4A

• Radiant flux (Φ)


  A "radiometric quantity" that refers to the time rate of flow of energy onto, off of, or through a surface
• Power


  Energy per unit time, measured in Watts (W) - 1 Watt = 1 Joules/s
• Remote sensing systems are located in space, and they usually look only at a relatively small portion of the Earth at a single instant
• Remote sensing systems are designed to only measure reflectance, absorptance, or transmittance radiometric quantities on a per area basis at a single instant
• Radiant Flux Density


  The amount of radiant flux intercepted divided by the area of the plane surface
• Irradiance (E)


  The amount of radiant flux incident upon a surface per unit area of the surface
• Exitance (M)


  The amount of radiant flux leaving ("reflected" from) a surface per unit area of the surface
• Radiance


  The radiant flux leaves the projected source area in a specific direction towards the remote sensor
• Solid angle


  A 3-dimensional cone that funnels radiant flux from a specific point source on the surface toward the sensor system
• Sensor


  The instrument or device that makes the measurement
• Platform


  The type of vehicle that supports or carries the sensor
• Vantage Points


  • Far-Space
  • Near-Space
  • Airborne
  • Terrestrial
• In order for a sensor to collect and record energy reflected or emitted from a target or surface, it must reside on a platform away from the target or surface being observed
• Commonest Platforms


  • Spaceborne - Satellite, Shuttle
  • Airborne - Aeroplane, Helicopter, Hot Air Balloon, Air Ship, Tethered Balloon
  • Ground-based - Hand-held, Raised platform
• Platforms


  • Diwata
  • Diwata 2
  • Maya-1
  • Maya-2
• Satellite Classification by Mass

  • Large Satellite - 1000 kg
  • Medium-sized Satellite - 500-1000 kg
  • Minisatellite - 100-500 kg
  • Microsatellite - 10-100 kg
  • Nanosatellite - 1-10 kg
  • Picosatellite - 0.1-1 kg
  • Femtosatellite - < 0.1 kg
• Sensor Categories (by Utilized Electromagnetic Spectrum)

  • Optical
  • Microwave
  • Infrared
• Sensor Categories (by Source of Energy Used for Illumination)

  • Passive
  • Active
• Passive Sensors


  Sensors which sense natural radiation, either emitted of reflected form the Earth
• Active Sensors


  Emit radiation which is directed toward the target to be investigated, and the reflected radiation is detected and measured
• Ground-based Remote Sensor


  • Spectroradiometer - an instrument that is used to determine spectral response of various features
• Aircraft-based Remote Sensors


  • Aerial Camera, LIDAR, Camera in an unmanned aerial vehicle (UAV)
• Space-based Remote Sensors


  • MODIS, Landsat 5, 7, 8, Quickbird, Worldview 1,2,3, ASTER VNIR
• First Generation (Multi-spectral) Satellite Imaging Systems

  • LANDSAT
  • NOAA-AVHRR
  • SPOT
  • IRS SERIES
• Commercial Satellite Imaging Systems

  • IKONOS
  • QUICKBIRD
  • GEOEYE
  • ALOS
  • WORLDVIEW
  • KOMPSAT SERIES
• Radar Satellite Imaging Systems

  • SIR SERIES
  • ERS SERIES
  • JERS-1
  • RADARSAT
  • SENTINEL
  • ALOS PALSAR
  • NOVASAR
• Orbit


  The path followed by the satellite, which varies in altitude, orientation and rotation related to the Earth
• Types of Orbit Patterns

  • Geostationary/Geosynchronous Orbit
  • Polar/Sun-synchronous
• Swath


  The area imaged on the surface as the satellite revolves around the Earth and the sensor "sees" a certain portion of the Earth's surface
• Instantaneous Field of View (IFOV)

  Defines the smallest area viewed by the sensor, establishing the lower limit for level of spatial detail
• Dwell time


  The time interval allowing accumulation of enough photons to generate strong signal, depends on altitude, speed, and
• Remote Sensing Systems


  • Framing System
  • Scanning System
• Framing System


  Instantaneously acquire an image of an area, or frame, on the terrain
• Scanning System


  Employs a sensor with a narrow field of view (IFOV) that sweeps over the terrain to build up and produce a two-dimensional image of the surface
• Common Scanning Modes


  • Across/Cross-track Scanning
  • Along-track Scanning
• Across/Cross-Track Scanning


  1. Scan the Earth in a series of lines oriented perpendicular to the direction of motion of the sensor platform (across the swath)

  2. Each line is scanned from one side of the sensor to the other, using a rotating mirror
• Across-track scanner Characteristics


  • The IFOV (C) of the sensor and the altitude of the platform determine the ground resolution cell viewed (D), and thus the spatial resolution
  • Because the distance from the sensor to the target increases towards the edges of the swath, the ground resolution cells also become larger and introduce geometric distortions to the images
• Along-Track Scanning


  1. Use the forward motion of the platform to record successive scan lines and build up a two-dimensional image, perpendicular to the flight direction

  2. Instead of a scanning mirror, they use a linear array of detectors (A) located at the focal plane of the image (B) formed by lens systems (C), which are "pushed" along in the flight track direction (along track)
• Along-track scanner Characteristics


  • Each individual detector measures the energy for a single ground resolution cell (D) and thus the size and IFOV of the detectors determines the spatial resolution of the system
  • A separate linear array is required to measure each spectral band or channel
  • For each scan line, the energy detected by each detector of each linear array is sampled electronically and digitally recorded
• Pushbroom Scanning: Advantages


  • Increase life of sensor
  • Eliminates geometric errors due to variation in scan mirror velocity
  • Longer dwell times
  • Increase Signal-to-Noise Ratio