The National Geodetic Survey and its predecessor agencies have collaborated withpublic and private organizations to establish reference stations at preciselydetermined locations over the last 200 years, setting a geodetic standard inprecise positioning. NGS defines official geodetic datums for all federalmapping activities in the U.S as part of the National Spatial Reference System(NSRS). Currently the NGS is working to remove inaccuracies in the existingdatums of the US. By tracking the dynamic nature of the Earth, and giving userstools to account for it, NGS will provide a new National Spatial ReferenceSystem that is semi-dynamic. To support the Modernization of the NSRS, constituents in the Southwest Regionhave been working to improve geodetic control and to prepare to enhance the database that forms the foundation for the new NSRS. Teams have been workingsteadily in the region improving monumentation and operations of NationalContinuously Operating Reference Station Network (NCN) sites in partnership withNGS through braced monument workshops and the formation of new federal, state,and local partnership working groups. Additionally, four new Foundation CORSsites are being developed in partnership with NGS at Space GeodeticObservatories across the Southwest at Kitt Peak National Observatory in Arizonaand at Los Alamos National Laboratory, the Pietown NRAO VLBA, and the ApachePoint Observatory in New Mexico. Partners from the National Geospatial Agency,the National Radio Astronomy Observatory and the Applied Research Laboratory atUniversity of Texas are working with NGS to begin project planning for both theNGS Foundation CORS sites and the National Science Foundation funded High RateTracking Receivers for Awareness of Spectrum and Timing Enhancements (HASTE)Project. The HASTE Project will provide multi-constellation GNSS observationdata distributed to all project partners, improved situational awareness atNRAO's Very Long Baseline Array (VLBA) sites, improve the VLBA data qualitythrough better timing, and support geodesy research tying the terrestrial andcelestial reference frames.
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The ionosphere is an unavoidable pathway through which all space-based radiocommunication, navigation, and surveillance signals must travel. Understandingionospheric effects on radio signals propagation and using radio waves to studyionosphere phenomena have been active research areas for many decades. Inrecent years, global navigation satellite systems (GNSS) signals have gainedrecognition as a powerful and versatile means for ionospheric remote sensingbecause of their well-defined signal structure, global coverage, and distributedand passive nature. For satellite position, navigation, and timing engineers,the ionosphere is a complex and dynamic medium characterized by erratic behaviorand spatial irregularities, which interfere with GNSS signal propagation,adversely impact applications such as aviation, intelligent transportation,guided weapons systems, precision agriculture, surveying, tracking andcommunications that have grown to rely on GNSS services.In this presentation, I will first discuss a globally-distributed autonomousdata collection network of GNSS receiver arrays at strategically selectedlocations to facilitate a data-driven approach to study the complexity ofionospheric phenomena and their impact on GNSS. I will highlight severaladvanced GNSS receiver signal processing algorithms developed to process thesedata for scientific studies of ionosphere, for accurate estimation of ionosphereinduced GNSS errors, and for robust and assured navigation during ionospheredisturbances. Ionosphere TEC distributions, higher order ionospheric error,space weather event characteristics, such as their temporal, spatial, spectral,and seasonal distributions, as well space plasma dynamics derived from the datawill also be presented.
Absolute and relative gravity measurements play an important role in the work of NOAA's National Geodetic Survey (NGS). When NGS decided to replace the US national vertical datum, the Gravity for the Redefinition of the American Vertical Datum (GRAV-D) project added a new dimension to the NGS gravity program. Airborne gravity collection would complement existing satellite and surface gravity data to allow the creation of a gravimetric geoid sufficiently accurate to form the basis of the new reference surface. To provide absolute gravity ties for the airborne surveys, initially new FG5 absolute measurements were made at existing absolute stations and relative measurements were used to transfer those measurements to excenters near the absolute mark and to the aircraft sensor height at the parking space. In 2011, NGS obtained a field-capable A10 absolute gravimeter from Micro-g LaCoste which became the basis of the support of the airborne surveys. Now A10 measurements are made at the aircraft location and transferred to sensor height. Absolute and relative gravity play other roles in GRAV-D. Comparison of surface data with new airborne collection will highlight surface surveys with bias or tilt errors and can provide enough information to repair or discard the data. We expect that areas of problem surface data may be re-measured. The GRAV-D project also plans to monitor the geoid in regions of rapid change and update the vertical datum when appropriate. Geoid change can result from glacial isostatic adjustment (GIA), tectonic change, and the massive drawdown of large scale aquifers. The NGS plan for monitoring these changes over time is still in its preliminary stages and is expected to rely primarily on the GRACE and GRACE Follow On satellite data in conjunction with models of GIA and tectonic change. We expect to make absolute measurements in areas of rapid change in order to verify model predictions. With the opportunities presented by rapid, highly accurate absolute gravimetry, we expect that GRAV-D may be affected in a number of ways. 1) Areas requiring re-measurement as a result of poor quality data or temporal change could be measured with such a new meter. With a meter capable of field measurement with observation times that are very short, surveys previously conducted only with the relative meters could be performed with the absolute meter with no loss of time and a significant increase in accuracy. 2) Regions of rapid change due to hydrological change associated with aquifers could be measured and re-measured rather quickly. Such accuracy may provide more accurate snapshots of the aquifers over time. 3) NGS conducts absolute gravity comparisons at its Table Mountain facility for validating the performance of absolute meters through their co-located operation at gravity piers. An increase in accuracy of an order of magnitude may change the entire nature of absolute meter performance evaluation.
Coastal engineers routinely rely on the NSRS for consistency in coordinates andheights pertaining to activities such as obstruction design and floodplainmapping. The time-dependent nature of the modernized NSRS, combined with moresystematic ties between NAPGD2022 and tidal datums, will significantly improvethe quality of geospatial data in coastal environments by increasing confidencein the definition of heights in areas experiencing relative sea level change.Furthermore, primary access to the NSRS with GNSS will create new efficienciesand create an easier spatial framework for GNSS-based technology, such asunmanned infrastructure monitoring systems or precision navigation.
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