The first is a line plot of the return signal as a function of time for each shot. Since time can be related to distance through the speed of light, this is equivalent to a plot of the return energy as a function of depth for each laser pulse. At 30 pulses per second, this display produces 30 plots per second, which can be hard to follow. Therefore, we have another display that shows depth in the vertical axis, shot number in the horizontal axis, and encodes return power as a gray level. This is similar to the display in a conventional echo sounder.
Fish schools show up a regions of more return power.
We have the option to identify the surface in each shot and relate the vertical axis to actual depth. Another option is to estimate the background water return and subtract it from each shot to make fish schools easier to see. The photo on the left shows the optics package. This is the part that mounts over the port in the aircraft. A different mounting plate is made to fit each plane.