NASA Technical Reports Server (NTRS)
Randel, David L.; Vonder Haar, Thomas H.
1990-01-01
Broadband observations from the Nimbus-7 Earth Radiation Budget (ERB) instrument package were used to calculate the outgoing-longwave-radiation (OLR) anomalies as well as the net balance anomalies. The areas of anomalous net balance and OLR were correlated with the ECMWF 500-mb geopotential height anomalies, and many areas of significant correlation were found. Their most interesting teleconnection area was associated with the net balance anomaly near Indonesia, where a series of alternating correlation waves was found similar to the wave pattern reported by Hoskins and Karoly (1981) in their model study of tropical heat sources. The strongest OLR anomaly correlation occurred in central Pacific.
Monthly mean global climatology of temperature, wind, geopotential height and pressure for 0-120 km
NASA Technical Reports Server (NTRS)
Chandra, Sushil; Schoeberl, Mark R.; Fleming, Eric L.; Barnett, John J.
1990-01-01
This paper presents a monthly mean climatology of zonal mean temperature, zonal wind, and geopotential height with nearly pole-to-pole coverage (80 deg S-80 deg N) for 0-120 km which can be used as a function of altitude and pressure. This climatology reproduces most of the characteristic features of the atmosphere such as the lowering and cooling of the mesopause and the lowering and warming of the stratopause during the summer months at high latitudes. A series of zonal wind profiles is also presented comparing this climatological wind with monthly mean climatological direct wind measurements in the upper mesosphere and lower thermosphere. The two data sets compare well below 80 km, with some general seasonal trend agreement observed above 80 km. The zonal wind at the equator presented here simulates the observed features of the semiannual oscillation in the upper stratosphere and mesosphere.
Linear trends in Northern Hemisphere tropospheric geopotential height and temperature patterns
NASA Technical Reports Server (NTRS)
Reiter, E. R.; Westhoff, D. R.
1982-01-01
Gridded National Meteorological Center data for 500 mb geopotential height and 300-500 mb and 500-700 mb thickness for the period 1951-1978 are subjected to linear trend analyses. The analyses are carried out for each calendar month. Significant geographical and seasonal distributions of cooling and warming patterns are found. An atmospheric cooling trend over the North Pacific during the winter months is seen in a region where oceanic cooling has also been observed, but planetary-wave adjustments rather than ocean-atmosphere feedback mechanisms appear to be dominant in the atmospheric cooling on climatic time scales. Consistently large temperature trends are also seen over the continent of Asia. Comparisons between thickness trends in the layer 300-500 mb and those in the layer 500-700 mb reveal pronounced patterns of stabilization and destabilization.
Description of data on the Nimbus 7 LIMS map archive tape: Temperature and geopotential height
NASA Technical Reports Server (NTRS)
Haggard, K. V.; Remsberg, E. E.; Grose, W. L.; Russell, J. M., III; Marshall, B. T.; Lingenfelser, G.
1986-01-01
The process by which the analysis of the Limb Infared Monitor of the Stratosphere (LIMS) experiment data were used to produce estimates of synoptic maps of temperature and geopotential height is described. In addition to a detailed description of the analysis procedure, several interesting features in the data are discussed and these features are used to demonstrate how the analysis procedure produced the final maps and how one can estimate the uncertainties in the maps. In addition, features in the analysis are noted that would influence how one might use, or interpret, the results. These include subjects such as smoothing and the interpretation of wave components. While some suggestions are made for an improved analysis of the data, it is shown that, in general, the maps are an excellent estimation of the synoptic fields.
NASA Astrophysics Data System (ADS)
He, Chao; Lin, Ailan; Gu, Dejun; Li, Chunhui; Zheng, Bin; Wu, Bo; Zhou, Tianjun
2016-11-01
The western North Pacific subtropical high (WNPSH) is crucial to the East Asian summer climate, and geopotential height (H) is widely used to measure the WPNSH. However, a rapidly rising trend of H in the future is projected by the models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Diagnoses based on the hypsometric equation suggest that more than 80% of the rise in H are attributable to zonal uniform warming. Because circulation is determined by the gradient of H rather than its absolute magnitude, the spatially uniform rising trend of H gives rise to difficulties when measuring the WNPSH with H. These difficulties include an invalid western boundary of WNPSH in the future and spurious information regarding long-term trends and interannual variability of WNPSH. Using CMIP5 model simulations and reanalysis data, the applicability of a metric based on eddy geopotential height (H e ) to the warming climate is investigated. The results show that the H e metric outperforms the H metric under warming climate conditions. First, the mean state rainfall-H e relationship is more robust than the rainfall-H relationship. Second, the area, intensity, and western boundary indices of WNPSH can be effectively defined by the H e = 0-m contour in future warming climate scenarios without spurious trends. Third, the interannual variability of East Asian summer rainfall is more closely related to the H e -based WNPSH indices. We recommend that the H e metric be adopted as an operational metric on the WNPSH under the current warming climate.
NASA Technical Reports Server (NTRS)
Fleming, Eric L.; Chandra, Sushil; Schoeberl, Mark R.; Barnett, John J.
1988-01-01
A monthly mean climatology is presented of temperature, wind, and geopotential height with nearly pole-to-pole coverage (80 S to 80 N) for 0 to 210 km, which can be used as a function of altitude and pressure. The purpose is to provide a reference for various atmospheric research and analysis activities. Data sources and methods of computation are described; in general, hydrostatic and thermal wind balance are maintained at all levels and latitudes. As observed in a series of cross-sectional plots, this climatology accurately reproduces most of the characteristic features of the atmosphere such as equatorial wind and the general structure of the tropopause, stratopause, and mesopause. A series of zonal wind profiles is also represented comparing this climatological wind with monthly mean climatological direct wind measurements in the upper mesosphere and lower thermosphere. The temperature and zonal wind climatology at stratospheric levels is compared with corresponding data from the National Meteorological Center, and general agreement is observed between the two data sets. Tables of the climatological values as a function of latitude and height for each month are contained in Appendix B, and are also available in floppy disk.
The Evaluation of Winds from Geopotential Height Data in the Stratosphere.
NASA Astrophysics Data System (ADS)
Randel, William J.
1987-10-01
Several methods of obtaining horizontal wind fields in the extratropical stratosphere from geopotential height data are evaluated and compared to geostrophic estimates, with focus on the poleward fluxes of momentum and heat and on the resulting Eliassen-Palm (EP) flux divergence estimates. Winds derived from a coupled iterative solution of the zonal and meridional momentum equations (`balance' winds) are proposed and tested, in addition to winds derived from linearizing these equations about the zonal mean flow (`linen' winds). Comparison of the different analysis methods are made for a general circulation model simulation of the Northern Hemisphere (NH) winter stratosphere, and for NH and Southern Hemisphere (SH) winter observational data.The balance and linear wind estimates of poleward momentum flux are similar and substantially smaller than geostrophic values in the high-latitude stratosphere; neglect of local curvature effects is the primary cause of the geostrophic overestimate. The relative errors are larger in the southern winter stratosphere due to the stronger polar night jet. Poleward beat flux estimates are not substantially changed. Use of the improved wind fluxes results in a sizable reduction in the EP flux divergence in the high-latitude stratosphere.Comparison with model winds suggests that the balance method is the superior analysis technique for evaluating local winds, particularly in the NH winter where local nonlinear effects can be important. Based on observed balance winds, estimates are made of the relative importance of rotational versus divergent motions in the winter stratosphere.
Regional Analysis of Northern Hemisphere 50 kPa Geopotential Heights from 1946 to 1985.
NASA Astrophysics Data System (ADS)
Shabbar, Amir; Higuchi, Kaz; Knox, John L.
1990-05-01
In Knox et al., the interannual variation of the Northern Hemisphere 50 kPa geopotential height field averaged between 30° and 80°N was investigated for the 40-year period from 1946 to 1985. We presented strong statistical evidence supporting the notion that a rather abrupt transition in the climate system took place during the early 1960s. There was no attempt to compare the spatial distribution of the 50 kPa height difference between Regime 1 (1946-62) and Regime 2 (1963-85).As a sequel to the first paper, we investigate the spatial characteristics of the transition height field. We find that the difference in the 50 kPa height field between Regime 1 and Regime 2 is characterized by low frequency circulation modes of the Pacific/North American (PNA) teleconnection pattern, the North Atlantic Oscillation (NAO), and an Arctic oscillation. There was an increase (in the residual sense) of the frequency and amplitude of the positive phase of the PNA in Regime 2 relative to Regime 1.Fourier analysis is applied to interpret the regime changes in terms of planetary and long waves during the winter season. The change in the Arctic circulation is primarily associated with an amplification of the wave 2 component in its normal phase location, while in the midlatitudes the primary contributor is wave 1, again in its normal location.We also examine the 40-year time series of 50 kPa height at the three centers of the winter PNA and confirm a strong negative correlation between the first two centers and a significant positive correlation between the first and third.To assess the current trend, the 50 kPa anomaly field averaged over the 1981-87 period is examined. The winter season shows an eastward shift of the North Pacific Ocean cooling pattern and amplified warming over most of North America, the maximum centered over western Canada. The NAO phase changed to negative.Our results are discussed in relation to the interregime sea surface temperature change over the North
NASA Astrophysics Data System (ADS)
Visheratin, K. N.
2016-01-01
We present the results of the analysis of the phase relationships between the quasi-decadal variations (QDVs) (in the range from 8 to 13 years) in the total ozone content (TOC) at the Arosa station for 1932-2012 and a number of meteorological parameters: monthly mean values of temperature, meridional and zonal components of wind velocity, and geopotential heights for isobaric surfaces in the layer of 10-925 hPa over the Arosa station using the Fourier methods and composite and cross-wavelet analysis. It has been shown that the phase relationships of the QDVs in the TOC and meteorological parameters with an 11-year cycle of solar activity change in time and height; starting with cycle 24 of solar activity (2008-2010), the variations in the TOC and a number of meteorological parameters occur in almost counter phase with the variations in solar activity. The periods of the maximum growth rate of the temperature at isobaric surfaces 50-100 hPa nearly correspond to the TOC's maximum periods, and the periods of the maximum temperature correspond the periods of the decrease of the peak TOC rate. The highest correlation coefficients between the meridional wind velocity and temperature are observed at 50 hPa at positive and negative delays of ~27 months. The times of the maxima (minima) of the QDVs in the meridional wind velocity nearly correspond to the periods of the maximum amplification (attenuation) rate of the temperature of the QDVs. The QDVs in the geopotential heights of isobaric surfaces fall behind the variations in the TOC by an average of 1.5 years everywhere except in the lower troposphere. In general, the periods of variations in the TOC and meteorological parameters in the range of 8-13 years are smaller than the period of variations in the level of solar activity.
