3D Streaming Fish Finder, Simulated This page was modified on From: Dolphin Inspired Sonar

These are Quick Notes on an improvement to a popular kind of fish finder -- making it show fish in 3D rather than just 2D.
Below is an example of the screen of a streaming, 2D fish-finder currently for sale. The arcs "stream" out from the left side of the screen, under the boat. The arcs are made from echoes. The thickness and color of an arc relate to the loudness of echoes. Arcs to the left and arcs to the right of the line-of-travel of the boat cannot to discriminated.
On this page are some screen shots of our new simulator of a 3D, streaming fish-finder. They are hot-off-the-computer and not made pretty yet.
For example, looking obliquely at fish down to bottom at 12.5 feet in depth. Fish to right of the path of the boat are blue:
How Does a Streaming Fish-Finder Work?
Consider the commercially available 2D, streaming fish-finder.
A boat's sonar is pinging downward from the top left of the screen. The boat is moving to the left. At each sonar ping, all the columns of pixels on the screen are shifted one column to the right. For each ping, the echoes produce new dots in the column of pixels leftmost on the screen, below the sonar of the boat. Each echo makes a point in the new column. But, sonar pings do not travel in a thin line like a laser beam, they spread as they travel down a cone. So the resulting image is partly an illusion.
When a fish enters the cone of the ping, its range to the pinger is greater than when that fish is directly under the pinger - causing fish to appear as arcs. The wider the angle-of-opening of the cone, the taller the arcs -- because the greater is the difference between the nearest and farthest range in the cone.

A fish on a longer path, left to right, through the cone of insonification will produce a longer arc.
Fish near the surface can be missed. Simple geometry suggests that a fish whose depth is in the lower one half of the axis of the cone is three times more likely to pass through the cone than is a fish at a depth greater than one half the length of the axis of the cone.
If the angle of the cone is A degrees then the width of the base of the cone at depth D is 2*D*Tan(A). For examples: when D = 50 feet, the width is about 17 feet for A = 20 degrees and is about 36 feet for A = 40.
In the video of the screen indicated above, the columns move from left to right, and a viewer gets the impression of seeing into the water from a position on the left of the boat. This is an illusion. Seeing into the distance is also an illusion. The dark brown arcs are not nearer to the "eye" than are the light blue arcs. They represent louder echoes. And the loudness has to do with the reflectivity, possibly the size, of a fish's swim bladder, not so much the fish itself.
Two fish at about the same depth in the cone of the ping will overlap each other on the screen no matter how far apart they are left and right or fore and aft. So, to reduce the confusion of large numbers of overlapping echoes, the angle of the beam is made smaller. But, this reduces the distance covered left and right, and fish are missed. 3D streaming largely overcomes that problem.
Below is a view of the full water column top to bottom at 50 feet:
The view above is like that of an existing 2D streaming fish-finder. The angle-of-opening of the cone-of-insonification is 20 degrees.
The cross-sections of that cone are circles. 3D streaming can take advantage of cones-of-insonification whose cross-sections are elliptical.
The same body of fish is shown below, color-coded by left and right, in a 3D streaming fish-finder:
Top-to-bottom is 50 feet. Left-to-right is 300 ft. Front-to-back is 36 ft. The cone-of-insonification has elliptical cross-sections.
Below, the angle of the cone, left to right of the boat is 40 degrees but is 10 degrees fore and aft (left and right in the picture).
The "arcs" are short because the cone being narrow in the direction of the boat's motion. The arcs seem even shorter than they are because the picture is distorted: the left-to-right field of view is artificially narrow.
Below is a Side View then a Top View from the 3D streaming fish-finder.

Here is someone's illustration of the cone of insonification and how its width near the bottom allows fish to "hide" by being near enough to and deeper than some part of that bottom. The 3D fish-finder can find some of those "hiding" fish, though it too can have a blind region. Fish cannot be "seen" if they are outside of the circle indicated by the big arc in the rear-view below.
You can also compare the coverage of a 20 degree cone with a larger 40 degree cone. Obviously, the smaller the cone is, left to right, the fewer fish will be seen.

How Does the 3D Streamer Work?
If 3D streaming were easy, fish-finders would have it already!
The main idea came from this break-through hypothesis about the imaging sonar of dolphins: the echo-sensors are not the ears but are tiny touch-like sensors in the chin. 3D imaging sonar is made possible by an array of sensors of time-of-arrival of echoes at those sensors. In the case of streaming, the sensor are in a straight line. There is some magical mathematical computation that overcomes problems inherent in deducing images from such an array. These are subjects of an application for a US patent.

Miscellaneous Notes:
Sound reflects much more strongly from the air in the swim-bladder of a fish than from tissue (whose density is only a bit more than that of sea water).
Sound intensity is not homogeneous within a cone of insonification. In addition to being weaker with distance, it is loudest down the axis of the cone and weaker with distance laterally from that axis. Electronics can partially compensate for differences in loudness as a function of the known distance to the pinger. But, at a given distance, a fish will return a louder echo as it is nearer to the axis of the cone.