By Becky Lewis
Tech Beat Magazine
When officers need to investigate an unwitnessed vehicle crash, especially a fatal one, they can usually find plenty of physical evidence: tire tracks, skid marks, broken trees, damaged guardrails, and of course, the vehicle itself.
Unless, of course, it ends up underwater.
Lt. Michael Mitchell of the Texas Parks and Wildlife Department says that sometimes he envies officers who work on the 29 percent of Earth’s surface not covered by water.
“In Texas, my agency is the primary water patrol agency,” Mitchell says. “We were looking for persons or evidence under the water by using either hooks, which is a laborious process, or divers, which is an inefficient and expensive process, and we wanted to find a way to do it better.”
The way that Mitchell devised for doing it better involved taking off-the-shelf technology used for commercial and recreational fishing, and putting it to a different use. Taking a side scan sonar imagining device, which is typically hard-mounted into one vessel, Mitchell devised a portable box, power supply and transducer mount that can be used in any available boat on the fly, “including one belonging to a civilian volunteer who is just in the right place at the right time to help expedite the search. We’ve been doing this for more than six years. It’s passé, it’s proven and it’s in place.”
A former member of the U.S. Navy, Mitchell knew that the military used similar, but expensive, technology. A setup similar to the ones used by Texas Parks and Wildlife, in contrast, costs only a few thousand dollars yet produces vitally important results. He explains that every drowning or other underwater investigation has its own unique characteristics, and recovery can often take many hours or even many days.
However, using side scan sonar technology, Texas Parks and Wildlife has seen success in as little as 30 minutes. In that particular incident, other agencies had used manual searching methods for many hours before the device arrived. Within a half-hour, the device had located three specific areas of interest, and divers had investigated and located the victim, a 14-year-old boy who went swimming with friends in a flood-swollen river. The two other boys swam to safety.
“It’s not average, but it is a great success story,” Mitchell says. “Every drowning event is personal because it affects a family. With this device, I’m confident that we can at least decrease the amount of time a family is suffering the pain of not knowing. We know it at least puts us in areas of interest more so than manual hook and line dragging.”
Investigating officers can keep a device available in their vehicle back seats because it takes up only a few square feet of space, and more than 100 side scan sonar units are now in use throughout Texas. However, in a state that big, an official vessel could still be hours away from the scene. Thus, in many cases, officers have welcomed volunteer assistance and mounted the side scan sonar in a personally owned watercraft.
Although the device can be, and has been, mounted in many types of boats, Mitchell cautions that it takes training to interpret the sonar images that result. To help with that interpretation, he teaches a multi-day training course that includes classroom sessions and a field exercise to find an object in a lake.
Students start with studying images of more easily identifiable objects, such as a sailboat that sank off the coast of Florida and an airplane immersed in a lake, and move on to more obscure results. Key points emphasized in the training include that because the technology sweeps across the bottom, the investigating boat has passed the object before the officer sees the image and it might sometimes be easier to identify an object from its shadow rather than its actual image. Side scan sonar also has its shortcomings; for example, it cannot identify objects as small as a handgun, which often sink into the mud and are almost impossible to find through that means.
“The images admittedly are difficult to interpret. In our investigations, we also use photography, including aerial photography, and combine the results. We use free software to help pull it all together,” he says.
Investigators from outside Texas who are interested in the technology could start by researching side scan sonar technology on the Internet, then contact Mitchell for more information.
“A lot of people might want to patent this type of portable transducer concept and sell it, but I’m the opposite. I just want to help.”
For more information on Texas Parks and Wildlife’s use of side scan sonar in underwater investigations, which was the subject of a presentation at the June 2013 National Institute of Justice (NIJ) Technology Institute for Law Enforcement, contact Lt. Michael Mitchell at michael.mitchell@tpwd.texas.gov. For more information on NIJ Technology Institutes, contact NIJ Senior Law Enforcement Program Manager Mike O’Shea at (202) 305-7954 or michael.oshea@usdoj.gov.
