Rescue swimmers aboard NAS Jax have been conducting training in the St. Johns for the past 40 years. In order to avoid boat traffic in the river channel, the rescue swimmers conduct training closer to the shore in water depths of about 13 feet. “Where the SAR (search and rescue) jumps are being conducted is also an area where crabbers are placing their crab pots. Our concern is when a swimmer jumps from a helicopter from 10 feet and goes eight-to-10 feet underwater – they could snap their ankle on a submerged crab pot,” said NAS Jax Operations Officer Cmdr. Mark McManus during a meeting with Rob Downs, NOAA information technology specialist, and Ian Colvert, NOAA (National Oceanic and Atmospheric Administration) physical science technician.
“NAS Jax is working with the U.S. Coast Guard, St. Johns River Water Management District, and the Army Corps of Engineers to designate an area in the river to be a crab-pot-free zone,” continued McManus.
In order to get an accurate depiction of any underwater obstructions, the NOAA team traveled to NAS Jax to conduct a survey of the area. “We are searching for any abandoned crab pots, old logs sticking up from the bottom, or anything that could be a hazard to rescue swimmers during training,” McManus briefed the NOAA team.
To seek out potential hazards, the NOAA team brought an autonomous underwater vehicle (AUV), also known as an unmanned underwater vehicle. The NAS Jax Boat House assisted the mission by operating a support boat to take the NOAA team to the designated area.
To carry out the mission, the AUV maintains a constant altitude of two meters below the water surface and survey the area using side scan sonar set to a 20-meter range scale. The AUV travels in lines every 35 meters to get full coverage of the 1,200 meter by 800 meter area. “Side scan sonar is acoustic imagery. It uses the reflection of the sound to create a picture. It looks like a charcoal sketch of what’s on the river floor,” explained Downs.
The AUV surfaced approximately every 25 minutes of the six hour mission to update the GPS and make an Iridium satellite call to the data laptop. The AUV conducted the survey mission without operator intervention. When the mission was complete, the AUV surfaced at a pre-programed location.
The data is logged internally in the AUV. The NOAA team was able to download the data by connecting the AUV to the data laptop using an Ethernet cable. “The NOAA crew discovered numerous objects which could pose a safety hazard to rescue swimmers. We are very grateful for the assistance of the NOAA Office of Coast Safety for helping us out with this project. This is just one more step towards our goal of establishing a dedicated SAR swimmer training area in the river near to NAS Jax,” said McManus.