Positioning for St. Louis River Search

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Positioning for St. Louis River Search

Postby scott_bentley » Fri Mar 04, 2005 2:22 pm

On January 10-12, Marcus Kolb and I are scheduled to fly to Duluth, MN to participate in a search for a drowning victim in the St. Louis River. The victim was in his forties, surveying part of the river near a marina he owned in a rear-tiller motorboat. He fell out of the boat, and was seen clinging to the side at the boat continued in circles before he succumbed somewhere. Due to the lack of good information on the exact circumstances, the search area is fairly large (multiple acres of river.)

At this point the river has ice that is 2-6 inches thick, with 6 inches of snow on it. But the time we get there the ice will likely be thicker, and the snow will be deeper.

Our plan is to bring a fleet of VideoRays (almost the entire VideoRay demonstration fleet – plus the units owned by St. Louis County, for a total of at least 6 VideoRay Pros and Explorers), and drill a grid of holes 200-300 feet apart over the entire search area. We’re planning to use ice fishing shacks for operations, though we may use recreational vehicles on shore and wireless operations for some units.

The visibility should be pretty good – maybe 5-15 feet. The water is fairly shallow – 20 feet in a ship channel in the middle of the river, but as shallow as 2 -3 feet at the edges of the search area.

We should have no trouble getting several volunteers to help. St. Louis county has experienced operators, though we’re planning to have more units than operators. The St. Louis County Sheriff’s Office Rescue Squad is running this operation – we will be assisting them.

At any rate, where we need help is ideas for positioning. We have a few Desert Star Pilot systems, but not enough for all the units, and given that we can walk on the ice (wearing Mustang suits) and drill holes wherever we want, we think other, less sophisticated solutions might work. We’re thinking, for example, of green lasers mounted on painting poles, or strobe lights we could aim for, to keep units on a specific search pattern. We might be able to see the lights of the units through the ice, particularly at night, but the snow will make that difficult.

Does anyone have experience with this or ideas they could share?
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Positioning for St. Louis River Search

Postby henning_føsker » Fri Mar 04, 2005 3:11 pm

My experience is that the Pilot Positioning system has limitations in shallow waters. I've also experienced that it is difficult to operate VideoRay when current exceeds 2ft/sec since it hasn't got lateral truster. Given theese limitations I would have approached this assignment by systematically search the cross section of the river, going upstream or downstream depending current velocity. Sonar and compass are my most important tools for navigating in limited visability. With sonar in horizontal mode of operation it will provide a cross sectional view of the river when flying along the river and you should be able to determine distance to shore and hopefully identify target. Typically the current is strongest where the river is deepest and almost no current in shallow shores. Experience from drowning accidents in rivers in Norway is that victims are found on shallow shores in the river and where the shape of the river creates a "backflow" or "eddy current" in low or moderate velocity rivers. In high velocity rivers victim is either not found at all or found on the intake trash rack on the first downstream hydro power plant.
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Positioning for St. Louis River Search

Postby marcus_cardew » Fri Mar 04, 2005 3:26 pm

Before now, I looked at using a high brightness Green LED flasher on a vehicle, and tracked it using a downward looking camera from the surface to give me vertical and horizontal angles. This was mid Atlantic, (good vis) but I could track the LED flasher down to about 50-70m in daylight. I know this may not be much help, but it's definitely worth taking along some diver 'firefly' flashers and your green lasers for a vehicle to steer towards, or you could consider putting a flasher onto the top of vehicle, and use a camera (or another vehicle) looking down the hole from the surface to get a bearing.. As the water is shallow you are more interested in horizontal bearings.

Dave has also got his SeaKing Head, which could be deployed from the surface on a stick, to control direction. which should allow a fairly good sonar survey to be made from multiple holes. I would do that first, taking some screen snapshots and try and make a bit of a bottom chart to indicate any significant sonar targets, which would help a vehicle with a sonar to estimate position.

