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For the past twenty-eight years Dennis Clark has been working
on ways to see microscopic marine plant life and ocean sediments
from the vantagepoint of space. To do this he and a group
of scientists from the National Oceanic and Atmospheric Administration
(NOAA) have sampled seawater from all over the globe. Their
purpose is to uncover the precise coloring (pigments) of the
microscopic materials that drift in mass through the upper
layers of the seas. They can then use the orbiting MODIS instrument
to look for these colors and determine how much of a given
material is floating around in the ocean.
The key to the NOAA team's success lies in reflected light.
As can be seen through a prism, sunlight contains all the
colors (wavelengths) of the visual spectrum from violet to
red. When sunlight strikes an organism with pigment, certain
colors of the spectrum are absorbed and others are reflected.
These reflected wavelengths give an object its color.
Most widespread sediments and organisms in the ocean have
a distinct coloring, which varies slightly over different
regions of the ocean. By measuring the different wavelengths
of light from the ocean and then sampling the water, Clark
and his team have been able to determine which materials give
off which colors in which regions. This is not always easy
work, since varying substances with varying pigments are often
mixed together in a murky soup. However, once the researchers
have the colors sorted out, they can then use MODIS to easily
view these materials from the vantagepoint of space.
Probably the most important and predominant pigment that Clark
measures is chlorophyll-a. In algae (phytoplankton), chlorophyll-a
absorbs blue and red light and reflects green light. Before
MODIS's launch, Clark's team has been recording how algae
in different conditions and different regions reflect and
absorb these colors. Knowing these values, Clark's team can
use MODIS to pick-up all the blue light coming off the ocean
and compare this to the green light. If the ratio of blue
to green is low for that region, then there are many plants
in the area absorbing blue light.
Since MODIS retrieves pictures from the entire globe once
every two days, scientists can look at such data and observe
the way these materials change over time. This will allow
researchers to measure phenomena like the flow of ocean currents,
the number of plants in the ocean, meteorological events and
the rate at which harmful pollution is spilling into our seas
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