Search Technology

The Right Tools for the Job

The archeology team used a combination of high and low technology to locate ships and debris fields in the underwater search area. The paths of the search boats and locations of wreck sites and debris fields were controlled with hand-held, data-logging GPS receivers in conjunction with highly detailed,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.

The team also employed a remote-sensing package consisting of a magnetometer and GPS to survey the area outside the fringing reef.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 highly useful tools for shipwreck searches and studies.

Tow fish and computer for data collection

However, a magnetometer must be towed relatively close to the object to detect it. 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 lane spacing of 10 to 15 meters. The magnetometer is integrated with a very 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 delineate survey areas, process and edit the data, and generate final products such as contour maps and plotting sheets.

Tow boarding on East Caicos in shallow water

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 were identified they were marked with buoys and divers were dispatched to begin the documentation process (photography, mapping, and sampling as appropriate). Divers also used underwater metal detectors to 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.