Calibration Assistant dialog box
The Calibration Assistant dialog box is used to calculate specific calibration values that need to be entered into an ECS file in order to obtain calibrated acoustic data. Input values and single target calibration sphere data are used in calculations. The Calibration Assistant dialog box is available for a region or selection on a single targets echogram. Echoview allows the configuration of Calibration Assistant settings per variable and supports the COM export of Calibration Assistant results. In-dialog-box graphs of Targets, Wideband Output format, Angle offset, 3dB beam angle and RMS Error data enable quick calibration sensitivity analyses. The Calibration Assistant responds to real time data for echograms and selections under live viewing. Calibration Assistant data and outputs results may also be exported.
To display the Calibration Assistant dialog box, on a single targets echogram:
- Select a region or make a selection.
- On the region or selection, right-click and select Calibration Assistant (Region)... or Calibration Assistant (Selection)...
- - OR -
- Display the single targets echogram.
- On the Echogram menu select Calibration Assistant...
Notes:
- Calibration Assistant calculations only consider the data associated with the region, selection or single target echogram that initiated the display of the Calibration Assistant dialog box. The Assistant takes calibration values from the first ping of the region or selection. If a region or selection starts before the ping data and overlaps the ping data, calibration values are provided by the first ping of the ping data.
Calibration Assistant settings:
Dialog box controls
Click Save Report... to save Calibration Assistant settings and results to a file.
Click Calculate to calculate new output values.
Click Close to save changes and close the Calibration Assistant dialog box.
Click Help to open the Calibration Assistant dialog box page.
The Messages section displays diagnostic messages when calculations can't be completed.
Variable and Selection / Region
Variable name displays the single target variable used for calculations. The Calibration Assistant settings are stored under the Variable name.
Region / Selection displays the Region name used for calculations, or indicates that the Echogram is used for calculations instead.
Note that transects (if present) are ignored by the Calibration Assistant.
Input tabs
Enter input data for calculations under the Required Settings, Sphere Settings and the Two Way Beam Angle tabs.
View Target statistics and target graphs on the Target Summary tab.
Enter metadata and other data under the Notes tab.
Required Settings
Values displayed under Required Settings are read from the echosounder data file that underlie the single targets data.
Narrowband / Wideband
Selects the data type for Sv and TS offset/correction, angle and RMS Error calculations.
Narrowband (CW) is for single frequency data and numeric output.
Wideband (FM) is for wideband (refer to calibrating a wideband echosounder) frequency modulated data and graphical/tabular output.
- Frequency step for results (kHz) specifies the frequency steps that affect the Target summary, wideband Sphere Data graph and the wideband Output graphs. Use the list or enter a value. The Calibration Assistant rounds to 1 decimal place.
- Sv calibration is not available under Wideband (FM).
Measured Data
Sv variable
Use the Sv Variable list to specify the Sv variable to use with Narrowband Calibration Assistant calculations. Sv calibration is not available under Wideband (FM)
Sv samples that contribute to a single target are determined by the single target range, the nominal Target Peak range and the type of single target pulse length. See also Integrate samples using and On-axis single target samples.
Notes:
- When a selected Sv variable becomes unavailable, None is displayed.
- A restriction is that the Sv variable has one ping per detected target in the region or selection being analyzed on the single target variable.
Integrate Sv samples using
Use the Integrate samples using list to specify the type of single target pulse length for Sv calibration. The selection is used to define the integration window - the Sv samples that are used to calculate the measured Sv of a single target. The integration window uses a SoundSpeedProfile when it is available.
List options include:
- Transmitted pulse length
- Target length at PLDL
- Target length at 6dB
- Target length at 12dB
- Target length at 18dB
Transmitted pulse length is the default option and ideal in most situations. The target length-based options may be useful if the target is not centered on the peak, or if a longer integration window is desired. Note that a longer integration window may be more susceptible to noise, and should be used with caution.
TS variable (wideband only)
Use the list to specify a pulse compressed wideband variable for Wideband calculations.
Note: The TS variable is used to calculate the TS frequency response of the targets on the single targets echogram. Ideally, the TS variable is the one used for the single target detection.
On-Axis Definition
Maximum limit for target to be considered on-axis.
TS and Sv calibration are only evaluated for on-axis measurements. In the field, it is difficult to position a calibration sphere exactly on the beam axis (0, 0). The choice of On-Axis Definition allows the identification of measurements that are considered near enough to the beam axis. On-axis data ideally have angles close to (0, 0) and TS values similar to the maximum TS (where the transducer gain is the highest and the beam compensation close to zero).
Off-axis angle (°)
Single target off-axis angle values less than Off-axis angle are defined as on-axis. The smaller the single target beam axis angles, the closer the target is to the beam axis (0, 0). The Off-axis angle option requires angular position data. See also Target Summary tab.
Beam compensation (dB)
The Beam compensation (dB) value for On-Axis Definition only operates with the input target data. A target is on-axis when (TS_comp - TS_uncomp) < Beam compensation (dB).
TS_comp is the compensated TS of the target.
