Geodesy Tools & Data
- DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite)- is a unique geodesy tool, where a dual frequency Doppler system is transmitted from global stations on the ground and received by specially equipped satellites. This system is mainly used to precisely determine orbits of satellites (then able to determine altimetry information), to monitor Earth's rotation, and is one of the tools used for the International Terrestrial Reference Frame.
- GPS (Global Positioning System)- is a USA managed network of 24 active satellites strategically positioned so that 6 are observable from nearly any location on Earth (at any given time). These satellites transmit radio signals to GPS receivers that can process information to determine position, velocity, and time. The Russian Federation manages a similar network, known as the Global Navigation Satellite System (GLONASS). The Global Navigation Satellite System (GNSS) is a network of permanent receivers that process data from GPS, GLONASS, and any future global transmitting satellites. GNSS data has been used to monitor Earth's rotation and deformation (including plate tectonics), monitor changes in the Earth's hydrosphere, ionosphere, and troposphere, to provide precise clock determinations, and is another tool used for the International Terrestrial Reference Frame. When GPS is combined with GIS and personal mobile GPS receivers, many new types of applications are emerging (more info) , such as disaster relief and real-time mapping.
- Gradiometer- Three pairs of proof masses oriented in orthogonal axes experience Earth's gravitational acceleration differently due to slightly different positions. Measurements taken produce gravity field data. Measurements can be taken terrestrially or via satellite.
- Radar Altimeter- sends pulses of radar to the earth that are reflected back to the satellite. The round trip time is converted to very accurate measurements of the satellite to ocean range (vertical distance). The range is equivalent to the Sea Surface Hight at that time. Satellites equipped with this technology also require information on the precise position of the satellite, thus requiring location systems, such as DORIS, for the data to be correctly interpreted.
- SAR- Synthetic Aperture Radar- satellites transmit wide beams of radar (frequencies of 1 to 10 GHz) towards Earth and measure the reflected waves; microwave images are generated from the results. SAR has the ability to penetrate clouds and vegetation to view high resolution ground variations. Ocean surface features can be detected (waves, fronts, eddies, oil slicks, ship wakes), wave and sea-ice forecasting, and all-weather measurements of snow and ice sheets.
- InSAR - Interferometric Synthetic Aperture Radar- is a variation of SAR, where data is taken more than once from the same location, the images can be stacked and any changes show up as a phase difference. The stacked or combined images are called Interferograms, which are useful to detect motion of sea ice and ice sheets, tectonic and volcanic hazards, and subsidence (particularly useful in urban areas).
- SLR- Satellite Laser Ranging- measures the round-trip time of pulses of light (from a station on Earth) to satellites with SLR reflectors. SLR can be used to detect temporal variations in Earth's gravity field, monitor tectonic motion and Earth's rotation, record variations of the location of Earth's center of mass (to a millimeter scale), measure glacial-rebound and subsidence, and is another tool to maintain the International Terrestrial Reference Frame.
- VLBI- Very-long Baseline Interferometry- is a technique that utilizes radio wavefronts emitted by a distant quasar (more info) by measuring the arrival time at two separate antennas located on Earth. VLBI can be used to directly measure changes in Earth's orientation, on the millimeter scale. These precise measurements can then be used to model ocean tides and currents, observe atmospheric variation, to record plate tectonic motion, to define the celestial reference frame and maintain the International Terrestrial Reference Frame
The University of Miami Geodesy lab web page contains illustrated primers on tools such as GPS, DORIS, and SAR.
Unavco supports geoscience education using geodesy, and has an extensive list of science applications of space geodesy, including: Solid Earth, Geotechnical, Cryosphere, Hydrology, Ocean, Atmosphere & Ionosphere applications.
DataNASA's Crustal Dynamics Data Information System (CDDIS) supports data archiving and distribution of raw data for GNSS (GPS and GLONASS), SLR, VLBI, and DORIS data sets.