The science of geodesy extends far back in history. In the 3rd century BC, Eratosthenes famously calculated the circumference of the Earth and even the tilt of its axis. In the 1700s and 1800s, the challenges of long-distance navigation over the ocean led to the invention of ship-borne clocks and surveying tools like the sextant—greatly advancing our ability to measure location.

But in the satellite era, positioning and navigation has improved even further. Global navigation satellite systems (like GPS), supported by ground-based technologies measuring Earth’s orientation in space, enable devices to calculate our location with astounding precision. That opens the door to technologies like precision agriculture and autonomous vehicles.

High-precision positioning also allows us to monitor natural hazards and resources. We can directly measure the movement of tectonic plates and changes in land elevation. And efforts to minimize errors resulting from navigation satellite signals passing through the atmosphere now even enable measurements of important atmospheric properties like water vapor content.

For earthquake hazards, we can monitor the accumulation of stress on faults over time—and even generate warnings when an earthquake occurs that can reach people before the shaking does. Similarly, subtle surface movements on volcanoes can reveal the movement of magma or changes in pressure that indicate the risk of an eruption.

Measurements of long-term ground subsidence (decreasing surface elevation) can highlight threats to built infrastructure from flooding or direct structural damage.

Apart from hazards, geodesy can also track global environmental change. Vertical movement can be associated with changes in water resources like groundwater depletion, for example. And many observations are critical to our understanding of sea level rise, from changing coastal land elevation to shrinking glaciers to accurate satellite measurements of ocean height and mass.

Read on to explore some of these topics and see how UNAVCO’s work contributes to a better understanding of Earth processes and hazards using geodesy.