Sensor Types

  • platforms and orbits
    • airborne sensors (balloons, planes, etc)
    • satellites
      • check out these satellite tracking web sites (some only work in Edge, not Chrome)
      • what is the difference of the orbits?
        • geostationary orbit (telecommunications, meteo)
        • mapping (pole-to-pole, or oblique) orbits
        • GPS (multiple overlapping orbits, 29 satellites and growing)
  • sensor mechanisms
    • photographic
      • earliest satellite photographic images from Corona spy satellite captured on mylar negatives and dropped from the satellite.
      • snagged in the air by planes near Hawaii.
      • now in the public domain (resolution down to 6 ft) at USGS Earth Explorer.
      • missions are named KH1 through KH9. The images extend possible landscape change analysis back at least a decade. Operated from 1959 to 1972, when a Soviet sub was found to be submerged near the recovery site.
    • active digital sensors – emit radiation and record reflection.
      • most common one is radar (RAdio Detection And Ranging) (JPL description)
        the new kid on the block is LIDAR (Light Detection and Ranging)
      • transmission and reception can be polarized and at different “bands”
        (C, X, etc, see radar bands)
        The Shuttle Imaging Radar  see this SIR Example image from Death Valley (Google map location) Why color? Note topography.
        Shuttle Radar Topography Mission (SRTM) produced 30 to 90 meter DEM data globally.
      • radar interferometry
        • what is it

        • pioneering study of earth movement during the Landers earthquake in So. Calif. in 1992
        • subsidence due to groundwater pumping link
    • passive digital sensors
      • most common sensor type
      • rely on sun’s radiation and reflectence/emission from surface of planet (or atmosphere)
      • resolution depends on orbit and energy available in bandwidth
      • visual and IR parts of spectrum
  • radiance collection mechanisms
  • spectral characteristics
    • “panchromatic” (SPOT and TM7 and Landsat8 OLI, band 8) versus narrow bands in the electromagnetic spectrum.
    • multiple, narrower bands (up to hyperspectral,tens to hundreds of bands)
    • TM Band 6 is lower resolution due to low radiance and desire to sense at night (was 120 m on landsat 4&5, now with ETM+ is 60 m)
  • errors due to
    • sensor calibration differences (spectral error)
    • scan line shift (geometric error)
  • data types
    • scale – resolution and scale are inversely related; can’t have both
      • large pixel size, broad coverage (1-10 km grids, weather, global land characterization, ocean temp/chlorophyll mapping)
      • small pixel size, detailed coverage (TM for landuse, spy sats, construction/planning, 30 to <1 m)
    • image type
      • panchromatic
      • multispectral (numerous “bands” of the EM Spectrum Sampled)
        • TM 7 & 8 vs ESA Sentinel 2

          plus ASTER and MODIS

      • hyperspectral (gazillions of bands, still on planes, not yet in space)