®
Winter 2019
IMAGE
interpretation
by Marc Marcantonio
Every picture tells a story. Improved screens and software make sonar easier to use, but many find interpretation of the images to be confusing. In this article we will look at some actual screen shots of my Lowrance HDS units and help clear up some of the mystery these images are solving. In case you are wondering, the following images were taken at Lake Washington, near Seattle.
page
14
MERCER ISLAND SWIM
This screen shot shows three panes I typically use on my Bow Lowrance.
This was taken with the LSS-1 DownScan transducer mounted on the transom jack plate, and a typical sonar transducer on the electric motor. The left panel is a chart with my waypoint “Drag 49” next to a route that follows a gravel ridge. The route is displayed by circles with intersecting lines. I follow this path with my electric motor; so that, I can spend all my fishing time in high percentage habitat.
The top right panel shows the regular sonar (called 2D Sonar) which gives a wide cone of sonar information. At 200 kHz this shows me about a 15-foot diameter circle of the bottom, which is in 47-feet. Just above the bottom are about four horizontal lines that are smallmouth bass. Of course, you can’t know they are smallmouth bass, unless you catch one or more (like I did shortly after taking this screenshot). What you can tell is that these bass are not perfectly under the transducer; because, the signal is not very strong. If the bass were directly under the transducer, the signal would have bolder yellow in the center.
Since I was standing at the bow of my Ranger, using my electric motor, the boat was not moving, and neither were the bass. You can tell this by the long horizontal lines marking stationary fish while the screen is scrolling. The angled two thin black lines dropping from the surface to the bottom are my 3/8-ounce QuickDrop weight, and four-inch Yamamoto Shad Shaped worm separated by 12-inches of leader.
This demonstrates the detail a good electronic and transducer can show. As the worm hits the bottom you can see the closest bass dropping to the bottom shortly before eating the worm.
The bottom right panel is my DownScan image, which doesn’t show these bass because it shows a much smaller area of the bottom (a thin slice) directly under the DownScan transducer at the transom. This image shows a fairly flat bottom on top of the gravel ridge.