[time-nuts] tracking position & orientation

[Tom Van Baak]

Eric,

Good idea to experiment with an antenna on each end of the house. You'll 
get all sorts of data and your eyes will be eager to read house movement 
into the plots. The problem is you won't know for sure if the results 
are real or not; there are many factors, especially for a house made of 
wood. See plots for my home/lab. [1]

So a suggestion is to place at least one of the antenna on a waterproof 
turntable and continuously rotate it, off center, very slowly, maybe one 
turn a week, or month. Then look at your data and see how well you can 
detect that *known* movement.

By comparing actual GPS data with your calculated turntable antenna 
location you can establish the position detection sensitivity of your 
setup. Which is to say, if you can't detect a *known* antenna movement 
of a few inches around a month there's little chance that you're going 
to confidently detect an *unknown* seasonal or tectonic ground motion of 
a few mm a year.

Alternatively, use a waterproof linear XY stage and each midnight shift 
the antenna 1 to 12 inches north and 1 to 31 mm east based on the month 
and day number. At the end of the year you will have created the coolest 
GPS plot ever seen. It's kind of a slow motion version of "geowriting". [2]

/tvb

[1] http://leapsecond.com/pages/quake/

[2] http://leapsecond.com/pages/geowrite/


On 11/21/2019 11:36 PM, Hal Murray wrote:
> eric at scace.org said:
>>     I moved to Boulder CO a few months ago. The “curiosity” is to determine
>> the position of two antennas at either end of my house and monitor it over
>> time, with the idea that one could see plate movement in 3 dimensions plus
>> rotation around the axes.
> How much does Boulder move?  I'd guess not much so measuring motion will be
> tough.  You could try to get a lower limit on the speed.
>
> Looks like that part of the country is not interesting to the USGS:
>    https://earthquake.usgs.gov/monitoring/gps
>
> Ballpark numbers.
>    With a good setup, GPS gives location to about 1 mm.
>    I live a few miles from the San Andreas fault system.  It is shifting about
> as fast as your fingernails grow, roughly an inch per year.
>
> Measuring rotation will be tough if your 2 stations are only 100 ft apart.  Do
> you have a friend 1, 10, or 100 miles away?
>
> PS: Make sure that your antenna mounts are sturdy.  You don't want them
> drifting as the house ages or you bump into them.
>
> ----------
>
> There is a major USGS campus on the Boulder side of Denver.  You might wander
> down there and ask around to see if you can find anybody familiar with either
> GPS or earthquakes.  Or try their web pages.  There is probably a public
> information contact.
>
> ----------
>
> >From a USGS talk tonight on Sea Level Rise.
>    California is rising about 2 mm per year.  Sea level is rising about 3 mm
> per year.  Net is 1.
>    East coast is sinking about 3 mm per year.
>    (Major risk is surge and waves from hurricanes.)
>
>
>
>
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