About Sound Wave Propagation - Simrad ES80 Reference Manual

erroneous depth detections are never shown. 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 ES80 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 for example a dense school of fish. The algorithm chooses the upper
boundary of the first layer when the bottom consists of layers.
The bottom detection algorithm locks to the first good bottom return. The depth at point
A rather than the depth along the transducer axis will be output for a sloped bottom. The
detected depth value is always smaller than the depth along the transducer axis implying
that a safety margin is automatically included.
Related topics
Choosing and
Range
Choosing and
Range
Range function, page 309
Start Range function, page 310

About sound wave propagation

The velocity of sound wave propagation in the sea varies slightly with temperature,
salinity and pressure.
The velocity varies between 1440 and 1520 m/s in shallow sea water, while a velocity
around 1480 m/s can be expected at 1000 m depth. In shallow fresh water the velocity is
approximately 1430 m/s. Unless you have a relevant sensor available, a good average
sound speed value is 1470 m/s.
The ES80 transmits high energy sound wave pulses into the sea. A flat bottom reflects
the transmitted wave as if it was a mirror. The propagating energy is spread over a larger
and larger area as it travels down to the bottom and up again. The energy is spread over a
four times larger area every time the travel distance doubles.
406273/C
values in a surface related echogram, page 94
Start Range
values in a bottom related echogram, page 95
Start Range
Concept descriptions
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