• | Pr(No TVG) TVG compensation is not implemented. This option is hardly ever used.
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• | Sv (20 Log) Volume backscattering strength
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• | Sp (40 Log) Point backscattering strength
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• | Surface A Surface echogram is mainly used when you wish to look at the entire water column starting from the sea surface and down to the sea
bottom. Since this echogram is referenced to the sea surface, the sea bottom contour will vary with the actual depth. If you set up the Start Range and Range depths to place the sea bottom contour at the lower end of the echogram, you will have good opportunity to study the echoes
from the water column.
In the surface echogram, all calculations are made from the sea surface and down to the detected sea bottom. Use this echogram type to obtain correct calculation of the biomass. It will also provide valid data for the Target Strength Histogram information field.
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• | Bottom A Bottom echogram is mainly used when you want to examine the echoes from fish close to the sea bottom. Since this echogram is referenced to the sea bottom, the sea surface will vary with the actual depth, while the bottom is
drawn flat. This makes it easy to study the echoes from the sea bottom. You can investigate the sea bottom conditions and hardness, and detect fish.
The echogram is only drawn for pings that have a successful bottom detection.
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• | Compression The Compression options describe the situation when the number of samples is higher than the number of pixels, and multiple samples are compressed into one pixel.
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• | Expansion The Expansion function provides a mean to adjust the presentation when the number of samples is lower than the number of pixels used to
display them. When this happens the sample values must be expanded to match the pixel values.
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