Data page

The Data page of the Variable Properties dialog box is used to enter settings that affect most operations in Echoview including echogram display, integration, schools and fish track detection and data exports. See the Variable Properties flow diagram for details.

This page displays settings relevant to the type of variable as follows:

  1. Sections for all acoustic variables
    Sections for Sv or TS variables only

    Sections for single target variables only

    Sections for H-mode and V-mode variables only

    Sections for position variables

Sections for all acoustic variables

Minimum threshold

The Minimum threshold section of the Data page is used to set the lowest data value for data samples. All samples with a value below the minimum threshold are re-assigned a zero value.

Settings

Description

Apply

Select this check box to apply the entered threshold value to the variable.

Lock to color display minimum

Select this check box to lock the minimum threshold to the color display minimum setting on the Echogram Display page.  

Choose this option to match the echogram display colors to the thresholded data. Once locked, you only need to change the color display settings to change the thresholds.

Maximum threshold

The Maximum threshold section of the Data page is used to set the highest data value to be displayed on an echogram or included in analyses.

Settings

Description

Apply

Select this check box to apply the entered value to the variable.

Lock to color display maximum

Select this check box to lock the maximum threshold value to the color display maximum value controlled on the Echogram Display page.

Choose this option to match the echogram display colors to the thresholded data. Once locked, you only need to change the color display settings to change the thresholds.

Set thresholded values to

Choose a value that will be applied to all samples above the maximum threshold value.

Note: This setting will affect the calculation of mean values. If the maximum threshold is set to No data the thresholded values are excluded from mean calculations. If the maximum threshold is set to the Threshold limit, all samples that are above the maximum threshold are converted to the threshold limit value and included in mean calculations.

Note: Threshold values can only be altered on the Data page if the data threshold is not locked to the color display and the Apply check box is checked.

Sections for Sv or TS variables only

Time-varied threshold

The Time-varied threshold section of the Data page is only available for Sv or TS variables.

Setting

Description

Apply

Select this check box to apply a TVT in Sv or TS at 1m (dB).

Note: The keyboard shortcuts, Ctrl+F11 and Ctrl+F12, will adjust this value when used in an echogram window. Whilst using the shortcuts the value of TVT is displayed in Panel 1 of the Echoview status bar.

See also

Time-varied threshold

Minimum TS threshold

The Minimum TS threshold section of the Data page is only available for Sv variables.

Setting

Description

Apply

Applies a TS threshold to the Sv echogram.

TS Threshold (dB)

Enter a value for the TS threshold (dB).

Refer to the Minimum TS threshold algorithm page for more details.

Calibration difference offset

A transducer related value required by the Converted Sv equation and is used when CSv and/or CTS are unavailable.

Refer to the Minimum TS threshold algorithm page for more details.

Sections for single targets

Single target settings

Settings for Single target detection, Single target detections raw, and Single target manipulation variables:

Settings

Description

Upper detection range

These settings are available to raw single target variables only. Enter the range in meters.

The settings change the (range) display limits of the raw single target variable.

Lower detection range

Thickness source

Allows you to select a Thickness source from a list. Together with the Thickness factor, this setting controls the display thickness of single target detections on an echogram.

Thickness source

Notes

Transmitted pulse length

Transmitted pulse length is a single beam property.

Pulse length at PLDL

Pulse length at 6 dB

Pulse length at 12 dB

Pulse length at 18 dB

These are single target pulse properties.

Under single target detection - wideband variables, this type of Thickness source is based on PulseCompressedEffectivePulseLength.

Under single target detection variables, this type of Thickness source is context sensitive. Wideband operands dictate that the Thickness source is based on the EffectivePulseLength.

Target thickness Target thickness is a multibeam target detection property,
Target range extent Target range extent is a multibeam target detection property.

Effective pulse length

Effective pulse length is single beam wideband property.

Under single target detection - wideband variables, this type of Thickness source is based on PulseCompressedEffectivePulseLength.