If it was me with a vehicle with no nav, I would look at deploying a vehicle straight to the bottom on a short leash, and steam around in a circle. Then progressively let out another few metres and repeat until at the end of the tether. If I did find anything, I would know the cable deployed length, awould try and estimate umbilical direction from the surface hole.

Still Thinking.....

Best Regards (and Happy New Year to All!)

Marcus Cardew
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Positioning for St. Louis River Search

Postby jeff_byars » Fri Mar 04, 2005 3:41 pm

Just got back after the Holidays. Not much help for ice and snow but concentrate the initial search in the nearest bends downstream of last siting. The water eddys here and usually drops objects in these locations.
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Positioning for St. Louis River Search

Postby ianbucc » Fri Mar 04, 2005 3:47 pm

Could be a tricky one, I would suspect the people on the ground will be your best advice to get certainly as regards the currents that may flow under the ice.

As to positioning, we would go for as simple as possible, much holes and short tethers !, possibly augment the search using the sonar, but the effectiveness of that depends on how much “clutter” you get on the image from the under ice returns, if there’s a current running the ice might be smooth on the bottom, and that would probably not be good for sonar shadow from the first returns.

Only other thing I would possibly try would be using big underwater lights, possibly augmented with small “radar reflectors”, under the ice forming a grid that you could fly the Videoray towards, but depends on conditions whether that would be a feasible operation.

The current flowing in the river (or that has flowed since he went in) is the thing I would be most concerned about, even a slack water river can move things about significantly (we have a tree complete with roots etc, in Aberdeen harbour, which they can’t catch as it’s not in the same place any two days!! As the water in the channels move it drags the tree in and out of the berths even though the water there is dead still on the surface!)

Hope you have success, but it sounds like a difficult one.
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Positioning for St. Louis River Search

Postby eivind_aarseth » Fri Mar 04, 2005 3:59 pm

I forwarded your email to Tom R. Hansen who I know have some experiences with search for bodies with his VideoRay. He informs me that your project below is very much similar to something they did here in Norway. That was in the mouth of a river but the bottom was 30 meter deep.

Their problems was as following:
- lot of trees and branches complicated the use of sonar
- soft bottom substrate with a lot of gras and leaves which clogged the thrusters

According to him it's very important with a thorough research before the search beginns
- current in the river
- what did the person whear (where the clothes negetive or positive)
- water temperature (could the body have started to develope gas and maybe have floated down current)

The search should be done in an overcrossing pattern. In the search Tom mention in his email they found the object at the third day in an area where they had been before. They started the searced according to information from the Sheriff and relatives, but after a while they more carried through the searc based on a hunch/feeling for where it could be. His experiences are that it's difficult to use sofisticated electronical methodes to "check out" searched areas even though the bottom is difficult. Simple devices, plenty of time and common sense is what it takes to have sucesss.

In this case he recommends you get a "guide light" placed on the ice or in a hole - get a number of lamps which can light down from the ice (remove the snow only around the light beam). Since it's relative dark under the ice not mutch light is needed to be very helpful when orientating with the ROV), It should the also be possible to search according to a pattern.

Be aware that the body/object also can be situated just below the ice.

I hope the information abow is at any help and whish you could luck (from Tom also).
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Positioning for St. Louis River Search

Postby scott_bentley » Wed Mar 16, 2005 5:39 pm

See Marco's post under Accessories for his input on this. Marco is the president of Desert Star, a manufacturer of positioning systems for VideoRay, and is very knowledgeable. We did use his systems on this search. We also, for the first time ever, connected the positioning system on the ice with the monitoring system in the command vehicle through an 802.11G wireless link - see http://www.videoray.com/Press_Room/multiple_rovs.htm and the picture in http://www.videoray.com/Press_Room/Images/jan05spiritlake/PICT0072.JPG .
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Positioning for St. Louis River Search

Postby ralph » Tue Apr 05, 2005 10:24 am

Here is some work I did on Search Techniques.


click here to download the full page fax
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