WGS 84 — Past, Present and Future

The World Geodetic System 1984 (WGS84) has been consistent with the International Terrestrial Reference Frame (ITRF) since 1994. After the original release of WGS84 in 1987 by the Defense Mapping Agency (since superseded by the National Geospatial-Intelligence Agency, NGA), there have been six subsequent realizations of the frame, designated WGS84 (G730), WGS84 (G873), WGS84 (G1150), WGS84 (G1674), WGS84 (G1762), and WGS84 (G2139). Users of WGS84 often fail to document metadata indicating the realization and epoch related to their data collections. As a result, when transforming between realizations or between other reference frames, the transformation can lead to incorrect results. We aim to bring awareness to the nature of WGS84 and the ambiguity in how it is defined. An internally consistent set of transformation parameters is derived that allows for transformation between the WGS84 realizations and other global reference frames while accounting for nuances and inconsistencies in the published literature. The derivations are based on existing (though not easily discoverable) information. Transformation accuracy is evaluated through comparison to other software and NGA-published GPS tracking station coordinates. After accounting for plate tectonic motion, the estimated uncertainties average ±0.03 m horizontally and ±0.08 m vertically for transformations involving all realizations other than the original WGS84. Uncertainties are at the meter level for transformations that include the original WGS84. If plate motion is ignored, the horizontal uncertainties can increase by several decimeters, depending on location within a plate.

The WGS84 (World Geodetic System 1984) reference system is, originally, mathematically defined from the NSWC-9Z2 (Naval Surface Weapons Center — 9Z2) reference system. The WGS84 associated realization, called in this paper WGS84-D, is a 1 meter consistency NNSS (US Navy Navigation Satellite System) Doppler realized reference frame. In contrast, the ITRF (IERS Terrestrial Reference Frame) is a 1 centimeter consistency reference frame realized through the most accurate techniques of Space Geodesy. This work intends to improve the transformation parameters between the WGS84-D and the ITRF through the use of both a NSWC-9Z2/Doppler realization and an extension of the ITRF network. A strong linear correlation was also modeled between the Doppler determined scale factor and the mean smoothed sunspot number, due to uncompensated ionospheric effects. This correction improved NSWC-9Z2 (i.e. WGS84) Doppler realization consistency. The uncertainty of adjusted transformation parameters between the ITRF and the WGS84-D is improved by a factor 2 over previous determinations.

Following the principles set forth in the Position Paper #3 at the 1998 Darmstadt Analysis Center (AC) Workshop on the new International GPS Service (IGS) International Terrestrial Reference Frame (ITRF) realization and discussions at the 1999 La Jolla AC workshop, a new clock combination program was developed. The program allows for the input of both SP3 and the new clock (RINEX) format (ftp://igsch.jpl.nasa.gov//igscb/data/format/rinex_clock.txt). The main motivation for this new development is the realization of the goals of the IGS/BIPM timing project. Besides this there is a genuine interest in station clocks and a need for a higher sampling rate of the IGS clocks (currently limited to 15 min due to the SP3 format). The inclusion of station clocks should also allow for a better alignment of the individual AC solutions and should enable the realization of a stable GPS time-scale. For each input AC clock solution the new clock combination solves and corrects for reference clock errors/instabilities as well as satellite/station biases, geocenter and station/satellite orbit errors. External station clock calibrations and/or constraints, such as those resulting from the IGS/BIPM timing pilot project, can be introduced via a subset of the fiducial timing station set, to facilitate a precise and consistent IGS UTC realization for both station and satellite combined clock solutions. Furthermore, the new clock combination process enforces strict strict conformity and consistency with the current and future IGS standards. The new clock combination maintains orbit/clock consistency at millimeter level, which is comparable to the best AC orbit/clock solutions. This is demonstrated by static GIPSY precise point positioning tests using GPS week 0995 data for stations in both Northern and Southern Hemispheres and similar tests with the Bernese software using more recent data from GPS week 1081. © 2001 John Wiley & Sons, Inc.

