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:

- Sv pulse compressed wideband data
- TS pulse compressed wideband data
- Single targets detected on pulse compressed wideband data

To display the Wideband Frequency Response graph:

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

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.

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:

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

The selection/region is sub-sampled as follows:

- Depending on the size of the selection/region, 10 to 20 uniformly spaced pings in the
**Reference**variable are identified. Reference variable ping-times are used to find the closest matching ping-times in other selected graph variables. - Identified pings with contiguous samples within the selection or region, generally output one frequency response per ping and per variable. A single frequency response is the average of adjacent and overlapping calculation windows evaluated over the samples in the ping. Windows overlap by 50%. The calculation
**Window size**is restricted to a odd number of samples. Where the specified**Window size**is an even number of samples, the**Window size**is adjusted to the nearest odd sample number. No frequency response is displayed when the selection or region spans an even number of samples and the**Window size**is the same (vertical) size as the selection or region. - Identified pings with non-contiguous samples within a region may output a frequency response per set of contiguous samples.
- When a variable does not have the samples to fill the Window size, that calculation is considered no data.
- The range for TVG calculations, in power to Sv or power to TS calculations, is the range of the sample in the center of a calculation Window.

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

- The single target variable is automatically used as the Reference variable and all single target pings are used as reference pings. The TS pings closest to the reference pings are used for TS calculations. When a target ping-time is exactly between two TS ping-times, the left TS ping is used. Note that multiple single target pings may be matched to the same TS ping.
- The single target range is used to calculate the TVG in the power to TS equation.
- The single target range is used for the center of the frequency response calculation
**Window**. In the case where there are not enough samples to fill the Window, the Window is padded with no data. - One frequency response is output for each single target.
- The graph always applies Beam compensation. The validity of frequency response values is affected by the evaluation of frequency dependent calibration values and by the limitations of the beam compensation equation. For further information refer to Simrad LOBE used by Simrad EK80 pulse compressed data.

**Notes**:

- When frequency-dependent calibration settings are read from the data file, graph calculations use frequency-interpolated values. When frequency dependent calibration settings are absent, graph calculations use a nominal frequency.
- Specified variables in the
**Filter variable list**may have varying sampling thickness. In this case, the calculation Window may be different per specified variable. - Specified variables may contain only some of the ping-times that exist in the selection/region. When a Reference variable ping time or a single target ping time is outside the bounds of a variable in the
**Filter variable list**, the calculation interval is treated as no data. As a result, no response is displayed and the export outputs -9.9e+37. - The fast Fourier transform (FFT) calculations use a minimum of 1024 points, but the number of points may be greater.
- No data and thresholded data samples are handled as the value (0 + 0i). Thresholding introduces edge noise and abrupt starts and stops to the data. FFT calculations handle such data poorly and the frequency response may behave unexpectedly.
- Echoview Sv frequency response calculations use the TransmittedPulseLength and a (frequency adjusted) TwoWayBeamAngle.
- At the top and bottom of a ping, the sample calculation
**Window**may be clamped to the extent of the echogram. As a result, the actual**Window size**can be smaller than that specified under Graph or Export Properties. Under a smaller**Window size**, the FFT calculation is padded with samples of zero value and the autocorrelation is the same as for all other FFT calculation windows in the ping. - Wideband Frequency Response graph data may be exported.
- See also Wideband Frequency Response Properties: Window size notes.
- The Wideband single target detection operator and the Wideband Frequency Response graph are under active development.

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

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.

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

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

See also: Wideband Frequency Response export file format.

About graphs

About Linking Graphs

Relative Mean dB graph

About transmitted pulse: Chirp data and advanced signal processing