FFS How Live Sonar Works
Sonar, whether it is traditional sonar, side imaging, or live imaging, all works on the same basic principle: sound pulses are produced by a transducer and the reflection of those sound pulses from bottom, cover, or fish is detected by the transducer as a signal. The computing power of the graph unit then turns those signals into a visual representation of the object from which the sound reflected.
Unlike other types of sonar, a live sonar transducer is an array of multiple individual transducers that produce sonar waves of high frequency. High frequencies are used to provide high detail. Traditional sonar uses lower frequencies that allow you to detect that there is a tree trunk under your boat, but you probably won’t be able to see individual branches of the tree. For this higher amount of detail, you’ll need higher frequencies (typically in the MHz range). This is why live sonar images can show so much detail; they operate in the MHz range of frequencies.
Sonar, like all sound, propagates through materials in a way that depends on the properties of that material (eg. density, elasticity, etc…). Sound waves that move from one material to another will reflect from the boundary between the two materials. An example is when the sonar pulse travels through water and then arrives at the bottom, which has a much different density and elasticity than water. However, only a fraction of the original sonar pulse is reflected. The remainder passes into the receiving material (i.e. the bottom). If the reflected fraction is large, the return is strong and represented visually on your graph as a bright return. If the reflected fraction is small, the return will be weak and represented as a dim return on your graph.
The strength of the reflection depends on how different the two materials are. The larger the difference between the sound-carrying properties of water and the sound-carrying properties of the bottom, the bigger the reflection strength will be. This is why hard bottom like sand and rock appears so much brighter on your sonar than muck. Of course, sonar can be used to detect more than just bottom. We use it to detect vegetation, fish, and our lures as well!
One important use of live sonar is to be able to see your lures during your retrieve. This is crucial for determining whether the depth and action you are imparting to the lure are what you intend. The ability to see your lures at range is strongly affected by the size and composition of the lure. Obviously, large lures are easier to see. But it turns out that even more crucial is the sonar reflectivity of that lure’s components. I discovered this accidentally when trolling Livingston lures along with other baits in my spread. The EBS system contained within Livingston lures causes them to have a much higher sonar reflectivity than the other baits I was using. The live sonar pulses are strongly reflected from those EBS components, making the baits stand out more strongly on the screen.
While this initial discovery was made while trolling, the more important use for me has been in precision casting applications. While casting for muskies, I can observe my lure using live sonar even when it is within thick cover; it stands out as a bright sonar return within the dimmer returns associated with aquatic vegetation (lures with high sonar reflectivity are a must in this case). When the lure reaches the weed edge, I can pause the lure in the ambush zone just beyond the wall of weeds. Short twitches of the lure, keeping it in position, can entice wary muskies to explode out of the weed edge. Dive-and-rise lures with high sonar reflectivity like a weighted Titan or the slow-rise Flipper are ideal choices for this technique.
Live sonar can allow us to refine our presentations, and high visibility is key when observing your lures at long ranges or within thick cover. Enterprising anglers can certainly find many applications for this use of live sonar that allow them to put more fish in their net.
Best of luck on the water!
Dr. Bob Klindworth