Several context-sensitive pages in the Variable Properties dialog box are displayed for virtual variables. The pages that are displayed depend on the operator that was used to create the virtual variables.
One or more of the following virtual variable pages will be present if Multibeam operators have been used:
Angle Select page
Beam Convolution 3x3 page
Beam Scan page
Beam Select page
Beam Subset page
Bottom Echo Bitmap page
Bottom Echo Bitmap H-mode - Furuno page
Double Threshold page
FIR Filter page
IIR Filter page
Mean of N Previous Pings page
Median of N Pings page
Minimum of N Pings page
Multibeam Target Detection page
Sample statistic subtract page
Target page
Target Conversion page
The Angle Select page is displayed on the Variable Properties dialog box if the Angle select operator has been applied to a multibeam echogram to create the selected virtual variable.
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Setting |
Description |
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Angle (degrees) |
Enter an angle an angle measured from the vertical (i.e. 0 degrees for vertical, 90 degrees for horizontal, positive in the direction of increasing beam number, negative in the direction of decreasing beam number). The selected angle will be used to create the variable which can then be displayed as a two dimensional echogram. |
The 3x3 Convolution page is displayed on the Variable Properties dialog box if the Beam convolution 3x3 operator has been applied to create the selected virtual variable.
It is used to specify the 9 values of the 3x3 convolution matrix.
For details on how convolutions are applied in Echoview see Convolution algorithms.
The Beam Scan page is displayed in the Variable Properties dialog box if the Beam scan operator has been applied to create the selected virtual variable.
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Setting |
Description |
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Window size |
The Window size setting determines the number (n) of previous pings from which data is drawn if available. |
The Beam Select page is displayed on the Variable Properties dialog box if the Beam select operator has been applied to a multibeam echogram to create the selected virtual variable. See Beam selection for more information.
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Setting |
Description |
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Beam number |
Enter a beam number from 0 to 127 for *.bmf data files, or from 0 to 79 for *.raw data files. The selected beam will be used to create the variable which can then be displayed as a two dimensional echogram. |
The Beam Subset page is displayed on the Variable Properties dialog box if the Beam subset operator has been applied to a multibeam echogram to create the selected virtual variable.
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Setting |
Description |
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Beam Ranges |
Enter a beam range to be retained or discarded. The selected beam range will be used to create a variable which can then be displayed as a two dimensional echogram. |
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Beam Retention |
Choose whether to retain or discard the specified beam range. |
The Bottom Echo Bitmap page is displayed on the Variable Properties dialog box if the Bottom echo bitmap operator has been applied to a multibeam echogram to create the selected virtual variable.
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Setting |
Description |
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Surface to use a bottom |
Choose a surface which defines the bottom. The surface must intersect with the echogram data for it to be of any use, and should ideally be:
|
|
Threshold (in units of operand) |
Specify the threshold value above which signal is considered to be bottom and below which it is considered not to be bottom. |
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Set below bottom samples to false |
Choose whether to set all samples below the chosen surface to false, or only those which are above the chosen threshold. Samples above the chosen surface will be set to false if they are above the chosen threshold |
Warning: When the Surface to use a bottom intersects a no data value and the Set below bottom samples to false is selected a "true" value is returned. This may be contrary to your expectations of this operator. In this situation, Echoview support advises you to create a 3D bottom surface that does not intersect with no data samples.
See Bottom echo bitmap algorithm for further details on how the resulting bitmap is created.
The Bottom Echo Bitmap H-mode - Furuno page is displayed on the Variable Properties dialog box if the Bottom echo bitmap H-mode - Furuno operator has been applied to a multibeam echogram to create the selected virtual variable.
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Setting |
Description |
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Start depth |
Specify the minimum depth at which you expect to find the bottom. The operator will not examine any data above this depth (these samples will remain true) and only examine samples below this depth. |
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Stop depth |
Specify the minimum depth at which you expect to find the bottom. The operator will not examine any data above this depth (these samples will remain true) and only examine samples below this depth. |
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Threshold (in units of operand) |
Specify the threshold value above which signal is considered to be bottom and below which it is considered not to be bottom. |
See Bottom echo bitmap H-mode algorithm for further details on how the resulting bitmap is created.
The Double Threshold page is displayed on the Variable Properties dialog box if the Double threshold operator has been applied to create the selected virtual variable.
The following settings are used in the double threshold algorithm.
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Settings |
Description |
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Lower threshold |
Specifies the lowest data value for the criteria applied in the double threshold algorithm. |
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Upper threshold |
Specifies the highest data value for the criteria applied in the double threshold algorithm. |
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Influence radius |
Specifies the radius for the area of influence around particular samples. The Influence radius is used for the criteria applied in the double threshold algorithm. |
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Set thresholded values to |
Specifies a single value that is applied to all samples that need to be changed, when the double threshold algorithm is applied. |
Note: The performance of this operator degrades linearly with increasing difference between the two thresholds and in the square (second order) with Influence radius. This operator completes within 30 seconds on common computer configurations available in August 2004 with a difference in thresholds of 100 units, and Influence radius of 0.3m. It was found to take of the order of 10 minutes with a difference in thresholds of 300 and an Influence radius of 1.00.
The FIR (Finite Impulse Response page) is displayed on the Variable Properties dialog box if the FIR filter has been applied to create the selected virtual variable.
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Setting |
Description |
|
Coefficient |
Enter the coefficient to be used to alter signal content. |
The IIR (Infinite Impulse Response page) is displayed on the Variable Properties dialog box if the IIR filter has been applied to create the selected virtual variable.
