with multi-beam data acquisition, this will provide a very realistic bathymetric
map in real time on board a ship. In 1997, using formerly classified satellite data
sets and a specific modeling algorithm, David Sandwell and Walter Smith
produced a new sea-floor physiographic map of the World’s oceans. The
de-classification of Geosat images by the US Navy and the European Space
Agency’s (ERS-1) altimetry data allowed scientists to further generate computer
models that inferred the features of the sea floor. This satellite image declassification started in the mid 80’s and full declassification was achieved by 1995. The
satellite data covers the entire World’s oceans but there are some limitations to its
resolution. Satellite altimetry data is based on measurements of the Earth’s geoids
that approximately follow the average surface of the sea. The fact that the satellite
tracks are spaced between 1 and 5 km and because the sampling rates along each
satellite track are on the order of 4-6 km, it is true that we do not have a totally
accurate resolution for recognizing small scale topographic features.
The wavelengths for satellite observation are on the order of 15–30 km hence
the topography of structures less than 30 km in length will be difficult to interpret.
For this reason, a diving program cannot be based simply on satellite altimetry data
because of the inaccuracy in defining the details the topography of the ocean floor.
In fact, satellite altimetry observation of the ocean floor is unable to replace the
bathymetric data obtained from surface ships. However, satellite images will
certainly help to decipher large structures hiding under water and they can provide
very useful information for preparing ocean-going expeditions.
The discovery of inactive plate boundaries such as paleo-plates (ancient
microplates), fracture zones, pseudo-faults, linear ridges, and seamount chains has
become more frequent since the 1980s. This is due to the results from new
developments in satellite altimetry and multi-beam bathymetric surveys conducted
over the various regions of the World’s Oceans. In addition, the interpretation of
satellite altimetry data enables us to observe the crustal structures created at ridge
axes, which are often preserved during spreading so they could be detected at a
distance from their original source. This information is very helpful for retracing
the history of oceanic basins and their evolution.
If we wish to reconstruct the history of oceanic basins, it is important to be able
to recognize and differentiate ancient structures formed on divergent plate
boundary regions (such as oceanic spreading centers) from younger intraplate
constructions (i.e. of hotspot origin). Although some of the linear structures representing fracture zones are well delineated when consulting general satellite
altimetry data, abyssal hill provinces with their numerous volcanic cones forming
discontinuous structures of unknown origin are more difficult to identify. For this
reason, it is best to combine satellite observations with swath bathymetry data and
even include on-site (manned or unmanned submersible) observations of the sea
floor.
56
3 Diving into the Abysses
map in real time on board a ship. In 1997, using formerly classified satellite data
sets and a specific modeling algorithm, David Sandwell and Walter Smith
produced a new sea-floor physiographic map of the World’s oceans. The
de-classification of Geosat images by the US Navy and the European Space
Agency’s (ERS-1) altimetry data allowed scientists to further generate computer
models that inferred the features of the sea floor. This satellite image declassification started in the mid 80’s and full declassification was achieved by 1995. The
satellite data covers the entire World’s oceans but there are some limitations to its
resolution. Satellite altimetry data is based on measurements of the Earth’s geoids
that approximately follow the average surface of the sea. The fact that the satellite
tracks are spaced between 1 and 5 km and because the sampling rates along each
satellite track are on the order of 4-6 km, it is true that we do not have a totally
accurate resolution for recognizing small scale topographic features.
The wavelengths for satellite observation are on the order of 15–30 km hence
the topography of structures less than 30 km in length will be difficult to interpret.
For this reason, a diving program cannot be based simply on satellite altimetry data
because of the inaccuracy in defining the details the topography of the ocean floor.
In fact, satellite altimetry observation of the ocean floor is unable to replace the
bathymetric data obtained from surface ships. However, satellite images will
certainly help to decipher large structures hiding under water and they can provide
very useful information for preparing ocean-going expeditions.
The discovery of inactive plate boundaries such as paleo-plates (ancient
microplates), fracture zones, pseudo-faults, linear ridges, and seamount chains has
become more frequent since the 1980s. This is due to the results from new
developments in satellite altimetry and multi-beam bathymetric surveys conducted
over the various regions of the World’s Oceans. In addition, the interpretation of
satellite altimetry data enables us to observe the crustal structures created at ridge
axes, which are often preserved during spreading so they could be detected at a
distance from their original source. This information is very helpful for retracing
the history of oceanic basins and their evolution.
If we wish to reconstruct the history of oceanic basins, it is important to be able
to recognize and differentiate ancient structures formed on divergent plate
boundary regions (such as oceanic spreading centers) from younger intraplate
constructions (i.e. of hotspot origin). Although some of the linear structures representing fracture zones are well delineated when consulting general satellite
altimetry data, abyssal hill provinces with their numerous volcanic cones forming
discontinuous structures of unknown origin are more difficult to identify. For this
reason, it is best to combine satellite observations with swath bathymetry data and
even include on-site (manned or unmanned submersible) observations of the sea
floor.
56
3 Diving into the Abysses