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Which echo sounder is good up to (almost) zero depth?

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Salomon Fringe Salomon Fringe is offline

Salomon Fringe is offline

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First recorded activity by BoatBanter: Jun 2008

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Which echo sounder is good up to (almost) zero depth?

wrote:
On Jun 11, 1:49 pm, Salomon Fringe wrote:

Some people said I am asking for the impossible when I asked for a
near-zero-water-below-the-keel sounder, but when you do the math it sure
doesn't seem impossible, at 200khz one cycle takes 5 microseconds, the
speed of sound in water is approx. 1500m/s so in principle you should be
able to measure down to 0,75 cm. About 1/3 of an inch. Perhaps you can't
make the pulse that short or something, dunno.

S

It's not sending a single 360 degree cycle. It's sending a short
pulse of 200 khz and then waiting for the return. The duration
defines how shallow it can read, not the frequency.

I realise that, but I suppose the sounder calculates the depth based on
receipt of the wavefront of that pulse. To determine it is receiving
its own signal it needs at least a 360. I'm just guessing here because
it seems that in reality they need much more than one cycle.

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