3D Fish Finder
3D Streaming Fish Finder, Simulated

Sonar methods inspired by dolphins will improve fish-finders and show fish in more realistic, 3D images. Here is an existing 2D fish-finder.

Below, from simulated echoes, is what a prototype 3D streaming fish-finder might show.

In both fish-finders, fish appear as arcs. These arcs "stream" out from the left side of the screen, under the boat.

In the existing, 2D, fish-finder, some arcs appear nearer to your eye than others. This is an illusion. Arcs to the left and arcs to the right of the line-of-travel of the boat cannot, actually, be distinguished.

In the simulation of the 3D fish finder, red fish are to the left of the path of the boat and blue fish, to the right. An actual device that one will be able to obtain in stores will allow you to change the angle of view.
This work is presented by
Douglas Moreman, who also presents:
Dolphin Inspired Sonar
How Does a Streaming Fish-Finder Work?
Consider the commercially available 2D, streaming fish-finder that made the top-most picture above.
Imagine that the 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 just 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. The on-screen distance downward to a colored pixel relates to the distance from sonar device to reflector, which usually is slightly greater than the depth of the reflector, or several reflectors at the same range. So the resulting image is partly an illusion -- each column of pixels combines echoes from everywhere in a cone.
When a fish enters, or leaves, the cone of the ping, its range to the pinger is greater than when that fish is more directly under the pinger - causing the fish to appear as an arc. The wider the angle-of-opening of the cone, the taller the arcs -- because the difference between the nearest and farthest ranges is greater. An arc can be short because the path of its fish through the cone of the ping was short -- not because that fish was small.

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 2D geometry suggests that a fish whose depth is in the lower one half of the axis of the cone is about 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). So, for examples, suppose D = 50 feet. Then if A = 20 degrees, the width is about 17 feet. And if A = 40, the width is about 36 feet.

In the video whose screen is shown 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 that loudness has to do mostly with the reflectivity of a fish's swim bladder.
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 more fish are missed. 3D streaming will largely correct this defect.
Below is a view of the full water column top to bottom at 50 feet:
The view above is from my simulator but imitates an existing 2D streaming fish-finder. The arcs are small because 1) the left-right distance of the image is large, showing more fish but compressing the arcs, and 2) the cone of insonification is narrow in the direction of the boat's motion.
3D streaming can take advantage of a cone-of-insonification whose cross-sections are elliptical.
Below is a Side View, similar to the one above but color-coded via an extra dimension of information. The body of fish is about the same as above but these fish are color-coded by left and right:
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.
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).
Next below is a Top View. Ellipses are shown at various depths on the cone of insonification.

A button on the fish-finder could allow a user to cycle through the various views.

Here is someone's illustration of the cone of insonification and how its width near the bottom allows fish to "hide" by being deeper than some insonified part of that bottom.
You can compare, below, 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. Here is a rear-view showing both a 20 degree cone and a 40 degree cone:
Rear View, also available to be available in the commercial product.
Fish cannot be "seen" if they are below the circular arc.

How Does the 3D Streamer Work?
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 each reporting of times-of-arrival of echoes. In the case of streaming, the sensor are in a straight line. There is some proprietary mathematical computation that overcomes problems inherent in deducing images from such an array. These are subjects of an application for a US patent. The work grew upon my earlier
United States Patent 7,379,384 Echo scope".

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.
This might make false impressions in some existing fish-finders? But be corrected for in a 3D streaming fish-finder.

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