July 20, 2008 – Sunday – An Imperfect Process at Best

By Michael Krivor

A well-respected underwater archaeologist named Charlie Pearson once said “The analysis of remote sensing data is an imperfect process at best…it relies on sound judgment, an understanding of the usage of the body of water [you are working on], and common sense.”

This has been running through my head the past few days since we have concluded the remote sensing survey around East Caicos. Once the magnetometer data is collected you must process it to identify those targets most likely to represent a shipwreck. Usually this is done after the fieldwork has been completed and in the comfort of an air-conditioned office. However, on the Trouvadore Project it has been done during the evening hours, after we get off the survey boat so we have targets to investigate the next day.

During the data analysis I look at each magnetic targets “signature” in hopes of locating a potential shipwreck… Here is where Pearson’s “sound judgment” comes into play. If a target has significant gamma strength and a sufficient duration, and is associated with other magnetic targets, it becomes a high-probability target worthy of identification. I have learned that “sound judgment” actually means “years of experience”.

Michael doing data analysis

When Pearson referred to the “usage of a body of water” he meant that if you are surveying an area that has a significant history of ship traffic, anchorage, industrial use, etc, there is likely to be a number of magnetic targets, most of which will be insignificant. These targets are typically associated with debris from vessels, wire rope, fuel drums, and maybe an occasional dredge pipe. Fortunately along the north shore of East Caicos there was little notable historic use…it is a beautiful stretch of desolate reef and beach. A “high-probability” target off East Caicos has the potential to represent something historically significant.

Within the Drum Point survey area there were 33 magnetic anomalies. Of these we had three clusters of magnetic targets that we considered high probability. Follow-up diver investigation revealed a web of wire rope (insignificant), an iron deck winch (isolated historic find), and an unidentified buried target. This meant it would have to be uncovered to make an identification. The mystery target had a similar magnetic signature to the Black Rock Wreck…could it be another historic sailing vessel?

After returning to the site with a dredge, our mystery target turned out to be a 10-foot 5-inch iron deck stanchion from a shipwreck that struck Drum Point some time after the Trouvadore. Our magnetometer had passed along the length of the rod gave it a similar signature to the Black Rock Wreck…not really a significant find and especially not the wreck I had imagined.

Mystery target revealed

Getting back to Pearson’s comment about the analysis of remote sensing data…I can’t help think that maybe common sense got the best of me. While our mystery target turned out to be an isolated piece of shipwreck debris, as Charlie Pearson puts it… “The analysis of remote sensing data is an imperfect process at best…” Thanks Charlie – I couldn’t have said it better myself.