Validation of the Aura Microwave Limb Sounder Temperature and Geopotential Height Measurements
NASA Technical Reports Server (NTRS)
Schwartz, M. J.; Lambert, A.; Manney, G. L.; Read, W. G.; Livesey, N. J.; Froidevaux, L.; Ao, C. O.; Bernath, P. F.; Boone, C. D.; Cofield, R. E.; Daffer, W. H.; Drouin, B. J.; Fetzer, E. J.; Fuller, R. A.; Jarnot, R. F.; Jiang, J. H.; Jiang, Y. B.; Knosp, B. W.; Krueger, K.; Li, J.-L. F.; Mlynczak, M. G.; Pawson, S.; Russell, J. M., III; Santee, M. L.; Snyder, W. V.
2007-01-01
This paper describes the retrievals algorithm used to determine temperature and height from radiance measurements by the Microwave Limb Sounder on EOS Aura. MLS is a "limbscanning" instrument, meaning that it views the atmosphere along paths that do not intersect the surface - it actually looks forwards from the Aura satellite. This means that the temperature retrievals are for a "profile" of the atmosphere somewhat ahead of the satellite. Because of the need to view a finite sample of the atmosphere, the sample spans a box about 1.5km deep and several tens of kilometers in width; the optical characteristics of the atmosphere mean that the sample is representative of a tube about 200-300km long in the direction of view. The retrievals use temperature analyses from NASA's Goddard Earth Observing System, Version 5 (GEOS-5) data assimilation system as a priori states. The temperature retrievals are somewhat deperrdezt on these a priori states, especially in the lower stratosphere. An important part of the validation of any new dataset involves comparison with other, independent datasets. A large part of this study is concerned with such comparisons, using a number of independent space-based measurements obtained using different techniques, and with meteorological analyses. The MLS temperature data are shown to have biases that vary with height, but also depend on the validation dataset. MLS data are apparently biased slightly cold relative to correlative data in the upper troposphere and slightly warm in the middle stratosphere. A warm MLS bias in the upper stratosphere may be due to a cold bias in GEOS-5 temperatures.
NASA Astrophysics Data System (ADS)
Grombein, Thomas; Seitz, Kurt; Heck, Bernhard
2016-12-01
National height reference systems have conventionally been linked to the local mean sea level, observed at individual tide gauges. Due to variations in the sea surface topography, the reference levels of these systems are inconsistent, causing height datum offsets of up to ±1-2 m. For the unification of height systems, a satellite-based method is presented that utilizes global geopotential models (GGMs) derived from ESA's satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE). In this context, height datum offsets are estimated within a least squares adjustment by comparing the GGM information with measured GNSS/leveling data. While the GNSS/leveling data comprises the full spectral information, GOCE GGMs are restricted to long wavelengths according to the maximum degree of their spherical harmonic representation. To provide accurate height datum offsets, it is indispensable to account for the remaining signal above this maximum degree, known as the omission error of the GGM. Therefore, a combination of the GOCE information with the high-resolution Earth Gravitational Model 2008 (EGM2008) is performed. The main contribution of this paper is to analyze the benefit, when high-frequency topography-implied gravity signals are additionally used to reduce the remaining omission error of EGM2008. In terms of a spectral extension, a new method is proposed that does not rely on an assumed spectral consistency of topographic heights and implied gravity as is the case for the residual terrain modeling (RTM) technique. In the first step of this new approach, gravity forward modeling based on tesseroid mass bodies is performed according to the Rock-Water-Ice (RWI) approach. In a second step, the resulting full spectral RWI-based topographic potential values are reduced by the effect of the topographic gravity field model RWI_TOPO_2015, thus, removing the long to medium wavelengths. By using the latest GOCE GGMs, the impact of topography
NASA Astrophysics Data System (ADS)
Grombein, Thomas; Seitz, Kurt; Heck, Bernhard
2017-03-01
National height reference systems have conventionally been linked to the local mean sea level, observed at individual tide gauges. Due to variations in the sea surface topography, the reference levels of these systems are inconsistent, causing height datum offsets of up to ±1-2 m. For the unification of height systems, a satellite-based method is presented that utilizes global geopotential models (GGMs) derived from ESA's satellite mission Gravity field and steady-state Ocean Circulation Explorer (GOCE). In this context, height datum offsets are estimated within a least squares adjustment by comparing the GGM information with measured GNSS/leveling data. While the GNSS/leveling data comprises the full spectral information, GOCE GGMs are restricted to long wavelengths according to the maximum degree of their spherical harmonic representation. To provide accurate height datum offsets, it is indispensable to account for the remaining signal above this maximum degree, known as the omission error of the GGM. Therefore, a combination of the GOCE information with the high-resolution Earth Gravitational Model 2008 (EGM2008) is performed. The main contribution of this paper is to analyze the benefit, when high-frequency topography-implied gravity signals are additionally used to reduce the remaining omission error of EGM2008. In terms of a spectral extension, a new method is proposed that does not rely on an assumed spectral consistency of topographic heights and implied gravity as is the case for the residual terrain modeling (RTM) technique. In the first step of this new approach, gravity forward modeling based on tesseroid mass bodies is performed according to the Rock-Water-Ice (RWI) approach. In a second step, the resulting full spectral RWI-based topographic potential values are reduced by the effect of the topographic gravity field model RWI_TOPO_2015, thus, removing the long to medium wavelengths. By using the latest GOCE GGMs, the impact of topography
NASA Astrophysics Data System (ADS)
Wang, Xujia; Zheng, Zhihai; Feng, Guolin
2017-02-01
The contribution of air-sea interaction on the extended-range prediction of geopotential height at 500 hPa in the northern extratropical region has been analyzed with a coupled model form Beijing Climate Center and its atmospheric components. Under the assumption of the perfect model, the extended-range prediction skill was evaluated by anomaly correlation coefficient (ACC), root mean square error (RMSE), and signal-to-noise ratio (SNR). The coupled model has a better prediction skill than its atmospheric model, especially, the air-sea interaction in July made a greater contribution for the improvement of prediction skill than other months. The prediction skill of the extratropical region in the coupled model reaches 16-18 days in all months, while the atmospheric model reaches 10-11 days in January, April, and July and only 7-8 days in October, indicating that the air-sea interaction can extend the prediction skill of the atmospheric model by about 1 week. The errors of both the coupled model and the atmospheric model reach saturation in about 20 days, suggesting that the predictable range is less than 3 weeks.
NASA Astrophysics Data System (ADS)
Brigode, Pierre; Brissette, François; Caya, Daniel; Nicault, Antoine; Perreault, Luc; Kuentz, Anna; Mathevet, Thibault; Gailhard, Joël
2015-04-01
For the next couple of decades, the impacts of climate change on hydrological extremes are likely to be masked by climate natural variability. Thus, a better understanding and quantification of natural climate variability on hydrological extremes would be helpful for short-term adaptation. However, studying natural variability requires long instrumental records, which are inexistant in remote regions such as Northern Québec. Different methods have been proposed to extend observed hydroclimatic time-series, based on other data sources such as tree rings or sedimentological datasets. For example, tree ring multi-proxies have been studied for the Caniapiscau Reservoir in Northern Québec (Canada), leading to the reconstruction of spring flood series (Boucher et al., 2011) and of annual and seasonal mean flow series (Nicault et al., 2014), for the last 150 years. Here, we apply a different reconstruction method on the same catchment, using historical reanalysis of geopotential height fields, to compare the flood series obtained and study the observed flood variability over the 1871-2012 period. The applied method, named ANATEM (Kuentz et al., 2013), aims firstly at producing climatic time series (temperature and precipitation) which are then used as inputs to one or several hydrological model previously calibrated in order to obtain streamflow time series. The climatic reconstruction is based on the analog method, using the link between atmospheric pressure situations and local climatic variables and thus requires (i) a geopotential height field reanalysis (here the NOAA reanalysis, available over the 1871-2012 period (Compo et al., 2011)), and (ii) the available observed temperature and precipitation time series (here available over the 1960-2012 period). The hypothesis of the analog method is that two different days having similar atmospheric circulations are expected to produce similar temperature and precipitation patterns. Using this hypothesis, the method
NASA Astrophysics Data System (ADS)
Brigode, Pierre; Brissette, François; Nicault, Antoine; Perreault, Luc; Kuentz, Anna; Mathevet, Thibault; Gailhard, Joël
2016-09-01
Over the last decades, different methods have been used by hydrologists to extend observed hydro-climatic time series, based on other data sources, such as tree rings or sedimentological datasets. For example, tree ring multi-proxies have been studied for the Caniapiscau Reservoir in northern Québec (Canada), leading to the reconstruction of flow time series for the last 150 years. In this paper, we applied a new hydro-climatic reconstruction method on the Caniapiscau Reservoir and compare the obtained streamflow time series against time series derived from dendrohydrology by other authors on the same catchment and study the natural streamflow variability over the 1881-2011 period in that region. This new reconstruction is based not on natural proxies but on a historical reanalysis of global geopotential height fields, and aims firstly to produce daily climatic time series, which are then used as inputs to a rainfall-runoff model in order to obtain daily streamflow time series. The performances of the hydro-climatic reconstruction were quantified over the observed period, and showed good performances, in terms of both monthly regimes and interannual variability. The streamflow reconstructions were then compared to two different reconstructions performed on the same catchment by using tree ring data series, one being focused on mean annual flows and the other on spring floods. In terms of mean annual flows, the interannual variability in the reconstructed flows was similar (except for the 1930-1940 decade), with noteworthy changes seen in wetter and drier years. For spring floods, the reconstructed interannual variabilities were quite similar for the 1955-2011 period, but strongly different between 1880 and 1940. The results emphasize the need to apply different reconstruction methods on the same catchments. Indeed, comparisons such as those above highlight potential differences between available reconstructions and, finally, allow a retrospective analysis of the
Geopotential Research Mission (GRM)
NASA Technical Reports Server (NTRS)
1985-01-01
The Geopotential Research Mission (GRM) is a satellite system proposed to determine variations in the gravitational and magnetic fields to a resolution of about 100 kilometers. Knowledge and interpretations of the potential fields on scales of 100 kilometers and greater, to clarify the needs for better data in this range of wavelengths were reviewed. The potential contribution of these data to the determination, by satellite altimetry, of a more accurate geoidal reference was discussed.
Satellite techniques for determining the geopotential for sea-surface elevations
NASA Technical Reports Server (NTRS)
Pisacane, V. L.
