h a l f b a k e r yWhat was the question again?
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As you know, measuring gravity, G, as a constant is still a terribly vexing problem.
Absolute gravimeters are highly specialized and well, apparently, don't agree with each other.
To construct our own relative gravimeter, a spring of standardized length would be provided for the iphone or equivalent
device. An app on the iphone would track and broadcast losses of height over time with Apple's altimeter, when for example you were bored and wanted to drop your iphone to advance the cause of science.
Realtime gravity readings would be transmitted to a central server and collated for relative, admittedly inexact measures.
Given that this gravimeter is essentially a prototype of the description of relative gravimeters on a Wikipedia page, which again, apparently isn't reliable in an absolute sense, the idea passes along that invisible membrane between farce, satire and nonsense through which we all move.
Gravity slows scientists down
http://scienceblogs...ravity-aint-nothin/
Another reason General Relativity uses so many equations [4and20, Aug 12 2012]
MEMS gravimeters
https://www.google....h?q=mems+gravimeter
[notexactly, Feb 03 2018]
Blitzortung Lightning Detection
http://en.blitzortu...ing_maps.php?map=10
Another supposed triumph of quantity over quality. [Wrongfellow, Feb 08 2018]
MacSaber
https://www.youtube...arch_query=macsaber
Mentioned in my anno as an application of the accelerometers in laptops [notexactly, Feb 11 2018]
[link]
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You mean g (little g, which varies around the Earth), not G (big G, which is a fundamental constant). |
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You might be able to measure g with a phone.
(actually, given the presence of an accelerometer in
the iPhone, this is trivial). G, not so much. |
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Yes, you can measure g with the accelerometer already. Although collating data from multiple phones would probably be more a measure of the variance in calibration than variance in g. |
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The practical difference between an accelerometer and a
gravimeter is accuracy and precision. The gravimeter has
more.
(Also, the accelerometer might have two or three axes,
while the
gravimeter usually has only one, and the gravimeter is
probably a
lot larger, but that's beside the point.) |
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If you use an accelerometer as a gravimeter, there are
two
possible outcomes: you don't get usable data, or you get
to sell
your accelerometer for at least 1000× as much by calling
it a
gravimeter now. |
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On the other hand, see the newish MEMS gravimeters,
which could make everything I said wrong: [link] |
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Yes, I'm for distributed scientific investigation but probably something for the Caterpillar CAT S60. |
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There seems to be a recurring theme that it is somehow possible to
collect good-quality data from a large number of poor-quality sensors.
The [link] is another example of this idea. |
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I'm sceptical that it will ever yield anything more than a large quantity
of poor-quality data. |
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I agree generally, but Blitzortung is actually pretty good, as far as I know. |
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In their favour, they do rely on speed-of-light delays over long
distances, which are fairly easy to calibrate. |
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Yes. Their detector kit also seems to work well - strikes are simultaneously reported by tens of detectors up to a few hundred miles away. And, whenever there's a storm near me, I can see the strikes appearing on the site, so it seems to work well. |
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Blitzortung seems to work well in my experience (though I don't
have a station yet, so this is only as a viewer). I don't think I'd
consider it to use low-quality sensors, though, because timing to
the resolution required is easy with GPS. |
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Same for the airplane tracking systems that use distributed ADS-
B receivers (i.e. FlightAware & Flightradar24). Those use cheap
SDR receivers, but those are not low-quality sensors when you
consider the signals they're receiving (digital, with the airplanes'
locations encoded). |
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Maybe a better comparison would be the networks that attempt
to detect earthquakes using the accelerometers in phones and
laptops (used for parking the hard drive heads when the laptop
is dropped, and for lightsaber toys [link]). I don't know how well
those work. (I do know that they only pay attention to the
accelerometer readings when the devices seem to be sitting
still.) |
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