Stories
Slash Boxes
Comments

SoylentNews is people

posted by on Monday May 08 2017, @03:17PM   Printer-friendly
from the also-detects-mouse-farts dept.
Arthur T Knackerbracket has found the following story:

The Global Positioning System consists of 31 Earth-orbiting satellites, each carrying an atomic clock that sends a highly accurate timing signal to the ground. Anybody with an appropriate receiver can work out their position to within a few meters by comparing the arrival time of signals from three or more satellites.

And this system can easily be improved. The accuracy of GPS signals can be made much higher by combining the signals with ones produced on the ground. Geophysicists, for example, use this technique to determine the position of ground stations to within a few millimeters. In this way, they can measure the tiny movements of entire continents.

This is an impressive endeavor. Geophysicists routinely measure the difference between GPS signals and clocks on the ground with an accuracy of less than 0.1 nanoseconds. They also archive this data providing a detailed record of how GPS signals have changed over time. This archival storage opens the possibility of using the data for other exotic studies.

Today Benjamin Roberts at the University of Nevada and a few pals say they have used this data to find out whether GPS satellites may have been influenced by dark matter, the mysterious invisible stuff that astrophysicists think fills our galaxy. In effect, these guys have turned the Global Positioning System into an astrophysical observatory of truly planetary proportion.

The theory behind dark matter is based in observations of the way galaxies rotate. This spinning motion is so fast that it should send stars flying off into extra-galactic space.

But this doesn't happen. Instead, a mysterious force must somehow hold the stars in place. The theory is that this force is gravity generated by invisible stuff that doesn't show up in astronomical observations. In other words, dark matter.

-- submitted from IRC


Original Submission

 
This discussion has been archived. No new comments can be posted.
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
  • (Score: 2) by kaszz on Monday May 08 2017, @04:51PM (3 children)

    by kaszz (4211) on Monday May 08 2017, @04:51PM (#506426) Journal

    Where are these stations located?

    Starting Score:    1  point
    Karma-Bonus Modifier   +1  

    Total Score:   2  
  • (Score: 2) by VLM on Monday May 08 2017, @04:58PM (2 children)

    by VLM (445) Subscriber Badge on Monday May 08 2017, @04:58PM (#506429)

    I think this is what you're looking for?

    https://www.navcen.uscg.gov/?pageName=dgpsSiteInfo&All [uscg.gov]

    MultiPSK can demodulate DGPS signals. 100 baud MSK modulation or something like that.

    I guess "several" former aviation / coastal NDBs were converted to DGPS transmission although thats hearsay at best.

    Ironically you don't need DGPS for the discussion topic.

    GPS signals have noise added or inherent and its pretty well characterized so if you weld your GPS antenna to a post stuck in the motionless ground then sample data for 10 years you'll get a pretty good idea of where the post is (relative to the rest of the GPS coordinate system anyway) and any noise in excess of the predicted and predictable could be dark matter Fing up propagation. Of course the ionosphere naturally and normally Fs up propagation so good luck filtering all that out.

    • (Score: 2) by Kromagv0 on Monday May 08 2017, @05:21PM (1 child)

      by Kromagv0 (1825) on Monday May 08 2017, @05:21PM (#506438) Homepage

      The US Gov is no longer adding noise, well not until there is a military reason to scramble it. There is however a fair amount of random error introduced as the signals pass through the various atmospheric layers and bounce off of crap near by. If we as regular civilians were granted access to the encrypted L2 channel it would be easy to correct for these errors and we would all have access to GPS units with absolute position accuracy of an inch or so. There are of course ways to work around that by basically collecting phase angle data of the L2 carrier, your pseudo ranges, combining it with the same info from one or more nearby base stations and then doing a whole bunch of math. The general rule is you can get really good position accuracy from a single GPS unit if you let it average over a day. If you can get additional data from a DGPS ground station or a CORS station over the internet you can easily reach 1 inch absolute position accuracy within a day and then have a nice base station for getting relative position accuracy to it in the couple of mm range.

      --
      T-Shirts and bumper stickers [zazzle.com] to offend someone
      • (Score: 2) by VLM on Monday May 08 2017, @05:40PM

        by VLM (445) Subscriber Badge on Monday May 08 2017, @05:40PM (#506453)

        Yeah the noise level is due to propagation and is white enough that averaged long enough it goes away.
        "long enough" being on the order of a satellite orbit.

        I suppose this is a big problem if its assumed the dark matter is moving faster than the satellites (insert frown emoji)

        There is an interesting way around this where a truly enormous mesh of receivers can do the bistatic radar thing. You'd get a nice high res map of the ionosphere and whatever else is interfering (weather fronts or something) Then I guess the experimental limit would be telling the difference between swirlies in the ionosphere vs dark matter just passing thru. I suppose that would be self evident over time.

        I'm too lazy to run the math but its interestingly easy and useful to bounce radio waves off ionized gas in the upper atmosphere, likewise now that the world has its first gravity wave detector presumably clouds of "dark matter" would F with those gravitational signals, if only we could install gravity wave detectors on all the planets and moons. Its a good excuse to go colonize the solar system.