Under single target detection variables, the Thickness source is context sensitive. Wideband operands dictate that the Thickness source is based on the EffectivePulseLength.

 

Thickness factor

Controls the display thickness of single target detections on an echogram. Use in conjunction with the Thickness source. See Configuring single target display thickness for more information.

See also:

Filter Targets page

Sections for H-mode and V-mode variables only

Target-locking

A variable can be made target-locked by specifying its partner under Target-locked variable. If this is an H-mode variable, a list of V-mode variables will be available for selection. If this is a V-mode variable, a list of H-mode variables will be available for selection.

You must select a Target-locked variable here if you intend to detect schools on this variable using the target- locked scanning algorithm or use it as an Analysis variable when integrating from a scene using the Target-locked scanning algorithm (see the Analysis page of the Scene properties dialog box)

Sections for position variables only

GPS Processing

The following settings are only available for position variables and provide basic filtering (quality control) for GPS fixes. Echoview uses the settings to determine whether the status of GPS fixes is good or bad (see Processing GPS data for more information).

Hint: You may have to experiment to find optimal settings. To view the results achieved using different settings: ensure Show good fixes and Show bad fixes are selected on the Cruisetrack Display page of the Variable Properties dialog box; arrange the cruise track window and Variable Properties dialog box so both windows are visible; enter settings; then click Apply and observe the status assigned to the GPS fixes and the resulting cruise track. If you have optimized the settings but are not satisfied that the cruise track accurately represents the path followed by the logging vessel, you can create a smoothed cruise track using the Kalman GPS smoothing filter

Settings

Description

Hemisphere

Used to force the logged GPS latitudes to be treated as northern or southern hemisphere if required. The default setting, "As recorded", is normally used unless there is a problem with the GPS data.

Maximum apparent speed

Enter a speed, in knots, of the logging vessel's maximum speed through the water.

A GPS fix will be marked bad if the calculated speed traveled between the previous good fix and the current fix (calculated from the difference in position and time) is faster than the maximum speed entered. Such fixes are discarded as errors on the basis that the vessel could not have moved this quickly.

Maximum acceptable gap

Enter a value, in seconds, for the maximum time interval allowed between two good GPS fixes, for the positions between the fixes to be given a good status. If the gap between two fixes exceeds this time, the ping positions between these two fixes will be given a status of uncertain.

This setting is included to flag occasions when there are gaps in the stream of GPS fixes. Echoview assumes the vessel traveled in a straight line between two fixes. If those fixes are too far apart, this assumption becomes unreliable. The uncertain position status does not affect calculations made with the ping positions, but is displayed on the echogram and exported bathymetric data can be filtered on the basis of this position status.

Minimum acceptable gap

Enter a value, in seconds, for the minimum time interval between good GPS fixes. If the gap between two fixes is less than this time, the second GPS fix will be given a bad status.

This setting is used to remove random variation in position from GPS fixes where it is large compared to the actual change in ship's position between fixes.

Hint: You may wish to choose an initial value based on the known error radius of the GPS and the known speed of the vessel.

Example:   Assume the error radius of a given GPS is 50 m (your system may have a higher or lower error radius) and the ship is moving in straight line at a two meters per second. Based on this data, it is possible that fixes received within 25 seconds of the previous good fix could fall within the error radius of the previous fix. This can result in a cruise track with frequent changes in direction (it may even loop back on itself) and in which the along track distance is longer than the actual distance traveled by the vessel. In this example a Minimum acceptable gap of 25 seconds would remove all fixes that could fall within the error radius of the previous good fix.

Processing method

Select which method Echoview will use to determine the start of your cruise track.

Method 1 uses the first good GPS fix as the start of the cruise track. This method can result in the cruise track not being displayed if the first GPS fix in your data set is a bad fix.

Method 2 groups the good GPS fixes and displays a cruise track starting with the first good GPS fix. Use this method when your first GPS fix is bad.

See also

Variable Properties dialog box
About Variables