Chapter 6
CVS-841/851
Using the menu
6.5.2.5 Mix type
This mode of function enables quick and easy finding of small fish like young sardines utilizing the
intrinsic nature of acoustic wave. As widely known, small fish are sensitive to the high frequency
waves where the wavelength is closer to the length of the fish. Meanwhile, low frequency waves that
have a longer wavelength produce small amount of echoes from small fish.
The image-mixing mode is an image processing function that enables weak fish like young sardines to
be better defined by comparing or subtracting the images from both the HIGH and LOW frequencies.
When echoes are detected by the HIGH frequency wave, the sounder displays these echoes in a
pre-selected color to indicate small fish targets. The MIX function has three modes as, A (Comparison),
B (Subtraction) and C (Selection).
Normal image
(High or Low
Frequency)
Image detected only by high
frequency, which is painted in a
pre-selected color.
Mixed image
Figure 6.8 Mixed image
A (COMPARISON) mode:
This mode displays the result of the comparison between HIGH and LOW frequency echoes. If those
echoes are overlapped at the same depth, the resultant colors are displayed in mixed colors. However,
if the HIGH frequency echo is painted in red (strongest color), the mixed color will also be red to show
the echoes are from small fish. If the mixed fish school is partly displayed with mixed colors among red
color, it suggests the possibility of a larger fish school among the small fish school.
B (SUBTRACTION) mode:
This mode displays the resultant image by subtracting the HIGH frequency echoes from those of LOW
frequency. Using this method, you can discern a fish school by size. For instance, if the resultant
echoes are displayed in similar colors as the HIGH frequency echoes, this result suggests the majority
of the fish species is sensitive to the HIGH frequency transmission, i.e. the detected fish school could
be small fish like young sardine. If the resultant echoes are shown in different colors from the HIGH
frequency transmission, it indicates the fish school is sensitive to LOW frequency, therefore a larger
size of fish species.
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