Then Why Do They Call Earth the
Blue Planet?
Environment and Resource
Management
Originating Technology/ NASA Contribution
While the most common photographs of Earth taken
from space show the planet covered in blue water,
NASA has managed to produce detailed color images,
using satellite imagery, that show the remarkable
variation of colors that actually make up the oceanic
surface. An ocean’s color is determined by the
interaction of surface waters with sunlight, and
surface waters can contain any number of different
particles and dissolved substances, which could
then change the color.
The particles are mostly phytoplankton—the microscopic,
single-celled ocean plants that are the primary food
source for much marine life. Remote detection of
phytoplankton provides information about the uptake
and cycling of carbon by the ocean through photosynthesis,
as well as the overall health of the water. Inorganic
particles and substances dissolved in the water also
affect its color, particularly in coastal regions.
Satellite images can be used to calculate the concentrations
of these materials in surface waters, as well as
the levels of biological activity. The satellites
allow a global view that is not available from ship
or shore.
NASA’s orbiting satellites offer a unique vantage
point for studying the oceans. By resolving the biological,
chemical, and physical conditions in surface waters,
they have allowed the oceanographic community to
make huge leaps in its understanding of oceanographic
processes on regional and global fronts. The study
of ocean color, in particular, has been integral
in helping researchers understand the natural and
human-induced changes in the global environment and
establishing the role of the oceans in the biochemical
cycles of elements that influence the climate and
the distribution of life on Earth.
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The DOLPHIN “swims” behind research
vessels and samples the water to validate satellite
imagery. It provides valuable
information about ocean color and quality. |
These views provide researchers with a great deal
of data that have a vast range of applications. The
first level of data describes the optical properties
of the water, such as the transmission and scattering
characteristics. From this data, a second level of
derived products is generated that describes what
is in the water, including concentrations of chlorophyll
(the primary photosynthetic pigment), particles,
and dissolved substances. These derived products
are used in research on global warming, ecosystem
composition and health, fisheries research, pollution
monitoring, coastal eutrophication (very high levels
of phytoplankton growth, which lead to dangerously
low oxygen levels), seasonal variability, sediment
transport, river outflows, currents, and the regional
influences of weather patterns and monsoons. Satellite
data are invaluable for studying global phenomena
and phenomena occurring over large regions, like
El Niño.
The first observations of ocean color from space
were carried out by the Coastal Zone Color Scanner
(CZCS), which operated on NASA’s Nimbus-7 research
satellite from 1978 to 1986. This groundbreaking
research provided scientists with an unprecedented
view of the world’s oceans and opened wide this field
of oceanographic study. The CZCS was the longest
running observational satellite of this type, and
spawned a series of other satellite missions with
the specific goals of adding to this wealth
of knowledge.
Partnership
Through a Phase II Small Business
Innovation Research (SBIR) contract with the
Earth Science Applications Directorate at NASA’s
Stennis Space Center, WET
Labs, Inc., of Philomath,
Oregon, developed a new technology for validating
ocean color images from satellitess. It calls the
device the Diving Optical Profiler and High-speed
Integration Network, or DOLPHIN.
Product Outcome
DOLPHIN is a much-needed research system that can
provide high-quality field data to validate data
from ocean color satellite imagery.
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Casey Moore (WET Labs president),
Dr. Richard Miller (NASA Stennis Space Center),
and Dr. Michael Twardowski (WET Labs project
director) hoist the portable DOLPHIN unit into
the research vessel. |
Validation of satellite images is done by collecting
1) in-water optical data to validate the level one
data described above and 2) discrete water samples
to validate the level two data with conventional
laboratory analyses. The traditional method for sample
collection involved lowering instruments from boats
at stations set apart
at periodic intervals. The problem with this method
of sampling for validation work is that the ocean
is dynamic in space and time. A more synoptic method
of sampling is required that is more consistent with
the synoptic views obtained by remote aircraft and
satellites. In the time expended setting up for sampling
and relocation for conventional vertical profiling,
water shifts and the aircraft or satellite data become
dated.
With DOLPHIN, a single research vessel tows the sampling
unit while it undulates vertically in the surface
waters. Optical parameters are measured on the underwater
vehicle while water for conventional laboratory analyses
of biological, chemical, and geological parameters
is simultaneously pumped to the surface through a
hose in the tow cable. The results are more synoptic
in space and time than with the traditional method,
since the craft need not stop to gather samples.
DOLPHIN provides researchers with a continuous transect
of points for validation, as opposed to single stationary
points. Gathering all this data for validation of
both the level one and level two oceanic properties
on-the-fly makes the validation exercise more accurate
and efficient. This saves time and money.
The unit can gather data as it bobs and swims like
a dolphin behind the boat. The bobbing has features
other than making its name appropriate, though, as
the raising and lowering of the unit allows sampling
of the water at different depths, giving researchers
more than just surface conditions. This sampling
below the very surface is important, because the
ocean can have considerable vertical layering of
its biological and chemical constituents, especially
in coastal waters. The reflected light seen by the
aircraft or satellite comes from a surprisingly large
range of depths in the upper ocean, extending as
deep as 300 feet, so vertical sampling in surface
waters is required for validation.
Besides the validation applications for the DOLPHIN,
the package also has the potential to be used for
water quality monitoring, to track freshwater in-flows,
to map dispersion points of nutrients, hydrocarbons,
and other pollutants, as well as track harmful algal
blooms.
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