1984-01-01
Spaceborne altimetry with measurement accuracies of a few centimeters which has the potential to determine sea surface elevations necessary to compute accurate three-dimensonal geostrophic currents from traditional hydrographic observation is discussed. The limitation in this approach is the uncertainties in knowledge of the global and ocean geopotentials which produce satellite and height uncertainties about an order of magnitude larger than the goal of about 10 cm. The quantative effects of geopotential uncertainties on processing altimetry data are described. Potential near term improvements, not requiring additional spacecraft, are discussed. Even though there is substantial improvements at the longer wavelengths, the oceanographic goal will be achieved. The geopotential research mission (GRM) is described which should produce goepotential models that are capable of defining the ocean geid to 10 cm and near-Earth satellite position. The state of the art and the potential of spaceborne gravimetry is described as an alternative approach to improve our knowledge of the geopotential.
Evaluation and comparisons of recent geopotential solutions
NASA Technical Reports Server (NTRS)
Khan, M. A.
1974-01-01
A statistical evaluation of some of the recent satellite determined gravity models, including some with distinct data base, indicates that the geopotential coefficients of these models are individually meaningful for frequencies with wave numbers n = 2 through 7 certainly and wave numbers n = 8 through 10 probably. Geopotential coefficients in higher frequency ranges while apparently important for computing accurate satellite orbits seem to have little geophysical significance in an individual sense. Differences between various gravity models and those satellite purely between determined geopotential models and their associated combination models show no consistent relationship to surface gravimetric coverage. Additional classical tracking data are important in improving the existing description of the earth's gravity field but their contribution in extending its frequency range beyond what is now available is uncertain.
Geopotential measurements with synchronously linked optical lattice clocks
NASA Astrophysics Data System (ADS)
Takano, Tetsushi; Takamoto, Masao; Ushijima, Ichiro; Ohmae, Noriaki; Akatsuka, Tomoya; Yamaguchi, Atsushi; Kuroishi, Yuki; Munekane, Hiroshi; Miyahara, Basara; Katori, Hidetoshi
2016-10-01
According to Einstein's theory of relativity, the passage of time changes in a gravitational field. On Earth, raising a clock by 1 cm increases its apparent tick rate by 1.1 parts in 1018, allowing chronometric levelling through comparison of optical clocks. Here, we demonstrate such geopotential measurements by determining the height difference of master and slave clocks separated by 15 km with an uncertainty of 5 cm. A subharmonic of the master clock laser is delivered through a telecom fibre to synchronously operate the distant clocks. Clocks operated under such phase coherence reject clock laser noise and facilitate proposals for linking clocks and interferometers. Taken over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be 1,652.9(5.9) × 10-18, consistent with an independent measurement by levelling and gravimetry. Our system demonstrates a building block for an internet of clocks, which may constitute ‘quantum benchmarks’, serving as height references with dynamic responses.
NASA Technical Reports Server (NTRS)
Schutz, Bob E.; Baker, Gregory A.
1997-01-01
The recovery of a high resolution geopotential from satellite gradiometer observations motivates the examination of high performance computational techniques. The primary subject matter addresses specifically the use of satellite gradiometer and GPS observations to form and invert the normal matrix associated with a large degree and order geopotential solution. Memory resident and out-of-core parallel linear algebra techniques along with data parallel batch algorithms form the foundation of the least squares application structure. A secondary topic includes the adoption of object oriented programming techniques to enhance modularity and reusability of code. Applications implementing the parallel and object oriented methods successfully calculate the degree variance for a degree and order 110 geopotential solution on 32 processors of the Cray T3E. The memory resident gradiometer application exhibits an overall application performance of 5.4 Gflops, and the out-of-core linear solver exhibits an overall performance of 2.4 Gflops. The combination solution derived from a sun synchronous gradiometer orbit produce average geoid height variances of 17 millimeters.
NASA Astrophysics Data System (ADS)
Lion, Guillaume; Guerlin, Christine; Bize, Sébastien; Wolf, Peter; Delva, Pacôme; Panet, Isabelle
2016-04-01
Current methods to determine the geopotential are mainly based on indirect approaches using gravimetric, gradiometric and topographic data. Satellite missions (GRACE, GOCE) have contributed significantly to improve the knowledge of the Earth's gravity field with a spatial resolution of about 90 km, but it is not enough to access, for example, to the geoid variation in hilly regions. While airborne and ground-based gravimeters provide the high resolution, the problem of these technics is that the accuracy is hampered by the heterogeneous coverage of gravity data (ground and offshore). Recent technological advances in atomic clocks are opening new perspectives in the determination of the geopotential. To date, the best of them reach a stability of 1.6×10-18 (NIST, RIKEN + Univ. Tokyo) in just 7 hours of integration, an accuracy of 2.0×10-18 (JILA). Using the relation of the relativistic gravitational redshift, this corresponds to a determination of geopotential differences at the 0.1 m²/s² level (or 1 cm in geoid height). In this context, the present work aims at evaluating the contribution of optical atomic clocks for the determination of the geopotential at high spatial resolution. To do that, we have studied a test area surrounding the Massif Central in the middle of southern of France. This region, consists in low mountain ranges and plateaus, is interesting because, the gravitational field strength varies greatly from place to place at high resolution due to the relief. Here, we present the synthetic tests methodology: generation of synthetic gravity and potential data, then estimation of the potential from these data using the least-squares collocation and assessment of the clocks contribution. We shall see how the coverage of the data points (realistic or not) can affect the results, and discuss how to quantify the trade-off between the noise level and the number of data points used.
Determination of a high spatial resolution geopotential model using atomic clock comparisons
NASA Astrophysics Data System (ADS)
Lion, G.; Panet, I.; Wolf, P.; Guerlin, C.; Bize, S.; Delva, P.
2017-01-01
Recent technological advances in optical atomic clocks are opening new perspectives for the direct determination of geopotential differences between any two points at a centimeter-level accuracy in geoid height. However, so far detailed quantitative estimates of the possible improvement in geoid determination when adding such clock measurements to existing data are lacking. We present a first step in that direction with the aim and hope of triggering further work and efforts in this emerging field of chronometric geodesy and geophysics. We specifically focus on evaluating the contribution of this new kind of direct measurements in determining the geopotential at high spatial resolution (≈ 10 km). We studied two test areas, both located in France and corresponding to a middle (Massif Central) and high (Alps) mountainous terrain. These regions are interesting because the gravitational field strength varies greatly from place to place at high spatial resolution due to the complex topography. Our method consists in first generating a synthetic high-resolution geopotential map, then drawing synthetic measurement data (gravimetry and clock data) from it, and finally reconstructing the geopotential map from that data using least squares collocation. The quality of the reconstructed map is then assessed by comparing it to the original one used to generate the data. We show that adding only a few clock data points (less than 1% of the gravimetry data) reduces the bias significantly and improves the standard deviation by a factor 3. The effect of the data coverage and data quality on the results is investigated, and the trade-off between the measurement noise level and the number of data points is discussed.
Determination of an Optimal Geopotential Value for the North American Geoid
NASA Astrophysics Data System (ADS)
Roman, D. R.; Li, X.
2011-12-01
Canada, The United States, Mexico and other countries in North America having been working under the auspices of the International Association of Geodesy to develop a common geoid height model for the continent. Such a model would provide a common vertical reference system of orthometric heights accessed using GNSS technology. Canada and the U.S.A. already have plans to implement this for new national datums in 2013 (Canada) and 2022 (U.S.A.). The resulting geopotential values would also serve as the basis for determining dynamic heights as a part of the International Great Lakes Datum due to be updated around 2015. A critical aspect of this process then is the determining the most optimal geopotential value (W_0) for these datum definitions. A number of different data sets were compared in this analysis including various geoid height models, GNSS-determined ellipsoidal coordinates on tidal bench marks (TBM's), models of mean ocean dynamic topography (MODT) determined from physical oceanography, and altimeter-derived mean sea surface heights (MSSH). The expectation of this analysis is that the geoid and MODT heights should equal the heights observed either at TBM's or in the MSSH models. The requirement that the MODT models be based on physical oceanography reduces potential correlation with the MSSH in the results. The aim of this study then was to evaluate independent data sets to determine uncorrelated and unambiguous results. Any biases would potentially indicate an incorrect choice of W_0. Current models of the U.S.A. and Canada use a W_0 value of 62636856.88 m^2/s^2. The result of the comparisons show that this number is near optimal though some small change may be required depending pending refinement of the results along the eastern coast of the U.S.A., where the effects of the Gulf Stream complicate this analysis.
Accuracy of the GEM-T2 geopotential from Geosat and ERS 1 crossover altimetry
NASA Astrophysics Data System (ADS)
Wagner, C. A.; Klokočník, J.
1994-05-01
Extensive analyses of altimetrically determined sea height differences at crossovers have been used to assess the accuracy of the GEM-T2 geopotential. The orbits used were determined with GEM-T2 for Geosat in its 17-day Exact Repeat Mission (ERM) in 1986-1989 and ERS 1 in both its 3-day ERM in 1991-1992 and its 35-day ERM in 1992. The data examined are completely independent of the data used in GEM-T2's development though GEM-T2 had considerable use of Doppler tracking information on Geosat. The test of the radial accuracy of the ERS 1 orbit (98.5° inclination) is especially significant because it is not ``close'' to any other orbit well represented in GEM-T2. The assessment consists of a comparison of observed mean height differences at thousands of distinct geographic locations with error projections from the GEM-T2 covariance matrix which was estimated from other data sources. This first comprehensive, independent test of the purely radial accuracy of an orbit-geopotential model clearly shows that the covariant predictions for GEM-T2 are broadly reliable for this purpose. Thus, the agreement of crossover predictions and observations suggests that the total radial errors for these ERMs, due to only to GEM-T2 (but excluding the effects of initial state error) are about 23 cm for Geosat and 115 cm (rms) for ERS 1. However, there is little detailed agreement of measurements and predictions for ERS 1 and only partial agreement in detail for Geosat. Our 30,000 mean crossover discrepancies for Geosat (derived from ERM cycles 1-44) are also shown to reduce substantially the crossover height differences in cycles 45-61, almost exactly as predicted if these are the true GEM-T2 errors for this orbit.