Ground station receivers or networks’ location uses different geodetic datums. The geodetic datum defines size and shape of the Earth model and origin of orientation of coordinate systems used to map the Earth. They are modified to converge to the International Terrestrial Reference Frame (ITRF). The Thailand geodetic reference frame has been maintained by the Royal Thai Survey Department (RTSD); currently, it is based on GNSS permanent networks. Precise orbit and clock solutions, earth orientation parameters and tropospheric gradients are applied as fixing parameters to estimate station positions using a network approach where all station coordinates are simultaneously adjusted; defined as a zero-order network. They are determined with respected to ITRF with centimetre precisions and accuracies. The shape of the Earth varies over time due to oceanic tides and plate movements. Changing are more gradually when earthquakes and volcanic eruptions happen. ITRF and other geodetic datums are changing continually; therefore, frame transformations are required. The latest adjusted coordinates are based on ITRF2005, 2008 and 2014 frame and velocities are set at the epoch 2008.83, 2013.81 and 2021.93 respectively. Constraints are cast in form of transformation parameters. The grid shift is then generated to transform from global coordinate systems to local geocentric reference frames. GNSS measurements obtained from another set of ground stations are used as check coordinates. Transformed coordinates are at 1 centimetre-level of accuracy both horizontally and vertically at 95 percent confidence level. Coordinate transformations can be applied to map Thailand based on one map on one datum policy.

: Using 10 days of Global Positioning System (GPS) pseudorange and carrier phase data collected in 1995 from 31 stations and 24 Block II/IIA satellites, estimates of GPS clocks, orbits, and tracking station coordinates were generated. The 31 sites consisted of the 12 National Imagery and Mapping Agency (NIMA) and Air Force operational stations, an additional NIMA site at Holloman Air Force Base, and 18 International GPS Service for Geodynamics (IGS) Rogue receiver sites. Ten of the NIMA and Air Force operational sites had their coordinates previously determined using GPS data. The results of this work suggest that the estimated 10 cm, one sigma, per component accuracy indicated for these 10 stations was conservative. The new World Geodetic System 1984 (WGS 84) coordinates generated for the 12 NIMA and Air Force operational stations are reported at the 1994.0 and 1997.0 epochs. The estimated accuracy of the new coordinates is better than 5 cm, one sigma, per component. Orbits estimated using the new WGS 84 coordinates agree better with the IGS final combined orbits, derived in the International Earth Rotation Service Terrestrial Reference Frame 1994, than orbits estimated using the old coordinates. The overall rms orbit-URE of the new orbits is estimated to be 12 cm, an improvement of 2 cm rms over the old orbits. Systematic differences with respect to the IGS orbits have been significantly reduced.

The BeiDou Navigation Satellite System (BDS) has used the BeiDou Coordinate System (BDCS) as its geodetic reference system since December 2017. After a brief description of the background, definitions of the origin, scale, and orientation of BDCS are given, which are consistent with China’s Geodetic Coordinate System 2000 (CGCS2000). Then the first realization of the BDCS aligning with the International Terrestrial Reference Frame 2014 (ITRF2014) is addressed. Coordinates at epoch 2018.0 and velocities at eight BDS monitoring stations were obtained achieved by processing four-phase GPS data for a global navigation satellite system (GNSS) network, including the monitoring stations, and by the frame alignment and linear regression fitting of station coordinate series. Assessment of the precision of the coordinates and Helmert parameters with respect to ITRF2014 reveals that the differences between the first frame of BDCS and ITRF2014 are less than 1 cm, which is compatible with WGS84 (G1762), PZ-90.11, and the latest Galileo terrestrial reference frame.

