February 2005: Operating Through Ice

In February of 2005 three GPR lines were taken to see exactly how well the GPR would work on the lake. Ice still covered Half Moon Lake but we had a successful test on all three lines. We needed to take a few test runs because, initially, we were unsure how or if we would be able to get readable data. The FM radio tower that lies to the north/northwest of Half Moon Lake was one of our worries but it ended up affecting us very little, if at all.

Below are two of the three lines we took. As can be seen from the GPS page, line one was taken from the Sea Sprites dock south across the lake to the north edge of Carson Park. Line two was then taken between that point and the opposite side of the lake along an east-west transect.

Line 1

This line has the Sea Sprites dock as its starting point, located on the right end of the line. Here it is easily seen how the lake bottom gradually gets deeper and bottoms out at roughly 9 feet and gets shallower abruptly.

North Tip of Carson Park......................................................................................Sea Sprites Dock

The left scale on this image shows time in nanoseconds, the right scale shows depth in meters.

Line 2

Below is our second line from the GPR. The left side of the photo is where Luther Hospital is located and the right side ends near the north tip of Carson Park. Again, from the east (left) edge it gradually gets shallower and shallower before bottoming out at roughly 9 feet on the Carson Park side.

 

.East end ......................................................................................Line 2 of GPR Survey................................................................. West end ......

Near Luther Hospital ........................................................................................................................................................North Tip of Carson Park

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LINE DESCRIPTION

This is Line 2 shown with color schemes added to it in Adobe Illustrator. It outlines and highlights the different layers below the surface of Half Moon Lake.

RED: Shows the water below the ice surface. The two lines shown above the red area are radar signal reflections that bounced off the ice we were walking on and the surface of the water. Radar signals tend to bounce back with every transition between materials being penetrated -- creating the lines.

YELLOW: The yellow highlights how much sediment is in this particular transect (the nasty muck at the bottom of the lake). As you can see, it varies in depth as you cross the lake. The lines are from signals that bounced back with every change in composition in the sediment.

GREEN: This illustrates the location of the bedrock or bottom materials beneath the organic sediment. It shows where the bottom of the river bed channel is now located. Clearly, the channel has been considerably filled with sediment.

Photos from the February test run

Getting things underway for first test run

Craig and Chad pulling GPR antennae on initial test run

Harry trying to view the computer screen in the sunlight

Craig and Chad hoping they are doing what Harry wants

 

Harry taking the readings in on his computer

Taking a rest after the second line was taken

View from Harry's perspective as Craig pulls the antennae for the GPR.

I wish to go on record that I had not yet joined the UWEC Half Moon Lake Study for the February, 2005, data collection test runs presented above. - N. Trombly