NASA Astrophysics Data System (ADS)
Shen, Ziyu; Shen, Wen-Bin; Zhang, Shuangxi
2016-08-01
In this study, we propose an approach for determining the geopotential difference using high-frequency-stability microwave links between satellite and ground station based on Doppler cancellation system. Suppose a satellite and a ground station are equipped with precise optical-atomic clocks (OACs) and oscillators. The ground oscillator emits a signal with frequency fa towards the satellite and the satellite receiver (connected with the satellite oscillator) receives this signal with frequency fb which contains the gravitational frequency shift effect and other signals and noises. After receiving this signal, the satellite oscillator transmits and emits, respectively, two signals with frequencies fb and fc towards the ground station. Via Doppler cancellation technique, the geopotential difference between the satellite and the ground station can be determined based on gravitational frequency shift equation by a combination of these three frequencies. For arbitrary two stations on ground, based on similar procedures as described above, we may determine the geopotential difference between these two stations via a satellite. Our analysis shows that the accuracy can reach 1 m2 s- 2 based on the clocks' inaccuracy of about 10-17 (s s-1) level. Since OACs with instability around 10-18 in several hours and inaccuracy around 10-18 level have been generated in laboratory, the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.
Stabilized determination of geopotential coefficients by the mixed hom-BLUP approach
NASA Technical Reports Server (NTRS)
Middel, B.; Schaffrin, B.
1989-01-01
For the determination of geopotential coefficients, data can be used from rather different sources, e.g., satellite tracking, gravimetry, or altimetry. As each data type is particularly sensitive to certain wavelengths of the spherical harmonic coefficients it is of essential importance how they are treated in a combination solution. For example the longer wavelengths are well described by the coefficients of a model derived by satellite tracking, while other observation types such as gravity anomalies, delta g, and geoid heights, N, from altimetry contain only poor information for these long wavelengths. Therefore, the lower coefficients of the satellite model should be treated as being superior in the combination. In the combination a new method is presented which turns out to be highly suitable for this purpose due to its great flexibility combined with robustness.
NASA Astrophysics Data System (ADS)
Majkráková, Miroslava; Papčo, Juraj; Zahorec, Pavol; Droščák, Branislav; Mikuška, Ján; Marušiak, Ivan
2016-09-01
The vertical reference system in the Slovak Republic is realized by the National Levelling Network (NLN). The normal heights according to Molodensky have been introduced as reference heights in the NLN in 1957. Since then, the gravity correction, which is necessary to determine the reference heights in the NLN, has been obtained by an interpolation either from the simple or complete Bouguer anomalies. We refer to this method as the "original". Currently, the method based on geopotential numbers is the preferred way to unify the European levelling networks. The core of this article is an analysis of different ways to the gravity determination and their application for the calculation of geopotential numbers at the points of the NLN. The first method is based on the calculation of gravity at levelling points from the interpolated values of the complete Bouguer anomaly using the CBA2G_SK software. The second method is based on the global geopotential model EGM2008 improved by the Residual Terrain Model (RTM) approach. The calculated gravity is used to determine the normal heights according to Molodensky along parts of the levelling lines around the EVRF2007 datum point EH-V. Pitelová (UELN-1905325) and the levelling line of the 2nd order NLN to Kráľova hoľa Mountain (the highest point measured by levelling). The results from our analysis illustrate that the method based on the interpolated value of gravity is a better method for gravity determination when we do not know the measured gravity. It was shown that this method is suitable for the determination of geopotential numbers and reference heights in the Slovak national levelling network at the points in which the gravity is not observed directly. We also demonstrated the necessity of using the precise RTM for the refinement of the results derived solely from the EGM2008.
NASA Astrophysics Data System (ADS)
Yazid, N. M.; Din, A. H. M.; Omar, K. M.; Som, Z. A. M.; Omar, A. H.; Yahaya, N. A. Z.; Tugi, A.
2016-09-01
Global geopotential models (GGMs) are vital in computing global geoid undulations heights. Based on the ellipsoidal height by Global Navigation Satellite System (GNSS) observations, the accurate orthometric height can be calculated by adding precise and accurate geoid undulations model information. However, GGMs also provide data from the satellite gravity missions such as GRACE, GOCE and CHAMP. Thus, this will assist to enhance the global geoid undulations data. A statistical assessment has been made between geoid undulations derived from 4 GGMs and the airborne gravity data provided by Department of Survey and Mapping Malaysia (DSMM). The goal of this study is the selection of the best possible GGM that best matches statistically with the geoid undulations of airborne gravity data under the Marine Geodetic Infrastructures in Malaysian Waters (MAGIC) Project over marine areas in Sabah. The correlation coefficients and the RMS value for the geoid undulations of GGM and airborne gravity data were computed. The correlation coefficients between EGM 2008 and airborne gravity data is 1 while RMS value is 0.1499.In this study, the RMS value of EGM 2008 is the lowest among the others. Regarding to the statistical analysis, it clearly represents that EGM 2008 is the best fit for marine geoid undulations throughout South China Sea.
Geopotential research mission, science, engineering and program summary
NASA Technical Reports Server (NTRS)
Keating, T. (Editor); Taylor, P. (Editor); Kahn, W. (Editor); Lerch, F. (Editor)
1986-01-01
This report is based upon the accumulated scientific and engineering studies pertaining to the Geopotential Research Mission (GRM). The scientific need and justification for the measurement of the Earth's gravity and magnetic fields are discussed. Emphasis is placed upon the studies and conclusions of scientific organizations and NASA advisory groups. The engineering design and investigations performed over the last 4 years are described, and a spacecraft design capable of fulfilling all scientific objectives is presented. In addition, critical features of the scientific requirements and state-of-the-art limitations of spacecraft design, mission flight performance, and data processing are discussed.
Modelling of the Global Geopotential Energy & Stress Field
NASA Astrophysics Data System (ADS)
Schiffer, C.; Nielsen, S. B.
2012-04-01
Lateral density and topography variations yield in and important contribution to the lithospheric stress field. The leading quantity is the Geopotential Energy, the integrated lithostatic pressure in a rock column. The horizontal gradient of this quantity is related to horizontal stresses through the Equations of equilibrium of stresses. The Geopotential Energy furthermore can be linearly related to the Geoid under assumption of local isostasy. Satellite Geoid measurements contain, however, also non-isostatic deeper mantle responses of long wavelength. Unfortunately, high-pass filtering of the Geoid does not suppress only the deeper sources. The age-dependent signal of the oceanic lithosphere, for instance, is of long wave length and a prominent representative of in-plane stress, derived from the horizontal gradient of isostatic Geoid anomalies and responsible for the ridge push effect. Therefore a global lithospheric density model is required in order to isolate the shallow Geoid signal and calculate the stress pattern from isostatically compensated lithospheric sources. We use a linearized inverse method to fit a lithospheric reference model to observations such as topography and surface heat flow in the presence of local isostasy and a steady state geotherm. Subsequently we use a FEM code to solve the Equations of equilibrium of stresses for a three dimensional elastic shell. The modelled results are shown and compared with the global stress field and other publications.
Simulation and analysis of a geopotential research mission
NASA Technical Reports Server (NTRS)
White, Lisa K.
1987-01-01
Methods for the determination of the initial conditions for the two satellites that will satisfy Geopotential Research Mission (GRM) requirements are investigated. For certain gravitational recovery techniques, the satellites must remain close to a specified separation distance and their groundtracks must repeat after a specified interval of time. Since the objective of the GRM mission is to improve the gravity model, any pre-mission orbit predicted using existing gravity models will be in error. A technique has been developed to eliminate the drift between the two satellites caused by gravitational modeling errors and return them to repeating groundtracks. The concept of frozen orbits, which minimize altitude variations over given latitudes, was investigated. Finally, the effects of temporal perturbations on the relative range-rate signal were studied. At the proposed altitude of 160 km, the range-rate signal produced by perturbations other than the static geopotential field are dominated by the luni-solar effect. This study demonstrates that the combined effects of all the temporal perturbations does not prevent the orbit from being frozen or the satellites from obtaining a repeating groundtrack to within a specified closure distance.
Evaluation of flat-Earth approximation results for geopotential missions.
NASA Astrophysics Data System (ADS)
Tapley, M. B.
1997-04-01
Simplified calculations can approximate the formal uncertainties in estimates of the spherical harmonic coefficients representing the Earth's gravitational potential. The calculations model the Earth locally as a plane, producing errors negligible for wavelengths shorter than the radius of the Earth. Information derived from observations of low altitude polar orbiting satellites is considered. With some constraints, the final model uncertainties derive from a priori gravitational field information, specific orbital elements, and parameters describing instrumentation characteristics. The author demonstrates how to refine the technique to accept inputs from the currently operational Navstar Global Positioning System (GPS) constellation and how to use information from partial tensor gravitational gradiometers. This approach is beneficial when evaluating prospective satellite geodesy missions because the covariance analyses for various mission scenarios can be made efficiently and expeditiously. The author demonstrates the utility of the flat Earth approach by comparing results with those of more elaborate and time consuming calculations performed for the European Space Agency ARISTOTELES proposed geopotential mapping mission, the NASA Gravity Probe B Relativity mission, and the NASA/Center National d'Etudes Spatiales Topographic Ocean Experiment Satellite (TOPEX)/Poseidon mission.
NASA Astrophysics Data System (ADS)
Nerem, R. S.; Hardy, R. A.
2015-12-01
The gravity field of the Earth has changed dramatically over the last few decades as it responds to the melting of continental ice, depletion of groundwater, glacial isostatic adjustment, earthquakes, and other effects. The GRACE mission, launched in 2002, allows us to quantify these effects on gravity anomalies, geoid heights, deflections, and geopotential-based vertical reference systems at long wavelengths. We will examine these changes in different parts of the world and discuss the potential implications for different applications employing static (mean) gravity field models. We will furthermore show that GRACE and future satellite gravity missions can inform the changes in these vertical datums as the Earth's gravity field continues to evolve.
Study of geopotential error models used in orbit determination error analysis
NASA Technical Reports Server (NTRS)
Yee, C.; Kelbel, D.; Lee, T.; Samii, M. V.; Mistretta, G. D.; Hart, R. C.
1991-01-01
The uncertainty in the geopotential model is currently one of the major error sources in the orbit determination of low-altitude Earth-orbiting spacecraft. The results of an investigation of different geopotential error models and modeling approaches currently used for operational orbit error analysis support at the Goddard Space Flight Center (GSFC) are presented, with emphasis placed on sequential orbit error analysis using a Kalman filtering algorithm. Several geopotential models, known as the Goddard Earth Models (GEMs), were developed and used at GSFC for orbit determination. The errors in the geopotential models arise from the truncation errors that result from the omission of higher order terms (omission errors) and the errors in the spherical harmonic coefficients themselves (commission errors). At GSFC, two error modeling approaches were operationally used to analyze the effects of geopotential uncertainties on the accuracy of spacecraft orbit determination - the lumped error modeling and uncorrelated error modeling. The lumped error modeling approach computes the orbit determination errors on the basis of either the calibrated standard deviations of a geopotential model's coefficients or the weighted difference between two independently derived geopotential models. The uncorrelated error modeling approach treats the errors in the individual spherical harmonic components as uncorrelated error sources and computes the aggregate effect using a combination of individual coefficient effects. This study assesses the reasonableness of the two error modeling approaches in terms of global error distribution characteristics and orbit error analysis results. Specifically, this study presents the global distribution of geopotential acceleration errors for several gravity error models and assesses the orbit determination errors resulting from these error models for three types of spacecraft - the Gamma Ray Observatory, the Ocean Topography Experiment, and the Cosmic
Effect of Varying Crustal Thickness on CHAMP Geopotential Data
NASA Technical Reports Server (NTRS)
Taylor, P. T.; Kis, K. I.; vonFrese, R. R. B.; Korhonen, J. V.; Wittmann, G.; Kim, H. R.; Potts, L. V.
