Comparing on-site water color and quality measurements with satellite views
The Chesapeake Bay watershed starts in New York and drains into the
Atlantic Ocean near Norfolk, Virginia. Heavy rainfall can wash detrimental
loads of sediments and nutrients into the Bay. These inputs degrade the
health of the Bay's ecosystem.
By observing the color and strength of light leaving the water,
satellite instruments can monitor the quality of the water, the presence
of marine organisms, especially plankton, and properties of water
associated with particular species.
In the Chesapeake Bay, drainage of fresh water from rivers profoundly
affects the ecosystem of this normally brackish Bay. Sometimes plumes of
fresh water are associated with sediment washed from the land; the
sediment is rendered visible by a unique gray color which is observable
from space. At other times, river water exhibits a brown or orange tint
from dissolved material like decaying leaves or tannins. This tint can be
measured by an index known as "chromophoric dissolved organic matter
(CDOM)" – a measure of organic matter associated with the color of light
exiting the water.
CoastWatch true color images from July 4 to 9, 2006, illustrate the
progression of the fresh water plume down the Chesapeake Bay.
Between July 5 and 7, 2006, a team from the Marine Optical
Characterization Experiment (MOCE – organized by the Ocean Sensors Branch
of NESDIS-STAR) took samples from the upper portion of the Chesapeake Bay
near Baltimore and the Bay Bridge. The team documented a discharge of
fresh water having high amounts of sediment into the Bay, which then
advanced down the Bay following record-breaking rainfall in the Chesapeake
Bay watershed. This plume of fresh water was potentially devastating to
marine species. The team collected measurements of total suspended matter,
chlorophyll-a, CDOM, and the color of the light coming from the subsurface
water, to better enable the detection of fresh water and its associated
pollution in the future. The purpose of developing such satellite-based
techniques for observing the quality of the water is to maintain and
protect the health of the watershed ecosystem.
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