Fully operational Global Navigation Satellite Systems (GNSS) include the United States' Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), China's BeiDou Navigation Satellite System, and the European Union's Galileo. The GNSS observations enable end users to determine precise locations on Earth and relate different observing stations to a global reference system. Since the 1980s, NOAA’s National Geodetic Survey has been investigating how to improve the accuracy gained from GNSS observations by developing calibration procedures for modeling errors and biases encountered when calculating positions using GNSS satellite signals, and coding new processing algorithms into software that can be used by the public in a variety of services and tools.
Navigation satellites, through their orbital dynamics and geometry, establish the fundamental reference frame upon which all modern terrestrial reference frames, including the US National Spatial Reference System (NSRS), depend. Satellite ephemeris–that is, the precise data on where these satellites are at any moment–serve as datums in space for computing ranges to the satellites using Continuously Operating Reference Stations (CORS) to figure out exactly how Earth is oriented in space, and where things are located on Earth’s surface. As such, NOAA’s National Geodetic Survey is now developing the capability to generate precise orbital products for multiple satellite constellations. There is a clear economic benefit associated with a multi-GNSS capable NSRS service. As a result, US-based stakeholders that are increasingly reliant on applications requiring multi-GNSS data will benefit from multiple cost- and time-saving benefits, such as decreasing the data-collection times required to achieve a given precision, and ensuring higher precision in ports, cities, canyons, forests, or other environments with obstructed sky visibility.
Read moreIn providing geospatial infrastructure for our nation, NOAA’s National Geodetic Survey routinely processes vast amounts of data collected from Global Navigation Satellite Systems (GNSS). In recent years, the National Geodetic Survey focused on research to operate geospatial tools and services expanded from the U.S. GNSS constellation, Global Positioning System (GPS), to include European and Asian GNSS constellations. Outcomes of this research include the ability to increase accuracy for positioning, and the ability to determine a location more reliably using shorter survey times.
Read moreSurveying using high accuracy GNSS is used for safe navigation, road construction, and maintenance, including the evaluation of the structural integrity of facilities and their drainage capability to mitigate flooding and inundation. However, the accuracy of survey-grade GNSS receivers is greater than 10 cm for height determination. After several years of research, NOAA’s National Geodetic Survey established an Absolute (3D) Antenna Calibration Service. Using a robotic arm that rotates a GNSS antenna in all directions while collecting GNSS signals, it is possible to determine the offsets between the GNSS signal point of reception to the physical antenna structure. As a result, survey accuracy can be determined to the 1 cm level (a tenfold increase). This service is one of only five services available worldwide and the first in North America. These antenna calibration services provide the surveying community more accurate GNSS services for high-accuracy regional land and marine surveying operations.
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