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Marine Surveys

A marine gravity survey involves the use of a gravity meter similar to that of a long-line meter, but with a water-tight housing. The power and data lines are connected to a battery and laptop computer aboard the watercraft at the surface. Unlike the long-line survey, the cables are usually much longer so that the meter can reach the lake or ocean bottom, perhaps as much as 800 meters in depth. The software is identical to the long-line setup since the operation is the same.

What makes the survey unique is the delivery system. You will see in the following photographs techniques for raising and lowering the meter from the deck of the ship, the winch and the cables. The water-tight housing is usually made from steel and is very heavy out of the water. Surprizingly, without additional weights added to the outside, the meter will float. The interior volume displaces enough water to be positively bouyant without the additional weight, just like a human diver needs a weight belt. A winch is definitely required.

One additional and very important item is the watercraft itself. It must be large enough to accommodate the crew, the meter, and the winch as it lifts the meter over the side of the boat without capsizing. Further, depending on the weather and openwater conditions, the boat should be large enough to handle the wave action and size of the swells that will occur. A boat that is too small is simply not safe.

The survey proceeds in much the same way as with long-line surveys and production rates are very similar, assuming water depths are not extreme. As water depths increase, the speed of the winch becomes the rate-determining step.

 

Eastern Canada

Boat Crew at Work

Boat Crew at Work
Cape Breton, Nova Scotia, Canada

Meter Docked in Anti-sway Hoist

LaCoste & Romberg Underwater Meter
Docked in anti-sway hoist for travel between stations
Cape Breton, Nova Scotia, Canada

 

 

Lowering the meter into the water

LaCoste & Romberg Underwater Meter
Cape Breton, Nova Scotia, Canada

 

 

Arctic Ocean

Off Northern Coast

Off Northern Coast
Northwest Territories, Canada

Typical Boat Size and Hoist System for
Transition Zone Surveys
Northwest Territories, Canada

 

 

Mediterranean Sea

Survey Boat in Naples, Italy

Survey Boat in Naples, Italy

Survey Boat coming in to Dock

 
 
 
 
 
 
 
 

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Last Modified on Mon 10-Oct-2016

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