3 ms·

Isn't that relative sea level changes in places like Scandinavia - the sea isn't dropping, the land is rising? https://en.wikipedia.org/wiki/Relative_sea_level

Isn't that relative sea level changes in places like Scandinavia - the sea isn't dropping, the land is rising? https://en.wikipedia.org/wiki/Relative_sea_level https://en.wikipedia.org/wiki/Relative_sea_level

jdontillman 4y ago
Exactly. Because the sensors are mounted on that very land. So tectonic movement will certainly have an effect. And you can see remnants of earthquakes in some of the data.
- AnimalMuppet 4y ago
  In Scandinavia, isn't it glacial rebound rather than tectonic?
  - bell-cot 4y ago
    > 3. (geology) Of, relating to, or caused by large-scale movements of the Earth's (or a similar planet's) lithosphere - https://en.wiktionary.org/wiki/tectonic https://en.wiktionary.org/wiki/tectonic
    - LeifCarrotson 4y ago
      I expect the parent is referring to human-caused melting of glaciers as the root cause of that tectonic movement, rather than the expected natural motion of the tectonic plates.
      - Scarblac 4y ago
        It's the glaciers melting at the end of the last Ice Age that Scandinavia is still rising from. https://en.wikipedia.org/wiki/Last_Glacial_Period#Weichselian_glaciation_(Scandinavia_and_northern_Europe) https://en.wikipedia.org/wiki/Last_Glacial_Period#Weichselia... > As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland, where the land is rising at a rate of as much as 8–9 mm per year, or 1 m in 100 years. This is important for archaeologists, since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.
BurningFrog 4y ago
Yeah, the sea must be "level" in some sense across the planet. Don't know if local variations in gravity may have a measurable impact?
- beerandt 4y ago
  The absolute value of gravity is (to oversimplify) the sea-level datum for current generation datums, like the delayed NGS (nominal year) 2022 datums. They've (NGS) been flying absolute gravity measurement equipment in planes with precision GPS and lidar since ~2005 as part of the GRAV-D program. Additionally, slight 'variations' (ie deviations from the expected circular/elliptical) in the orbits of GPS satellites can be used to infer slight variations in the gravity below. Separately, the military likely has had all of this measured and modeled for decades as part of ballistic missile targeting, but remains mostly classified at useful resolutions. The transitions from NGVD27 to NAVD88 to the work-in-progress 22 datum is exactly because the idea of a simple "universal" sea-level doesn't exist in the manor you would expect it to. But even with the GRAV-D based datums, the actual observed water levels will occur at slightly different datum heights in different locations, for various geophysical reasons.
- CorrectHorseBat 4y ago
  The melting of glaciers themselves can have an impact on gravity, causing water levels to drop around them. https://www.theguardian.com/environment/ng-interactive/2018/sep/12/greenland-antarctic-ice-sheet-sea-level-rise-science-climate https://www.theguardian.com/environment/ng-interactive/2018/...
- deleted 4y ago
  [deleted]
- cwillu 4y ago
  PDF of gravitational correction factors by geographical region for use in theoretical weighscale calibration (vs calibrating with actual test weights): https://hardyinst.custhelp.com/app/answers/detail/a_id/1588/~/what-is-gravity-correction-and-how-do-i-use-it%3F https://hardyinst.custhelp.com/app/answers/detail/a_id/1588/...

jdontillman 4y ago

Exactly. Because the sensors are mounted on that very land. So tectonic movement will certainly have an effect. And you can see remnants of earthquakes in some of the data.

AnimalMuppet 4y ago
In Scandinavia, isn't it glacial rebound rather than tectonic?
- bell-cot 4y ago
  > 3. (geology) Of, relating to, or caused by large-scale movements of the Earth's (or a similar planet's) lithosphere - https://en.wiktionary.org/wiki/tectonic https://en.wiktionary.org/wiki/tectonic
  - LeifCarrotson 4y ago
    I expect the parent is referring to human-caused melting of glaciers as the root cause of that tectonic movement, rather than the expected natural motion of the tectonic plates.
    - Scarblac 4y ago
      It's the glaciers melting at the end of the last Ice Age that Scandinavia is still rising from. https://en.wikipedia.org/wiki/Last_Glacial_Period#Weichselian_glaciation_(Scandinavia_and_northern_Europe) https://en.wikipedia.org/wiki/Last_Glacial_Period#Weichselia... > As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland, where the land is rising at a rate of as much as 8–9 mm per year, or 1 m in 100 years. This is important for archaeologists, since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.

BurningFrog 4y ago

Yeah, the sea must be "level" in some sense across the planet. Don't know if local variations in gravity may have a measurable impact?

beerandt 4y ago
The absolute value of gravity is (to oversimplify) the sea-level datum for current generation datums, like the delayed NGS (nominal year) 2022 datums. They've (NGS) been flying absolute gravity measurement equipment in planes with precision GPS and lidar since ~2005 as part of the GRAV-D program. Additionally, slight 'variations' (ie deviations from the expected circular/elliptical) in the orbits of GPS satellites can be used to infer slight variations in the gravity below. Separately, the military likely has had all of this measured and modeled for decades as part of ballistic missile targeting, but remains mostly classified at useful resolutions. The transitions from NGVD27 to NAVD88 to the work-in-progress 22 datum is exactly because the idea of a simple "universal" sea-level doesn't exist in the manor you would expect it to. But even with the GRAV-D based datums, the actual observed water levels will occur at slightly different datum heights in different locations, for various geophysical reasons.
CorrectHorseBat 4y ago
The melting of glaciers themselves can have an impact on gravity, causing water levels to drop around them. https://www.theguardian.com/environment/ng-interactive/2018/sep/12/greenland-antarctic-ice-sheet-sea-level-rise-science-climate https://www.theguardian.com/environment/ng-interactive/2018/...
deleted 4y ago
[deleted]
cwillu 4y ago
PDF of gravitational correction factors by geographical region for use in theoretical weighscale calibration (vs calibrating with actual test weights): https://hardyinst.custhelp.com/app/answers/detail/a_id/1588/~/what-is-gravity-correction-and-how-do-i-use-it%3F https://hardyinst.custhelp.com/app/answers/detail/a_id/1588/...