Browsing by Author "Lemoine, F. G."
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Item The Development of the Joint NASA GSFC and the National Imagery and Mapping Agency (NIMA) Geopotential Model EGM96(NASA) Lemoine, F. G.; Kenyon, S.C.; Factor, J.K.; Trimmer, R.G.; Pavlis, N. K.; Chinn, D.S.; Cox, C. M.; Klosko, S.M.; Luthcke, S.B.; Torrence, M.H.; Wang, Y. M.; Williamson, R.G.; Pavlis, Erricos C.; Rapp, R. H.; Olson, T. R.The NASA Goddard Space Flight Center (GSFC), the National Imagery and Mapping Agency (NIMA), and The Ohio State University (OSU) have collaborated to develop an improved spherical harmonic model of the Earth's gravitational potential to degree 360. The new model, Earth Gravitational Model 1996 (EGM96), incorporates improved surface gravity data, altimeter-derived gravity anomalies from ERS-1 and from the GEOSAT Geodetic Mission (GM), extensive satellite tracking data-including new data from Satellite Laser Ranging (SLR), the Global Postioning System (GPS), NASA's Tracking and Data Relay Satellite System (TDRSS), the French DORIS system, and the US Navy TRANET Doppler tracking system-as well as direct altimeter ranges from TOPEX/POSEIDON (T/P), ERS-1, and GEOSAT. The final solution blends a low-degree combination model to degree 70, a block-diagonal solution from degree 71 to 359, and a quadrature solution at degree 360. The model was used to compute geoid undulations accurate to better than one meter (with the exception of areas void of dense and accurate surface gravity data) and realize WGS84 as a true three-dimensional reference system. Additional results from the EGM96 solution include models of the dynamic ocean topography to degree 20 from T/P and ERS-1 together, and GEOSAT separately, and improved orbit determination for Earth-orbiting satellites.Item GLOBAL GEODETIC OBSERVING SYSTEM— CONSIDERATIONS FOR THE GEODETIC NETWORK INFRASTRUCTURE(Candadia Science) Pearlman, M.; Altamimi, Z.; Beck, N.; Forsberg, R.; Gurtner, W.; Kenyon, S.; Behrend, D.; Lemoine, F. G.; Ma, C.; Noll, C. E.; Pavlis, Erricos C.; Malkin, Z.; Moore, A. W.; Webb, F. H.; Neilan, R.E.; Ries, J. C.; Rothacher, M.; Willis, P.Properly designed and structured ground-based geodetic networks materialize the reference systems to support sub-millimetre global change measurements over space, time, and evolving technologies. The Ground Networks and Communications Working Group (GN&C WG) of the International Association of Geodesy’s Global Geodetic Observing System (GGOS) has been working with the IAG measurement services (the IGS, ILRS, IVS, IDS and IGFS) to develop a strategy for building, integrating, and maintaining the fundamental network of instruments and supporting infrastructure in a sustainable way to satisfy the long-term (10 to 20 years) requirements identified by the GGOS Science Council. Activities of this Working Group include the investigation of the status quo and the development of a plan for full network integration to support improvements in terrestrial reference frame establishment and maintenance, Earth orientation and gravity field monitoring, precision orbit determination, and other geodetic and gravimetric applications required for the long-term observation of global change. This integration process includes the development of a network of fundamental stations with as many co-located techniques as possible, with precisely determined intersystem vectors. This network would exploit the strengths of each technique and minimize the weaknesses where possible. This paper discusses the organization of the working group, the work done to date, and future tasks.Item High-Resolution Gravity Field Models from GRAIL Dataand Implications for Models of the DensityStructure of the Moon's Crust(American Geophysical Union, 2019-11-06) Goossens, S.; Sabaka, T. J.; Wieczorek, M. A.; Neumann, G. A.; Mazarico, E.; Lemoine, F. G.; Nicholas, J. B.; Smith, D. E.; Zuber, M. T.We present our latest high-resolution lunar gravity field model of degree and order 1200 in spherical harmonics using Gravity Recovery and Interior Laboratory (GRAIL) data. In addition to a model with the standard spectral Kaula regularization constraint, we determine