Path: csiph.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail
From: Thomas Heger <ttt_heg@web.de>
Newsgroups: sci.physics.relativity
Subject: Re: Idiocy of Plate Tectonics
Date: Fri, 08 Jul 2016 10:59:29 +0200
Lines: 43
Message-ID: <du98blFor78U1@mid.individual.net>
References: <dsmnurF2tdnU1@mid.individual.net> <6q2dnd8Y2I6KT_vKnZ2dnUU7_83NnZ2d@giganews.com> <dsrt9tF3r17U1@mid.individual.net> <nkbfdt$og4$2@gioia.aioe.org> <dsuipsFk891U1@mid.individual.net> <nke3b1$lqk$1@gioia.aioe.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-15; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: individual.net rHa1hZWgxKyKfl1DR6i0aginRrjd7n+IFTk5iNuQxUvigncCHH
Cancel-Lock: sha1:L1JdQNj4tkwmeaEfE3r2PaG+5Yc=
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:8.0) Gecko/20111105 Thunderbird/8.0
In-Reply-To: <nke3b1$lqk$1@gioia.aioe.org>
Xref: csiph.com sci.physics.relativity:387428

Am 22.06.2016 15:20, schrieb Odd Bodkin:
>> GPS does not measure the interior of the Earth, since the satellites
>> circle around in orbit, what is outside of the Earth.
>>
>> The interior is impossible to access.
>>
>> But it would be eventually be possible to measure changes of the
>> diameter of the Earth indirectly.
>>
>> How could the GPS system be used to measure such changes?
>
> Thomas, please.
> The GPS orbit is well known, including the orbit path circumference and
> its diameter, which means that the location of the center of the earth
> is well known just because of the circle the satellites travel through.

Simply not true, since in reality they use 'differential GPS' for high 
precision measurements:

https://en.wikipedia.org/wiki/Differential_GPS

Quote:

"DGPS uses a network of fixed, ground-based reference stations to 
broadcast the difference between the positions indicated by the GPS 
satellite systems and the known fixed positions."

 From 'fixed known positions' follows the inability to measure changes 
of those positions.

This is so, because 'known fixed position' is an axiom, on which further 
measurements are based.

If these positions would in fact change, you need something else as 
reference.

This could actually be the orbit itself. But this is not usable for high 
precision measurements, because it would allow only a precision in the 
range of 15 m (not the required mm).



TH