2003-01-01
To determine the effect of crustal thickness variation on satellite-altitude geopotential anomalies we compared two regions of Europe with vastly different values, Central/Southern Finland and the Pannonian Basin. Crustal thickness exceeds 62 km in Finland and is less than 26 km in the Pannonian Basin. Heat-flow maps indicate that the thinner and more active crust of the Pannonian Basin has a value nearly three times that of the Finnish Svecofennian Province. Ground based gravity mapping in Hungary shows that the free-air gravity anomalies across the Pannonian Basin are near 0 to +20 mGal with shorter wavelength anomalies from +40 to less than +60 mGal and some 0 to greater than -20 mGal. Larger anomalies are detected in the mountainous areas. The minor value anomalies can indicate the isostatic equilibrium for Hungary (the central part of the Pannonian Basin). Gravity data over Finland are complicated by de-glaciation. CHAMP gravity data (400 km) indicates a west-east positive gradient of greater than 4 mGal across Central/Southern Finland and an ovoid positive anomaly (approximately 4 mGal) quasi-coincidental with the magnetic anomaly traversing the Pannonian Basin. CHAMP magnetic data (425 km) reveal elongated semicircular negative anomalies for both regions with South-Central Finland having larger amplitude (less than -6 nT) than that over the Pannonian Basin, Hungary (less than -5 nT). In both regions subducted oceanic lithosphere has been proposed as the anomalous body.
NASA Technical Reports Server (NTRS)
Pavlis, Nikolaos K.
1991-01-01
An error analysis study was conducted in order to assess the current accuracies and the future anticipated improvements in the estimation of geopotential differences over intercontinental locations. An observation/estimation scheme was proposed and studied, whereby gravity disturbance measurements on the Earth's surface, in caps surrounding the estimation points, are combined with corresponding data in caps directly over these points at the altitude of a low orbiting satellite, for the estimation of the geopotential difference between the terrestrial stations. The mathematical modeling required to relate the primary observables to the parameters to be estimated, was studied for the terrestrial data and the data at altitude. Emphasis was placed on the examination of systematic effects and on the corresponding reductions that need to be applied to the measurements to avoid systematic errors. The error estimation for the geopotential differences was performed using both truncation theory and least squares collocation with ring averages, in case observations on the Earth's surface only are used. The error analysis indicated that with the currently available global geopotential model OSU89B and with gravity disturbance data in 2 deg caps surrounding the estimation points, the error of the geopotential difference arising from errors in the reference model and the cap data is about 23 kgal cm, for 30 deg station separation.
NASA Astrophysics Data System (ADS)
Ramillien, G. L.; Seoane, L.; Frappart, F.; Biancale, R.; Gratton, S.; Vasseur, X.; Bourgogne, S.
2012-09-01
We propose a "constrained" least-squares approach to estimate regional maps of equivalent-water heights by inverting GRACE-based potential anomalies at satellite altitude. According to the energy integral method, the anomalies of difference of geopotential between the two GRACE vehicles are derived from along-track K-Band Range-Rate (KBRR) residuals that correspond mainly to the continental water storage changes, once a priori known accelerations (i.e. static field, polar movements, atmosphere and ocean masses including tides) are removed during the orbit adjustment process. Newton's first law merely enables the Difference of Potential Anomalies from accurate KBRR data and the equivalent-water heights to be recovered. Spatial constraints versus spherical distance between elementary surface tiles are introduced to stabilize the linear system to cancel the effects of the north-south striping. Unlike the "mascons" approach, no basis of orthogonal functions (e.g., spherical harmonics) is used, so that the proposed regional method does not suffer from drawbacks related to any spectrum truncation. Time series of 10-day regional maps over South America for 2006-2009 also prove to be consistent with independent data sets, namely the outputs of hydrological models, "mascons" and global GRACE solutions.
Zonal and tesseral harmonic coefficients for the geopotential function, from zero to 18th order
NASA Technical Reports Server (NTRS)
Kirkpatrick, J. C.
1976-01-01
Zonal and tesseral harmonic coefficients for the geopotential function are usually tabulated in normalized form to provide immediate information as to the relative significance of the coefficients in the gravity model. The normalized form of the geopotential coefficients cannot be used for computational purposes unless the gravity model has been modified to receive them. This modification is usually not done because the absolute or unnormalized form of the coefficients can be obtained from the simple mathematical relationship that relates the two forms. This computation can be quite tedious for hand calculation, especially for the higher order terms, and can be costly in terms of storage and execution time for machine computation. In this report, zonal and tesseral harmonic coefficients for the geopotential function are tabulated in absolute or unnormalized form. The report is designed to be used as a ready reference for both hand and machine calculation to save the user time and effort.
Dynamic Heights in the Great Lakes using OPUS Projects
NASA Astrophysics Data System (ADS)
Roman, D. R.; Li, X.
2015-12-01
The U.S. will be implementing new geometric and vertical reference frames in 2022 to replace the North American Datum of 1983 (NAD 83) and the North American Vertical Datum of 1988 (NAVD 88), respectively. Less emphasized is the fact that a new dynamic height datum will also be defined about the same time to replace the International Great Lakes Datum of 1985 (IGLD 85). IGLD 85 was defined concurrent with NAVD 88 and used the same geopotential values. This paper focuses on the use of an existing tool for determining geometric coordinates and a developing geopotential model as a means of determining dynamic heights. The Online Positioning User Service (OPUS) Projects (OP) is an online tool available from the National Geodetic Survey (NGS) for use in developing geometric coordinates from simultaneous observations at multiple sites during multiple occupations. With observations performed at the water level gauges throughout the Great Lakes, the geometric coordinates of the mean water level surface can be determined. NGS has also developed the xGEOID15B model from satellite, airborne and surface gravity data. Using the input geometric coordinates determined through OP, the geopotential values for the water surface at the water level stations around the Great Lakes were determined using the xGEOID15B model. Comparisons were made between water level sites for each Lake as well as to existing IGLD 85 heights. A principal advantage to this approach is the ability to generate new water level control stations using OP, while maintaining the consistency between orthometric and dynamic heights by using the same gravity field model. Such a process may provide a means for determining dynamic heights for a future Great Lakes Datum.
Evaluation of the Recent GOCE-based Global Geopotential Models in North America
NASA Astrophysics Data System (ADS)
Sideris, M. G.; Amjadiparvar, B.; Rangelova, E. V.
2014-12-01
The Gravity field and steady-state Ocean Circulation Explorer (GOCE) dedicated satellite gravity field mission was launched on March 17, 2009. The GOCE came to an end in October 21, 2013. Five generations of global geopotential models (GGMs) have been computed and released based on the data collected by GOCE so far. The models are available via IAG's International Centre for Global Earth Models (ICGEM, http://icgem.gfz-potsdam.de/ICGEM/). The first generation models were computed from the first two months of the data, but the final generation models have been recently computed based on approximately 42 months of GOCE observations. Evaluation of these models in North America is important in view of the availability of high quality geodetic data in Canada and USA and the upcoming redefinition of the North American vertical datum through a continental geoid model based on a GOCE GGM. In this study, the performance of the models, developed by ESA's High-level Processing Facility (HPF), is evaluated by degree variances and also by comparing to the GNSS-levelling geoid undulations as independent control values. The GNSS-leveling stations in Canada, USA, Alaska and Mexico are used in this study. The results provide evidence that the signal of the Earth's gravitational field has been obtained solely from GOCE measurements up to degree and order (DO) 220, which corresponds to the spatial resolution of approximately 91 km. The cumulative global geoid error of TIM5 and DIR5 models up to DO 220 are 3.6 and 1.2 cm, respectively. The evaluation of the models by the North American GNSS-leveling stations in different spectral bands showed that the TIM5 and DIR5 models have slightly better performance than the EGM2008 model in the spectral band between DO 100 and 210 in Canada and the USA. The improvement brought by GOCE to Alaska and Mexico is more significant. In Alaska, the TIM5 and DIR5 models improve the geoid signal in the spectral band between DO 100 and 250. In Mexico
NASA Astrophysics Data System (ADS)
Bobojć, Andrzej
2016-12-01
This work contains a comparative study of the performance of six geopotential models in an orbit estimation process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For testing, such models as ULUX_CHAMP2013S, ITG-GRACE 2010S, EIGEN-51C, EIGEN5S, EGM2008, EGM96, were adopted. Different sets of pseudo-range simulations along reference GOCE satellite orbital arcs were obtained using real orbits of the Global Positioning System satellites. These sets were the basic observation data used in the adjustment. The centimeter-accuracy Precise Science Orbit (PSO) for the GOCE satellite provided by the European Space Agency (ESA) was adopted as the GOCE reference orbit. Comparing various variants of the orbital solutions, the relative accuracy of geopotential models in an orbital aspect is determined. Full geopotential models were used in the adjustment process. The solutions were also determined taking into account truncated geopotential models. In such case, an accuracy of the solutions was slightly enhanced. Different arc lengths were taken for the computation.
Geopotential coefficient determination and the gravimetric boundary value problem: A new approach
NASA Technical Reports Server (NTRS)
Sjoeberg, Lars E.
1989-01-01
New integral formulas to determine geopotential coefficients from terrestrial gravity and satellite altimetry data are given. The formulas are based on the integration of data over the non-spherical surface of the Earth. The effect of the topography to low degrees and orders of coefficients is estimated numerically. Formulas for the solution of the gravimetric boundary value problem are derived.
