Show calibration gain adjustments difference
This procedure explains how to calculate and display gain adjustment difference between two separate calibrations.
Prerequisites
Calibration data set for two calibrations of the same beam mode must be available
Context
The calibration procedure will result in adjusting a set of coefficients. These coefficients are in turn used when processing target strength data in order to get a correct and as optimum result from surveys as possible. The gain adjustments is calculated for each beam in the swath. This procedure explains how to calculate and display gain adjustment difference between two separate calibrations. Normally the gain adjustment values for two sets of calibration data will be small. Sometimes there are differences in certain beams and sometimes there are differences throughout all of the beams. Such erroneous results may occur due to disturbances during calibration such as jellyfish, fish or other and will in turn affect the target strength calculations in surveys.A comparison between gain adjustments in two different calibrations will reveal such errors in an easy and visual way.
Procedure
1 Select Beam Mode.
a Open the Setup menu.
b Select Beam Mode Adm.
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Selecting Beam Mode Adm opens the Beam Mode Administration dialog box in edit mode. In edit mode you will be able to edit, create and delete beam modes.
2 Select the beam mode you wish to use for the calibration.
The Beam Modes page lists the beam modes that have been created. You can select any beam mode from the list. The Mode Description page displays a short description of the beam mode.
Gain adjustment differences can only be calculated for calibration data sets with the same beam mode.
a Select Edit.
This opens the Beam Mode dialog box for the appropriate beam mode. The name of the dialog box reflects the name of the beam mode. In edit mode you will be able to edit, create and delete beam modes.
3 Select the calibration data set to display.
a Open the Calibration page.
The Calibration page displays all calibration data sets made and a short description of them.
b Select the primary calibration data set.
c Select Apply to calculate the gain adjustment difference.
d Select Show calibration gain adjust difference.
A dialog box opens to confirm proceeding to the next step of choosing calibration data.
e Select OK.
f Select the secondary calibration data set.
This opens the Beam Direction Plot page in the Beam Mode dialog box.The plot shows the resulting gain adjustment difference for primary calibration data set minus the secondary calibration set.The Beam Direction Plot displays all the gain adjustments (in dB) that have been made to all the beams. The colour of the beam represents the calculated adjustment. The colour scale is shown at the bottom of the page.
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In this example a plot of the gain adjustments difference of two not overlapping calibrations is made The gain adjustments differences are large in a number of beams. Normally the comparison will be between identical calibrations, performed at different dates only. The difference should be close to zero.