Ping interval determines the rate at which acoustic energy is sent into the water column. In choosing a ping interval, the goal is to select the fastest rate that will not cause shadow bottoms in the data (Fig. 18). To avoid a shadow bottom originating from the “third” bottom return, the minimum ping interval (i, sec) is:
BD is the expected maximum water column depth (m), and;
c is the speed of sound in water (m•s-1)
For BD=100 m and c=1450 m•s-1,
The minimum ping interval is 0.4 s, or 2.5 pings•s-1.
Ping interval is a collection setting and cannot be changed during analysis, although the data can be “resampled” to a slower (but not faster) rate in post-processing software. Ping rates used in the Great Lakes range from 0.25 to 1 ping s-1. The acquisition software often warns the user of ping rates that are too high, but some may adjust this value without warning (e.g., Simrad EK60).