capted: I wanted to address this post before but it slipped by. When you made reference to, I believe it was a Datasonic Chirp sub-bottom profile system, the one shown in the link you provided is a very, very expensive piece of equipment.It is a technology better leased along with a trained operator for the purpose of discernment and interpretation of targets. It also requires a boat with an adequate crane or davit for safely discharging and recovering the towed instrumentation.
I once had the honor to work as a deck assistant with Earl Van Reenan of Van Reenan International, Inc.
Van Reenan is a geophysicist and leading expert in the usage of Datasonic Chirp systems and second to none in the interpretation of the sub-bottom profile data. He was once Chief Geophysicist for Dr. Harold Edgerton, MIT professor, inventor of the strobe and pioneer of sub-bottom profile systems resulting in the creation of the company EG&G. Van Reenan is up in years now but if SFRX were to consider this type of survey, I would recommend him. The survey I was involved in was off the east coast of Florida so I can share some the encountered problems.
These systems are ideal for surveys with sub-bottom geology of silt, light mud concentrations and certain (not all) types of sand. The concept of using this kind of survey for SFRX in quest of the site #3 wreck is viable but these things must be taken into consideration. Normally, before committing to the cost of such a survey, a sample core of sub-bottom material is produced and analyzed by the geophysicist to determine if the instrumentation is applicable with expectation of positive results. No, it won't penetrate clay, corals or certain types of sands. Based upon a sub-bottom geology condition of penetrable sand, the operator is looking for suspended or on sub-bottom parabolic point-source reflections, such as would be produced by a hard igneous rock ballast pile or sometimes single but more recognizable concentrations of cannons or bars of precious metals. These create parabolas like similar to the McDonald golden arches. The problem is that when encountering concentrations - coagulants of ancient dead shells and corals, the same parabolas are produced. Normally, a sensitive (Cesium) off bottom depth controlled magnetometer is towed over the position. Later the large coil ferrous/non-ferrous detector (as you addressed before although I don't agree with the range) is suspended (not towed) right over the location target. The sub-bottom profiler has already provided the depth at which the questionable target is buried.
On the previously posted subject of the Drake's silver bar, I and allot of others in this industry would love to see a photo of that bar. Undoubtedly representing the most historically famous silver bar ever recovered.
