Search Technology
|
|
During the 2004
survey an innovative high-low tech approach proved extremely effective,
and will be employed again this season. The control of the paths of the search boats and the
locations of wreck sites and debris fields was accomplished with hand-held, data-logging
GPS receivers
During the 2006 survey the team used a similar combination of high and low technology to locate ships and debris fields in the underwater search area. The high tech approach employed a remote-sensing package consisting of a magnetometer and GPS to survey the area outside the fringing reef.
The magnetometer is integrated with a highly accurate Differential Global Positioning System (DGPS) providing sub-meter accuracy for the location of any target or anomaly. Specialized navigation software allowed the survey team to design and delineate survey areas, process and edit the data, and generate final products such as contour maps and plotting sheets.
|
in conjunction with highly detailed, digital, “geo-referenced” aerial
images of the north coast of East Caicos. Geo-referencing is a technique that imposes
map grid coordinates on an aerial image so that it can be used like a map: all measurements
and directions taken from the image are true and tied into standard mapping conventions.
The Universal Transverse Mercator grid convention was used, which facilitated distance calculations.
A magnetometer is a passive device that can detect concentrations of ferrous
material, such as iron anchors, chain, or ships’ fittings, which produce
a variation, or anomaly, in the earth’s magnetic field. This makes
magnetometers a highly useful tool for shipwreck searches and studies. However,
a magnetometer must be towed relatively close to the object to detect it.
For example, a site with iron ballast and fittings can be detected at 80
to 100 meters, an isolated anchor at 30 meters. Shallow water surveys are
generally done at close lane spacing of 30 to 50 feet.
On
the reef top and in some areas in the lagoon the shallow water and
numerous coral outcrops make deployment of towed equipment problematic. In
those areas a low tech approach is most appropriate. This was accomplished
using mostly towed divers but also included the
use of diver propulsion vehicles (DPV), which facilitated speedy coverage of large areas.
In
both situations, as sites are identified they were buoyed and divers dispatched to
begin the documentation process (photography, mapping, and limited sampling as appropriate).
Divers also used underwater metal detectors as an aid in determining site
limits. Rough sketches and precise measurements were made for reference on
very meticulous drawings of the site that were created later.
© 2006 Windward Media / HoustonPBS