Calibrations are conducted to ensure that the echosounder and transducer are operating properly and to ensure system stability over time (i.e., among survey periods). Calibrations characterize system parameters relative to expected standard values. Calibrations are performed by the manufacturer and the user.
Echosounder calibrations conducted in most Great Lakes surveys use the standard-target method (Foote et al. 1987), which relates acoustical energy to an absolute standard. The standard-target method calibrates the overall acoustic system, which consists of the echosounder, transducer, and cable. The calibrations consist of two parts:
- on-axis sensitivity, and;
- beam pattern measurements
On-axis TS and sa measurements calibrate gain parameters; beam pattern measurements supply beam width and angle offset values. They are not independent.