NASA Astrophysics Data System (ADS)
Bobojc, Andrzej; Drozyner, Andrzej
2016-04-01
This work contains a comparative study of performance of twenty geopotential models in an orbit estimation process of the satellite of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission. For testing, among others, such models as JYY_GOCE02S, ITG-GOCE02, ULUX_CHAMP2013S, GOGRA02S, ITG-GRACE2010S, EIGEN-51C, EGM2008, EGM96, JGM3, OSU91a, OSU86F were adopted. A special software package, called the Orbital Computation System (OCS), based on the classical method of least squares was used. In the frame of OCS, initial satellite state vector components are corrected in an iterative process, using the given geopotential model and the models describing the remaining gravitational perturbations. An important part of the OCS package is the 8th order Cowell numerical integration procedure, which enables a satellite orbit computation. Different sets of pseudorange simulations along reference GOCE satellite orbital arcs were obtained using real orbits of the Global Positioning System (GPS) satellites. These sets were the basic observation data used in the adjustment. The centimeter-accuracy Precise Science Orbit (PSO) for the GOCE satellite provided by the European Space Agency (ESA) was adopted as the GOCE reference orbit. Comparing various variants of the orbital solutions, the relative accuracy of geopotential models in an orbital aspect is determined. Full geopotential models were used in the adjustment process. However, the solutions were also determined taking into account truncated geopotential models. In such case, an accuracy of the orbit estimated was slightly enhanced. The obtained solutions refer to the orbital arcs with the lengths of 90-minute and 1-day.
Spatial and Temporal scales of time-averaged 700 MB height anomalies
NASA Technical Reports Server (NTRS)
Gutzler, D.
1981-01-01
The monthly and seasonal forecasting technique is based to a large extent on the extrapolation of trends in the positions of the centers of time averaged geopotential height anomalies. The complete forecasted height pattern is subsequently drawn around the forecasted anomaly centers. The efficacy of this technique was tested and time series of observed monthly mean and 5 day mean 700 mb geopotential heights were examined. Autocorrelation statistics are generated to document the tendency for persistence of anomalies. These statistics are compared to a red noise hypothesis to check for evidence of possible preferred time scales of persistence. Space-time spectral analyses at middle latitudes are checked for evidence of periodicities which could be associated with predictable month-to-month trends. A local measure of the average spatial scale of anomalies is devised for guidance in the completion of the anomaly pattern around the forecasted centers.
Present-day secular variations in the zonal harmonics of earth's geopotential
NASA Technical Reports Server (NTRS)
Mitrovica, J. X.; Peltier, W. R.
1993-01-01
The mathematical formulation required for predicting secular variation in the geopotential is developed for the case of a spherically symmetric, self-gravitating, viscoelastic earth model and an arbitrary surface load which can include a gravitational self-consistent ocean loading component. The theory is specifically applied to predict the present-day secular variation in the zonal harmonics of the geopotenial arising from the surface mass loading associated with the late Pleistocene glacial cycles. A procedure is outlined in which predictions of the present-day geopotential signal due to the late Pleistocene glacial cycles may be used to derive bounds on the net present-day mass flux from the Antarctic and Greenland ice sheets to the local oceans.
Report of the panel on geopotential fields: Gravity field, section 8
NASA Technical Reports Server (NTRS)
Anderson, Allen Joel; Kaula, William M.; Lazarewics, Andrew R.; Lefebvre, Michel; Phillips, Roger J.; Rapp, Richard H.; Rummel, Reinhard F.; Smith, David E.; Tapley, Byron D.; Zlotnick, Victor
1991-01-01
The objective of the Geopotential Panel was to develop a program of data acquisition and model development for the Earth's gravity and magnetic fields that meet the basic science requirements of the solid Earth and ocean studies. Presented here are the requirements for gravity information and models through the end of the century, the present status of our knowledge, data acquisition techniques, and an outline of a program to meet the requirements.
2014-08-01
using data obtained from the GRACE mission. Principal investigators for GRACE at the University of Texas at Austin Center for Space Research ( CSR ...Researchers at CSR have also developed the Grace Gravity Model (GGM) geopotential series. The first GGM series model (GGM01) was released in 2003.19...Potsdam and GCGS Toulouse,” AGU Fall Meeting Abstracts, 2013, Abstract G51A-0860. 24Eanes, R. J. and Bettadpur, S., “The CSR 3.0 Ocean Tide Model: Diurnal
Preliminary Goddard geopotential using optical tracking data and a comparison with SAO models
NASA Technical Reports Server (NTRS)
Lerch, F. J.; Wagner, C. A.; Putney, B. H.; Nickerson, K. G.
1971-01-01
A preliminary Goddard Space Flight Center (GSFC) geopotential and center of mass station coordinate solution was obtained from satellite orbital data using numerical integration theory. This geodetic solution is a prelude to a more general solution which will combine the 1971 International Satellite Geodesy Experiment (ISAGEX) laser data with the present data being employed. The present GSFC geopotential solution consists of the spherical harmonic coefficients through degree and order eight with higher order satellite resonant coefficients. The solution represents a first iteration result from 17 satellites with approximately 150 weekly orbital arcs containing some 40,000 optical observations. The GSFC preliminary result is compared with final results from the Smithsonian Astrophysical Observatory (SAO) solutions including the 1969 SAO Standard Earth II solution. One aspect of interest for the comparison is that SAO uses an analytic theory for the orbital solution whereas GSFC uses a numerical integration theory. The comparison of geopotential results shows that good agreement exists in general but that there are some areas of minor differences.
A series expansion of the solid Earth tide effect on geopotential
NASA Astrophysics Data System (ADS)
Kudryavtsev, Sergey M.
2013-04-01
We develop analytical series representing the main part of corrections to the geopotential coefficients caused by the solid Earth tides, where Love numbers are assumed to be frequency-independent. The series are compact, precise and valid over 1800 A.D.-2200 A.D. The maximum difference between the corrections given by the analytical series and their numerical values, obtained with use of the DE/LE-423 planetary/lunar ephemerides, does not exceed 0.7× 10^{-12}. A new algorithm is proposed for calculating amplitudes of the additional variations of the geopotential coefficients for frequency dependence of Love numbers. It uses the representation of the Earth tide-generating potential in the standard HW95 format and takes into account the phase of tidal waves. Corrections of up to 2× 10^{-12} to the published by the IERS Conventions (2010) amplitudes of the additional variations of the geopotential coefficients are suggested. Examples of use of the obtained series in analytical theories of motion of low-altitude STARLETTE and high-altitude ETALON-1 satellites are given.
Results from the simulations of geopotential coefficient estimation from gravity gradients
NASA Astrophysics Data System (ADS)
Bettadpur, S.; Schutz, B. E.; Lundberg, J. B.
New information of the short and medium wavelength components of the geopotential is expected from the measurements of gravity gradients made by the future ESA Aristoteles and the NASA Superconducting Gravity Gradiometer missions. In this paper, results are presented from preliminary simulations concerning the estimation of the spherical harmonic coefficients of the geopotential expansion from gravity gradients data. Numerical issues in the brute-force inversion (BFI) of the gravity gradients data are examined, and numerical algorithms are developed that substantially speed up the computation of the potential, acceleration, and gradients, as well as the mapping from the gravity gradients to the geopotential coefficients. The solution of a large least squares problem is also examined, and computational requirements are determined for the implementation of a large scale inversion. A comparative analysis of the results from the BFI and a symmetry method is reported for the test simulations of the estimation of a degree and order 50 gravity field. The results from the two, in the presence of white noise, are seen to compare well. The latter method is implemented on a special, axially symmetric surface that fits the orbit within 380 meters.
Evaluation of geopotential and luni-solar perturbations by a recursive algorithm
NASA Technical Reports Server (NTRS)
Giacaglia, G. E. O.
1975-01-01
The disturbing functions due to the geopotential and Luni-solar attractions are linear and bilinear forms in spherical harmonics. Making use of recurrence relations for the solid spherical harmonics and their derivatives, recurrence formulas are obtained for high degree terms as function of lower degree for any term of those disturbing functions and their derivative with respect to any element. The equations obtained are effective when a numerical integration of the equations of motion is appropriate. In analytical theories, they provide a fast way of obtaining high degree terms starting from initial very simple functions.
A comparative study of spherical and flat-Earth geopotential modeling at satellite elevations
NASA Technical Reports Server (NTRS)
Parrott, M. H.; Hinze, W. J.; Braile, L. W.
1985-01-01
Flat-Earth and spherical-Earth geopotential modeling of crustal anomaly sources at satellite elevations are compared by computing gravity and scalar magnetic anomalies perpendicular to the strike of variably dimensioned rectangular prisms at altitudes of 150, 300, and 450 km. Results indicate that the error caused by the flat-Earth approximation is less than 10% in most geometric conditions. Generally, error increase with larger and wider anomaly sources at higher altitudes. For most crustal source modeling applications at conventional satellite altitudes, flat-Earth modeling can be justified and is numerically efficient.
The Ohio State 1991 geopotential and sea surface topography harmonic coefficient models
NASA Technical Reports Server (NTRS)
Rapp, Richard H.; Wang, Yan Ming; Pavlis, Nikolaos K.
1991-01-01
The computation is described of a geopotential model to deg 360, a sea surface topography model to deg 10/15, and adjusted Geosat orbits for the first year of the exact repeat mission (ERM). This study started from the GEM-T2 potential coefficient model and it's error covariance matrix and Geosat orbits (for 22 ERMs) computed by Haines et al. using the GEM-T2 model. The first step followed the general procedures which use a radial orbit error theory originally developed by English. The Geosat data was processed to find corrections to the a priori geopotential model, corrections to a radial orbit error model for 76 Geosat arcs, and coefficients of a harmonic representation of the sea surface topography. The second stage of the analysis took place by doing a combination of the GEM-T2 coefficients with 30 deg gravity data derived from surface gravity data and anomalies obtained from altimeter data. The analysis has shown how a high degree spherical harmonic model can be determined combining the best aspects of two different analysis techniques. The error analysis was described that has led to the accuracy estimates for all the coefficients to deg 360. Significant work is needed to improve the modeling effort.
