Using the motion correction operator

It is recommended that the Motion correction (Dunford method) operator is applied immediately to a raw variable, prior to other operators, analysis or processing. The resulting virtual variable can then be processed and analyzed as normal.

To prepare your data for use with the motion correction operator:

Calibrate your raw variable

For the nominated raw variable:

Assess the calibration settings on the Calibration page of the Variable Properties dialog box.
If required, set values for calibration settings and the Major axis 3dB angle and the Minor axis 3dB angle in an ECS file.

Prepare roll data

Check if your fileset contains a roll variable. Echoview can derive roll data from some data formats.
When no roll data is available with your raw variable, you can add a *roll.csv file to a separate fileset.

Prepare pitch data

Check if your fileset contains a pitch variable. Echoview can derive pitch data from some data formats.
When no pitch data is available with your raw variable, you can add a relevant *pitch.csv file to a separate fileset.

To apply motion correction to an acoustic variable:

On the Dataflow window:

On the Shortcut menu, select New>Variable.
In Name, enter the name of your new variable.
In Select operator, select Motion correction (Dunford method).
Click OK.
On the Operands page, select a variable from the Operand 1 list.
Select a roll variable from the Operand 2 list.
Select a pitch variable from the Operand 3 list.
On the Calibration page, in the Inherit calibration settings from: section, select the variable you nominated as Operand 1.
Click OK.

Notes:

The correct use of the motion correction operator relies on using the sound speed of Operand 1 (for time and motion correction calculations). Hence it is important to successfully complete step 8 (above).
Dunford's algorithm is applicable for circular transducers where the Major axis 3dB angle and the Minor axis 3dB angle are identical. It is also applicable to those transducers whose main lobe (beam pattern) approximates to that of a circular transducer. The limits of this approximation are not explicit in Dunford's paper. For implementation, Echoview will accept 3dB angles that are within one degree of each other. The average of the angles is used. However, it is unknown if Echoview's one degree tolerance for the 3dB angles satisfies the approximation.
Echoview design constraints, relating to transducer geometry and the behavior of operators, require the Motion correction (Dunford method) operator to be used before the Towed body operator. A significant error in sample values will be encountered if these operators are used in the reverse order.