TS_uncomp is the uncompensated TS of the target. TS_comp is calculated using the uncompensated TS of the target, single target angles and a Beam compensation model (that is usually specified under the single target detection variable).
Drop in TS from maximum value (dB)
The Drop in TS from maximum value specifies the acceptable deviation of single target TS from the Maximum TS. The TS maximum value (dB) is the peak uncompensated TS of the single targets in the region, selection or echogram.
See also: The Off-axis angle equation, an example Off-axis angle plot of calibration sphere data and the RMS Error associated with Angle Offsets.
Beam Compensation
Use the Model list to specify a Beam compensation model to use for Calibration Assistant calculations on On-Axis Definition filtered targets. Minor-axis and major-axis beam compensation graphs may be useful in analyzing the suitability of calibration values with respect to beam compensation. See also: Calibrating an echosounder: Angle Offsets and 3dB beam angles.
Available Models include:
Sphere Settings
Sphere Data
Model
Displays sphere details and a TS frequency response graph. Click Edit... to specify sphere TS Distribution data and frequency response Exclusion Zones on the Calibration Sphere Settings dialog box.
Additional calibration sphere information can be entered under the Notes tab.
Note: It can be useful to compare the Sphere Data Model TS frequency response graph to the Wideband frequency response graph of measured calibration sphere data.
Target Summary
The Target Summary tab displays statistics and selected graphs for the targets in the Variable/Selection/Region. See also About beam geometry, Beam compensation graph for on-axis calibration sphere data.
- Under Narrowband (CW), target statistics are calculated at the nominal frequency specified by Frequency on the Calibration page of the Variable Properties dialog box.
- Under Wideband (FM), target statistics consider a range of frequencies specified by:
- FrequencyStart and FrequencyStop on the Calibration page of the Variable Properties dialog box, and describes the bandwidth of the transducer
- Frequency step for results (kHz) that describes the frequency step over the bandwidth
A Mean TS is evaluated in the linear domain for the set of single targets and then expressed in dB.
A Mean angle is evaluated for the angles of the set of single targets.
A Mean range is evaluated for the ranges of the set of single targets.
A Minimum value is evaluated as the minimum for the values of the set of single targets.
A Maximum value is evaluated as the maximum for the values of the set of single targets.
A Standard deviation value is
Where:
s is the corrected sample standard deviation. In the case of Uncompensated TS, the estimate is a relative measure of how likely single target values differ from the mean TS. The expression is evaluated wholly in the dB domain.
n is the sample size displayed in Count, and is set in the Target Selection field.
xj is the value of the jth target in the sample.
is the mean value of the targets in the sample.
| Statistic | Description |
| Count | Number of single targets or on-axis single targets in the region, selection or echogram. |
| Uncompensated TS | The uncompensated TS (dB) of the single targets or on-axis single targets in the region, selection or echogram. |
| Major-axis angle | Single target major-axis angle (°) or on-axis major-axis angle in the region, selection or echogram. |
| Minor-axis angle | Single target minor-axis angle (°) or on-axis minor-axis angle in the region, selection or echogram. |
| Range | Single target range (m). |
Target Selection
All targets uses every target in the region, selection or echogram.
On-axis targets uses targets identified under On-Axis Definition.
Display Data
Pre-calibration displays uncalibrated target data.
Post-calibration displays calibrated target data.
Graph Type
Graph type allows you to select a display graph. Displayed targets are displayed using their target color from the underlying single target variable. The last target in the echogram is represented by a plus sign, this can be useful while live viewing.
The graph's color legend is linked to the single target variable color scheme. On the color legend, right-click and use the menu to configure the graph and color legend. Note, any changes to the color scale affects the single target variable.
Move the mouse pointer over a target and target details are shown in a tooltip. On Scatter graphs, left-click the target to Synchronize to Point with open echogram windows; Echoview centers the window on the target position.
See also Calibrating an echosounder: Angle Offsets and 3dB beam angles.
Select the graph:
- Minor vs Major-axis
- Scatter: The graph is based on the Single target angles graph, however, the point color is based on the uncompensated TS.
- Contour: The graph is based on the Single target angles graph. Contours and fill color represent target uncompensated TS and follow the beam pattern of the transducer. Contour fill colors are based on the target color scheme. Contour calculations are based on a 0.3 degree grid in X and Y. The TS is a weighted average with respect to the distance between targets and the center of the grid cell. Demer et al (ICES CRR No. 326, Figure 2.9, 2015) observe for a circularly-symmetric split beam transducer "... Indications of a good quality calibration are: uniform coverage of the sphere-TS measurements (+), and smooth, circular, and concentric contours...".
- Scatter + Contour1: This graph displays the data points of the Scatter graph overlayed on the Contour graph. This graph can show where target data is sparse.
- Scatter + Contour2: The graph is similar to the graph for Scatter + Contour1, however, the contour fill colors are not displayed and the contour line colors are based on the target color scheme.
- TS vs Off-axis: The graph is based on the Off-axis beam compensation graph. Values for uncompensated and compensated TS are displayed.
- TS vs Major-axis: The graph is based on the Major-axis beam compensation graph. Values for uncompensated and compensated TS are displayed.
