Slashdot Mirror
New Mexico Is Stretching, GPS Reveals
Velcroman1 writes "New Mexico's borders are gradually gaining girth, according to the Albuquerque Journal. It's not much, and it's not happening very fast — the state is getting about an inch wider every 40 years — but the state is unquestionably expanding, according to University of Colorado geophysicist Henry Berglund and his colleagues. Using a collection of 25 extra-precise GPS receivers planted across New Mexico and Colorado, Berglund determined that the cities of Albuquerque and Santa Fe are creeping away from each other. The rate of change seems ever so slow to the untrained ear, described as approximately 1.2 'nanostrains' per year."
The key thing is that this level of accuracy is not achieved in realtime.
The receivers would be recording more than the information contained in the GPS messages, they would be recording phase and signal strength data for all the satellites in the visible constellation.
Sophisticated post processing software would combine this information across multiple receivers, along with published satellite ephemeris data, to produce an accurate position solution.
Realtime positions cannot be that accurate due to affects like ionospheric refraction etc.
I used to work with a mobile system that recorded the GPS data along with inertial information (at 200Hz) that in realtime gave a solution that was usually accurate to within 30cm, and got to better than 10cm when combined with static ground station data in the post-processing step.
There are systems used in agriculture that are very accurate (10cm-ish) that use differential-GPS in realtime. The trick is your mobile unit has to be in constant communication with the differential ground station. Works ok for tractors, not so well for an aircraft 200-300km away. For differential-GPS to work well both units need to see the same satellites.
They also use very large antennas (relative to commercial/handheld units).
The antenna's Henry is using are about 20" across and have some shielding to protect from signals reflected from the ground.
See:
http://facility.unavco.org/kb/questions/325/5%7B47%7D8%22+Stainless+Steel+All-thread+Mast+Overview
I know, because I work there.
There are two types of people in the world: Those who crave closure
I'm not sure New Mexico can get any wider--it's borders are set along latitude and longitude lines.
It's borders are not defined by the latitude and longitude lines, but by the markers set by the surveying team which attempted to follow the latitudes and longitudes. In pretty much every country, certainly all regions of North America, boundaries that were intended to follow specific latitudes or longitudes don't change as our ability to more accurately define these imaginary lines on the globe. Typically the act in Canada or the U.S. that defines the national, state/province or county borders as following specific lat. or long. lines also includes the phrase "as defined by" and the specific survey mission that defined the border using the technology then available.
So every border that is popularly defined by a latitude or longitude is rarely accurate as the technology was often quite crude compared to what we can do today. ;-)
Therefore, yes New Mexico can and is getting wider and Albuquerque and Santa Fe are going to remain part of N.M. as long as some kind of hispanic revolution doesn't occur.