Pearl and
Hermes Reef, Hawaii
High-resolution
image (1.4 Mb)
Looking out
the window of the International Space Station, astronauts often
take the time to admire and photograph tropical islands and coral
reefs. From an altitude of 400 kilometers and with only a digital
camera as a tool, it seems impossible to make detailed measurements
of the depth of underwater features. However, a new technique developed
by National Oceanic and Atmospheric Administration (NOAA) scientists
has done just that -- plotted the depths of lagoon features at Pearl
and Hermes Reef, northwest Hawaii, using digital astronaut photography
from the ISS.
Measuring water
depth is an important step in mapping coral reef environments. Even
though digital cameras are designed to visually approximate film
photographs, the information they collect is similar to the bands
of different wavelengths of light collected by multispectral instruments
on satellites. NOAA scientists developed an algorithm that could
estimate bathymetry from the blue and green bands in IKONOS satellite
data. After calibrating the astronaut photography to the signal
in the IKONOS data, the same algorithm could be successfully used
with the blue and green channels in the astronaut photography. An
accuracy assessment of the bathymetry
map shows good correspondence between reference data, IKONOS,
and ISS data.
Astronaut photograph
ISS005-E-13929
was provided by the Earth Sciences and Image Analysis Laboratory
at Johnson Space Center. The International Space Station Program supports the laboratory to help astronauts
take pictures of Earth that will be of the greatest value to scientists
and the public, and to make those images freely available on the
Internet. Additional images taken by astronauts and cosmonauts can
be viewed at the NASA/JSC Gateway
to Astronaut Photography of Earth.
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