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44-538: The National Geodetic Survey ( NGS ) is a United States federal agency based in Washington, D.C. that defines and manages a national coordinate system , providing the foundation for transportation and communication, mapping and charting, and a large number of science and engineering applications. Since its founding in 1970, it has been part of the National Oceanic and Atmospheric Administration (NOAA),

88-527: A glacier in West Antarctica was named after the GRACE mission. The monthly gravity anomalies maps generated by GRACE are up to 1,000 times more accurate than previous maps, substantially improving the accuracy of many techniques used by oceanographers , hydrologists , glaciologists , geologists and other scientists to study phenomena that influence climate. From the thinning of ice sheets to

132-469: A day, they sense minute variations in Earth's gravitational pull. When the first satellite passes over a region of slightly stronger gravity, a gravity anomaly , it is pulled slightly ahead of the trailing satellite. This causes the distance between the satellites to increase. The first spacecraft then passes the anomaly, and slows down again; meanwhile the following spacecraft accelerates, then decelerates over

176-712: A division within the Department of Commerce . The National Geodetic Survey's history and heritage are intertwined with those of other NOAA offices. It traces its history to the Survey of the Coast , which was formed in 1807 as the first scientific agency of the U.S. federal government . It became the United States Coast Survey in 1836 and the United States Coast and Geodetic Survey in 1878,

220-511: A highly precise BlackJack GPS receiver and digital signal processing system was provided by JPL in Pasadena. The highly precise accelerometer that is needed to separate atmospheric and solar radiation pressure effects from the gravitation data was manufactured by ONERA . GRACE's key measurement, satellite gravimetry , is not derived from electromagnetic waves. Instead, the mission uses a microwave ranging system to accurately measure changes in

264-400: A near-polar inclination of 89°. During normal operations, the satellites were separated by 220 km along their orbit track. This system was able to gather global coverage every 30 days. GRACE far exceeded its 5-year design lifespan, operating for 15 years until the decommissioning of GRACE-2 on 27 October 2017. Its successor, GRACE-FO , was successfully launched on 22 May 2018. In 2019,

308-708: A record of mass loss within the ice sheets of Greenland and Antarctica. Greenland has been found to lose 280 ± 58  Gt of ice per year between 2003 and 2013, while Antarctica has lost 67 ± 44  Gt per year in the same period. These equate to a total of 0.9 mm/yr of sea level rise. Increases in ocean heat content resulting from Earth's Energy Imbalance of about 0.8 W/m were similarly found spanning 2002 thru 2019. GRACE data have also provided insights into regional hydrology inaccessible to other forms of remote sensing: for example, groundwater depletion in India and California. The annual hydrology of

352-492: A region. GRACE is also sensitive to permanent changes in the gravity field due to earthquakes. For instance, GRACE data have been used to analyze the shifts in the Earth's crust caused by the earthquake that created the 2004 Indian Ocean tsunami. In 2006, a team of researchers led by Ralph von Frese and Laramie Potts used GRACE data to discover the 480-kilometer-wide (300 mi) Wilkes Land crater in Antarctica , which

396-718: A small number of independent agencies that are not considered part of the executive branch, such as the Congressional Research Service and the United States Sentencing Commission , which are legislative and judicial agencies, respectively. The U.S. Congress is the bicameral legislature of the United States government, and is made up of two chambers: the United States Senate (the upper chamber) and

440-541: A spacecraft about 220 kilometres (140 mi) away. This laser approach will generate much more accurate measurements than the previous GRACE satellite mission. The GRACE-FO satellites obtain electricity from gallium arsenide solar cell array panels covering the outside of each satellite. GRACE-FO will continue to monitor Earth's gravity and climate. The mission will track gravitational changes in global sea levels, glaciers, and ice sheets, as well as large lake and river water levels, and soil moisture. In addition, each of

484-559: A typical latency of 1–2 months. These geopotential coefficients may be used to compute geoid height, gravity anomalies, and changes in the distribution of mass on Earth's surface. Gridded products estimating changes in mass in units of liquid water equivalent thickness are available at JPL's GRACE Tellus website. Following an age-related battery issue on GRACE-2 in September 2017, it became apparent that GRACE-2's remaining battery capacity would not be sufficient to operate. Therefore, it

