Radius of Earth at Great Salt Lake Desert Rte 80

Screenshot from the Geo-Data Visualisation and Calculator App, showing Route 80 at the Great Salt Lake Desert near Salt Lake City (Bonneville Salt Flats, Utah) showing a distance of 48.7 km.

Measuring the radius of the earth from 3 selected vectors. Each small circle represents the endpoint of a vector from the center of the earth to the location of the GNSS receiver at the time the measurement was taken.
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Salt Flats from Wendover, Michelle Pilling

The points are measured using Differential GPS to about 5 cm accuracy. The points were measured in earth centered earth fixed (ECEF) vectors in cartesian (x,y,z) coordinates by Multilateration of distances to multiple satellites in view at the same time, e.g. NAVSTAR, GLONAS and Galileo. The NAVSTAR satellites orbit the earth in an altitude of 20,200 km. No measured distance to any satellite was less than 20,200 km.

So the received signals can not be emitted by transmitters on earth. No shape of the earth assumed, no refraction and no perspective involved. The App shows the vectors as they were measured. If the earth were flat, all points would lie on a plane with Z-Axis about 1287 m, the elevation of the Lake. But the coordinates for a typical point are (−1,903,316.178, −4,451,650.518, 4,140,256.711) in meters. If you calculate the length of the vector l = √x2 + y2 + z2 = 6,370,363.447 m, which is the distance of the point from the center of the earth or about the radius of the earth.



Here are the GPS coordinates for the two observation points:

  • 40°44'24"N 114°05'59"W
  • 40°44'41"N 114°06'15"W

At the top of Wendover Blvd, there's a place to turn out just by the water basin, the time lapse and 2 other videos are from there. Then I climbed up a big hill (Wendover Viewpoint on Google Earth) and that's where I got the shot that's more straight on. I believe it's roughly 900ft higher than the salt bed. ~ David Cook (Don't Stop Motion)

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Created Tuesday, April 30, 2019
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Changed Monday, May 29, 2023