Wideband Frequency Response graph

The Wideband Frequency Response graph displays the frequency response of a selection or region on an active echogram. The graph can be linked to selections or regions. The graph can be set up to display the frequency response for matching pings in specified multiple variables.

Note: Be aware that applied minimum or maximum thresholds, no-data, bad data and empty water values in graph input variables will be result in a degraded wideband frequency response. The same warning is true for any upstream variables of operands used to detect single targets.

The frequency response may be displayed for:

To display the Wideband Frequency Response graph:

  1. On the View menu, select Graph, Wideband Frequency Response.
  2. On the graph, use right-click Graph Properties.
  3. Configure the graph.
  4. Make a selection or click a region on a pulse compressed wideband echogram.

Graph calculations

Echoview uses pulse compressed complex data to calculate the frequency response of selections or regions on echograms. The Fourier calculations are time consuming and, to maximize performance, the frequency response is calculated by processing contiguous samples in selected pings within the selection or region. Where a single target mask variable is specified, the frequency response centered around each single target within the selection or region is evaluated. Pings included in graph calculations have times that lie within the allowed time separation from reference variable pings.

Bad data samples and samples and targets within exclusion lines are not included in graph calculations.

Graph assumptions

The graph displays an error or the Wideband Frequency Response export is aborted (and a message is displayed) when any graph assumption fails.

The Wideband Frequency Response graph requires that:

  1. Variables must exist and be available.
  2. Variables have the correct data type.
  3. All pings in the selection/region have the same calibration.
  4. Reference variables are the correct data type for the selected graph configuration.
    1. TS for TS variable configuration and Single target for (TS variable, single target variable) configuration.
    2. Sv for Sv variable configuration.

Sv variable and TS variable configurations

The selection/region is sub-sampled as follows:

TS variable, single target variable configuration

Within the selection/region, single target pings is processed as follows:

Notes:

Graph linking

Initially, Graph menu Linking is set to Selection and Region. This enables the graph to update as the selection changes.

Graph Properties

Graph Y axis, variables, (calculation) window size, graph averaging and allowed time separtion from reference pings may be specified using the Wideband Frequency Response Graph Properties dialog box.

Graph export

To export frequency response data from a Wideband Frequency Response graph:

  1. Click on the Wideband Frequency Response graph.
  2. On the Graph menu select Export Data.
  3. Enter a Filename and click Save.

See also: Wideband Frequency Response export file format.

See also

About graphs
About Linking Graphs
Relative Mean dB graph
About transmitted pulse: Chirp data and advanced signal processing