When discussing rising land measurements relative to Earth’s center, the concept you’re referring to involves measuring the vertical movement of land (uplift or subsidence) with respect to a fixed point — the center of mass of the Earth, also called the geocenter.

This measurement is used in geodesy, Earth sciences, and satellite navigation, and is particularly important in understanding:

• Tectonic uplift

• Glacial isostatic adjustment (GIA)

• Sea level rise

• Volcanic inflation or deflation

How It’s Measured

Land elevation changes relative to the Earth’s center are typically measured using:

1. GNSS (Global Navigation Satellite Systems), especially GPS
   High-precision GPS stations record the vertical motion of the land over time in a reference frame tied to the center of the Earth.

2. Satellite Radar Altimetry and Interferometry (InSAR)
   Used to detect small-scale vertical motions (e.g., from earthquakes or volcanic activity), although relative to a satellite, not directly the geocenter.

3. GRACE and GRACE-FO Satellites
   These measure mass changes (such as from melting glaciers), which relate to vertical land movement.

Units and Reference Frame

• Vertical motion is usually measured in millimeters per year (mm/yr).

• The reference frame used is the International Terrestrial Reference Frame (ITRF), which is centered at the Earth’s center of mass.

Examples

• Fennoscandia (Scandinavia): Rising up to ~10 mm/year due to glacial rebound after the last Ice Age.

• Alaska and Canada: Similar post-glacial rebound uplift.

• Antarctica and Greenland: Complex motion due to ongoing ice loss and isostatic adjustment.

Would you like recent data on specific locations or global vertical land motion maps?

Yes, you’re absolutely right — in Swedish, “geoiden” refers to the geoid, and it’s a crucial concept in measuring elevations and Earth’s shape.

Let me explain how measurements relative to the geoid differ from those relative to the Earth’s center.

🌍 Two Key Reference Surfaces in Earth Measurements

1. Earth’s Center (Geocentric Reference Frame)

• This is a purely geometric reference, using the Earth’s center of mass as the origin.

• Used by GNSS (e.g., GPS) systems and satellite orbit models.

• Gives ellipsoidal heights (called “h”), based on the mathematical shape of the Earth (an ellipsoid, not a perfect sphere).

2. Geoid (Swedish: Geoiden)

• This is a physical reference surface, defined as the mean sea level extended under the continents.

• The geoid is an equipotential surface of Earth’s gravity field — meaning water would settle along it if allowed to flow freely under only gravity.

• Heights measured relative to the geoid are called orthometric heights (or “height above sea level” in everyday terms).

🧮 Relationship Between Them

The three common vertical measurements are related like this:

$$\text{Orthometric Height (H)}=\text{Ellipsoidal Height (h)}-\text{Geoid Height (N)}$$

Where:

• H = height above the geoid (i.e. “sea level”)

• h = height above ellipsoid (measured from Earth’s center)

• N = geoid height (offset between ellipsoid and geoid)

So if you’re measuring land rising due to tectonic uplift, you might get:

• A rise relative to the geocenter (GNSS)

• A different value when interpreted relative to the geoid (how it would affect sea level)

🧭 Why This Matters

• Sea level studies: The geoid is key — sea level is defined relative to it.

• GNSS positioning: Uses Earth’s center (ellipsoidal heights).

• Engineering & surveying: Use geoid-based heights (what people call “height above sea level”).

Would you like a diagram showing the ellipsoid, geoid, and terrain — or real data (e.g. Sweden’s land rise in both systems)?