Average Offsets of the Local Vertical Datums in New Zealand Relative to the World Height System
NASA Astrophysics Data System (ADS)
Tenzer, Robert; Abdalla, Ahmed; Vatrt, Viliam; Dayoub, Nadim
2010-05-01
We determine the average offsets of 12 major local vertical datums (LVDs) in New Zealand relative to the World Height System (WHS). The LVD offsets are estimated using the EGM2008 global geopotential model coefficients complete to degree 2160 of spherical harmonics and the GPS-levelling data. The WHS is defined by the currently adopted best-estimated geoidal geopotential value W0= 62636856 m2s-2. Our test results reveal that the average offsets of 12 major local vertical datums situated throughout the South and North Islands of New Zealand range from -0.25 to 1.34 m. The EGM2008 and GPS-levelling data are further used to compute the differences between the NZGeoid05 regional quasigeoid model and the EGM2008 global quasigeoid model. The same analysis is done for the NZGeoid09 which is the latest version of the official national quasigeoid model for New Zealand. The numerical results at the network of GPS-levelling points show that the differences between the NZGeoid05 and the EGM2008 quasigeoid models vary from 0.24 to 0.81 m with the mean of 0.56 m. The corresponding differences between the NZGeoid09 and the EGM2008 quasigeoid models vary from 0.27 to 1.14 m with the mean of 0.51 m. Keywords: geoidal geopotential value, GPS-leveling data, local vertical datum, World Height System
NASA Astrophysics Data System (ADS)
Godah, Walyeldeen; Szelachowska, Malgorzata; Krynski, Jan
2014-06-01
The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) has significantly upgraded the knowledge on the Earth gravity field. In this contribution the accuracy of height anomalies determined from Global Geopotential Models (GGMs) based on approximately 27 months GOCE satellite gravity gradiometry (SGG) data have been assessed over Poland using three sets of precise GNSS/levelling data. The fits of height anomalies obtained from 4th release GOCE-based GGMs to GNSS/levelling data were discussed and compared with the respective ones of 3rd release GOCE-based GGMs and the EGM08. Furthermore, two highly accurate gravimetric quasigeoid models were developed over the area of Poland using high resolution Faye gravity anomalies. In the first, the GOCE-based GGM was used as a reference geopotential model, and in the second - the EGM08. They were evaluated with GNSS/levelling data and their accuracy performance was assessed. The use of GOCE-based GGMs for recovering the long-wavelength gravity signal in gravimetric quasigeoid modelling was discussed. Misja GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) przyczyniła się do znacznego poprawienia znajomości pola siły ciężkości Ziemi. W artykule przedstawiono wyniki oszacowania dokładności anomalii wysokości, wyznaczonych z globalnych modeli geopotencjału opracowanych na podstawie blisko 27 miesięcy pomiarów z satelitarnej misji gradiometrycznej GOCE. Do oszacowania wykorzystano trzy zbiory dokładnych danych satelitarno-niwelacyjnych z obszaru Polski. Omówiono wyniki wpasowania wartości anomalii wysokości otrzymanych z czwartej wersji globalnych modeli geopotencjału wyznaczonych na podstawie danych misji GOCE do danych satelitarno-niwelacyjnych oraz porównano je z wynikami odpowiedniego wpasowania trzeciej wersji globalnych modeli geopotencjału otrzymanych z GOCE oraz z modelu EGM08. Ponadto, wykorzystując wysokorozdzielczy zbiór grawimetrycznych anomalii Faye'a, wyznaczono dla
Assessment and Improvement of GOCE based Global Geopotential Models Using Wavelet Decomposition
NASA Astrophysics Data System (ADS)
Erol, Serdar; Erol, Bihter; Serkan Isik, Mustafa
2016-07-01
The contribution of recent Earth gravity field satellite missions, specifically GOCE mission, leads significant improvement in quality of gravity field models in both accuracy and resolution manners. However the performance and quality of each released model vary not only depending on the spatial location of the Earth but also the different bands of the spectral expansion. Therefore the assessment of the global model performances with validations using in situ-data in varying territories on the Earth is essential for clarifying their exact performances in local. Beside of this, their spectral evaluation and quality assessment of the signal in each part of the spherical harmonic expansion spectrum is essential to have a clear decision for the commission error content of the model and determining its optimal degree, revealed the best results, as well. The later analyses provide also a perspective and comparison on the global behavior of the models and opportunity to report the sequential improvement of the models depending on the mission developments and hence the contribution of the new data of missions. In this study a review on spectral assessment results of the recently released GOCE based global geopotential models DIR-R5, TIM-R5 with the enhancement using EGM2008, as reference model, in Turkey, versus the terrestrial data is provided. Beside of reporting the GOCE mission contribution to the models in Turkish territory, the possible improvement in the spectral quality of these models, via decomposition that are highly contaminated by noise, is purposed. In the analyses the motivation is on achieving an optimal amount of improvement that rely on conserving the useful component of the GOCE signal as much as possible, while fusing the filtered GOCE based models with EGM2008 in the appropriate spectral bands. The investigation also contain the assessment of the coherence and the correlation between the Earth gravity field parameters (free-air gravity anomalies and
User-driven update of a high-resolution geopotential model
NASA Astrophysics Data System (ADS)
Sebera, Josef; Bezděk, Aleš; Kostelecký, Jan; Pešek, Ivan
2014-05-01
Almost every year, there is a lot of (not only) new gravity data from satellite altimetry available to the users. This is in contradiction to the situation over the lands where financial and time costs are usually much higher. Hence, it might be reasonable to update global gravity field models in specific areas with new data. In this contribution, we outline a simple and user-driven concept for updating geopotential models over the oceans if relevant new data become available. The approach employs a grid-wise ellipsoidal harmonic analysis applied to gravity disturbance, while the resolution can achieve a higher maximum degree compared to recent combination models like EGM2008. The obtained harmonic coefficients represent global but regionally updated gravity information. As a test case, we present the concept using EGM2008 and DTU10.
Influence of the inner core geopotential variations on the rotation of the Earth
NASA Astrophysics Data System (ADS)
Escapa, A.; Getino, J.; Miguel, D.; Ferrándiz, J. M.
2011-10-01
In this investigation we determine a new contribution to the rotation of a three layer Earth model composed by an axial-symmetric mantle, a fluid core, and an axial-symmetric inner core. This contribution emerges as a consequence of the variation of the geopotential induced by the differential rotation of the solid inner core. Within the framework of the Hamiltonian theory of the rotation of the non-rigid Earth, and following the same guidelines as those described in Escapa et al. (2001, 2008), we discuss the influence of this effect on the motion of the Earth figure axis. We also provide numerical estimations for the amplitudes of the nutational motion of this axis.
Effects of height acceleration on Geosat heights
NASA Technical Reports Server (NTRS)
Hancock, David W., III; Brooks, Ronald L.; Lockwood, Dennis W.
1990-01-01
A radar altimeter tracking loop, such as that utilized by Geosat, produces height errors in the presence of persistent height acceleration h(a). The correction factor for the height error is a function of both the loop feedback parameters and the height acceleration. The correction, in meters, to the sea-surface height (SSH) derived from Geosat is -0.16 h(a), where h(a) is in m/sec per sec. The errors induced by accelerations are produced primarily by changes in along-track geoid slopes. The nearly circular Geosat orbit and dynamic ocean topography produce small h(a) values. One area studied in detail encompasses the Marianas Trench and the Challenger Deep in the west central Pacific Ocean. Histograms of SSH corrections due to range accelerations have also been determined from 24-hour segments of Geosat global data. The findings are that 20 percent of the Geosat measurements have acceleration-induced errors of 2 cm or more, while 8 percent have errors of 3 cm or more.
NASA Astrophysics Data System (ADS)
Reubelt, T.; Sneeuw, N.; Visser, P. N. A. M.; van Dam, T.; Losch, M.
2009-04-01
With the successful GRACE mission (data collection since Spring 2002), global time-variable gravity fields can be recovered beyond the lower degrees for the first time. Although GRACE is able to detect significant features of the time-variable geopotential, e.g. the continental hydrological cycle, trends in ice-mass change in Antarctica or Greenland or sea level rise, its mission concept suffers from inherent deficiencies. The main limitations of GRACE are (i) the range-rate measurements (insufficient accuracy, anisotropy of the leader-follower-formation), (ii) aliasing due to spatial and temporal undersampling and (iii) inaccurate de-aliasing products. This leads to an erroneous North-South striping pattern and a limited accuracy and resolution for many scientific studies. Within the ESA project „Monitoring and Modeling Individual Sources of Mass Distribution and Transport in the Earth System by Means of Satellites" potential future satellite mission concepts, which could improve time-variable geopotential-recovery, have been studied. An improved accuracy of a future laser instrument as well as an enhanced temporal sampling have been regarded in the simulations, which were based on repeat orbits. An enhanced sampling can be achieved by means of multi-satellite-missions, where the spatial and/or temporal resolutions are improved by: 1) additional satellites on interleaved groundtracks and/or 2) time shifted satellites on the same groundtrack. Another possibility is the so-called Pete-Bender-design, where the satellites fly on different repeat-orbits with different inclinations, which also allows for more homogeneous groundtrack coverage. Sophisticated satellite-formations such as cartwheels or gravity wheels have not been regarded so far due to the unsolved technical problems (e.g. control of the laser instrument) related to these designs. The primary objective of the simulation studies was the precise recovery of the input hydrological signal and the trends of
NASA Technical Reports Server (NTRS)
Sumrall, Daniel R.; Nichols, Vincent P.
1992-01-01
Gauge aligns itself and retains indication for later reading. Measuring tool indicates height of protrusion of pin from flat surface. Tool surrounds pin and holds itself square with flat surface, ensuring proper alignment and accuracy of measurement. Used in hard-to-see and hard-to-reach places. Holds indication of height until read. Metal scale slides in and out through slot in top plate. Scale value at slot gives height of pin under piston. Dimensions in inches.
Estimation of geopotential from satellite-to-satellite range rate data: Numerical results
NASA Technical Reports Server (NTRS)
Thobe, Glenn E.; Bose, Sam C.
1987-01-01
A technique for high-resolution geopotential field estimation by recovering the harmonic coefficients from satellite-to-satellite range rate data is presented and tested against both a controlled analytical simulation of a one-day satellite mission (maximum degree and order 8) and then against a Cowell method simulation of a 32-day mission (maximum degree and order 180). Innovations include: (1) a new frequency-domain observation equation based on kinetic energy perturbations which avoids much of the complication of the usual Keplerian element perturbation approaches; (2) a new method for computing the normalized inclination functions which unlike previous methods is both efficient and numerically stable even for large harmonic degrees and orders; (3) the application of a mass storage FFT to the entire mission range rate history; (4) the exploitation of newly discovered symmetries in the block diagonal observation matrix which reduce each block to the product of (a) a real diagonal matrix factor, (b) a real trapezoidal factor with half the number of rows as before, and (c) a complex diagonal factor; (5) a block-by-block least-squares solution of the observation equation by means of a custom-designed Givens orthogonal rotation method which is both numerically stable and tailored to the trapezoidal matrix structure for fast execution.
Modeling and estimation of a low degree geopotential model from terrestrial gravity data
NASA Technical Reports Server (NTRS)
Pavlis, Nikolaos K.
