A guide for planners and managers - IUCN

100 MARINE AND COASTAL
PROTECTED AREAS
platforms produce images where each pixel represents an area of 1 - 5 sq. meters.
Classified remote sensing platforms from the National Technical Means (NTM)
Programme produce images where each pixel represents an area of less than 1 sq.
meter.
Aircraft Platforms: High-resolution benthic habitat maps of extensive coastal
areas have been produced from colour aerial photography. An important advantage
to using colour photographs is their widespread availability and ease of analysis.
Photographs of 1:12,000 to 1:24,000 scale can be used to identify features of 0.5 to 1
meter in size. Using textures and colours in the image and their own knowledge of
the distribution of benthic habitats, photointerpretation experts identify polygons of
10 to 20 sq. meters in size from these images. An alternative approach is to digitally
scan the image and classify the digital file using computer-based image-analysis
software. While typically faster than photointerpretation in producing maps, this
technique is affected by the ability of the software to discriminate subtle variations
in colour patterns for certain features of water depth, turbidity and light penetration.
Aircraft-based multi- and hyperspectral remote sensing systems offer the advantage
of increased spectral discrimination over colour aerialphotography.
Multispectral systems: (typically, four colour bands) have been successfully
used to map coral reef ecosystems. Hyperspectral sensors (typically, 10-277 colour
bands) have been used in small geographic areas to map benthic habitats, including
coral reef features.
Satellite Platforms: Satellite imagery has been used to map benthic habitat types
(e.g. sand, seagrass, coral, hard substrate) in coral reef environments. While lacking
the spatial or spectral resolution of aircraft-based imagery, satellite imagery offers the
advantages of increased frequency of coverage, extensive coverage at low cost, archival
data, and fast results.
Other Technologies: Rather than depend on reflected sunlight, some remote
sensing technologies use "active" systems to characterize marine environments. For
example LIDAR (Light Detection and Ranging) uses a laser to measure bathymetry.
Multibeam sonar, also used to characterize bathymetry and seafloor composition, uses
an acoustic out-beam. LIDAR can measure bethymetry in water to depths of 20-50
meters. Multibeam sonar can measure bathymetry in waters from 20-4000 meters
or more in depth.
Mapping Requirements: Field validation of maps derived from remotely sensed
data sources is essential. Any map produced from a remote sensing platform must
be validated by field observation (“ground truth”). Because of the highly variable nature
of the marine ecosystem, visiting as many areas to be mapped as possible is important.
If some areas are difficult to access, extrapolating from maps of known areas to
unknown areas may be required but is risky.