Towed Body

The Towed Body operator is only suitable in specific circumstances. The operator is designed to be used with towed body data and should be the last operator in a virtual chain. If you are analyzing or exporting data, do so from this last variable. This minimizes range errors (see Notes). It is not advisable to use the Towed body operator workaround for heave compensation. Heave data for a platform may be applied with the Heave source setting. See also: About heave compensation.

This operator adjusts ping depths using the depths of a specified line or virtual line. It is useful for adjusting depths for the effects of a transducer mounted on a towed body, e.g. you can create or import a line that tracks the depth of the towed body and adjust the ping start and stop depths based on the depths of this line.

You select the line that will be used on the Towed body page of the Variable Properties dialog box.

Echoview accepts a single operand of the following data types as input:

Angular position
Boolean
Color
Complex angular position
Complex power dB
Complex Sv
Complex TS
Current velocity
Linear
Power dB
Pulse compressed complex angular position
Pulse compressed complex power dB
Pulse compressed complex Sv
Pulse compressed complex TS
Sv
TS
Unspecified dB

Notes:

This operator is only useful for downward facing transducers.
This operator may produce a variable with irregular start ranges across pings. A school detection will not work on such variables. Echoview Software recommends that you use a resample operator to resample the towed body virtual variable. This will pad the resampled data range with no data samples and result in regular start ranges across all pings.
If you plan on using the Motion correction (Dunford method) operator, it is recommended that you use the Towed body operator after the Motion correction (Dunford method) operator.
Refer to Virtual variable applications - Towed body correction.
See also: The Effect of No data samples on the Wideband Frequency Response graph page.
This operator is intended for visualization and region detection purposes. It modifies the range values of the echogram such that any subsequent range-based measurements or calculations will be incorrect. This affects downstream virtual variable calculations and analysis calculations that use range. For this reason we recommend that data treatment such as noise removal be performed prior to applying this operator.

Settings

The Towed Body Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:

Operands page

Towed Body page

Setting	Description
Using line	Select the line that represents the path of the towed body. The depth of this line at each ping will be added to the depth of all samples in that ping to create the virtual echogram.