[PSUBS-MAILIST] Reversed echo sounder

[Jens Laland via Personal_Submersibles]

Lasse

** Is it possible to turn an echo sounder towards the surface to measure the
** distance to the surface?

Because of the extreme (large) difference in characteristic acoustic
impedance of seawater versus air, you will experience a sound power
reflection coefficient of (typical) 0.99893 between seawater (@ +15°C) and
air at sea level (@ +20°C).

Simply stated, you will receive (echo) 99.893% of the sound send upwards
from a submarine towards the surface.

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SEAWATER (15°C)
   characteristic acoustic impedance    : 1.5443675
   density                              : 1.025 SG
   longitudinal velocity of sound waves : 1506.7 m/sec
   wavelength @ 300 Hz                  : 5.02 m
   wavelength @ 948.683 Hz (center)     : 1.59 m
   wavelength @ 3000 Hz                 : 50.2 cm    (  19.773 inches )

AIR, AT SEA LEVEL (+20°C)
   characteristic acoustic impedance    : 0.0004132128
   density                              : 0.001204 SG
   longitudinal velocity of sound waves : 343.2 m/sec
   wavelength @ 300 Hz                  : 1.14 m
   wavelength @ 948.683 Hz (center)     : 36.2 cm    (  14.243 inches )
   wavelength @ 3000 Hz                 : 11.4 cm    (   4.504 inches )

sound power reflection coefficient      : 0.99893    (  99.893 percent )

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Best regards,
Jens Laland

http://traktoria.org
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