- TS vs Minor-axis: The graph is based on the Minor-axis beam compensation graph. Values for uncompensated and compensated TS are displayed.
Two Way Beam Angle
Two Way Beam Angle Correction
The TwoWayBeamAngleCorrected calculation requires values for SoundSpeed and TwoWayBeamAngle. The value for TwoWayBeamAngleCorrected is used in Sv correction calculations.
| Algorithm: (drop-down list) |
Description |
Manual |
Manual allows for the entry of a value for Two way beam angle (dB re 1sr). |
Sound speed corrected |
Sound speed corrected allows the entry of a value for Manufacturer Two way beam angle (dB re 1sr). This value may appear on the Transducer's manufacturer data sheet. The Corrected Two way beam angle calculation requires two sound speeds which can be specified under the selection Sound speed algorithm: Manual (in the Sound Speed Calculation section). A Corrected Two way beam angle value is displayed when you click Calculate. |
Input data |
Input data reads and displays the Two way beam angle (dB re 1sr) value from the data file. |
Sound Speed Calculation
SoundSpeed is a parameter for calibration sphere TwoWayBeamAngle calculations. This section allows you to enter environmental values for Sound Speed calculations.
| Variable | Description |
| Sound speed algorithm | Select a SoundSpeed equation method from the Sound speed algorithm list:
The sound speed algorithms are the same as those offered by the Sonar calculator. |
| Temperature | Temperature (degrees Celsius) of the water in which the echosounder data was recorded. May be used when a SoundSpeed algorithm is selected. |
| Salinity | Salinity (ppt) of the water in which the echosounder data was recorded. May be used when a SoundSpeed algorithm is selected. |
| Depth | Depth (m) of the water in which the echosounder data was recorded. |
| Pressure | Pressure (kPa) of the water in which the echosounder data was recorded. |
| Sound speed | Entered SoundSpeed (m/s) when Sound speed algorithm: Manual is selected. - OR - Calculated SoundSpeed (m/s) when a Sound speed algorithm other than Manual is selected. |
Notes
The Notes tab provides a place to record calibration-related notes such the type of and variations to calibration processes.
Outputs
The Calibration Assistant outputs the following:
The output type must be pre-specified using the Output format list before Calculate is used. The Narrowband / Wideband selection affects the display of and resolution of output values.
In the graph legends
Current represents the calibration values that Echoview has read from the data file or ECS file. These are values used in calculating TS and Sv from received power measurements in your data file(s). The TS values shown on the Target Summary tab use these calibration values.
New represents new calibration values evaluated with respect to data entered under Required Settings, Sphere Settings and Two Way Beam Angle. Such values would produce TS, Sv and position measurements that are theoretically expected for a calibration sphere on the beam axis.
TS & Sv Offsets / Gain & Sa Correction
Use the Output Format list to specify the required calibration values. Narrowband (CW) outputs onscreen tabulated values. Wideband (FM) outputs onscreen graphed values.
- Generic specifies generic TS offset and Sv offset values that are added to uncalibrated TS and Sv data respectively.
- Simrad Specific specifies TransducerGain and SaCorrectionFactor values that are used in Simrad Ex60 and EK80 Power to TS and Sv equations.
These values are used to modify a calibration sphere measurement to match an expected theoretical TS or Sv value.
Note: Under Wideband (FM), Sv Offset and Sa Correction are not calculated.
TS & Sv offsets
The constants are listed for Generic output.
CalibrationOffsetTS is required to match the Sphere Data TS to the mean on-axis TS of single targets. See the TSoffsetNew equation.
CalibrationOffsetSv is required to match the theoretical SvCalSphere to the mean of the sample Sv contributions from the on-axis calibration sphere single targets. See the SvOffsetNew equation.
Gain and Sa correction
The constants are listed for Simrad Specific output.
Transducer gain (dB) is the value for the Simrad TransducerGain (dB) that is required to match the Sphere Data TS to the mean on-axis Simrad TS of single targets for Simrad Ex60 data. See also TransducerGainNew equation.
Sa correction (dB) is the SaCorrectionFactor value used to match the theoretical SvCalSphere to the mean of the sample Sv contributions from the on-axis calibration sphere single targets for Simrad Ex60 data. See also SaCorrectionNew equation.
Angle Offsets and 3dB Beam Angles
The calculation of angle offsets and 3dB beam angles requires single target angular position data and a specified beam compensation model. The evaluation of angles and angle offsets is an iterative process where the RMS error is minimized between the beam compensated TS and the expected calibration sphere TS. Note: Raw single target data with no 3dB Beam angle data is handled using a default 3dB beam width of 6°.
Root Mean Square Error is a measure of how close the region or selection's single target TS are to the calibration sphere TS.
ECS File Output
Click Calculate to display new calibration values as ECS snippets. Any issues with calculation results will be printed in the Messages box.
Click Copy to copy the ECS snippets to the Clipboard to use in an ECS file.
See also
About calibrated data
Calibrating an echosounder
Minor-axis beam compensation graph
Major-axis beam compensation graph
Target samples bitmap operator
About single targets
Single target detection operators
Beam angle parameters and related calculations in Echoview