European Space Agency to measure Earth at millimeter scale The European Space Agency has committed €76.6 million ($83 million) toward the development of Genesis – a flying observatory that will provide positioning services accurate to a single millimeter. The cash is roughly one third of the €233 million ($253 million) awarded for contracts related to position calculating satellite …
Plate Tectonics and weathering move places on the Earth by more than 1mm a year relative to each other.
Presumably they have their grid's origin defined as one particular point and measure movement relative to that?
Does anyone know what that point will be?
Greenland.Has stayed pretty much where it's currently at for a LONG time. Before the splitting of the atlantic, Scotland (north of Inverness) was connected to greenland until the splitting of the atlantic. However, south of carlisle was once 60 degrees south of the equator! Cornwall: well, that's another story. But, the north american plate is relatively stable
Shirley the problem with that is Greenwich (and everywhere else) is slowly changing latitude, altitude and orientation compared to the rest of the world's land masses. Greenland may have stayed mostly in the same latitude and orientation for millions of years. Land heaves for ,millennia after the removal of ice sheets from the last ice-age, sea levels a re rising, volcanic eruptions in South America are correlated with the amount of snowfall in winter, and, of course, the axis of rotation of the Earth wobbles.
>Shirley the problem with that is Greenwich (and everywhere else) is slowly changing latitude, altitude and orientation compared to the rest of the world's land masses.
No, the rest of the world may move relative to Greenwich - but that's their problem
Interesting though, Greenwich was the reference because the telescope was built on the meridian (or rather the meridian was the axis of the telescope). now you have to combine the various meridian telescopes all around the world all on different continental plates - so solving their relative locations to each other to within mm is interesting.
From the ESA Genesis Device website...
"Fix a satellite’s own position in space accurately enough and you can measure Earth beneath it much more precisely too. To achieve this goal down to millimetre level, ESA’s GENESIS satellite will combine and co-locate the four reference existing ‘geodetic’ – or Earth-measuring – techniques on a single platform for the first time. "
So using the satellite itself as zero point, and measuring relative to that.
So using the satellite itself as zero point, and measuring relative to that.
Presumably if it were needed, existing surveying techniques could provide reference markers anyway to cross-check or calibrate? Survey markers already exist and can be fun to find while hiking. Or on Google Earth, finding other satellite calibration markers. Sounds like a fun project though with a lot of potential, even if it won't immediately give me a 1mm resolution DTED model of the Earth's surface.
If I recall correctly -- and remember the early sixties were six long decades ago -- the USAF back then anchored their 3D cartesian coordinate system for tracking satellites to the ecliptic plane and something from astronomy called the First Point of Aires which I won't attempt to describe. (Look it up if you are curious) Anyway, I think that'd likely work fine for a fixed, reproducible coordinate system independent of slightly motile earthly landmarks.
"... something from astronomy called the First Point of Aires which I won't attempt to describe."
Simple. It's where the sun is at the vernal equinox. As it happenss, right about now. But it's really only any use for angles for navigation - not for 3-D positions.
"It's where the sun is at the vernal equinox. As it happenss, right about now. But it's really only any use for angles for navigation - not for 3-D positions."
Right and not so right.. Right in that it's the point on the (imaginary) celestial sphere where the sun (apparently) is located when the celestial equator's tilt with regard to the ecliptic plane is zero and the sun is (apparently) moving from South to North. And right that it was defined millennia ago because you need a fixed reference to do celestial navigation (as well as, I think, astrology). Not so right in that the line from the Earth's Center to the FPA is a perfectly OK 3rd element required to anchor an 3D coordinate system based on the Earth's Center and the ecliptic plane. What else would you use that would be any better? And maybe it simplifies conversion between Cartesian and spherical coordinates based on the Celestial sphere if that's necessary which it very likely is at times.
See Wikipedia for a probably clearer description of the first points of Aires and Libra
https://en.wikipedia.org/wiki/First_point_of_Aries
I think this accuracy is a taste of things to come.
https://www.theregister.com/2024/01/29/esa_lisa_experiment/
"" The plan is to send three spacecraft, trailing the Earth as it orbits the Sun, forming a highly accurate equilateral triangle in space. Each side will be 2.5 million kilometers long, and the spacecraft will exchange laser beams over the distance.....This is where those laser beams come in. By firing beams from one spacecraft to another, scientists can determine changes in masses' distances down to a few billionths of a millimeter.""
A few billionths of a millimeter of a distance of 2.5 million KMs .....
What a cool mission to be part of.
Any mention of the Geoid?
My so-called smartphone disagrees with my hand-held GPS receiver to the tune of 50 - 60 cm altitude.
The latter agrees more closely with the Ordnance Survey maps (sea-level based, and I'm in Central Scotland.)
Perhaps this hyper-accurate system reports the distance to the earth's Centre of Gravity ...
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