U.S. Department of the InteriorU.S. Geological Survey

Multispectral Remote Sensing of Benthic

Environments

Christopher Moses, Ph.D.Jacobs Technology - USGS

NPS-USGS Servicewide Benthic Habitat Mapping WorkshopJune 3-5, 2008Lakewood, CO

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

Scales of benthic mapping

Organism

Community

Island and coastal geomorphology

Global ecosystem distribution

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

WAVELENGTHS (IN METERS)

10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 101 102

VISIBLE

GAMMA RAYS X RAYSULTRA VIOLET INFRARED

MICROWAVE

RADIO WAVES

400 500 600 700 nanometers

longershorter

A sensor measures the amount of light being reflected or emitted by the earth’s surface at specific

wavelengths in the electromagnetic spectrum

Electromagnetic Spectrum

Irradiance Radiance

Attenuation due toabsorption and scattering

in water

Ocean

Cloud

Sea Surface

Atmosphere

Path radiance

Scattering at edgesof atmosphere

Attenuation due toabsorption and

scattering in atmosphere

Radiative Transfer Theory

3

4

5

6

7

8

9

10

1994 1995 1996 1997 1998 1999 2000

Scalar Wind [m/s]

SatelliteAirport

Temporal resolution

3

4

5

6

7

8

9

10

1994 1995 1996 1997 1998 1999 2000

Scalar Wind [m/s]

SatelliteAirport

Landsat

ASTER

Ikonos

AISA

Spatial resolution

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 $$

Landsat 7 ETM+ full scene

~180 km

Path 18, Row 48

8 Nov. 2000

Landsat 7 ETM+ Glover’s Reef

Landsat 7 vs. IKONOS

Photo interpretation of Glovers Reef

North Florida Reef Tract

Landsat 7 ETM+5 Feb 2000

Supervised habitat classification

Brock et al. (2006)

Satellite accuracy (supervised)

L7 = 86.2 (±2.3%) 5 classes

Need class separability Sand is most easily

misclassified

Benthic habitat mapping with airplanes

Aerial imagery of BISC

Not just for corals!

http://gis.esri.com/library/userconf/proc01/professional/papers/pap900/p90011.jpg

http://www.nasa.gov/centers/goddard/earthandsun/nps_data.html

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)

Summary II Landsat 7 and IKONOS can reach accuracies of >80% 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