HSI Course

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Hyperspectral Imaging Basics Hyperspectral
Concepts Systems Tradeoffs
Dr. Richard B. Gomez, Instructor George Mason
University
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Outline

• Hyperspectral Concepts System Tradeoffs
• Signal-to-Noise Ratio (SNR)
• Spectral Resolution, Sampling Interval, Range
• Image Acquisition Mode Tradeoffs
• Data Collection Systems
• Classification of Hyperspectral Imaging Systems
• Ground, Airborne, Spaceborne

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Radiometric Quantities
Quantity Radiant Energy (J) - Q Radiant Energy
Density (J/m3) U Radiant Flux (W) Power
P Radiant Exitance (W/m2) M Irradiance (W/m2)
E Radiance (W/m2-sr) L Radiant Intensity (W/sr)
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Definition ?Pdt dQ/dV dQ/dt dP/dA dP/dA d2P/dAd?
dP/d?
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Space Reference System
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Basic Components of Remote Sensing System

• Energy Source
• Transmission Path
• Target
• Background
• Sensor

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Hyperspectral Imaging General Concept
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Hyperspectral Reflectance Measurements
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AURORA Hyperspectral Image of Hawaii, Courtesy of
APTI, Inc.
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Hyperspectral Signatures
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Object Information Derived From Signal
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Atmospheric Effects (Richards Fig. 2.1)
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Atmospheric Compensation (continue)
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Incident Radiation

• Incident Radiation Reflected Radiation
• Scattered Radiation
• Absorbed Radiation
• Transmitted Radiation

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Upward Radiance Components

• L L1 L2 L3 L4
• L1 Path Radiance independent of surface
  reflectance
• L2 Attenuated Signal depends only on the
  surface reflectance in the field of view.
  Provides Surface information.
• L3 Scattered by atmosphere to the surface and
  reflected to the sensor. Affected by
  non-Lambertian surface light.
• L4 Light radiance reflected by the surface
  with at least one scattering in the atmosphere
  before reaching the sensor. Affectedby
  nonuniform surface and by non-Lambertian surface
  reflectionthat may be out of the field of view
  of the sensor.

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Total Radiance Available to Sensor

• Total Irradiance EG at Earths Surface
• EG E??T?cos ? ?? ED (Path Irradiance
  ED)
• The Radiance LT Due to Global Irradiance EG of
  the pixel
• LT (R/?)E??T?cos ? ?? ED
• Total Radiance Available to Sensor
• LS (RT?/?)E??T?cos ? ?? ED LP
• See John Richards Book Page 42, Equation 2.4

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John Richards Equations
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John Richards Reflectance Calculation
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Basic System Capabilities

• Field-of-View (FOV) or Swath Width on the Ground
  
• Spectral Range
• Spectral Sampling Interval
• Spectral Resolution
• Spatial Resolution or Instantaneous FOV or
  Ground Sample Distance (GSD)
• Dynamic Range or Signal-to-Noise Ratio (SNR)
• Wavelength (Spectral) Calibration
• Radiometric Calibration
• Geometric Calibration
• Figure-of-Merit (indicator of overall system
  performance)

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Mission Requirements

• Mass
• Power
• Data Rate
• Altitude
• Ground Coverage
• Timeliness
• Speed (Ground Velocity)
• Platform Stability (Pointing Ability)
• Orbit Characteristics (Inclination, Offset,
  Type, etc.)
• Costs

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System Parameters

• Mass
• Power
• Data Rate
• Encoding Level
• Spectral Discrimination
• Integration Time
• Detector Technology (Focal Plane Array, Format,
  Pixel Size)
• Pixel Pitch
• Focal Ratio or F-Number
• Focal Length
• Aperture
• Etendue

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Linewidth Full Width at Half Maximum
Airborne Hyperspectral Systems
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Classification of HSI Systems

• Image Acquisition Modes
• Whiskbroom Imagers
• Pushbroom Imagers
• Staring Imagers
• Spectral Selection Modes
• Dispersion Element (grating, prism)
• Filter-Based Systems
• Interference Filters
• Acoustical-Optical Filters
• Liquid Crystal Tunable Filters (LCTF)
• Interferometer-Based Systems
• Michelson Interferometer
• Fourier Transform Interferometer System
• Other (e.g., Multi-order etalons)

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Image Acquisition Mode Tradeoffs
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Spatial versus Spectral Resolution Tradeoffs
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Spatial versus Spectral Resolution Tradeoffs
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Principle Calibration Needs

• Geometric imaging aspects scan jitter,
  platform motion
• Relative geometric calibration FOV, IFOV, SSI
• Absolute geometric calibration GPS, INS, DTED
  
• Spectral (wavelength) spectral response of
  each channel
• Atomic emission line spectra spectral matching
• A-prior knowledge of sensor spectral
  characteristics
• Radiometric spectral radiance response
• Input radiance versus output digitized signal
• Dynamic range, quantization level, RMS noise
  level

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Radiometric System Parameters
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Absorption Lines
When light from a luminous source passes through
a gas, the gas may extract certain specific
energies from the continuous spectrum. We then
see dark lines where the energy has been removed.
These dark lines are called absorption lines.