2
.
Distinguish of Fish School
●
Important tip is comparison between fish school image and actual catch
Possible to judge the fish type to some extent from the image of fish school. The shape
of fish school changes even for same fish group by time(day/night, season, current
change). The important tip to distinguish the fish type is to know fishing point and fish
type according to fishing season. Then, compare the fish image and actual catch and
look for the point.
44
3
.
Distinguish of Fish Quantity
●
Distinguish fish quantity from density/size of fish school.
Higher density of fish school has stronger reflected wave. Therefore, the fish density
can be seen from the color strength of image.
It is wrong that fish quantity is larger for large image on the screen. Fish school located
deeper area tends to appear bigger compared to the one at shallow water. This is
because the width of transmitted wave becomes wider as it go deeper. The reflected
ultrasonic wave becomes bigger as the distance (depth) gets further. The important tip
to distinguish the fish quantity is to know fish school located at deeper water appears
bigger. Judge from size of fish school and color strength.
Reflected
ultrasonic
Fish school A
Fish school B
Fish schoolA Image(Shallow)
Fish schoolB Image(Deep)
4
.
Distinguish of Sea Floor Condition
●
There are many types of sea floor conditions such as rocky, sandy, or muddy. The
condition can be judged by the upper/lower width of sea floor image and 2
nd
echo. The
reflection is stronger for hard bottom such as rocky area. The image width is thicker,
and 2
nd
echo tends to appear. On the other hand, the reflection is weaker for soft
bottom such as sandy and muddy area. The image width is thinner, and it’s harder to
have 2
nd
echo.
※
2
nd
echo… Ultrasonic wave initially transmitted from transducer, reflected from the
sea bottom, reflected back at water surface, and reflected again at sea bottom. In short,
it is the image (ultrasonic wave) which made 2-times round-trip.
Rocky area
Sandy or Muddy area
nd
echo
2