Deploying Fish Finders
Counting with sonar
The Carp and other fishes must pass through the bridge locations to make their way into Lake Mendota. The deepest water is found under the railroad bridge (denoted with the number 1 in the picture to the left) south of two lane HWY 113. The Bathymetry of the area can be seen in the links below. I would like to deploy a recreational acoustic fish finder in one or both of the locations and gather data on the movement of the fishes after the spring thaw and when the water becomes cooler in the fall and winter. The sonar or transducer must be deployed from the bottom facing up so that it does not interfere with recreational water navigation. The area is also heavily fished so theft or vandalism is a consideration that needs to be taken into account.
Locations to deploy instruments (click on them)
1) Railroad Bridge Bathymetry
2) Westport Bridge Bathymetry
The Carp and other fishes must pass through the bridge locations to make their way into Lake Mendota. The deepest water is found under the railroad bridge (denoted with the number 1 in the picture to the left) south of two lane HWY 113. The Bathymetry of the area can be seen in the links below. I would like to deploy a recreational acoustic fish finder in one or both of the locations and gather data on the movement of the fishes after the spring thaw and when the water becomes cooler in the fall and winter. The sonar or transducer must be deployed from the bottom facing up so that it does not interfere with recreational water navigation. The area is also heavily fished so theft or vandalism is a consideration that needs to be taken into account.
Locations to deploy instruments (click on them)
1) Railroad Bridge Bathymetry
2) Westport Bridge Bathymetry
The Sonar
I used a Side Imaging Sonar made by Humminbird to test the feasibility of finding fish in the two areas. The picture seen on the right is an upside down version of what can be found in the manual of the 987c SI fish finder.
The 262kHz side imaging works much like an MRI since it takes 100's of slices of an object and compiles them to create a highly detailed image of submerged objects at distances up to 300 ft to the starboard and port side of the vessel. In order to "see" an object the vessel the transducer is attached to must be moving. In my case the transducer was attached to a galvanized pipe and sent to the bottom of the lake in a "fixed position" and oriented so that it would be looking at the water surface. I suspected the transducer would see fish as long as they were moving. The resolution of the objects seen with the side imaging can be adjusted by switching to 455kHz. Click here to see the 455kHz schematic. The area directly above the transducer provides conical coverage much like traditional fish finders today. Area that is a striped shaded gray is a blind area that is not seen by the instrument. I calculated the area covered by the side imaging sonar when the left and right side beams are set at 100' to be equal to about 96% coverage when the water is 15 ft deep. When the distance on the starboard and port side is decreased so is the total coverage.
The 262kHz side imaging works much like an MRI since it takes 100's of slices of an object and compiles them to create a highly detailed image of submerged objects at distances up to 300 ft to the starboard and port side of the vessel. In order to "see" an object the vessel the transducer is attached to must be moving. In my case the transducer was attached to a galvanized pipe and sent to the bottom of the lake in a "fixed position" and oriented so that it would be looking at the water surface. I suspected the transducer would see fish as long as they were moving. The resolution of the objects seen with the side imaging can be adjusted by switching to 455kHz. Click here to see the 455kHz schematic. The area directly above the transducer provides conical coverage much like traditional fish finders today. Area that is a striped shaded gray is a blind area that is not seen by the instrument. I calculated the area covered by the side imaging sonar when the left and right side beams are set at 100' to be equal to about 96% coverage when the water is 15 ft deep. When the distance on the starboard and port side is decreased so is the total coverage.
Testing the instrument
Pictures above
Left: The interface of the Humminbird 987c SI that I borrowed
Middle: The transducer mounted to a galvanized pipe
Right: Looking down at the transducer from above
Left: The interface of the Humminbird 987c SI that I borrowed
Middle: The transducer mounted to a galvanized pipe
Right: Looking down at the transducer from above
Pictures above (objects tried to detect)
Left: Steel Sphere
Middle: Large Container
Right: Galvanized tube and PVC pipe
Left: Steel Sphere
Middle: Large Container
Right: Galvanized tube and PVC pipe
