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Copyright © John Lindsay, 2015

Forward Motion Compensation

Multiband Cameras

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

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!

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
• Complementary metal-oxide semiconductors (CMOS)
  • Cheaper but more noisy than CCDs
  • Faster and require less power

Digital Image Detectors

Readings

Jensen Chapter 7

How remotely sensed data are transformed into useful information

Orbital altitude and period are related

Altitude vs. Period vs. Speed

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

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

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

The Landsat Program Timeline

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

Fine-resolution Commercial Satellites

• Starting with SPOT-5 we have entered into a new era of fine-resolution commercial satellite 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

WorldView-3

Advantages of fine-res sat data

• 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

• 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