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528-563: Is Byron Tapley of the University of Texas Center for Space Research, and the co-principal investigator is Christoph Reigber of the GeoForschungsZentrum (GFZ) Potsdam . The two GRACE satellites, GRACE-1 and GRACE-2, were launched from Plesetsk Cosmodrome , Russia, on a Rockot ( SS-19 + Briz upper stage) launch vehicle on 17 March 2002. The spacecraft were launched to an initial altitude of approximately 500 km at

572-408: Is a network of orthometric heights obtained through spirit leveling . Because of the close relationship between height and Earth's gravity field, NGS also collects and curates terrestrial gravity measurements and develops regional models of the geoid (the level surface that best approximates sea level) and its slope, the deflection of the vertical . NGS is responsible for ensuring the accuracy of

616-543: Is the Arabian Aquifer System , upon which more than 60 million people depend for water. GRACE also detects changes in the gravity field due to geophysical processes. Glacial isostatic adjustment —the slow rise of land masses once depressed by the weight of ice sheets from the last ice age—is chief among these signals. GIA signals appear as secular trends in gravity field measurements and must be removed to accurately estimate changes in water and ice mass in

660-447: Is to meteorologists. For example, measuring ocean pressure gradients allows scientists to estimate monthly changes in deep ocean currents. The limited resolution of GRACE is acceptable in this research because large ocean currents can also be estimated and verified by an ocean buoy network. Scientists have also detailed improved methods for using GRACE data to describe Earth's gravity field. GRACE data are critical in helping to determine

704-680: The Administrative Procedure Act definition of "agency" applies to most executive branch agencies, Congress may define an agency however it chooses in enabling legislation, and through subsequent litigation often involving the Freedom of Information Act and the Government in the Sunshine Act . These further cloud attempts to enumerate a list of agencies. The executive branch of the federal government includes

748-560: The Amazon basin provides an especially strong signal when viewed by GRACE. A University of California, Irvine -led study published in Water Resources Research on 16 June 2015 used GRACE data between 2003 and 2013 to conclude that 21 of the world's 37 largest aquifers "have exceeded sustainability tipping points and are being depleted" and thirteen of them are "considered significantly distressed." The most over-stressed

792-666: The Executive Office of the President and the United States federal executive departments (whose secretaries belong to the Cabinet ). Employees of the majority of these agencies are considered civil servants . The majority of the independent agencies of the United States government are also classified as executive agencies (they are independent in that they are not subordinated under a Cabinet position). There are

836-585: The Executive Residence (EXR) maintained by the Office of Administration (OA). To effectively run the country's affairs, the President also maintains councils regarding various issues, including: GRACE and GRACE-FO By measuring gravity anomalies, GRACE showed how mass is distributed around the planet and how it varies over time. Data from the GRACE satellites is an important tool for studying Earth's ocean , geology , and climate . GRACE

880-498: The LAGEOS experiment to try to measure the relativistic frame-dragging effect. The spacecraft were manufactured by Astrium of Germany, using its "Flexbus" platform . The microwave RF systems, and attitude determination and control system algorithms were provided by Space Systems/Loral . The star cameras used to measure the spacecraft attitude were provided by Technical University of Denmark . The instrument computer along with

924-659: The National Ocean Service ). In 2009, former NOAA Commissioned Officer Corps officer Juliana P. Blackwell was named NGS Director, becoming the first woman to head either NGS or any of its ancestor organizations. The National Geodetic Survey is an office of NOAA's National Ocean Service . Its core function is to maintain the National Spatial Reference System (NSRS), "a consistent coordinate system that defines latitude, longitude, height, scale, gravity, and orientation throughout

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968-540: The United States House of Representatives (the lower chamber). Together, the two chambers exercise authority over the following legislative agencies: The legislature also oversees the Library of Congress (LOC), a national library dedicated to national records, which administers various programs, agencies, and services including: The federal judiciary consists of courts established under Article Three of

