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Copyright © John Lindsay, 2015

aircraft used for aerial photography

Forward Motion Compensation

forward motion compensation


The Earth From Space

Airborne and Spaceborne
Imaging Systems Part 2

John Lindsay
Fall 2015

Multiband Cameras

Multi-band camera

Airborne Digital Cameras

  • Analog (film) versus digital cameras
  • Film camera uses film for image capture, display and storage
  • Digital systems may use film as a display and storage medium, but likely stored in digital form
  • Film is often transferred to digital format these days by scanning...why do you think?

The Digital Advantage

  • Environmental effects are lessened
  • Easily stored, reproduced, and transferred (over the Internet)
  • Pixels are uniform in size and shape, unlike silver halide crystals
  • Can be transmitted from satellites without need for physical collection

The Digital Advantage

  • Amenable to use with computers
  • Potential for advanced digital image enhancement and analysis using 'soft-copy' photogrammetry/RS software
  • Digital cameras can be made to have sensitivity to a broader portion of the spectrum than film

Disadvantages of Digital Imaging

  • Long-term storage in digital format
  • Very large file sizes...can be a challenge for storage and processing
  • Most available digital cameras still have significantly poorer resolutions compared to film
    • A large format (9 x 9 in.) digital camera would require 80-400MP! And what about colour?
    • This is changing rapidly with the use of imaging systems based on linear arrays and newer digital large format cameras
Microsoft Ultracam large format camera

Airborne Digital Cameras

  • Small format: typically < 15 MP
  • Medium format: usually 4000 x 4000 pixels or about 16 MP
  • Large format: usually based on a linear array of 12,000 detector elements
    • Can surpass the resolution of analog (film) cameras)
    • But they are very expensive!
    • That's equivalent to 144 MP and creates a 4.4GB image!
Sensor types

Digital Image Detectors

  • Charge-coupled devices (CCDs)
    • Light sensitive material embedded in silicon
    • Each ‘potential well’ is ~1 μm and many are connected to form an array
    • Respond to brightness more linearly than film
  • A CCD
  • Complementary metal-oxide semiconductors (CMOS)
    • Cheaper but more noisy than CCDs
    • Faster and require less power

Digital Image Detectors



Jensen Chapter 7

How remotely sensed data are transformed into useful information

Getting data from space
Orbital characteristics

Orbital altitude and period are related

Altitude vs period (speed)

Altitude vs. Period vs. Speed

Orbital characteristics

Orbital Characteristics

  • Orbit Type:
    • Equatorial
    • Polar
    • Near-polar
  • Prograde (<90°) or retrograde (>90 °)
Orbital characteristics

Orbital Characteristics

  • Geosynchronous
    • Satellite in the same position in the sky at the same time daily
  • Geostationary (special case of geosynchronous)
    • Circular equatorial orbit with 35,786 km orbital altitude
    • 23 hr 56 min 5 s orbital period
    • Appears to stay in the same location in the sky
  • Sun-synchronous
    • Crosses latitudes at the same time of day
    • 600–800 km altitude; periods 96–100 min; inclinations ~98° (i.e. retrograde)
    • Useful for Earth imaging applications

Typical sun-synchronous orbit

sun-sync orbit
Orbital altitudes

Low-Earth, Medium-Earth, & High-Earth Orbits

Orbital altitudes

Types of Satellite Imaging Systems

  • Thermal Scanners
  • Multi-spectral (MS) Scanners
  • Imaging Spectrometers (Hyperspectral)
  • Radar (SLAR) & laser altimeters (LiDAR)
  • Note: A single satellite platform may have more than one imaging system
Types of imaging systems

The Landsat Program Timeline

Landsat program

The SPOT Satellite Program

  • Data sold commercially by SPOT Image Inc.
  • A commercially oriented program intended to be operational rather than experimental
  • 832 km altitude, inclination of 98.7, crosses equator at 10:30AM
  • SPOT 6 launched Sept. 2012 and SPOT 7 launched on June 2014 and subsequently sold to Azerbaijan

SPOT satellite components

SPOT components
SPOT image
SPOT vs landsat
SPOT vs landsat

Fine-resolution Commercial Satellites

  • Starting with SPOT-5 we have entered into a new era of fine-resolution commercial satellite imagery.
GeoEye-1 provides 0.41 m pan and 1.65 m multi-spec imagery

Commercial satellite image providers

  • SPOT Image
  • DigitalGlobe
    • EarlyBird-1
    • IKONOS
    • QuickBird
    • GeoEye-1, (GeoEye-2 in 2016)
    • WorldView-1, WorldView-2, WorldView-3
  • Planet Labs (Blackbridge Ltd.; formerly RapidEye): 5 RapidEye sats


Is there need for aerial photos anymore? WorldView-3

Advantages of fine-res sat data

(compared to airborne imaging)
  • Wide swaths compared to aerial photos mean less need to mosaic images
  • Satellite is a much more stable platform
  • Potential for short-term repeat surveys, i.e. within days
  • Wider window for acquisition
  • Far cheaper ($2-$12 / km2)

Disvantages of fine-res sat data

(compared to airborne imaging)
  • Issues with atmospheric/weather conditions
  • Resolution is still not quite as good and may be degraded outside the US (20 in. or 50.8 cm; this has been relaxed as of 2014)
  • Tasking issues (can get bumped by priority)
  • Restrictive licences