Uzbekistan's coordinate system transformation from CS42 to WGS84 using distortion grid model

Aircraft for over four decades have been using radionavigation aids to safely navigate in controlled airspace. Navigation was relative to the navigation aid's broadcast signal consisting of distance to/from the navaid (navigation aid) and bearing from the radionavigation aid to the aircraft, known as a radial. The navigation aid is aligned to local magnetic North. Magnetic North drifts with time; the navigation aid is permitted to differ from 3-5 degrees from current magnetic North without realignment. The difference between magnetic north at the time of alignment and True North is known as magnetic declination or slaved magnetic variation. Navigation aids that broadcast erroneous signals are detected within 10 seconds by the ground monitor, which turns the broadcast signal off. The paths over the ground of the broadcast signals define the airways. Because the actual ground tracks of the signals define the airways, the impact of any errors in the latitude and longitude or magnetic declination of the navigation aid are negated. Area Navigation is computer based and uses a digital database to go via Great Circle from one latitude/longitude point to another. When one of the points is a TACAN station the radial and magnetic declination of the navigation aid are used to determine the path over the Earth required to be on the desired airway. Undetected errors in the data will provide misleading and hazardous information to the aircrews. This paper covers how systems engineering is being applied to the aeronautical digital database as part of the total systems solution. Specific areas addressed include changes proposed and adopted by the National Imagery and Mapping Agency in the production of the Digital Aeronautical Flight Information File.

The excellent article by Peter M. Vitousek et al . ([25 July, p. 495][1]) states: “The human population is concentrated near coasts—about 60% within 100 km [kilometers]… .” This assertion comes from a recent World Resources Institute report ([1][2], p. 254): “An estimated 60 percent of the global population lives within roughly 100 kilometers of the shore.” This statement comes from a 1990 book ([2][3], p. 7): “Probably 60 percent of humanity, or nearly 3 billion people, live on or within 100 km of a sea coast.” The author of the latter book, Don Hinrichsen, an environmental journalist, informed one of us (J.E.C.) ([3][4]) that this statement was his “own assessment based on extensive back-of-the-envelope estimates using the best available data at the time.” More recently, Hinrichsen reported ([4][5], p. 39): “Nearly two-thirds of the world's people make their homes within 150 kilometers of the shore.” To our knowledge, the first public digital map of the world's human population appeared in 1995 ([5][6]). The data are freely available on the World Wide Web ([6][7]). These data make it possible to obtain more precise estimates of coastal populations as of 1994. As part of larger research programs, two groups with interests in the interactions between the earth sciences and the social sciences have independently co-registered the global digital population map on digital maps of coastlines. Using the digital World Vector Shoreline ([7][8]), two of us (C.S. and J.E.C.) estimate that approximately 37% (2.07 billion) of the 1994 population (5.62 billion) lived within 100 km of a coastline, and approximately 44% (2.45 billion) within 150 km of a coastline. These percentages are lower than those of Hinrichsen. In addition, C.S. and J.E.C. estimate that 49% of the 1994 population lived within 200 km of a coastline, and 66% within 400 km. Using the boundaries (compounded from various sources) provided by the gridded population of the world ([6][7]) and a different algorithm for computing distance to coastline, three of us (A.M., J.G., and J.S.) estimate that 37% lived within 100 km of a coastline. This estimate agrees with that of C.S. and J.E.C. Both groups anticipate that these estimates could be refined by the use of better data and methods. While our estimates of coastal population size are considerably smaller than Hinrichsen's, we agree that very large numbers of people affect and are affected by coastal zones. 1. [↵][9]World Resources Institute, World Bank, World Resources 1996-97 (Oxford Univ. Press, New York, 1996). 2. [↵][10]D. Hinrichsen, Our Common Seas: Coasts in Crisis (Earthscan, London, and Nairobi, Kenya, 1990). 3. [↵][11]\___|, personal communication. 4. [↵][12]\___|, Issues Sci. Technol. 12 (no. 4), 39 (1996). 5. [↵][13]W. Tobler, U. Deichmann, J. Gottsegen, K. Maloy, “The global demography project” (Technical Report 95-6, National Center for Geographic Information and Analysis, University of California, Santa Barbara, CA, 1995). 6. [↵][14]CIESIN, “Gridded population of the world,” 7. [↵][15]National Imagery and Mapping Agency, “World Vector Shoreline,” # {#article-title-2} Response: We thank Cohen et al . for their analysis, which should become the standard statement on coastal populations. [1]: /lookup/doi/10.1126/science.277.5325.494 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #ref-4 [6]: #ref-5 [7]: #ref-6 [8]: #ref-7 [9]: #xref-ref-1-1 View reference 1 in text [10]: #xref-ref-2-1 View reference 2 in text [11]: #xref-ref-3-1 View reference 3 in text [12]: #xref-ref-4-1 View reference 4 in text [13]: #xref-ref-5-1 View reference 5 in text [14]: #xref-ref-6-1 View reference 6 in text [15]: #xref-ref-7-1 View reference 7 in text