1012-463: The Center of Mass Trim Assembly (MTA) which ensures the center of mass is modified throughout the flight accordingly. CSR, GFZ, and JPL process observations and ancillary data downloaded from GRACE to produce monthly geopotential models of Earth. These models are distributed as spherical harmonic coefficients with a maximum degree of 60. Degree 90 products are also available. These products have

1056-540: The ITRF. United States territories on the Pacific, Caribbean, and Mariana plates will have their own respective geodetic datums. The North American-Pacific Geopotential Datum of 2022 (NAPGD2022) will separately define the height system of the United States and its territories, replacing NAVD88. It will use a geoid model accurate to 1 centimeter (0.4") to relate orthometric height to ellipsoidal height measured by GPS, eliminating

1100-593: The NSRS over time, even as the North American plate rotates and deforms over time due to crustal strain, post-glacial rebound , subsidence , elastic deformation of the crust, and other geophysical phenomena. NGS will release new datums in 2022. The North American Terrestrial Reference Frame of 2022 (NATRF2022) will supersede NAD83 in defining the geometric relationship between the North American plate and

1144-611: The United States Constitution . These are the The United States bankruptcy courts , while not established as Article III courts, are legally designated as "units of the district courts." The judicial branch includes the following agencies: The President of the United States is the chief executive of the federal government. He is in charge of executing federal laws and approving, or vetoing, new legislation passed by Congress. The President resides in

1188-506: The United States in three-dimensional space. The datum may be accessed via NGS's network of survey marks or through the Continuously Operating Reference Station (CORS) network of GPS reference antennas. NGS is responsible for computing the relationship between NAD83 and the ITRF. The physical components of the NSRS are reflected in its height system, defined by the vertical datum NAVD88 . This datum

1232-540: The United States". NGS is responsible for defining the NSRS and its relationship with the International Terrestrial Reference Frame (ITRF). The NSRS enables precise and accessible knowledge of where things are in the United States and its territories. The NSRS may be divided into its geometric and physical components. The official geodetic datum of the United States, NAD83 defines the geometric relationship between points within

1276-482: The calculation of geodetic satellite orbits. GRACE is sensitive to regional variations in the mass of the atmosphere and high-frequency variation in ocean bottom pressure. These variations are well understood and are removed from monthly gravity estimates using forecast models to prevent aliasing . Nonetheless, errors in these models do influence GRACE solutions. GRACE data also contribute to fundamental physics. They have been used to re-analyze data obtained from

1320-606: The cause of sea level rise , whether it is the result of mass being added to the ocean – from melting glaciers , for example – or from thermal expansion of warming water or changes in salinity . High-resolution static gravity fields estimated from GRACE data have helped improve the understanding of global ocean circulation . The hills and valleys in the ocean's surface ( ocean surface topography ) are due to currents and variations in Earth's gravity field. GRACE enables separation of those two effects to better measure ocean currents and their effect on climate. GRACE data have provided

1364-452: The flow of water through aquifers and the slow currents of magma inside Earth, mass measurements provided by GRACE help scientists better understand these important natural processes. GRACE chiefly detected changes in the distribution of water across the planet. Scientists use GRACE data to estimate ocean bottom pressure (the combined weight of the ocean waters and atmosphere), which is as important to oceanographers as atmospheric pressure

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1408-452: The latter name change reflecting the increasing role of geodesy in its work. Upon the creation of NOAA in 1970, the Coast and Geodetic Survey was abolished and its responsibilities were split among various agencies and offices of NOAA. The Coast and Geodetic Survey′s former geodetic responsibilities were placed under the new National Geodetic Survey in NOAA's National Ocean Survey (later renamed

1452-465: The launch with five Iridium NEXT satellites. During in-orbit checks, an anomaly was discovered in the primary system component of the microwave instrument (MWI), and the system was temporarily powered down on 19 July 2018. After a full investigation by an anomaly response team at JPL, the backup system in the MWI was powered up on 19 October 2018 and GRACE-FO resumed its in-orbit checks. GRACE-FO entered

