BoatBanter.com - View Single Post - Which echo sounder is good up to (almost) zero depth?

Salomon Fringe

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.