PETOOL v2.0: Parabolic Equation Toolbox with evaporation duct models and real environment data

Two Earth-orbiting radar missions are planned for the near future by NASA-Shuttle Radar Topography Mission (SRTM) and LightSAR. The SRTM will fly aboard the Shuttle using interferometric synthetic aperture radar (IFSAR) to provide a global digital elevation map. SRTM is jointly sponsored by NASA and the National Imagery and Mapping Agency (NIMA). The LightSAR will utilize emerging technology to reduce mass and life-cycle costs for a mission to acquire SAR data for Earth science and civilian applications and to establish commercial utility. LightSAR is sponsored by NASA and industry partners. The use of IFSAR to measure elevation is one of the most powerful and practical applications of radar. A properly equipped spaceborne IFSAR system can produce a highly accurate global digital elevation map, including cloud-covered areas, in significantly less time and at significantly lower cost than other systems. For accurate topography over a large area, the interferometric measurements can be performed simultaneously in physically separate receive systems. Since LightSAR offers important benefits to both the science community and US industry, an innovative government-industry teaming approach is being explored, with industry sharing the cost of developing LightSAR in return for commercial rights to its data and operational responsibility. LightSAR will enable mapping of surface change. The instrument's high-resolution mapping, along with its quad polarization, dual polarization, interferometric and ScanSAR modes will enable continuous monitoring of natural hazards, Earth's surface deformation, surface vegetation change, and ocean mesoscale features to provide commercially viable and scientifically valuable data products. Advanced microelectronics and lightweight materials will increase LightSAR's functionality without increasing the mass. Dual frequency L/X-band designs have been examined.

Modern high-performance Synthetic Aperture Radar (SAR) systems have evolved into highly versatile, robust, and reliable tactical sensors, offering images and information not available from other sensor systems. For example, real-time images are routinely formed by the Sandia-designed General Atomics (AN/APY-8) Lynx SAR yielding 4-inch resolution at 25 km range (representing better than arc-second resolutions) in clouds, smoke, and rain. Sandia's Real-Time Visualization (RTV) program operates an Interferometric SAR (IFSAR) system that forms three-dimensional (3D) topographic maps in near real-time with National Imagery and Mapping Agency (NIMA) Digital Terrain Elevation Data (DTED) level 4 performance (3 meter post spacing with 0.8-meter height accuracy) or better. When exported to 3-D rendering software, this data allows remarkable interactive fly-through experiences. Coherent Change Detection (CCD) allows detecting tire tracks on dirt roads, foot-prints, and other minor, otherwise indiscernible ground disturbances long after their originators have left the scene. Ground Moving Target Indicator (GMTI) radar modes allow detecting and tracking moving vehicles. A Sandia program known as "MiniSAR" is developing technologies that are expected to culminate in a fully functioning, high-performance, real-time SAR that weighs less than 20 lbs. The purpose of this paper is to provide an overview of recent technology developments, as well as current on-going research and development efforts at Sandia National Laboratories.