1496-458: The link. This is made possible due to the onboard Ultra Stable Oscillator (USO) which produces the frequencies for the K-band ranging system. The micrometer-sensitivity of this measurement requires accordingly precise measurements of each spacecraft's position, motion, and orientation to be useful. To remove the effect of external, non-gravitational forces (e.g., drag , solar radiation pressure ),

1540-525: The need for future leveling projects. This geoid model will be based on airborne and terrestrial gravity measurements collected by NGS's GRAV-D program as well as satellite-based gravity models derived from observations collected by GRACE , GOCE , and satellite altimetry missions. NGS provides a number of other public services. It maps changing shorelines in the United States and provides aerial imagery of regions affected by natural disasters, enabling rapid damage assessment by emergency managers and members of

1584-494: The public. The Online Positioning and User Service (OPUS) processes user-input GPS data and outputs position solutions within the NSRS. The agency offers other tools for conversion between datums. List of federal agencies in the United States [REDACTED] [REDACTED] Legislative definitions of an agency of the federal government of the United States are varied, and even contradictory. The official United States Government Manual offers no definition. While

1628-472: The same point. By measuring the constantly changing distance between the two satellites and combining that data with precise positioning measurements from Global Positioning System (GPS) instruments, scientists can construct a detailed map of Earth's gravity anomalies. The two satellites (nicknamed "Tom" and "Jerry" ) constantly maintain a two-way, K-band microwave-ranging link between them. Fine distance measurements are made by comparing frequency shifts of

1672-456: The science phase of its mission on 28 January 2019. The orbit and design of GRACE-FO is very similar to its predecessor. GRACE-FO employs the same two-way microwave-ranging link as GRACE, which will allow for similar inter-satellite ranging precision. In addition, GRACE-FO employs laser-ranging interferometry (LRI) as a technological experiment in preparation for future satellites. The LRI allows for more accurate inter-satellite ranging due to

1716-490: The shorter wavelength of light, and additionally allows the angle between the two spacecraft to be measured as well as their separation via differential wavefront sensing (DWS). Using the LRI, scientists have improved the precision of the separation distance measurements by a factor of more than 20 relative to the GRACE mission. Each laser on the LRI has about the same power as four laser pointers. These lasers must be detected by

1760-402: The speed and distance between two identical spacecraft flying in a polar orbit about 220 kilometers (140 mi) apart, 500 kilometers (310 mi) above Earth. The ranging system is sensitive enough to detect separation changes as small as 10 micrometers (approximately one-tenth the width of a human hair) over a distance of 220 kilometers. As the twin GRACE satellites circle the globe 15 times

1804-420: The vehicles use sensitive Super STAR electrostatic accelerometers located near their respective centers of mass. GPS receivers are used to establish the precise positions of each satellite along the baseline between the satellites. The satellites use star cameras and magnetometers to establish attitude . The GRACE vehicles also have optical corner reflectors to enable laser ranging from ground stations using

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1848-546: Was a collaborative endeavor involving the Center for Space Research at the University of Texas at Austin , NASA's Jet Propulsion Laboratory , the German Aerospace Center and Germany's National Research Center for Geosciences , Potsdam. The Jet Propulsion Laboratory was responsible for the overall mission management under the NASA ESSP (Earth System Science Pathfinder) program. The principal investigator

1892-499: Was decided in mid-October to decommission the GRACE-2 satellite and end GRACE's science mission. Atmospheric reentry of GRACE-2 occurred on 24 December 2017 at approximately 00:16 UTC; atmospheric reentry of GRACE-1 took place on 10 March 2018 around 06:09 UTC. The GRACE-FO mission, a collaboration between NASA and GFZ , was launched on 22 May 2018 aboard a SpaceX Falcon 9 rocket from Vandenberg AFB, California, sharing

1936-420: Was probably formed about 250 million years ago. Data from GRACE has improved the current Earth gravitational field model , leading to improvements in the field of geodesy . This improved model has allowed for corrections in the equipotential surface which land elevations are referenced from. This more accurate reference surface allows for more accurate coordinates of latitude and longitude and for less error in

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