About entering calibration settings

There are two different processes of calibration referred to in Echoview documentation: Calibration of the echosounder (usually prior to data collection); and entering calibration settings (after loading into Echoview).

The calibration of an echosounder is the process of experimentally determining the value of some parameters that are required in obtaining a true quantitative measure of backscatter (Sv or TS) from the voltage (or power) signal output by the echosounder. An echosounder is said to be calibrated when the values of these parameters have been determined. Which parameters must be obtained by this procedure depends on the type of instrument, but can include parameters such as transducer gain, beam width, phase offsets etc. For further reading on this subject: Foote, et. al. (1987) and Honkalehto and Ryan (2003) describe techniques to calibrate split and dual beam echosounders, and Foote, et. al. (2005) describe the protocols developed to calibrate multibeam echosounders.

There are other parameters required in the calculation of backscatter, which are not a result of the calibration procedure but are either known or can be measured. For example, the frequency of an echosounder is a known parameter, whereas the sound speed must be measured for it to be known accurately.

In Echoview some of these parameters may be needed to calculate a backscatter value (Sv or TS), depending on the data type. The values for these calibration parameters appear on the Calibration pages of the Variable Properties dialog box for each individual acoustic variable. Echoview must know the correct values of all the relevant parameters to be able to calculate backscatter values correctly. The parameters on the calibration pages are referred to as 'calibration settings', although not all of them are obtained as a result of the echosounder calibration procedure.

'Entering calibration settings in Echoview' must not be confused with 'calibrating an echosounder'. The latter is typically a process performed on a boat using a calibration sphere, whereas the former is the specification of values for calibration settings. See About calibration settings.

Some or all of the calibration settings determined when an echosounder is calibrated may be recorded in the data files Echoview reads. Values may not be reliably available in data files and there is also the possibility that values are not consistent for all files within a fileset. When (required) values are absent from the data files, Echoview uses default values. As Echoview only permits one value per setting per variable for the whole fileset, it is up to you to determine which value to use if there is more than one value present in the data files the fileset contains.

Important!

It is very important to ensure that you check your calibration settings and verify they are correct. To fully understand how calibrated data fits into Echoview's workflow, view the calibrated data workflow diagram.

Note: Changes in calibration settings used for range calculations may shift ping data in the depth dimension but will not automatically adjust the position of regions and lines. You should review any existing regions and lines to ensure they are still valid. For more information refer to Range calculation effects on regions and lines.

See also

About calibration settings
How to enter calibration settings

About transducer geometry

Using Echoview in the calibration process