The European Datum 1950 (ED50) of the Turkish national geodetic network (TNGN) and the World Geodetic System 1984 (WGS84) of the Turkish national fundamental GPS network (TNFGN) are in use as geodetic reference frames in Turkey. According to the use of two reference systems, it is necessary to transform the three-dimensional (3D) coordinate data from ED50 to WGS84 or vice versa. The seven-parameter similarity transformation method is frequently used for 3D coordinate transformation in geodesy. In this study, a back propagation artificial neural network (BPANN) that has been more widely applied in engineering among all other neural network models is evaluated as an alternative 3D coordinate transformation method. BPANN is compared with a popular seven-parameter similarity transformation (Molodensky-Badekas) method over a test area, in terms of root mean square error (RMSE). The results indicated that the employment of BPANN transformed 3D coordinates (X, Y, Z) more accurate than Molodensky-Badekas method and can be useful for 3D coordinate transformation between ED50 and WGS84. Key words: 3D coordinate transformation, back propagation artificial neural network, seven-parameter similarity transformation, BPANN, Molodensky-Badekas.

Abstract. The interest in and use of 3D models in built environments is rapidly increasing, and they are now a key component of decision-making in areas including climate change mitigation (e.g., calculating solar panel potential, flood modelling, modelling housing age for retrofitting of thermal insulation), urban planning and cadastral systems (modelling rights, restrictions and responsibilities in complex buildings, streamlining the process to issue planning permits, design of existing or new developments) and infrastructure (construction, transport, utility management and modelling, asset management). 3D models are also an integrator for the data underpinning smart cities – knowing where a sensor is in 3D space allows the data to be integrated with the surrounding context – for example, noise data could be integrated with traffic information. Reflecting this interest, national mapping and cadastral agencies (NMCA) including Ordnance Survey (GB) are now increasingly generating 3D mapping at national scale, and there is extensive research as to how this data can be integrated with another emerging source of 3D models such as building information modelling (BIM).These trends were evident during the 3rd BIM/GIS Integration Workshop and 15th 3DGeoInfo 2020 events, which were co-hosted by University College London and Ordnance Survey (GB) in September 2020. The workshop and conference brought together international researchers from academia, industry, government and national mapping and cadastral agencies in the field of 3D geoinformation, in an interdisciplinary gathering of researchers in the fields of data collection, data management, data quality, data analysis, advanced modelling approaches, applications, users, visualisation, augmented reality, artificial intelligence and many more.This year’s theme was Users and Use Cases. The workshop and conference covered a wide range of topics including 3D data acquisition and processing, 3D city modelling and related standards, visualisation and dissemination of 3D data, augmented and virtual reality, 3D and Artificial Intelligence/Machine Learning. Three sessions of the BIM/GIS Integration Workshop were dedicated to Applications of BIM/GIS Integration, and an entire day of 3DGeoInfo 2020 to Users and Use Cases within 3DGeoInfo. Additionally, two sessions were specifically aimed at NMCA participants.Although initially intended to be a face-to-face event in London, the team rapidly adjusted to the emerging COVID-19 situation, identifying an online solution that facilitated and encouraged participant interaction. This meant that the events could still provide a platform for learning, discussion, and exchange of ideas that they have been able to in previous years, as well as providing opportunities to promote international collaboration in these topics. This special issue of the ISPRS International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences contains 23 papers selected by a double-blind peer review involving a minimum of two reviewers, presenting research on topics including visualisation, point cloud management, virtual reality, data interoperability, data quality, generating national 3D datasets, indoor 3D, urban planning/permits and underground data management.

The International Terrestrial Reference Frame (ITRF), the Earth Orientation Parameter (EOP) time series, and the International Celestial Reference Frame are obtained separately and may thus present inconsistencies. To solve this problem, a first step has been made with the latest ITRF realization (ITRF2005), which has been computed, for the first time, with consistent EOP time series. Another approach to better understand this issue is to directly estimate, in the same process, station positions and EOP time series, from all the space-geodetic measurements.