Marine Ecological Studies
Investigating the remote sensing of the oceans has lead ETL to develop
an airborne survey package which includes visual observations, digital
video, thermal imaging and FLOE: Fish Lidar, Oceanic, Experimental, a lidar instrument
which profiles fish densities.
This package has been
used on many national and international fish population and aquatic animal studies.
Current NOAA programs include:
Steller Sea Lions
The Steller sea lion in Alaska is in decline in the western part of its range, which
starts at about Prince William Sound and extends out through the Aleutian Islands. In the
eastern part of its range, throughout South East Alaska, it is thriving. There is currently a
large research effort underway to understand the reasons for the decline, so that effective
measures can be taken to ensure the survival of the species throughout its habitat. Climate
change and overfishing are two of the hypotheses that have been put forward. The NOAA
Fish Lidar is being used as part of an
designed to investigate these hypotheses.
Steller Sea Lion
photo by Rolf Ream, NOAA/NMFS
The fish lidar is part of an airborne package that includes visual observations, digital
video, and thermal imaging. Visual observations provide counts of sea lions, whales, and sea
birds. The digital video provides similar information, but color processing allows the video to
see deeper into the water. The thermal imager can see marine mammals and birds at night,
so that the day/night distributions can be compared. There is some evidence that sea lions
may remain away from the shore at night, and this could affect the accuracy of feeding
patterns based on collection of scat on the shore. Night surveys using the thermal imager will
help to answer this question.
The airborne surveys are coupled with ship surveys using echo sounders and sample
catches. The ship surveys can reach deeper into the water column than the lidar surveys and
see fish that are too deep for the lidar. Generally, the lidar can see the fish that are most
useful to the sea lions. These are the herring, capelin, and sand lance that have high fat
content. It can also see juveniles of pollock. The adult pollock are generally too deep for the
lidar to see, and are captured by the echo sounder. The speed of the aircraft allows the lidar
to survey the entire area in a single flight, and to do day and night surveys on the same day.
This helps resolve space/time scales that are impossible to resolve with at ship speeds. The
lidar is also able to survey in very shallow water, where the ships cannot work.
Prince William Sound and Kodiak Island
A number of studies have been completed in Prince William Sound and around Kodiak
Island. The objective has been to develop improved techniques for measuring various
elements of the ecosystem, including:
In May 2002 two studies of lidar detection of plankton were performed. The first was a
study, done in collaboration with the
Prince William Sound Science Center, of
zooplankton in Prince William Sound. We were particularly interested in Neocalanus, a
tiny shrimp. These form a large component of the diet of young salmon in the spring. A
comparison of the lidar results and the ship survey revealed a correlation of almost 80%
between the two techniques. The conclusion is that Fish Lidar can also be used as
Plankton Lidar. The other study was an
investigation of the extent of thin plankton layers
in the Gulf of Alaska. Patchy layers were observed all across the Gulf from Kodiak to
Juneau. A very strong nonlinear wave perturbed this layer in the open waters of the Gulf.
This perturbation showed up very clearly in the oscillation of the layer up and down as
the aircraft moved across.
In September 2002, the imaging lidar was flown over Kitoi Bay on Afognak Island in
Alaska. The lidar was able to record images of salmon that were in the bay near the
surface. The picture is an example of a school of pink salmon. A paper describing this
work has been accepted by Applied Optics.
J. H. Churnside and J. J. Wilson, "Airborne Lidar Imaging of Salmon," Appl. Opt. (in press).
In August 2001, the lidar was flown over regions of extensive ship surveys of pollock
east of Kodiak Island. While pollock are too deep to be seen by the lidar, we showed that
juvenile pollock can be surveyed. The reason lies in the behaviour of juvenile pollock.
During the day, they stay away from the surface to avoid being eaten by birds. At night,
the birds cannot see to hunt, so the pollock can come up to the surface to feed. A lidar
survey at night can detect these fish. To prove this, we compared the daytime results
from the ship survey with our nighttime results. The correspondence between our data
and the distribution of juvenile pollock was just over 70%, once the lidar data were
filtered to remove the plankton scatter.