Sonar needed for locating drowning victim

[Michael Margineanu]

I am writing to you from Romania, regarding a drowning case in a lake dam which took place few days ago. I am personally involved in the case, as member of a volunteer rescue team.
Divers from our team and the emergency inspectorate were unable to locate the body of the victim over the last five days, as the visibility is under 1m, depth around 30 m, and the sonars they possess are not suited for identifying bodies.
If you know anyone who has access to advanced sonars suitable for victim localization under water, and could share their contact details, it will be greatly appreciated.

Thank you very much.

 

[Rred]

You might be able to reach out through military or other diplomatic channels to request assistance from a professional team. Other than that your best bet may be to raise some money to buy recreational "fish finder" type sonars, $150-$1000 in the US market, and simply spend time doing a grid search until they show the victim. And they will show a target that large. Purchasing it and simply paying the import duties or shipping if necessary (surely they are available in Romania?) will be the most expedient solution.
Anything else will probably mean bring a team in (flying them in) at greater expense and complication, unless someone can authorize it as a humanitarian or training mission.

 

[Bert van den Berg]

Some sidescan sonars can be had relatively cheap (less than US$5000) and depending on terrain could potentially help. If the bottom is flat without too much weed sidescan can identify small objects but be ready to find a lot of derelict objects also.

 

[FinnMom]

Our club once tried having a diver lie flat on the bottom just to see how well we could spot him on our RIB's side-scan sonar. It worked surprisingly well at 6-12m but 30m is very different challenge.
In Finland they do use cadaver dogs to pinpoint an underwater victim's location (or indicate whether there is a victim underwater at all). But here again 30m may be too deep, causing the odor to spread over too wide an area.

 

[Johnoly]

You might want to ask the moderators to move this thread to the Public Safety Diver's section. You might hit a lucky contact in your region in that sub forum.
Public Safety Divers
(I'll hit the report button on myself, so they will see the request)

 

[Doogie38]

We always had a problem with them, good tool but we search patterns like grapenel, and search foot by foot. Also we have used dogs, you need a article of clothing from the victim. And the dog can hit the sent on top of the water on a calm day. Mark that and continue on. If you get multiple hits make that area hot. We found a jumpers jeans at 80-90ft (idk if it was luck or it actually worked but that's what our state police do)

 

[NAM001]

What you are looking for is a sonar that will identify the slightest change is depth. That property is a function of frequency. the higher the better. many fish finders can do it they are up to 200 kHz. Look at it this way a return is recognized by getting a return pulse that contains say 10 cycles of the smitted freq. if you have a item on he floor of the sea then yo need those 10 cycles to be a length of say 1/2 to one inch. in order to see changes of 1/2 inch in detail. so with these parameters ( not saying the sonar needs 10 but if it did) you would use the wave length formula to find the freq. one = freq over time. with the parameters above the wavelength is 1/10 of a 1/2 inch or .05 inch. So what freq has a wavelength of .05 inches sound travels about 4800 fps so 4800 feet devided by .05 inch. I think that comes out to about 100 kHz some one can check the math. The biggest problem will be the interference with the dirt in the water. The very thing that makes the vis so bad. even with the sonar it will be tough. the more rejection of dirty water comes from narrower beams and that makes it real easy not to hit the target with the transmission. Next problem is that high freqs bend in the water like a roller coaster, should not be a lot of this in 30 m but the issue is there. Next and most difficult is that a beam of say 6 degrees will give you a bottom coverage of say 3 meters. On the plus side of things sonar reflects off of air very well. so the tank(s) will be the target that stands out. Hopefully the diver will not be on his back and the tank sunk in the mud.

 

[Got2Go]

I've used fish finder type sidescan sonars to locate a lost SCUBA cylinder. You will need to use a tow fish with the transducer to be able to get a usable image from 30m.
Adjust the distance between the bottom and the tow fish as needed to get the desired coverage area and detail.