Multispectral Remote Sensing of Benthic Environments

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Multispectral Remote Sensing of Benthic
Environments

• Christopher Moses, Ph.D.
• Jacobs Technology - USGS
• NPS-USGS Servicewide Benthic Habitat Mapping
  Workshop
• June 3-5, 2008
• Lakewood, CO

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Outline

• Matters of scale
• Advantages and disadvantages
• Common principles
• Satellites
• Coral reefs applications

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Scales of benthic mapping
Global ecosystem distribution
Island and coastal geomorphology
Community
Organism
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Advantages and disadvantages

• Synoptic
• Repeated acquisition
• Possible time series and change detection
• Multi-spectral to hyperspectral

• Calibration and validation
• Expensive
• Clouds
• High-tech issues
• Rapid change, hard to follow literature
• Interpretation
• Products based on many assumptions
• Programming errors
• Unknown calibration problems
• Unknown orbit or sensor errors

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Electromagnetic Spectrum
A sensor measures the amount of light being
reflected or emitted by the earths surface at
specific wavelengths in the electromagnetic
spectrum
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Radiative Transfer Theory
Cloud
Atmosphere
Sea Surface
Ocean
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Temporal resolution
Satellite
Airport
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Spatial resolution
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Satellites by name

• Landsat 7 ETM
• 30 m spatial resolution
• 16 day revisit time, identical scene locations,
  LTAP
• NIR, R, G, B bands
• ASTER
• Advanced Spaceborne Thermal Emission and
  Reflection Radiometer
• 15 m spatial resolution
• 16 day revisit time
• NIR, R, G (no blue!)
• IKONOS
• 4 m spatial resolution
• Image acquisition by request
• NIR, R, G, B

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Landsat 7 ETM full scene
180 km
Path 18, Row 48 8 Nov. 2000
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Landsat 7 ETM Glovers Reef
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Landsat 7 vs. IKONOS
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Photo interpretation of Glovers Reef
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North Florida Reef Tract
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Supervised habitat classification
Brock et al. (2006)
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Satellite accuracy (supervised)

• L7 86.2 (2.3)
• 5 classes
• Need class separability
• Sand is most easily misclassified

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Benthic habitat mapping with airplanes
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Aerial imagery of BISC
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Not just for corals!
http//gis.esri.com/library/userconf/proc01/profes
sional/papers/pap900/p90011.jpg
http//www.nasa.gov/centers/goddard/earthandsun/np
s_data.html
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Summary I

• Advantages of satellites
• Synoptic repeated acquisition multi- or
  hyperspectral bands
• Disadvantages
• Expensive rapidly evolving technologies
  complications of interpretation
• Resolution depends on mapping needs
• Temporal and spatial resolution
• Useful satellites for benthic mapping
• Landsat 7 ETM (30 m spatial resolution)
• ASTER (15 m spatial resolution)
• No blue band!
• IKONOS (4 m spatial resolution)

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Summary II

• Landsat 7 and IKONOS can reach accuracies of gt80
  in reef areas
• Supervised classification of 5-6 classes
• Satellites and aerial photos reliable to max
  depth of 20 m
• Particularly useful in reef areas, but also good
  for kelp and other near surface habitats