<<  <  >  >>

 

O  C E A N C  O L O R (R E M O T E

S E N S I N G)

S9

What

What Is It?

BENCHMARK

Ocean color, in the context of this indicator, refers to a

No

No net increase in average ocean

satellite-derived characterization of the color of ocean

color (chlorophyll concentration) or the

waters.

severity of seasonal peaks.

The ocean color seen by the human eye or by a

TA R G E T

satellite sensor is influenced by the concentration and

To be developed.

To

composition of colored materials suspended near the

ocean surface. Clean, open-ocean waters typically

RED FL AG

appear bluish, for example, while nearshore waters,

To be developed.

rich in chlorophyll, often have a greener hue.

Satellite ocean color data are often given in terms of

SeaWiFS and MODIS sensors provide quantitative data

chlorophyll concentration.

and maps on global ocean bio-optical properties29,30.

Special data processing is sometimes required to

Why

Why Do We Measure It?

use these data in nearshore environments. Several

programs focusing on the coastal environment are

Ocean color measurements provide a way to study

underway, and real-time data are readily available on

large-scale patterns in the distribution of chlorophyll

the Internet31.

and other pigments, ocean primary productivity and

global biogeochemistry.

Usefulne s s

Usefulness

Ocean color can be used to track the movement

Ocean color data can contribute to our understanding

and evolution of waters colored by chlorophyll (from

of connectivity, sedimentation and nutrification

phytoplankton), colored dissolved organic matter

of coastal areas. More information is needed to

(CDOM) and suspended nearshore sediments. Ocean

determine the feasibility of using this information at

color data can also be used as a proxy for nutrients,

regional scales in nearshore environments. The MAR

which fuel the growth of phytoplankton and are

region has an exceptionally low percentage of usable

associated with colored material (sediment, detritus)

satellite images, due to the frequent cloud cover and

from fluvial sources.

fires (smoke) that obscure a satellite's view of the

ocean waters.

Researchers are now working to develop methods

for using ocean-color data not just in open-ocean

St atus

Status

waters, but in more challenging coastal areas as well.

Nearshore applications include the monitoring of

SeaWiFS imagery showed that terrestrial runoff

phytoplankton blooms, which can be associated with

from flooding caused by Hurricane Mitch (1998) in

red tides and can be fueled by large-scale runoff of

Honduras reached offshore coral reefs at Glover's

nutrients28.

Reef in Belize32.

Because coral reefs normally thrive in shallow, clear

Development of shallow-water algorithms (data-

waters, they present a special challenge and a special

processing  methods)  is  underway  in  several

opportunity for using satellite-derived ocean-color

universities and in conjunction with the International

measurements.  Eventually, such measurements

Coral Reef Action Network (ICRAN) Mesoamerican

might be useful as one "red flag" indicator of water

Reef Alliance. Preliminary data from this project

quality and even of potential red tides, which threaten

show a pronounced seasonal trend in ocean color,

some fisheries, marine mammals and human health.

probably associated with rainfall and fluvial runoff.

(See indicator SW3 ­ Cholera and Other Diseases).

The Gulf of Honduras region peak values for colored

dissolved matter are 2.2 times higher than average

How Do We Measure It?

How

values for the rest of the year, and the northern coast

of Honduras approximate peak values are 2.4 times

Specially designed, satellite-mounted sensors are

higher than average33.

used to estimate remotely sensed ocean color. NASA's

32