ITRF: What is the International Terrestrial Reference Frame? [2024]
The International Terrestrial Reference Frame (ITRF) is a reference frame for earth sciences and global positioning derived from the International Terrestrial Reference System (ITRS). The ITRF is approved by the International Association of Geodesy (IAG) to serve as a stable reference to measure Earth's deformation and crustal motion. The IAG also recommends ITRF as the standard reference frame for location positioning, satellite navigation, and earth science applications.
This article will examine ITRF in greater detail, explaining how it works and why it's so important in geodesy today. Whether you're in the industry or just curious about how changes in the planet are measured, this article will give you a clearer picture of the technology.
What is the International Terrestrial Reference Frame (ITRF)?
The International Terrestrial Reference Frame is a series of spatial datums that was developed and managed by the International Earth Rotation and Reference Systems Service (IERS). As a global reference frame, it provides precise, consistent, and globally recognized coordinate systems that are essential for high-accuracy geospatial measurements. It is used with technologies such as Global Positioning Systems (GPS) and satellite imaging, as well as remote sensing for precise mapping, location tracking, and infrastructure development.
Since 1997, there have been a total of 7 new ITRF realizations. Each one adds new data and the most recent advancements in surveying and mathematical methods.
How does ITRF work?
The ITRF works as a global framework, providing precise coordinates that are used to anchor various spatial data accurately. They basically serve as a benchmark and a foundation for geographical information systems (GIS), global navigation satellite systems (GNSS), inertial navigation systems (INS), and other geospatial mapping and navigation applications that can support robotics, drones, and self-driving applications.
ITRF Versions
Since the release of ITRF94, seven new versions have been released, each improving on the previous one.
ITRF96
ITRF96 is the first version of ITRF released since ITRF94. The main update is that it significantly improves the accuracy and consistency of the coordinates and velocities of the IGS sites, such as in Eastern Asia and the Western Pacific, compared with ITRF94.
ITRF97
The International Reference Framework of 1997 contains approximately 550 stations on 325 sites. It combines station positions simultaneously with velocities using full variance-covariance, which allows it to provide a full representation of the Earth's surface, enabling precise analysis and prediction of crustal movements.
ITRF2000
The ITRF2000 was a significant release since it reflected geodesy solutions free from external constraints. At release, ITRF2000 was praised for being the most extensive and accurate one ever developed, containing about 800 stations located at about 500 sites, a big improvement from ITRF97.
ITRF2005
The International Reference Framework 2005 introduced null translation parameters and rotation rates. There's also a null scale factor and a null scale rate which, when applied, ensure that the reference frame remains stable and consistent over time.
ITRF2008
The ITRF2008 improved on ITRF2005. It reprocessed the solutions of the four geodesy techniques: Very long baseline interferometry (VLBI), satellite laser ranging (SLR), GNSS, and Doppler orbitography and radiopositioning integrated by satellite (DORIS). It also used input data derived from weekly time series data from satellite techniques and daily time series data from VLBI.
ITRF2014
Unlike preceding ITRF releases, the ITRF2014 was generated with support for enhanced modeling of nonlinear station motions, including seasonal signals of station positions and postseismic deformation.
ITRF2020
ITRF2020 is the latest version of ITRF and is said to improve on ITRF2014. In addition to using four geodesy techniques for accuracy, ITRF2020 included local ties, equating station velocities, and seasonal signals.
How is ITRF used?
ITRF is a global framework for surveying and mapping fields for increased accuracy. Let’s see how that works with real-world applications including GPS and INS applications.
Observation in Earth System Science
ITRF is the foundation for all earth science system research, including ground-based and space-based observations. It establishes a consistent reference frame for analyzing and interpreting data across various geodetic and geophysical.
Location-based services
ITRF is used with GPS-enabled devices in smartphones and navigation systems to provide accurate positioning and navigation services. By incorporating ITRF coordinates into location-based services, users can accurately determine their positions, navigate to desired locations, and access location-specific information.
ITRF can also be used in RTK correction services like Point One’s Polaris to provide more accurate positioning data. Real-time kinematic systems use real-time corrections from ITRF to enhance the accuracy of GPS measurements, allowing for centimeter-level positioning in real-time applications.
Robotics
Robotics that operate outdoors, such as autonomous vehicles (including drones and self-driving cars), agricultural robots, or survey robots, use GPS or other GNSS to determine their position on the Earth’s surface.
The ITRF provides a consistent and accurate frame of reference for these systems to calculate positions to centimeter-level accuracy when augmented with techniques like RTK positioning.
For example, large-scale farmers can use robots to precisely map field boundaries, monitor crop health, optimize irrigation, and apply fertilizers and pesticides with greater accuracy. This precision agriculture allows for increasing efficiency and productivity.
Related Terms for ITRF
Here are some terms that relate to the international terrestrial reference frame:
NAD83
NAD83 is the third geometric control datum, succeeding NAD27. It’s a result of a collaborative project carried out by the National Geodetic Control Survey of the United States, the Geodetic Survey of Canada, and the Danish Geodetic Institute of Greenland.
Although termed NAD83, it was actually released in 1986. It wasn’t until 1990 that state-by-state adjustment was completed for NAD83, and it has been adjusted twice since then, first in 2007 and then in 2011.
WGS84
WGS84 is a global datum developed by the US National Geospatial-Intelligence Agency to define the Earth model from a mathematical perspective and comprises different elements. These include an ellipsoid that approximates the Earth's shape, a horizontal datum that establishes a standard for latitude and longitude, a vertical datum that defines the reference surface for altitude (height), and a coordinate system for mapping and collecting data.
ITRS
The ITRS is more of a standard than a system. It describes procedures for creating reference frames. Basically, geodesists and geophysicists have to figure out how to realize the ITRS with more accuracy and that's why there are new versions of ITRFs.
Both ITRS and its realization ITRF are maintained by the International Earth Rotation and Reference Systems Service (IERS), and all ITRS originate from the earth’s center of mass, which means that they are geocentric.
ICRF
ICRF is an acronym for the International Celestial Reference Frame. Just as the ITRF is a realization of ITRS, the ICRF is a realization of the international celestial reference system. Although not as popular as ITRF, the ICRF is also a coordinate reference system that comprises a catalog of precise coordinates of extragalactic radio sources using the VLBI technique.
More About the International Terrestrial Reference Frame
Here’s some more information on ITRF.
What is the origin of the ITRF?
As a geocentric datum, the origin of ITRF is the earth’s center of mass.
What does the ITRF stand for?
ITRF is an acronym for the International Terrestrial Reference Frame.
What is ITRF datum?
The ITRF datum is a series of spatial datums developed and managed by the International Earth Rotation and Reference Systems Service (IERS) for establishing a consistent reference frame for geodetic and geophysical applications worldwide.
Access the ITRF 2014 epoch coordinate reference system
The ITRF 2014 is one of the most advanced and accessible versions of ITRF, and it works with various GNSS (Global Navigation Satellite Systems) and RTK solutions like Point One Navigation’s Polaris.
Whether you want to use ITRF84, NAD83, or another datum appropriate to your location, Polaris makes it easy with intelligent assignment of datums based on your location. They invented automatic assignment of datums and base stations.
You can just connect to a single mount point and they ensure your devices are referencing the closest base stations and the appropriate local datum. You can easily switch between local and global datums because Point One does the transformation for you.
