📐 Measuring the Earth 🌎 The Science of Geodesy 🌐
GEODESY
Geodesy is the science of measuring Earth’s size, shape, orientation in space, and gravity field. Geodesy is one of the oldest sciences, dating back to Ancient Greece, and has many applications in modern society. Researchers use high-precision measurements to learn about Earth and how it changes over time. The most familiar geodetic instrument is the Global Positioning System (GPS), the U.S. component of a global navigation satellite system (GNSS).
EARTH ON THE MOVE
The motion of tectonic plates, along with erosion and deposition, alter Earth’s surface, creating mountains and valleys and causing earthquakes. Earth’s shape also constantly changes because of gravitational forces between our moon, sun, and other celestial bodies. Movements on the order of tens of centimetres could trigger geologic events like volcanic eruptions. Ali these motions can be monitored using tools such as high-precision GPS and Laser scanning (lidar).
SEA LEVEL AND TIDES
Measuring global level requires monitoring both tides and the vertical motion of landmasses. Shorelines subside under the weight of new sediments, raising sea level locally. Melting glaciers cause land to rebound, lowering local sea level. Modern tide gauges include GPS, providing more accurate timing and height of tides, as well as their long-term trends. Accurate measurements are invaluable for fishing and shipping industries, and for long-term planning of coastal infrastructure.
VEGETATION
Scientists can measure wavelengths of light either absorbed or reflected by green vegetation using remote sensing observations. Known as Normalized Difference Vegetation (NDVI), this can help scientists and conservationists track where vegetation is healthy and where it is stressed, due to human activities like deforestation or due to natural hazards like wildfires.
NAVIGATION
GPS systems are practically synonymous with navigation, even more so with the rise of autonomous vehicles. A highly precise and reliable way of tracking vehicle position and proximity to other things on the road is necessary for safe autonomous driving. Today, GPS systems with centimetre-level accuracy and lidar inform autonomous vehicles where they are, where they are going, and how close they are to other objects.
EARTHQUAKE EARLY WARNING
Real-time GPS data, in combination with seismic instrumentation, allows scientists to detect earthquakes quickly and warn people of impending shaking. Earthquake early warning systems are currently being developed for the western United States and could give enough warning to safely shut down public transportation, land planes, stop surgeries, and mobilize emergency services to prevent significant damage and loss of life.
DROUGHT MONITORING
Snow cover, lake levels, soil moisture, and changes in groundwater- level can all cause Earth’s surface to move up or down. The weight of lakes and snow pushes the surface down. A lack of water at the surface allows the land to rebound, or rise. GPS and gravity measurements record these small movements, allowing scientists, water management organizations, and the agricultural community to track the severity of drought and efficiently conserve water resources.
ATMOSPHERIC MOISTURE
The amount of water vapour in the atmosphere determines the weather that may occur. GPS can be used to measure water vapour in the atmosphere because signals from GPS satellites to ground-based GPS receivers are delayed by water vapour. This information is used to better forecast severe weather, as well as to study the hydrologic cycle and climate change. International networks, such as COCONet in the Caribbean, allow for data collection across national boundaries.
GRAVITY
Earth’s gravity field changes from place to place depending, in part, on topography. Gravity is an attraction between two objects with mass Since the distribution of mass is constantly changing (e.g., through mountain building and volcanic eruptions), the gravity field is, changing too. Scientists can monitor the varying gravity field with satellite missions like GRACE (Gravity Recovery and Climate Experiment).
TIMING AND WORLD MARKETS
GPS and financial markets, such as the New York Stock Exchange, have become intimately linked. Not only does GPS provide a precise location, it also provides a precise time from multiple atomic clocks onboard GPS satellites. These atomic clocks keep time within billionths of a second. Precise timing allows, for synchronization between global financial computers, in a system where time-stamping of trade orders could mean the difference of millions of dollars.
POLAR ICE
Scientists monitor polar ice conditions through a number of geodetic observations including GPS measurements of Earth’s surface motion, studies of Earth’s gravity field, and satellite lidar measurements of ice sheet elevations. Knowing the status of polar ice is important to understanding the interconnectivity of our global system, as ice affects global temperatures, ocean circulation, climate, weather, and wildlife.
SPACE WEATHER
Satellite and ground networks critical to geodesy can be negatively impacted by space weather, and can also measure it. Our Sun, the main source of space weather, emits charged particles that interact with Earth’s upper atmosphere. This can produce strong electromagnetic fields that interfere with power lines and radio transmissions, or produce beautiful aurora. As with water vapour, changes in the ionosphere can be measured by its effects on the signals from GPS satellites to ground-based receivers. Monitoring space weather activity allows us to take early action to protect infrastructure.
Source:unavco.org
