/c of hydroxyl molecule not found in sands absorbs at this wavelength
- As moisture increases, reflectance decreases and typical water absorption valleys become more pronounced
At what wavelength does clay have unique absorption because of the hydroxyl molecule?
- 2.2
- But also less unique at 1.4 (similar to water)
- 1.4 will be seen without water content and will become more pronounced with increasing moisture
Presence of organic material causes what in soil reflectance?
- Reduction in reflectance due to increased absorption
- Visible wavelengths will see increased absorption
- Soil appears darker
What will happen if organic matter is burned off?
Reflectance will increase, especially at shorter wavelengths
Where does Organic Matter absorb more?
- Blue spectrum
- Increase OM and absorption at short wavelengths increases
What can the absorption of water in soil infer?
- Soil moisture content
- Water stressed fields
- Use for precision farming, algorithm in almost real-time w/ satellite data (mostly in developed countries)
What are variables that affect ratio of organic?
- Soil composition, moisture content, organic content, mineral content, soil texture
What does mineral detection require?
- High spectral resolution
- Detail in SWIR
- Spectral absorbance happens at specific, small locations for different minerals
- W/o hyperspectral, small detailed features would be lost
- Most features in SWIR
AVIRIS
- Airborne Visible Infrared Imaging Spectrometer
- NASA
- 224 contiguous spectral channels (bands)
- Wavelengths 400 - 2500nm
GERIS
- 63 bands
- Hyperspectral
- Not great but better than Landsat
How should a company interested in exploring for minerals go bout doing that?
- Use hyper spectral because Landsat would be useless
- Airborne would be best but is expensive
- Use USGS spectral library for minerals
Why is SWIR and thermal important for mineral exploration?
- SWIR shows many small details specific to individual minerals
- Thermal bands important because some minerals emit, not reflect
ASTER
- Advanced Spaceborne Thermal Emission and Reflection Radiometer
- Designed for geological exploration by Japanese
- Free, USGS website
- 26m resolution
- Broad Vis bands b/c not goal of platform
- Narrow SWIR and TIR
What band combination should be used for ASTER mineral data?
- RGB all SWIR
Where are ASTER bands located?
- Broad Vis
- Many Narrow SWIR and TIR to see minerals detailed absorption peaks
- In atmospheric windows to avoid atm water absorption
Compare and contrast ASTER, Hyperion and Landsat ETM
- ASTER designed for minerals with broad
Vis and many narrow SWIR and TIR - Hyperion has many more narrow bands from Vis to SWIR but does not reach TIR
- Landsat has broad bands in Vis, SWIR and TIR but will not give small details of minerals
What was ASTER, Landsat and MODIS designed for?
- ASTER: minerals b/c of many narrow SWIR and TIR
- Landsat: Vegetation b/c broad bands
- MODIS: oceanographic b/c of narrow bandwidths in Vis, B and G in particular
What is ASTER band 6 and 8 designed for? 10, 11, 12?
6: Clays (kaolinite, gypsum)
8, 14: Carbonates (limestones, dolomites)
10, 11, 12: Silicates
Geobotany
- Vegetation spectral changes can be related to lithology, soil chemistry
- Helps ID underlying soil when vegetation density covers it
- ex. Copper enriched vegetation
How does Geobotany work
- Vegetation changes in presence of heavy metals or alteration zones
- Accumulation of heavy metals may stress vegetation and shift red-edge
- May be evident as abrupt changes in plant species indicating lithological change rather than stress
- Lack of vegetation b/c of toxic metals
- Basically, some veg uptakes compounds, some veg changes depending on minerals
Indicator plants
- Grow in soils enriched by certain elements
What happens to Balsam fir and Red spruce in metal enriched soil?
- Increased G reflectance for both
- Balsam: NIR increase
- Spruce: NIR decrease
