Side scan sonar operations for marine rescue situations can generally be divided into two broad categories:
1) locating a vessel, aircraft, automobile or other craft such as a snowmobile or four wheeler; or
2) searching for a victim without a vehicle or vessel.
Both search operations require a series of skills, however the victim searches require additional capabilities. Most importantly, once the equipment has been acquired, training and field operations are key to honing the necessary skills. Black Laser Learning® has identified team skill requirements as the
1) Operational Navigation and Search Planning
Phase one of any search is to gather all available information then plan the search operation. Set up a series of survey lines in the area with the required line spacing. Ensure proper overlap so as to cover the area directly under the sonar and account for when teh boat driver may be offline.
2) Small Boat Handling and Piloting
One team member needs to have enough small boat skills to pilot a vessel safely and follow navigational cues to drive straight and steady survey lines. Too much steerage or correcting to stay on line will degrade the sonar imagery. When the pilot finds him or herself offline, easy corrections minimize distortion in the imagery and the possibility of overshooting.
3) Equipment Operation (Sonar, GPS, Computer and Navigation Software)
4) Sonar Image Analysis
While not every team member must be proficient in every skill, as a functioning unit, all four skill sets are required to consistently locate and identify targets. While your boat pilot may not need to know how to operate the sonar, he does absolutely have to have the capability to navigate straight survey lines.
At least one team member should have enough experience to plan the survey. Decisions on where to search, survey line spacing and how much overlap all require careful consideration. The ability to adjust the survey plan to local environmental conditions is also critical. Current water depth bottom topography will influence how the survey is to be conducted. At the most basic level, the operator must know how to operate and adjust each piece of gear. If the operator cannot get the best available imagery or cannot find the target due to faulty navigation, the search will be ineffective.
The field operator must insure good quality data. While the operation of equipment is a basic necessity for the boat crew, image interpretation can be conducted onshore under more stable conditions by more senior team members. All of these skills are critical and can be taught and honed with practice.
Probably one of the most difficult search operations requires locating a drowning victim without some type of vehicle or automobile to act as a guide. Without a large, easily-detectable target, looking for drowning victims alone is a difficult task requiring advanced sonar analysis skills and a bit of luck. However side scan sonar manufacturers often post images such as the one below which clearly show a drowning victim or practise with a manikin shown left.
Notice how a clean, uncluttered and flat bottom makes the target easy to detect? Identification of the target is also very easy since the human figure with limbs is clearly visible.
This image was taken with a 500 kHz sonar. Normally for victim searches we prefer a higher frequency which has the potential to produce higher resolution images. Whether due to the frequency or many other factors, the victim is not always as clearly identifiable. Take a look at this next black and white sonar image albeit again with a 500 kHz sonar.
The victims, two teenage boys, were last seen clutching each other. While there are no distinct identifying features, the alert sonar operator coupled the story along with a paired target on an uncluttered, flat featureless bottom. The sonar image was confirmed by divers and the victims recovered. Divers could have found the victims but at depths over 80 feet and with only a vague position, it would have taken several days to do what the side scan did in a few hours.
Working on cluttered bottoms, even with high-frequency systems, can be challenging. The color image below recorded the final resting place of a drowning victim. However, the body was actually located by divers. The victim was not easily discernible on this image. If you cannot see the body, you’re not alone. I still have trouble locating the target.
Traditionally victim search operations have been dominated by towed side scan sonar systems. However now low-cost options such as the side imaging fish finders has given units more advanced capabilities that were previously only available to more robustly funded programs. These side-looking fish finders such as the Hummingbird 900 series are relatively inexpensive but effective in certain conditions.
Black Laser Learning® offer comprehensive classroom and field trainng for search and rescue professionals utilizing the HUmminbird series of side imaging sonars. Black Laser Learning Black Laser Hummingbird training page.
“Thank you very much, Vince, for the outstanding training. Our team learned more in your one-day class than we have in the last two years of reading manuals and trial and error.”
Thomas J. Cooper, Director, Tyler County Office of Emergency Management
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