4 Importing the echo data
The fourth page in the Calibration Wizard allows you to import the echo data into the calibration process. You can make changes to the single target detection, and add a brief description, but you are not permitted to do anything with the echo data.
Prerequisites
In order to import echo data, the EK80 must be "pinging" with a calibration target (sphere) inside the beam.
Context
The fourth page of the Calibration Wizard dialog box is divided into three fields.
Tip
To change the size of the individual field, click and drag the field borders. You can also increase the size of the dialog box. To make the dialog box cover the entire screen, double-click the title bar.
•  Target Position field
The left side of the Target Position field shows all the individual echoes that are imported into the calibration program. All echoes are placed inside a circle to reflect their locations in the beam. The right side of the field shows the calibration layer that is automatically created once the calibration starts.
•  Frequency/Target Strength field
The Frequency/Target Strength field shows a curve reflecting the target strength of the sphere for individual frequencies. This is the same curve as you can see in the Calibration Wizard dialog box page four, but with a few additional features.
•  Numerical field
The Numerical field provides several tabbed pages. The General page shows the common data and parameters for the system. Transceiver parameters common to all beams The Channel Data page displays numerical parameters related to the transceiver channel that was used to record the echo data. The TS Data page displays the numerical parameters related to each individual echo.
Procedure
1 Adjust the size of the Calibration Wizard dialog box so that you can also see the echogram.
2 If necessary, adjust the calibration layer.
When the calibration process is started, a dedicated layer is automatically created. If a strong and easily detected echo from the calibration sphere is shown in the echogram, the layer will position its borders over and under the target. During the calibration process, the calibration layer must be monitored and adjusted to compensate for the target’s depth changes.
3 In the Frequency/Target Strength field, verify that the calibration target (sphere) is useful for the chosen frequency range.
Due to their unique characteristics, the various calibration spheres offer different target strengths when the frequency changes. This is clearly seen when you calibrate in FM using a larger frequency band. If the shape of the curve shows significant differences in the target strength, the calibration using the related frequency band(s) will be inaccurate.
4 If necessary, change the TS Deviation to a lower numerical value than the default setting.
This setting is located on the General page in the Numerical field. The TS Deviation setting allows you to control the maximum permitted deviation for the echoes from the calibration target (sphere). Echoes outside the defined limit are not imported. The limit you select is shown in the Frequency/Target Strength field. Reducing the numerical value of the TS Deviation setting may be useful to filter out echoes from other targets than the sphere.
5 If necessary, adjust the Min Depth and/or the Max Depth settings.
These settings are located on the General page in the Numerical field. Use these parameters to adjust the depth limits of the calibration layer, thus creating a "depth window". Echoes from objects outside the defined limits are not imported. You must lower the sphere to a known depth. If you manage to keep the sphere at this depth when is moved in the beam during the calibration, you can adjust the calibration layer to make a smaller "depth window". This removes unwanted echoes.
6 Select Calibration Description to open the dialog box.
The Calibration Description dialog box allows you to record information about your current calibration operations. You can type in any kind of relevant information into the Calibration Description text field. This can be for example the vessel’s location, weather conditions, or the name of the people who did the calibration.
The information you type is added to the XML file with the calibration data. The date and time of the calibration are automatically added to the XML file names. The Calibration Description dialog box also shows you the serial number of the transducer that is used on the channel that is calibrated, as well as the name of the channel you are calibrating. This information is retrieved automatically.
7 Select Single Target Detection to check the settings.
Tip
Set the Minimum Threshold to about 10 dB below the nominal target strength of the calibration sphere. The remaining default values are acceptable for most purposes.
8 On the Operation menu, open the Record RAW button, and select On.
9 Select Start to start echo data import.
a During the data import, use the three winches to move the sphere inside the sound beam.
This can be done by adjusting the length of the winch wires in a programmed pattern.
To successfully calibrate the EK80 you need to place a number of target detections in each sector. The echoes must be distributed within the entire beam cross-section. In order to do this, the target sphere must be physically moved inside the beam during the calibration process. If the sphere location is constant, you will be rewarded with many echoes, but all will be inside the same sector. Several echoes on "top" of each other do not increase the calibration accuracy, but the distribution of the echoes within the beam does. The number of sphere detections should be approximately the same for each sector, and in total not more than 100 for the whole beam cross-section.
Tip
We have seen that some customers use automatic winches. These are controlled by a software program which methodically places the sphere in the different sections of the beam while maintaining the same depth.
b During the data import, monitor the coverage.
The General page in the Numerical field presents both numerical and a visual presentation of the coverage. The area covered by the transducer beam is shown as a circle with "slices" for each transducer sector. A split-beam transducer has three or four sectors. The circular cross-section is split into several slices.
The coverage circle uses colour coding to show you the current coverage.
•  Red colour means that you do not have enough echoes in the relevant sector (0 to 25%).
•  Yellow colour means that you have many echoes in the relevant sector, but not enough (25 to 50%).
•  Green colour means that you have enough echoes in the relevant sector for a successful calibration (better than 50% coverage).
A small circle in the middle represents the coverage in the centre of the beam. It uses the same colour coding. The numerical values for the center and overall coverage are shown over the coverage circle.
c During the data import, monitor the calibration layer, and adjust if required.
During the calibration process, the calibration layer must be monitored and adjusted to compensate for the target’s depth changes. These depth changes are easy to see in the echogram, or on the right side of the Target Position field.
The depth limits of the calibration layer can be adjusted in three different ways:
•  You can select a red line in the echogram, and drag it up or down.
•  You can select a red line on the right side of the Target Position field, and drag it up or down.
•  You can adjust the Min Depth and Max Depth settings on the General page in the Numerical field.
10 When the appropriate number of echoes have been imported, and the coverage plot is all green, select Stop.
11 Stop the recording.
12 Stop "pinging".
13 Select Save or Save As to save the calibration data.
You must save the calibration data before you continue to page four in the Calibration Wizard dialog box. You are not saving raw echo data here, but an XML file that contains the information necessary to run the calibration process.
14 Select Next to continue.
Further requirements
Proceed to the fourth page in the Calibration Wizard.