Side scan sonar operations for marine rescue or recovery 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 drowning victim without a vehicle or vessel
Both search operations require a series of skills but the victim searches require additional expertise and experience. 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 following:
- Operational Navigation & Search Planning
- Small Boat Handling & Piloting
- Equipment Operation
- 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 to overlap all require careful consideration. The ability to adjust the survey plan to local environmental conditions is also critical. Current water depth and 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 ensure 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.
1) Operational Navigation and Search Planning
Phase one of any search is to gather all available information and then plan the search operation. You need to set up a series of survey lines in the area with the line spacing and ensure proper overlap so as to cover the area directly under the sonar and account for when the boat driver may be offline. Ensure you have covered an area thoroughly before expanding your search. Where there any gaps in your coverage? Did you overlap survey lines to cover the gap under the towfish or transducer? The best way to be certain you have covered an area thoroughly is to plot sonar coverage using a sonar software.
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. Over steering or continuously correcting your course 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)
It is essential to understand how to operate your electronic systems correctly. YouTube offers a great many how-to videos and some are helpful but others provide misleading information or information important to fishermen but not SAR professionals. Know the source of your training materials. If you have questions, visit Black Laser Learning’s Forums to ask questions or share information with other SAR professionals.
4) Side Scan Sonar Image Analysis
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. Side scan sonar manufacturers often post images which clearly show a drowning victim or practice with a manikin. In the brown Enviroscan image, 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. This color image 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 have given units the more advanced capabilities that were previously only available to more robustly funded programs. These side-looking fish finders such as the Hummingbird® series are relatively inexpensive but effective in certain conditions. Click here for more information on the pros and cons of towed vs. hull mounted sonar systems.
5) Post Processing Sonar Data
Have I covered the search area thoroughly? Did I miss the target? These common questions can quickly be answered by post processing your data after the search. The more expensive towed systems such as EdgeTech, Marine Sonic Technology and Klein have software that allow the operator to easily play back and manipulate the data on a large monitor to see the full sonar resolution. These software programs also provide coverage maps. What if I have a hull mounted Humminbird®? It will take a 3rd party software such as SAR HAWK® to view your data on a high resolution monitor and ensure full coverage. If you’re working from a command center, as search teams rotate on and off boats, the data can be handed off to be reviewed and plotted on shore so the next shift knows what has been covered or which locations may have interesting targets that need to be re-examined.
Black Laser Learning® offers comprehensive classroom and field training for Search and Rescue professionals utilizing both towed and Humminbird® Side Imaging® sonars. See details under the “Training” tab and on the Black Laser Hummingbird Training page. We can also help in choosing a Humminbird® sonar and offer SAR HAWK® target acquisition software.
“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
© 2018 Black Laser Learning, Inc
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