models by applying a constraint based on topography called rank-minus-one (RM1). The new models using this RM1 constraint have high correlations with topography over the entire degree range by design. The RM1 models allow the determination of apparent crustal densities at all spatial scales (called effective density) covered by the model, whereas the Kaula-constrained model can only be used globally up to spherical harmonic degree 700. We find that the effective density spectrum has a smaller slope for the high degrees when compared to the medium degrees. We interpret this as indicative of a global average surface density, as opposed to an ever-decreasing effective density as one approaches the surface. We use the RM1 models to derive maps of lateral and vertical density variations in the lunar crust. These models allow us to increase the resolution of this analysis compared to previous studies, by increasing the degree range over which to fit theoretical models of vertical density variations, and by decreasing the size of the spherical caps used in a localized analysis. Several regions on the Moon, such as South Pole-Aitken and Mare Orientale, are distinct from their surroundings in terms of surface densities. The RM1 models are especially valuable in (localized) spectral studies of the structure of the lunar crust.Item Intercomparison and evaluation of some contemporary global geopotential models(OGS) Pavlis, N. K.; Cox, C. M.; Pavlis, Erricos C.; Lemoine, F. G.Item Modernizing and expanding the NASA Space Geodesy Network to meet future geodetic requirements(Springer Nature, 2018-10-06) Merkowitz, S. M.; Bolotin, S.; Elosegui, P.; Esper, J.; Gipson, J.; Hilliard, L.; Himwich, E.; Hoffman, E.D.; Lakins, D. D.; Lamb, R. C.; Lemoine, F. G.; Long, J. L.; McGarry, J. F.; MacMillan, D. S.; Michael, B. P.; Noll, C.; Pavlis, Erricos C.; Pearlman, M. R.; Ruszczyk, C.; Shappirio, M. D.; Stowers, D. A.NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC in Precise geodetic infrastructure: national requirements for a shared resource, National Academies Press, Washington, 2010. http://nap.edu/12954, Thriving on our changing planet: a decadal strategy for Earth observation from space, National Academies Press, Washington, 2018. http://nap.edu/24938). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame to have an accuracy of 1 mm and stability of 0.1 mm per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations colocated at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA’s Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.Item NASA’s Next Generation Space Geodesy Network Typical Core Site Requirements and Layout(NASA, 2014-10-14) Esper, J.; Long, J. L.; Lemoine, F. G.; McCormick, D. R.; Merkowitz, S. M.; Ma, C.; McGarry, J. F.; Hilliard, L.; Pavlis, Erricos C.; Pearlman, M. R.; Stowers, D. A.; Wetzel, S. L.NASA’s renewed commitment to the deployment of a new network of “core” space geodetic sites requires careful planning and consideration for location selection, instrument and facility layout, and required infrastructure. Following on National Research Council (NRC) recommendations [1] to upgrade U.S. stations with modern SLR, VLBI, and GNSS systems, and make a long-term commitment to maintaining the ITRF (among others), the Space Geodesy Project (SGP) at NASA Goddard has been defining the exact requirements and layout for a “typical” geodetic site, which includes Satellite Laser Ranging--SLR, Very Long Baseline Interferometry--VLBI, Global Navigation Satellite System--GNSS, and Doppler Orbitography and Radiopositioning Integrated by Satellite--DORIS stations (French system provided by CNES, France) tied together with a Vector Tie System (VTS), utilizing a Robotic Total Station (RTS). Within programmatic constraints, Core Site (CS) identification follows a systems engineering process where site characteristics are evaluated against identified requirements. Taking into consideration site stability, radiofrequency interference, infrastructure, and a host of other requirements this paper describes the process leading to identification, and it will illustrate the generic layout of an idealized CS with unencumbered terrain.