Domains of Information

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Domains of Information

• spectral
• spatial
• angular (BRDF)
• distance-resolved (e.g. LiDAR)
• multi-temporal

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EM Radiation

• emitted, scattered or absorbed
• energy out energy in scattering energy
  emitted
• intrinsic properties (emission,
  scattering/absorption)
• vary with wavelength
• vary with physical / chemical properties
• can vary with view angle

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EM Spectrum ( atmospheric transmission)
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Plancks law - intensities of radiation
(radiances) as a function of wavelength for
materials with different T
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Spectral reflectance

• Related to
• how much (illuminated) material (seen)
• reflectance / absorptance characteristics of
  materials
• ( multiple scattered effects)

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Leaves

• Absorbtance by leaf pigments, water etc
• Acting in different parts of the spectrum

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Leaves Factors affecting reflectance/transmittanc
e of plant elements

• pigment type/concentration
• e.g. Chlorophyll a,b - absorb visible radiation
• surface features
• hairs, spines, veins, cuticular wax - scattering
  (e.g. specular)
• cell morphology and content
• NIR - high refl. due to scattering at
  refractive index discontinuities
  (nair 0 ncell1.47)
• MIR - water absorption features

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• So attempt to take RS measurement and relate to
• cover type
• different spectral properties)
• amount of material (eg vegetation)
• eg leaf
• high NIR, low visible (basis of VIs)

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Interpretation complicated by

• variations in Sun/view angle

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Directional Information

• Describe directional reflectance by BRDF
• Bidirectional Reflectance Distribution Function
• e.g. plot as function of view zenith angle

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Directional Information
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Features of BRDF

• General upwards bowl shape for most biomes
• retro-reflectance peak (hot spot)

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Directional Information
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Features of BRDF

• Bowl shape
• increased scattering due to increased path length
  through canopy

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Features of BRDF

• Bowl shape
• increased scattering due to increased path length
  through canopy

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Features of BRDF

• Hot Spot
• mainly shadowing minimum
• so reflectance higher

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Use of directional information

• Parameterisation of surface conditions
• build model of physics of effect of surface
  properties on reflectence
• invert model against RS BRDF measurements

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Distance-resolved

• Can determine distance from satellites
• based on time-delay of signal

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Distance-resolved

• Can determine distance from satellites
• based on time-delay of signal

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Distance-resolved

• eg GPS

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Distance-resolved

• EO example
• radar interferometry

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Distance-resolved

• EO example
• radar interferometry
• assume know satellite position

(¾½)x360 315 degrees
¾ way through
270 degrees
2 x d1 (N1(¾½))x5.6
(360 degrees, 2? radians)
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Distance-resolved

• EO example
• radar interferometry

2 x (d2 - d1) (N2- N1) x 5.6 ((¾½)-0) x 5.6
0 way through
2 x d2 (N2) x 5.6
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Distance-resolved

• EO example
• position 1
• 2 x (d2 - d1) (N2- N1) x 5.6 ((¾½)-0) x 5.6
• position 2
• point on ground next to current point will have
  different phase change
• if its within the same cycle (height change less
  than 5.6cm)
• can tell relative height change between these
  points
• very precise (mm)

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Shuttle Radar Topography Mission
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Shuttle Radar Topography Mission
11 Feb 2000 (Endeavour) - 11 days 30m DEM of /-
60 degrees latitude
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Distance-resolved
Measure small change - subsidence
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Distance-resolved
Measure small change - earthquake
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Distance-resolved
RADAR
RAdio Detection And Ranging
LIDAR
LIght Detection And Ranging
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Distance-resolved LIDAR

• Send laser pulse from sensor
• measure round trip time
• 2x distance
• use NIR mostly
• atmospheric effects minimised

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Distance-resolved LIDAR

• Examples - EA
• fly aiborne LIDAR regularly for high resolution
  DEM
• use first/last return
• ground height / tree height

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Distance-resolved - LIDAR
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Distance-resolved LIDAR

• Examples - VCL
• Vegetation Canopy LIDAR
• NASA mission to fly 2000
• waveform LIDAR

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Distance-resolved VCL

• waveform LIDAR

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Distance-resolved

• waveform LIDAR

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LIDAR

• Simple form of measurement
• easy to use (? Simply)
• doesnt work (well) on high slopes
• requires highly-sensitive instrumentation
• potentials for new forms of information
• waveform LIDAR

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Interferometry

• Used for number of years
• operational (SRTM)
• different scales for different SAR frequencies
• doesnt work well (for height) if change between
  images
• wind in forests
• doesnt work on high slopes