Page 581 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

580 CHAPTER 21 Practical Applications
As introduced in Section 21.4, search and identification of underwater items are accomplished through four basic steps:
1. Research the operation to define the area of interest for mapping and limiting the search area. Examples of items used to outline the search area follow:
a. Intelligence
b. Witness interview/last seen point
c. Survey data, prior searches, etc.
2. Wide area search with instruments and sensors such as:
a. Towed or watercraft/aircraft-mounted imaging and profiling acoustics (such as side scan sonar)
b. Magnetic anomaly detection (MAD) equipment (such as a towed magnetometer)
c. Radiological and chemical instrumentation, etc.
3. Narrow area search with slow-speed instruments including:
a. Acoustics (such as a fixed location mechanically scanning imaging sonar)
b. Fixed or towed magnetometer
c. Optical equipment (towed/drop/ROV-mounted camera or laser line scanner), etc.
4. Final identification, classification, discrimination, and disposition of the item by a human—that is, through the diver’s eyes or through the camera mounted on an ROV that is propelled to the inspection site and viewed by the operator.
The ROV’s place within the PSD’s toolkit is through the narrow area search and final identifica- tion phases of the search plan. ROV intervention as a productive and cost-effective means of final item identification, discrimination, and disposition is the focus of this section. The four basic steps are discussed in more detail in the remainder of this section.
21.3.4.1 Planning and research
The planning and research segment of a search operation is by far the most important yet least practiced segment. A PSD dive team can never obtain too much information before a search. Inexpensive time spent asking questions and poring through data could save hours of expensive, high-risk, resource-intensive time on the water.
Suppositions can be made based upon witness interviews and some basic science. Calculations of travel time and distance to impact on accidents and drowning cases help narrow the search area. For an expanded text on drowning physics and underwater crime scene investigations, Teather’s work (1994) on the subject (referenced in the bibliography) is excellent.
There is a plethora of information available from many sources that contributes to the data needed to define the search area as well as to gain an understanding of the conditions and chal- lenges faced while on the water. Examples of these public-domain files include:
• Geographic Information Systems (GIS) database for the search area maintained by the local township
• The US Coast Guard, State Environmental Agencies
• Local land survey companies
• The US Geological Survey
• US Board of Reclamation