An underwater video camera designed to be towed behind a small
boat.
Courtesy: NOAA Coastal Services Center
Underwater video footage can be collected in a variety of ways. Cameras
can be vertically dropped from the ship, towed, hand-held by divers,
or mounted on remotely operated vehicles (ROVs). All of these methods
are subject to negative effects due to poor water clarity. The specific
method employed is determined based on water depth, water clarity,
size of survey area, purpose for survey, and costs of operating the
equipment.
All of the techniques used for collecting video images are limited
in the spatial coverage they provide. Therefore, mapping methods with
a wider range of coverage (such as side-scan
sonar and other acoustic techniques) are often employed first.
Areas to be sampled by video can then be determined and specific transects
can
be planned.
Click to view an underwater video of a shallow seagrass bed in the Dry Tortugas, Florida.
Courtesy: NOAA Coastal Services Center
Advantages and Limitations
Underwater videography presents a number of advantages over other
benthic habitat mapping techniques. It is preferable to direct
diver-collected
data for several reasons. First, it can be used in areas that are
too cold, deep, or dangerous for divers. Second, the data collected
are
permanently, objectively recorded and therefore not subject to the
diver's interpretation. Video data can be viewed later and manipulated
(paused, magnified, and so forth) to provide a more comprehensive view of
the habitat. Unlike acoustic, satellite, or aerial methods, underwater
video has high enough resolution to identify individual plant and
animal
species. This type of information may then be a further indicator
of habitat health and characteristics. For example, the amount
of encrusting
or epiphytic algae can be an indirect indicator of the extent of
nutrient loading.
As with other in-situ sampling methods, video data have a limited
sample footprint. So, relating information across an entire habitat
is very difficult. Additionally, data collection from video is time-consuming
and labor-intensive, so it is not practical to obtain comprehensive
coverage in a large study area.
Uses
Video data can be used for detailed assessment of biological conditions
in the water column and on the seafloor. It is especially useful
in areas with hard substrates such as rocks or reefs, where sediment
cores, grabs, and sediment
profile imaging cameras may not be able to penetrate
the seafloor. Video imaging can also be used in searches for specific
items, such as plane debris, shipwrecks, or marine organisms.
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