Echo sounder for fishing: myths and reality

Category: Fishing

We all heard a lot of tales and legends about the extraordinary capabilities of sonar that they can see. Now let us try to "separate the wheat from the chaff." It is really not easy, even if you spent three decades in conversations with technologists from most producing companies of echo sounders.

I will try to translate into ordinary language what I heard in those conversations. Here are some "grain of truth", which I still managed to get over the past 30 years.

ECHO LOGIC

Echo sounder operates by sending beams of sound pulses in water, which in its movement through the water obstacles bounces off like an echo. Sonar processor can calculate at what distance from the emitter is an obstacle we meet the waves, by measuring the time spent on the transmission of sound pulses from the emitter to the underwater object and back to the receiver.

But still, if we forget the myths and legends, from what is actually reflected and returns an echo? All that is different from the density of water, can reflect the sound wave and create an echo. The greater the density difference, the stronger the echo. For the occurrence of the echo there is no difference whether more or less than the density of water density of the object itself: the only important difference densities. Theoretically, the steel ball and a bubble of air can create an identical echoes.

Fish create one of the most interesting and surprising echoes what just happen. You've heard that from the swim bladder in the body of fish is reflected echo signal, which is in the form of tags seen on the sonar screen. This is true, because it is, but many species of fish have no swim bladder, and, nevertheless, they are also visible on the sonar screen!

Like us, fish are composed mainly of water, so that the echo of it would be of little use. But the body of fish has scales, skeleton and other body parts whose density is greater than the density of water. Although the swim bladder of a sound pulse is reflected, perhaps, the best, but other parts of the body of fish is also quite capable of becoming the cause of the echo signal.

Size matters

The main factor that provides a precise definition of the size of fish sonar - its sensitivity is correctly chosen and installed a range of depths. In general, the larger the fish, the more of it echo and larger label such a signal on the screen.

Check the fish on the screen, create larger creature, will be larger at any depth: bleak create on-screen tag the size of one pixel at the widest point of its arches (brackets), whereas polukilogrammovy will perch on the screen label width is 3-4 pixels.

The length of the arch on the screen from one end to another - not to the size of the fish has no relation, but merely refers to the time of finding fish in the cone of the emitted acoustic signal.

It is very important settings sonar, because an excessive increase in sensitivity may polukilogrammovogo perch on the screen to submit three-kilogram sigom. On the other hand, excessive decrease in sensitivity can lead to the fact that the signal on the screen will look like a 300-gramme plotvitsa. Switching range depth of 0-30 feet range from 0 to 60 feet reduces the label of fish on the screen almost doubled.

So, firstly, the need to manually set the range of browsed depths such as to see the bottom of the lake near the bottom of the screen shotgun in the deepest point to which it is planned to fish.

Then, by turning a knob to raise the sensitivity to such an extent that the entire screen were randomly appear and blow out point, then reduce the sensitivity so that these random points on the screen just stopped appearing. It should be noted found tuning sensitivity (80%, 90%, etc.), and try to repeat it in all other cases at the same depth of the reservoir.

MIRROR IN WATER

Thermocline as a magnet for fish at certain times of the year, and it is sounder to help us where to find fish. Thermocline - a horizontal layer in the neighborhood where the water changes temperature disproportionate change in depth. Status notes the depth of the thermocline, where the warm upper layers of lake water in contact with the underlying layers of the cold.

Cold water is denser than warm, and this difference in density is often enough to reflect the incident ultrasonic pulse. Sitting at the bottom of garbage and construction debris, and algae can cross the thermocline, thereby increasing the likelihood that the bottom under the thermocline can be seen on the sonar screen.

For years, I looked into a weak echo reflected from the thermocline, trying to see the bottom, under her, and saw only a horizontal strip of flickering pixels. Once at Lake Powell in Arizona, I met a strong thermocline, which my fishfinder perceived as the most currently bottom.

Sometimes on the sonar screen, all the fish is visible at the same depth, which should have been visible to the thermocline. For unknown reasons - but this may be a special level of illumination, the concentration of hydrogen ions, oxygen, or a special intensity of cosmic radiation - some days sounder can see the water column at the incredible depth and then any advice you can not stop.