Thread: Help With Reading A Sonar Display

Not my brand of sonar but they all basically work the same:
The transducer’s location is at the top right hand side of the display. All of the sonar returns from that 6 foot area, whether from in front behind or to the sides, all gets compressed into a single column of pixels on the display. This is why the display updates from the right to the left. What is within the transducers sonar cone is shown at the far right and older sonar data gets shown to the left as the display updates. Other than being under the transducer and within the sonar cone; there is no directional information available.


Greg Walters at Humminbird

What Gregg said. If you have Ascope, turn it on and you will see whats in the cone coverage area in the Ascope view at that instance. Not familiar with your unit.

Originally Posted by Cane Pole

What Gregg said. If you have Ascope, turn it on and you will see whats in the cone coverage area in the Ascope view at that instance. Not familiar with your unit.

Whats ascope ?? Another meter you,d have to buy just to see it once ??

Originally Posted by frank lawhead

Whats ascope ?? Another meter you,d have to buy just to see it once ??

Amplitude Scope. It has different names on different units. Lowrance calls it Fastrack on some units. It's like a flasher display that is in a straight line and basically displays the instantaneous return from the sonar. It can be turned on or off.

Originally Posted by CatFan

Amplitude Scope. It has different names on different units. Lowrance calls it Fastrack on some units. It's like a flasher display that is in a straight line and basically displays the instantaneous return from the sonar. It can be turned on or off.

Thanks

I think what he is trying to find out is when the object first enters the screen where is it in relation to the transducer. I would like to know that also. For instance if a you see a small brushpile say 3 ft. in dia. where would it be on the screen when the transducer is right on top of it.

I have heard that when a fish comes in contact with the signal if it isnt directly in line (straight down...centered) the arch could be tailing off either right or left, depending on which side of the 'ducer the fish is on. Also heard the reds and yellows say the fish is directly underneath where monochromed colored arches means it's within the reach of the signal, but not directly undermeath it sending a weaker signal. Might not be right...but it sounds like it makes a little sense.

Wilbur,
If you are parked over the top of a brushpile, the sonar will be showing it across the whole display. It won’t have the shape of a brushpile though as the sonar returns would be constant lines across the display if the boat were perfectly still.

Imagine this: you walk outside at night and turn on a flashlight pointed straight down at the ground. Now you have to take everything you see in the flashlights beam and draw it all out as a single column of information on a display. Things that are closer get shown at the top of the display and things that are farther away get drawn at the bottom of the display. You can even use colors to show how much light gets reflected back at you. Now, take a half step forwards and again draw everything in the flashlight’s beam but place it on the right side of the last column of information you drew. Do this multiple times and you will start to build up an image of what you have just passed over – basically this is what a sonar unit does. Now if you were to stand still and every second draw what is in the flashlights beam, you would be drawing the same thing over and over and over again until you moved. This is what happens when a sonar unit is stationary over structure or the bottom: it repeats the same data over and over again on the display.

I think the part about conventional “2D” sonar that most do not comprehend is that it must take all of the readings it gets within a circular or cone shaped area and show it in a 2D format as distance from the transducer (zero feet).


Gabowman,
As a fish enters, exits or passes though only the edge of the sonar cone of a transducer it is farther away from the transducer than when the fish is in the center of the transducer beam. This can result in an arc being formed on the display of the sonar unit. The left most part of the arc is when the fish is entering the sonar cone and the right most part of the arch is when the fish leaves the sonar cone. This is due to the sonar data moving from right to left on the display of the sonar unit. Now what you have to remember is that the angle of the transducer to the surface of the water will affect this as well – and this is when the boat is stationary or while moving, as these could be different depending on your boat and how it floats or rides through the water:
- A transducer that is angled forwards (the back end of the transducer is lower than the front end of the transducer) such that the sonar beam is actually shooting forwards of the transducer; will show more or possibly all sonar returns from fish with a long leading edge (left part of the arc) and either a small trailing edge (right part of the arc) or no trailing arc at all.
- A transducer that is angled backwards (the back end of the transducer is higher than the front end of the transducer) such that the sonar beam is actually shooting behind the transducer; will show more or possibly all sonar returns from fish with a long trailing edge (right part of the arc) and either a small leading edge (left part of the arc) or no leading edge at all.
- A transducer that is perfectly level to the surface of the water will be able to show perfectly formed arcs (left and right parts of the arc are equal) for fish that move into and out of the transducer’s sonar cone.

What these arcs do not show you is whether the fish was on the right or left side of the transducer. With a single element transducer this is not possible.