Mike Hord wrote:
>>>Anybody make a cheap, PIC based floating Tsunami sensor they would
>>>like to sell a few thousand of?
>>
>>Could you do that?  Floating GPS receiver that detects unusual changes
>>(speed and magnitude) in altitude?  Could it transmit info fast enough
>>to do any good?  Is the change in altitude in deep sea areas even
>>that significant?  Or are you talking about a big but shallow swell
>>that only reaches significant height in shallow water?

GPS does not have great accuracy in height. 10's of meters
vs. the centimeters of a Tsunami swell.

> As I understand, they are doing just that in the Pacific.  Some sort of buoy
> that somehow detects the passage of the tsunami.

http://www.prh.noaa.gov/itic/tsunami_events/media/factsheets/tsunami_detection_buoy_article.pdf

> As I understand it, a large number of those killed (in India and Sri Lanka,
> at least, where there was no sign of the quake) were people who had
> gathered to watch the sea recede.  Wikipedia claims that the recession
> of the sea can occur some tens of minutes prior to arrival of the wave,
> so even on foot, one stands a good chance of escaping a tsunami if one
> were to hoof it inshore quite quickly after that initial portent.  In fact, an
> alarm which sounds solely based on that may make an effective warning.

Albeit good for only 10 minutes (at most) advance notice. But given
the small area involved, it would be affordable by the local officials
if they wanted it.

DART buoy, $250,000 + $125,000/year to maintain + ship time.

If redesigned with GPS, Cell phone, sensors, batteries,
wave powered generator and a PIC (of course) how $$?

 > The other idea of detecting the ocean retreating could also be used by
 > having a pressure sensor just outside the normal wave line; this would
 > then detect lose of pressure as the water is sucked out for 10's of
 > seconds.
 >
 > This would require many cheaper sensors at every beach or headland.
 >
 > Then you have ongoing maintenance costs for both options - replacing
 > batteries etc.

Use recharable batteries where wave action powers a generator
(there are many commercial designs) to keep the batteries topped up.
Unfortunately the generators/system would likely be stolen if
it were small and lightweight. On the other hand, it could report
the fact that it was being stolen and provide real time tracking
if the thieves were dumb enough.

Would the idea of pressure measurement work if instead of
being on the ocean floor, the sensor were only a few 10s of
meters down on the anchor rope which was kept taunt by a
submerged float? This would make it a lot simpler and cheaper
to implement since long distance underwater comms would not
be needed.

Robert
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