8A
WORLD ATLAS OF CORAL REEFS
Astronaut photography of coral reefs
Astronauts have been photographing our planet
through spacecraft windows ever since the beginning of human spaceflight. To date, nearly AOO 000
photographs have been taken by astronauts on
NASA missions using hand-held cameras. Most are
in natural color and, due to selective photography by
astronauts, tend to have relatively low cloud cover
They are taken from a variety of angles out of the
spacecraft, including near vertical views down at
Earth, low oblique views at an angle, and high
oblique views that include the horizon. Once converted to digital form, these images typically have a
high resolution, with pixel sizes of 20-80 meters in
most images.
Earth observation training for astronauts
includes the study of phenomena in the realms of
ecology, geology, geograpy. oceanograpy. meteorology and the environment. Not surprisingly, the
photographs they bring back to Earth are used
by scientists of many different disciplines. Nearvertical or low-oblique angle photographs can be
digitized at high resolution and used as three-band
Ired, green, blue) remote sensing images in the
same way a scientist would use Landsat or SPOT
data. Image processing techniques can be applied
to determine landuse, cover or change over time.
Nearly 30 000 photographs of coral reef areas
have been taken by astronauts on board the Space
Shuttle providing a valuable but underutilized data
source for coral reef scientists and managers. To
facilitate the use of these public domain images.
NASA's Earth Sciences and Image Analysis
Laboratory has been collaborating with the
International Center for Living Aquatic Resources
Management IICLARMI to include astronautacquired photographs in the global coral reef
database, ReefBase.
Many astronaut photographs clearly show
shallow reefs, and can show submerged features up
to depths of about 15 meters in clear waters. It is
possible to distinguish major geomorphological
features within reef systems, including reef crests
and patch reefs. They can be combined with traditional satellite data to help distinguish between
clouds and lagoon features such as pinnacles.
Furthermore, astronaut photographs may provide
reef scientists and managers with information on
the location and extent of river plumes and sediment runoff, or facilitate identification of land cover
types, including mangroves.
Photographs taken by astronauts are used
to illustrate coral reefs throughout this book. They
have been selected to show the range of coral reefs
found in every region, and to further illustrate
places described in the text and features of particular interest, including human developments,
the plumes of sediments in river mouths, shallow
banks and remote atolls. Selected photographs
were scanned, and color and contrast were hand
corrected to give an approximation of natural color.
None of the photographs shown here has been
georeferenced, and a number were clearly taken at
and both have sensors which detect light in discrete
portions of the visible spectrum (bands). This is important
because infrared radiation will not penetrate water and,
generally speaking, more bands enable more subtle
changes in the light returning from the seabed to be
detected. Satellite images can be geometrically corrected
(assigned map properties) and used in a geographical
information system (GIS) quite easily.
Cloud cover is an important constraint in some areas.
It is often cloudy over reefs in the humid tropics and this
limits the availability of useful satellite images. There are
also some very real problems of accuracy. The technical
specifications of the sensors mean that, while coral reefs
may be mapped accurately and separately (in about 70
percent of cases) from seagrasses, algal beds and sand.
more detailed mapping of different reef habitats is only
possible to an accuracy of 20-40 percent. A new generation of high resolution satellites will become available
over the next few years, though their utility for reef mapping will probably depend on commercial factors. Initial
data collection from new sensors is usually concentrated
outside the tropics as a greater economic return can be
generated from temperate regions. At the present time,
therefore, satellite sensors are well suited for broad-scale
mapping of reefs over large areas, but other techniques are
required for more detailed interpretation.
In addition to satellites, manned spacecraft provide an
important opportunity for obtaining images of the Earth
from space (see box). Examples of such images taken from
the Space Shuttle are found throughout the present work.
WORLD ATLAS OF CORAL REEFS
Astronaut photography of coral reefs
Astronauts have been photographing our planet
through spacecraft windows ever since the beginning of human spaceflight. To date, nearly AOO 000
photographs have been taken by astronauts on
NASA missions using hand-held cameras. Most are
in natural color and, due to selective photography by
astronauts, tend to have relatively low cloud cover
They are taken from a variety of angles out of the
spacecraft, including near vertical views down at
Earth, low oblique views at an angle, and high
oblique views that include the horizon. Once converted to digital form, these images typically have a
high resolution, with pixel sizes of 20-80 meters in
most images.
Earth observation training for astronauts
includes the study of phenomena in the realms of
ecology, geology, geograpy. oceanograpy. meteorology and the environment. Not surprisingly, the
photographs they bring back to Earth are used
by scientists of many different disciplines. Nearvertical or low-oblique angle photographs can be
digitized at high resolution and used as three-band
Ired, green, blue) remote sensing images in the
same way a scientist would use Landsat or SPOT
data. Image processing techniques can be applied
to determine landuse, cover or change over time.
Nearly 30 000 photographs of coral reef areas
have been taken by astronauts on board the Space
Shuttle providing a valuable but underutilized data
source for coral reef scientists and managers. To
facilitate the use of these public domain images.
NASA's Earth Sciences and Image Analysis
Laboratory has been collaborating with the
International Center for Living Aquatic Resources
Management IICLARMI to include astronautacquired photographs in the global coral reef
database, ReefBase.
Many astronaut photographs clearly show
shallow reefs, and can show submerged features up
to depths of about 15 meters in clear waters. It is
possible to distinguish major geomorphological
features within reef systems, including reef crests
and patch reefs. They can be combined with traditional satellite data to help distinguish between
clouds and lagoon features such as pinnacles.
Furthermore, astronaut photographs may provide
reef scientists and managers with information on
the location and extent of river plumes and sediment runoff, or facilitate identification of land cover
types, including mangroves.
Photographs taken by astronauts are used
to illustrate coral reefs throughout this book. They
have been selected to show the range of coral reefs
found in every region, and to further illustrate
places described in the text and features of particular interest, including human developments,
the plumes of sediments in river mouths, shallow
banks and remote atolls. Selected photographs
were scanned, and color and contrast were hand
corrected to give an approximation of natural color.
None of the photographs shown here has been
georeferenced, and a number were clearly taken at
and both have sensors which detect light in discrete
portions of the visible spectrum (bands). This is important
because infrared radiation will not penetrate water and,
generally speaking, more bands enable more subtle
changes in the light returning from the seabed to be
detected. Satellite images can be geometrically corrected
(assigned map properties) and used in a geographical
information system (GIS) quite easily.
Cloud cover is an important constraint in some areas.
It is often cloudy over reefs in the humid tropics and this
limits the availability of useful satellite images. There are
also some very real problems of accuracy. The technical
specifications of the sensors mean that, while coral reefs
may be mapped accurately and separately (in about 70
percent of cases) from seagrasses, algal beds and sand.
more detailed mapping of different reef habitats is only
possible to an accuracy of 20-40 percent. A new generation of high resolution satellites will become available
over the next few years, though their utility for reef mapping will probably depend on commercial factors. Initial
data collection from new sensors is usually concentrated
outside the tropics as a greater economic return can be
generated from temperate regions. At the present time,
therefore, satellite sensors are well suited for broad-scale
mapping of reefs over large areas, but other techniques are
required for more detailed interpretation.
In addition to satellites, manned spacecraft provide an
important opportunity for obtaining images of the Earth
from space (see box). Examples of such images taken from
the Space Shuttle are found throughout the present work.