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Setting |
Description |
|
Coefficient |
Enter the coefficient to be used to alter signal content. |
The Mean of N previous pings page is displayed in the Variable Properties dialog box if the Mean of n previous pings operator has been applied to create the selected virtual variable.
|
Setting |
Description |
|
Window size |
The Window size setting determines the number (n) of previous pings over which the mean value of samples is calculated. For example if you select 10, then the data on ping i will be the mean of pings i-10 to ping i-1 in the operand. |
The Median of N pings page is displayed on the Variable Properties dialog box if the Median of N pings operator has been applied to create the selected virtual variable.
|
Setting |
Description |
|
Window size |
The Window size setting determines the number (n) of pings over which the median value of samples is calculated. For example if you select 10, then the data on ping i will be the median of pings i-9 to ping i in the operand. |
The Minimum of N pings page is displayed on the Variable Properties dialog box if the Minimum of N pings operator has been applied to create the selected virtual variable.
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Setting |
Description |
|
Window size |
The Window size setting determines the number (n) of pings over which the minimum value of samples is calculated. For example if you select 10, then the data on ping i will be the minimum of pings i-9 to ping i in the operand. |
The Multibeam target detection page is displayed on the Variable Properties dialog box if the Multibeam target detection operator has been applied to create the selected virtual variable. The Target page is also displayed for the Multibeam target detection operator. The Target page is used to specify target properties to calculate when targets have been identified.
The settings on the Multibeam Target Detection page are used to specify target detection and target linking criteria and eliminate bottom data from the target detection process. The settings are applied to each multibeam ping (a 2-dimensional echogram).
Under Bottom elimination choose one of the options:
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Settings |
Description |
|
None |
Choose this option if you do not want to eliminate bottom data or there is no bottom data in the echogram. |
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Specified maximum range |
Choose this option if you want to exclude data outside a specific range. Enter the range in meters. |
Under Target Linking the settings for a target linking algorithm are available:
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Settings |
Description |
|
Link target clusters |
Select Link target clusters when you want to apply seed-satellite linking to detected targets. For more information refer to the Target linking algorithm. |
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Seed threshold |
Specifies the seed classification threshold (cm2). |
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Satellite threshold |
Specifies the satellite classification threshold (cm2). |
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Link distance |
Specifies the linking distance for classified targets. This value is used to determine candidate targets to link to a target of interest. The distance between the target of interest and the candidate must be less than the Link distance. For more information refer to Target linking algorithm - Linking distance. |
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Link satellite clusters |
Select Link satellite clusters when you want to apply satellite-satellite linking to detected targets. |
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Retain unlinked satellites |
Select Retain unlinked satellites when you want to retain unlinked satellites as detected targets. |
When you click Advanced the Target Detection settings are displayed:
|
Settings |
Description |
|
Maximum horizontal linking distance (beams) |
Maximum horizontal distance (in beams) allowed between two beams being linked to form a detected target. Note: The two linking distances form the vertical and horizontal semi-axes of an ellipse. The ellipse is, in effect, moved around the boundary of a target candidate. If any part of any other target candidate falls within the ellipse, a link is created between the candidates. |
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Maximum vertical linking distance (samples) |
Maximum vertical distance (in samples) allowed between two samples being linked to form a target. |
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Minimum candidate length (cm) |
Minimum length allowed for a target candidate. |
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Minimum candidate height (cm) |
Minimum height allowed for a target candidate. |
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Minimum target length (cm) |
After linking is completed, targets shorter than this length will not be included in detections. |
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Minimum target height (cm) |
After linking is completed, targets shorter than this height will not be included in detections. |
Notes:
Warning: The target detection algorithm uses a nominal value to represent the parallel and non-diverging width of a typical beam in the sector plot. This nominal value is not a 3dB beam angle. These advanced settings have been provided for experimental purposes only and changes to these settings may not produce the expected results.
The Sample Statistic Subtract page is displayed on the Variable Properties dialog box if the Sample statistic subtract operator has been applied to create the selected virtual variable. This operator subtracts the average on one variable from another variable in either the linear or dB domain as specified here.
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Setting |
Description |
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Subtraction domain |
Specifies the domain for the subtraction:
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|
Enter the factor for percentage range from the mean for data inclusion. For more information refer to the Sample statistic subtract algorithm. |
The Target page and the Multibeam Target Detection page are displayed on the Variable Properties dialog box if the Multibeam target detection operator has been applied to create the selected virtual variable.
Under Multibeam target properties the following calculations are available:
|
Setting |
Description |
|
Multibeam target properties |
Select or clear the target properties that you want the Multibeam target detection algorithm to calculate. Available target properties are: Target area Notes:
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Under Target strength source the following settings are available:
|
Settings |
Description |
|
Mean Sv |
Choose this option to set the detected target TS value to the mean Sv of the samples in the target. |
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Maximum Sv |
Choose this option the set the detected target TS value to the maximum Sv of the samples in the target. |
The Target conversion page is displayed on the Variable Properties dialog box if the Target conversion operator has been applied to create the selected virtual variable.
|
Setting |
Description |
|
Filter targets |
Select the check box to apply a filter to targets in the operand variable. If enabled targets that have a similar range, up to the valued entered under Minimum range difference, will be excluded. Note: This option is useful for improving fish tracking on the resulting single target variable. Without this enabled, most fish tracks created will be invalid, as for a particular ping the fish track may include multiple targets. See About fish track detection. |
| Minimum range difference | Enter a Minimum range difference in meters. |
Variable Properties dialog box
About virtual variables
Operators