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But what are the moving dots in the animation? Planes, satellites? (seems to move like neither). GPS being a military technology, I presume those fixed gps sta

by cm2187 4y ago

But what are the moving dots in the animation? Planes, satellites? (seems to move like neither). GPS being a military technology, I presume those fixed gps stations are only located in US-friendly countries. You wouldn't get that adjustment if you are flying over Russia or China, or any ocean. How much of an error in absolute distance are we talking about here? A few cm or meters or a km?

krisoft 4y ago
> But what are the moving dots in the animation? Planes, satellites? Neither. The stations are in Japan. Imagine a line going from each of those stations to the satellite. Where this line crosses the ionoshpere that spot is what is measured. That is what you have information about. Those spots are the dots. So you basically see the arc of the Japanese islands projected up towards each satelite which is visible from these stations. When the satelite is low on the horizon this projection seems to move fast, and when it is near the zenit it seems to move slow. This is what you are seeing with the dots. Their location is calculated here: https://github.com/tylerni7/missile-tid/blob/main/tid/tec.py#L161 https://github.com/tylerni7/missile-tid/blob/main/tid/tec.py... "Given a receiver and a satellite, where does the line between them intersect with the ionosphere?" And then that is called here: https://github.com/tylerni7/missile-tid/blob/00c5fd25e2ab3c226df0581678675e4ba7a93cf5/tid/connections.py#L251 https://github.com/tylerni7/missile-tid/blob/00c5fd25e2ab3c2... "The locations where the signals associated with this connection penetrate the ionosphere."|
- jwsteigerwalt 4y ago
  This explanation helps understand the video.
- layer8 4y ago
  What are the stations/receivers? Is this crowdsourced data?
  - williamscales 4y ago
    They have a GPS receiver in a fixed, known location. They measure the received signal and from the variations infer corrections for ionospheric effects. They are part of the GPS network. [0] https://en.wikipedia.org/wiki/GNSS_augmentation https://en.wikipedia.org/wiki/GNSS_augmentation
    - layer8 4y ago
      The video is data from just a single receiver?
      - krisoft 4y ago
        No. These are the receivers from japan’s GEONET.[1] “Geospatial Information Authority of Japan (GSI) operates GNSS CORSs that cover Japanese archipelago with over 1,300 stations at an average interval of about 20km for crustal deformation monitoring and GNSS surveys in Japan.” [2] Basically the government of Japan pepered their country with GPS base stations and they let researchers use the data from them. This is just a novel use of that data. 1: https://mobile.twitter.com/tylerni7/status/1593466486714421249 https://mobile.twitter.com/tylerni7/status/15934664867144212... 2: https://www.gsi.go.jp/ENGLISH/geonet_english.html https://www.gsi.go.jp/ENGLISH/geonet_english.html
danbruc 4y ago
But what are the moving dots in the animation? I would guess the moving dots are fixed GPS receivers, or more precisely the intersections of lines between fixed GPS receivers and moving GPS satellites with a sphere around Earth representing the ionosphere. If you look at the shape of the moving clusters, some look like Japan.

by cm2187 4y ago

krisoft 4y ago

> But what are the moving dots in the animation? Planes, satellites? Neither. The stations are in Japan. Imagine a line going from each of those stations to the satellite. Where this line crosses the ionoshpere that spot is what is measured. That is what you have information about. Those spots are the dots. So you basically see the arc of the Japanese islands projected up towards each satelite which is visible from these stations. When the satelite is low on the horizon this projection seems to move fast, and when it is near the zenit it seems to move slow. This is what you are seeing with the dots. Their location is calculated here: https://github.com/tylerni7/missile-tid/blob/main/tid/tec.py#L161 https://github.com/tylerni7/missile-tid/blob/main/tid/tec.py... "Given a receiver and a satellite, where does the line between them intersect with the ionosphere?" And then that is called here: https://github.com/tylerni7/missile-tid/blob/00c5fd25e2ab3c226df0581678675e4ba7a93cf5/tid/connections.py#L251 https://github.com/tylerni7/missile-tid/blob/00c5fd25e2ab3c2... "The locations where the signals associated with this connection penetrate the ionosphere."|

jwsteigerwalt 4y ago
This explanation helps understand the video.
layer8 4y ago
What are the stations/receivers? Is this crowdsourced data?
- williamscales 4y ago
  They have a GPS receiver in a fixed, known location. They measure the received signal and from the variations infer corrections for ionospheric effects. They are part of the GPS network. [0] https://en.wikipedia.org/wiki/GNSS_augmentation https://en.wikipedia.org/wiki/GNSS_augmentation
  - layer8 4y ago
    The video is data from just a single receiver?
    - krisoft 4y ago
      No. These are the receivers from japan’s GEONET.[1] “Geospatial Information Authority of Japan (GSI) operates GNSS CORSs that cover Japanese archipelago with over 1,300 stations at an average interval of about 20km for crustal deformation monitoring and GNSS surveys in Japan.” [2] Basically the government of Japan pepered their country with GPS base stations and they let researchers use the data from them. This is just a novel use of that data. 1: https://mobile.twitter.com/tylerni7/status/1593466486714421249 https://mobile.twitter.com/tylerni7/status/15934664867144212... 2: https://www.gsi.go.jp/ENGLISH/geonet_english.html https://www.gsi.go.jp/ENGLISH/geonet_english.html

danbruc 4y ago

But what are the moving dots in the animation? I would guess the moving dots are fixed GPS receivers, or more precisely the intersections of lines between fixed GPS receivers and moving GPS satellites with a sphere around Earth representing the ionosphere. If you look at the shape of the moving clusters, some look like Japan.