Measurement and removal of echo integration noise

Pushing scientific echo sounders to the limit involves the consideration of “noise”, which is inherently frequency dependent and which also depends on bottom depth. Here, noise is quantified by measurement with a standard echo sounder, the SIMRAD EK500, at 18, 38, 120 and 200 kHz. The use of empirical relationships of noise as a function of range to reduce echo integration is described in general, and illustrated in particular, for data collected on the stock of Norwegian spring spawning herring (Clupea harengus) when wintering in the Vestfjord system.