[PSUBS-MAILIST] Reversed echo sounder

[Lasse Schmidt via Personal_Submersibles]

wow, this is awesome thanks for the help. We´ll have the chance to try this out next week. If it works, we will have both analogue and digital depth gauges.
I´ll make sure to  take some photos and upload them later.

Lasse Schmidt
Upplevelsepresent.se
Skeppsbron 21, Tullhus 1
11130 Stockholm
070-28 32 660

21 jun 2014 kl. 07:28 skrev Jens Laland via Personal_Submersibles <personal_submersibles at psubs.org>:

> 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.
> 
> -------------------------------------------------------------------------
> 
> 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 )
> 
> -------------------------------------------------------------------------
> 
> Best regards,
> Jens Laland
> 
> http://traktoria.org
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