Simrad ES60
6
857-160970 / Rev.H
Bottom echo
A hard flat bottom reflects the transmitted signal as if it were a
mirror. The transmitted pulse hits the illuminated bottom area at
nearly the same instant, and the echo from different parts of this
area arrive back at the surface also at nearly the same instant.
Figure 2
Bottom echo
The received echo signal is basically an attenuated copy of the
short transmit pulse. The echo signal from a sloped bottom is
characterised by having a longer duration and a slower rise and
fall time. The transmitted pulse first hits the slope at point A,
and as time elapses the reflection point travels along the slope
towards point B. Many locations do not have a solid hard
bottom. Frequently, the bottom is composed of layers of mud,
clay and sand which can be observed as coloured bands on the
echo sounder display.
The bottom detection algorithm is implemented solely in
software, and separate algorithms are run for each frequency
channel. The algorithm is designed with emphasis on reliability
in the sense that erroneous depth detections are never output.
Whenever the quality of a detection is questionable the
algorithm outputs a depth of 0.00 to indicate that no reliable
detection was obtained. The ES60 algorithm is designed to
handle a number of difficult situations. The algorithm maintains
bottom lock for a discontinuous jump in bottom depth. It avoids
false bottom detections on a dense school of fish. The algorithm
chooses the upper boundary of the first layer when the bottom
consists of layers.
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