1988-01-01
The development of appropriate modeling and adjustment procedures for the estimation of harmonic coefficients of the geopotential, from surface gravity data was studied, in order to provide an optimum way of utilizing the terrestrial gravity information in combination solutions currently developed at NASA/Goddard Space Flight Center, for use in the TOPEX/POSEIDON mission. The mathematical modeling was based on the fundamental boundary condition of the linearized Molodensky boundary value problem. Atmospheric and ellipsoidal corrections were applied to the surface anomalies. Terrestrial gravity solutions were found to be in good agreement with the satellite ones over areas which are well surveyed (gravimetrically), such as North America or Australia. However, systematic differences between the terrestrial only models and GEMT1, over extended regions in Africa, the Soviet Union, and China were found. In Africa, gravity anomaly differences on the order of 20 mgals and undulation differences on the order of 15 meters, over regions extending 2000 km in diameter, occur. Comparisons of the GEMT1 implied undulations with 32 well distributed Doppler derived undulations gave an RMS difference of 2.6 m, while corresponding comparison with undulations implied by the terrestrial solution gave RMS difference on the order of 15 m, which implies that the terrestrial data in that region are substantially in error.
Analogs in the wintertime 500 mb height field. [recurrent flow patterns
NASA Technical Reports Server (NTRS)
Gutzler, D. S.; Shukla, J.
1984-01-01
Lorenz (1969) has considered the possibility that an atmospheric circulation pattern might recur, taking into account the definition of a pair of analogous flows or 'analogs'. The present investigation is concerned with a search of time series of Northern Hemisphere wintertime geopotential heights for possible analogs. Attention is given to data and analysis procedure, analog quality, and error growth rates. The obtained results imply that the found analogs are not a useful tool for forecasting the evolution of the midlatitude flow on time scales of several days. It is pointed out, however, that the negative results should not be extended to other applications of analog forecasting.
Height, health, and development
Deaton, Angus
2007-01-01
Adult height is determined by genetic potential and by net nutrition, the balance between food intake and the demands on it, including the demands of disease, most importantly during early childhood. Historians have made effective use of recorded heights to indicate living standards, in both health and income, for periods where there are few other data. Understanding the determinants of height is also important for understanding health; taller people earn more on average, do better on cognitive tests, and live longer. This paper investigates the environmental determinants of height across 43 developing countries. Unlike in rich countries, where adult height is well predicted by mortality in infancy, there is no consistent relationship across and within countries between adult height on the one hand and childhood mortality or living conditions on the other. In particular, adult African women are taller than is warranted by their low incomes and high childhood mortality, not to mention their mothers' educational level and reported nutrition. High childhood mortality in Africa is associated with taller adults, which suggests that mortality selection dominates scarring, the opposite of what is found in the rest of the world. The relationship between population heights and income is inconsistent and unreliable, as is the relationship between income and health more generally. PMID:17686991
NASA Astrophysics Data System (ADS)
Oladele, S.; Ayolabi, E. A.; Dublin-Green, C. O.
2016-09-01
The structural dispositions of the Nigerian sector of the Benin Basin have been investigated using attributes of geomagnetic and gravimetric fields. Aeromagnetic anomalies were reduced to the equator to improve the correspondence of the anomalies with the causative bodies. The residual, upward continued, tilt and horizontal derivatives, and pseudogravity attributes and forward models of both geomagnetic and gravimetric anomalies were computed to accentuate geological features including shallow and regional faults, fracture network, basement block pattern and depth to magnetic basement. Three generations of sinistral faults were identified. The oldest generation of faults (F1) is the NE-SW trend corresponding to the oceanic fracture zones trend. The F1 is truncated by the second generation of faults (F2) with E-W trends. The third generation of faults (F3) assumes NW-SE trend and is offset by F2. Shallow and deep regional faults and fractures envisaged to play major role in migration and entrapment of hydrocarbons and localization of mineral resources in this area were imaged. The coastline, Lagos and Lekki Lagoons surface geometry showed high degree of similarity with their underlying basement block pattern, thus implying that these surface features are structurally controlled. The basement morphology is not flat but of horst and graben architecture in which sediment thickness attained about 4 km within the graben. Hence, the graben has significant hydrocarbon potential. This study has shown the capabilities of geopotential field attributes in providing information about the structural architecture of frontier basin. Such knowledge will aid the understanding of the geology of the basin and its resources.
NASA Technical Reports Server (NTRS)
Greatorex, Scott (Editor); Beckman, Mark
1996-01-01
Several future, and some current missions, use an on-board computer (OBC) force model that is very limited. The OBC geopotential force model typically includes only the J(2), J(3), J(4), C(2,2) and S(2,2) terms to model non-spherical Earth gravitational effects. The Tropical Rainfall Measuring Mission (TRMM), Wide-field Infrared Explorer (WIRE), Transition Region and Coronal Explorer (TRACE), Submillimeter Wave Astronomy Satellite (SWAS), and X-ray Timing Explorer (XTE) all plan to use this geopotential force model on-board. The Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) is already flying this geopotential force model. Past analysis has shown that one of the leading sources of error in the OBC propagated ephemeris is the omission of the higher order geopotential terms. However, these same analyses have shown a wide range of accuracies for the OBC ephemerides. Analysis was performed using EUVE state vectors that showed the EUVE four day OBC propagated ephemerides varied in accuracy from 200 m. to 45 km. depending on the initial vector used to start the propagation. The vectors used in the study were from a single EUVE orbit at one minute intervals in the ephemeris. Since each vector propagated practically the same path as the others, the differences seen had to be due to differences in the inital state vector only. An algorithm was developed that will optimize the epoch of the uploaded state vector. Proper selection can reduce the previous errors of anywhere from 200 m. to 45 km. to generally less than one km. over four days of propagation. This would enable flight projects to minimize state vector uploads to the spacecraft. Additionally, this method is superior to other methods in that no additional orbit estimates need be done. The definitive ephemeris generated on the ground can be used as long as the proper epoch is chosen. This algorithm can be easily coded in software that would pick the epoch within a specified time range that would
NASA Technical Reports Server (NTRS)
Antreasian, Peter G.
1988-01-01
Two orbit simulations, one representing the actual Geopotential Research Mission (GRM) orbit and the other representing the orbit estimated from orbit determination techniques, are presented. A computer algorithm was created to simulate GRM's drag compensation mechanism so the fuel expenditure and proof mass trajectories relative to the spacecraft centroid could be calculated for the mission. The results of the GRM DISCOS simulation demonstrated that the spacecraft can essentially be drag-free. The results showed that the centroid of the spacecraft can be controlled so that it will not deviate more than 1.0 mm in any direction from the centroid of the proof mass.
Goldsworthy, W.W.
1958-06-01
A differential pulse-height discriminator circuit is described which is readily adaptable for operation in a single-channel pulse-height analyzer. The novel aspect of the circuit lies in the specific arrangement of differential pulse-height discriminator which includes two pulse-height discriminators having a comnnon input and an anticoincidence circuit having two interconnected vacuum tubes with a common cathode resistor. Pulses from the output of one discriminator circuit are delayed and coupled to the grid of one of the anticoincidence tubes by a resistor. The output pulses from the other discriminator circuit are coupled through a cathode follower circuit, which has a cathode resistor of such value as to provide a long time constant with the interelectrode capacitance of the tube, to lenthen the output pulses. The pulses are then fed to the grid of the other anticoincidence tube. With such connections of the circuits, only when the incoming pulse has a pesk value between the operating levels of the two discriminators does an output pulse occur from the anticoincidence circuit.
NASA Astrophysics Data System (ADS)
Barkin, Yu. V.
2003-04-01
TIME VARIATIONS OF GEOPOTENTIAL, GRAVITY AND VERTICAL CRUSTAL DEFORMATIONS: NATURE AND UNITY OF CYCLICITIES Yu.V.Barkin Sternberg Astronomical Institute, Moscow, Russia, barkin@sai.msu.ru Gravitational action of the Moon and the Sun on the Earth generates very big additional mechanical forces and moments of the interaction of its neighboring shells (liquid core, mantle and another layers) and produces cyclic perturbations of the tensional state of the shells, their deformations, small relative translational displacements and small relative rotational oscillations of the shells, redistribution of the plastic and fluid masses and others. These additional forces and moments of the cyclic celestial-mechanical nature produce deformations of the all layers of the Earth and organize and control practically all natural processes. In given report we analyze these forces and moments caused by the Moon attraction. We have shown that they are conditionally periodic functions of time with definite basis of frequencies, which are some combinations of the frequencies of perturbations in the Moon orbital motion. Very important conclusion follows from our approach - natural processes are controlled and dictated by pointed mechanism and are subjected by cyclic variations with general for all processes base of frequencies. The fundamental basis of frequencies was established in result of theoretical study of the gravitational interaction of the Earth’s core and mantle with the Moon and the Sun and in result of analysis of observed variations of the many natural processes [1]. Predicted periods of variations of the natural processes were conformed by last results of the spectral analysis of gravity at Moscow fidicial station and by similar studies of the Earth rotation, vertical crustul deformations [2]. In particular periods, amplitudes (in a few microGal) and phases for about 20 harmonics of gravity variations were discovered in result of spectral analysis of the absolute
NASA Astrophysics Data System (ADS)
Grombein, T.; Seitz, K.; Heck, B.
2013-12-01
In general, national height reference systems are related to individual vertical datums defined by specific tide gauges. The discrepancy of these vertical datums causes height system biases that range in an order of 1-2 m at a global scale. Continental height systems can be connected by spirit leveling and gravity measurements along the leveling lines as performed for the definition of the European Vertical Reference Frame. In order to unify intercontinental height systems, an indirect connection is needed. For this purpose, global geopotential models derived from recent satellite missions like GOCE provide an important contribution. However, to achieve a highly-precise solution, a combination with local terrestrial gravity data is indispensable. Such combinations result in the solution of a Geodetic Boundary Value Problem (GBVP). In contrast to previous studies, mostly related to the traditional (scalar) free GBVP, the present paper discusses the use of the fixed GBVP for height system unification, where gravity disturbances instead of gravity anomalies are applied as boundary values. The basic idea of our approach is a conversion of measured gravity anomalies to gravity disturbances, where unknown datum parameters occur that can be associated with height system biases. In this way, the fixed GBVP can be extended by datum parameters for each datum zone. By evaluating the GBVP at GNSS/leveling benchmarks, the unknown datum parameters can be estimated in a least squares adjustment. Beside the developed theory, we present numerical results of a case study based on the spherical fixed GBVP and boundary values simulated by the use of the global geopotential model EGM2008. In a further step, the impact of approximations like linearization as well as topographic and ellipsoidal effects is taken into account by suitable reduction and correction terms.
Vertical datum unification for the International Height Reference System (IHRS)
NASA Astrophysics Data System (ADS)
Sánchez, Laura; Sideris, Michael G.
2017-01-01