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Space Station Science

Picture of the Day

May 20, 2003

Red Sea Reefs
Photo credit: The Crew of ISS Expedition 6, NASA

May 20, 2003: Crowded, bustling, full of life: coral reefs are the
big cities of the sea. One-fourth of all known marine species live in
reefs, including at least 4000 varieties of fish and thousands of
kinds of plants and microorganisms. Reefs are critically important to
our planet's ecosystem. 

They're also endangered. Pollution, global warming, cyanide fishing
and coral mining are among the threats. Even tourism can be a
problem. "We're loving them to death," says Cindy Evans, an earth
scientist at the Johnson Space Center (JSC). Resorts are built near
reefs to attract snorkelers and divers. Construction and human
traffic, however, are bad news for these delicate marine communities. 

Today's picture from the International Space Station shows more than
a dozen underwater reefs in the Red Sea. Six percent of all the
world's reefs are found in the Red Sea, and while these particular
reefs look well, 60% of the reefs in the area are thought to be in
peril. 

The space station is a good place to study reefs. Four hundred km
above Earth, the crew can take pictures with both a wide field of
view (capturing entire reef communities) and high resolution. "It's a
wonderful combination," says Evans. This Red Sea image, for example,
spans 85 km from side to side and reveals details as small as 100 m.
Other photographs of coral reefs from the space station can discern
details as small as 5.5 m. 

And that's not all:

When ordinary Earth-observing satellites pass over a spot, it's
usually at the same local time. The sun is in the same part of the
sky ... flyby after flyby. Because their sensors look straight down
the view never changes. 

The ISS is different. Each time the space station passes over some
location, like the Red Sea, the sun is in a different place in the
sky. With different lighting, the camera can capture different
features. "Furthermore," adds JSC earth scientist Julie Robinson,
"astronauts are able to look out different windows of the station,
and they can look out each window at a variety of angles. This
allows humans in orbit to observe features in ways that satellites
cannot." 

A remarkable feature of today's image is the bright spot in the lower
right--a reflection of the sun overhead. "We call this 'sunglint,'"
says Evans. Snaking away from that spot are silvery tendrils where
sunlight is glinting from oily surface films. The oils come from
shipping traffic and the natural biological activity of marine life.
Wave motions and flows concentrate the films into telltale patterns.
"By tracing their shape, we can identify eddies, flow features
between the islands, and the overall water dynamics."

Flowing water helps shape and sustain reefs, so this is important
information. 

"For most Earth satellites, sunglint off the surface of the ocean is
considered a nuisance," adds Robinson. "It interferes with
observations of underwater features. However, glint can be used to
interpret the physical properties on the sea surface, and even infer
wind speed and direction in a local area." 

Sunglint a nuisance? It all depends on your point of view....

This image is a mosaic of two digital photographs taken from the
International Space Station on April 11, 2003: ISS006-E-45935 and
ISS006-E-45936. The mosaic was provided by the Earth Sciences and
Image Analysis Laboratory at Johnson Space Center. Additional images
taken by astronauts and cosmonauts can be viewed at the NASA-JSC
Gateway to Astronaut Photography of Earth. 

Credits & Contacts
Author: Dr. Tony Phillips 
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Catherine Watson

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