A Joint Analysis of GPS Displacement and GRACE Geopotential Data for Simultaneous Estimation of Geocenter Motion and Gravitational Field

Gravitational potential data from GRACE are being used to study mass redistribution within and between the atmosphere, hydrosphere, cryosphere, and solid Earth. The GRACE data are made available in a reference frame with its origin at the center of mass of the Earth system (geocenter) while many other geophysical models and data sets refer to a reference frame attached to the Earth's surface. Changes in the offset between these reference frames (geocenter motion) must be accounted for when GRACE data are used to quantify surface mass changes. In this study, we developed a technique for coestimation of geocenter motion and gravitational potential field seamlessly from degree 1 to 90 by simultaneously inverting a set of globallydistributed GPS displacement time series and the temporallyvarying GRACE gravity data. We found that the effect of geocenter motion was evident particularly in the GPS time series of horizontal displacements. Our estimates of geocenter motion are most consistent with the Satellite Laser Ranging (SLR) results within 1 mm in X and Z components and a submillimeter in Y component, when compared to monthly variability averaged over the period of 20032016. The overall magnitude of the degree1 (l = 1) surface mass load is estimated to be ~3 cm in equivalent water height annually migrating southwestward from Europe (DecemberJanuary) to the South Pacific (JuneJuly). Our results also show that dense GPS network data improve water storage recovery in major river basins in the United States and Europe by contributing significantly to the recovery of higherdegree (l ~20) geopotential coefficients

Efficient Global Gravity Determination from Satellite-to-Satellite Tracking (SST)

This report was prepared by Shin-Chan Han, a graduate student, Department Civil and Environmental Engineering and Geodetic Science, under the supervision of Professors C. Jekeli and C.K. Shum.This research is supported by grants from the Center for Space Research, University of Texas under a prime contract from NASA (CSR/GRACE #735367), and from NASA's Solid Earth and Natural Hazards Program (NASA/GRACE #736312).This report was also submitted to the Graduate School of Ohio State University as a thesis in partial fulfillment of the requirements for the degree Doctor of Philosophy.By the middle of this decade, measurements from the CHAMP (CHAllenging of Minisatellite Payload) and GRACE (Gravity Recovery And Climate Experiment) gravity mapping satellite missions are expected to provide a significant improvement in our knowledge of the Earth's mean gravity field and its temporal variation. For this research, new observation equations and efficient inversion method were developed and implemented for determination of the Earth’s global gravity field using satellite measurements. On the basis of the energy conservation principle, in situ (on-orbit) and along track disturbing potential and potential difference observations were computed using data from accelerometer- and GPS receiver-equipped satellites, such as CHAMP and GRACE. The efficient iterative inversion method provided the exact estimates as well as an approximate, but very accurate error variance-covariance matrix of the least squares system for both satellite missions. The global disturbing potential observable computed using 16-days of CHAMP data was used to determine a 50´50 test gravity field solution (OSU02A) by employing a computationally efficient inversion technique based on conjugate gradient. An evaluation of the model using independent GPS/leveling heights and Arctic gravity data, and comparisons with existing gravity models, EGM96 and GRIM5C1, and new models, EIGEN1S and TEG4 which include CHAMP data, indicate that OSU02A is commensurate in geoid accuracy and, like other new models, it yields some improvement (10% better fit) in the polar region at wavelengths longer than 800 km. The annual variation of Earth’s gravitational field was estimated from 1.5 years of CHAMP data and compared with other solutions from satellite laser ranging (SLR) analysis. Except the second zonal and third tesseral harmonics, others second and third degree coefficients were comparable to SLR solutions in terms of both phase and magnitude. The annual geoid change of 1 mm would be expected mostly due to atmosphere, continental surface water, and ocean mass redistribution. The correlation between CHAMP and SLR solutions was 0.6~0.8 with 0.7 mm of RMS difference. Although the result should be investigated by analyzing more data for longer time span, it indicates the significant contribution of CHAMP SST data to the time-variable gravity study. Considering the energy relationship between the kinetic and frictional energy of the satellite and the gravitational potential energy, the disturbing potential difference observations can be computed from the orbital state vector, using high-low GPS tracking data, low-low satellite-to-satellite GRACE measurements, and data from 3-axis accelerometers. Based on the monthly GRACE simulation, the geoid was obtained with an accuracy of a few cm and with a resolution (half wavelength) of 160 km. However, the geoid accuracy can become worse by a factor of 6~7 because of spatial aliasing. The approximate error covariance was found to be a very good accuracy measure of the estimated coefficients, geoid, and gravity anomaly. The temporal gravity field, representing the monthly mean continental water mass redistribution, was recovered in the presence of measurement noise and high iii frequency temporal variation. The resulting recovered temporal gravity fields have about 0.2 mm errors in terms of geoid height with a resolution of 670 km. It was quantified that how significant the effects due to the inherent modeling errors and temporal aliasing caused by ocean tides, atmosphere, and ground surface water mass are on monthly mean GRACE gravity estimates. The results are based on simulations of GRACE range-rate perturbations due to modeling error along the orbit; and, their effects and temporal aliasing on the estimated gravitational coefficients were analyzed by fully inverting monthly simulated GRACE data. For ocean tides, the study based on the model difference, CSR4.0–NAO99, indicates that some residual constituents like in S2 may cause errors 3 times larger than the measurements noise at harmonic degrees less than 15 in the monthly mean estimates. On the other hand, residual constituents in K1, O1, and M2 are reduced by monthly averaging below the measurement noise level. For the atmosphere, the difference in models, ECMWF–NCEP, produces errors in GRACE range-rate measurements as strong as the measurement noise. They corrupt all recovered coefficients and introduce 30 % more error in the global monthly geoid estimates up to maximum degree 120. However, the analysis based on daily CDAS-1 data for continental surface water mass redistribution indicates that the daily soil moisture and snow depth variations affect the monthly mean GRACE recovery less than the measurement noise

Intra-Project Externality and Layout Variables in Residential Condominium Appraisals

This study examines the impact of intra-project externalities and layout variables on the selling prices of 897 condominium units in the cities of Irvine and Santa Ana in Orange County, California. It documents that, at a micro-level, proximity to intra-project externalities such as greenspace, swimming pools, recreational areas, traffic noise, and the like, and project layout variables representing the location of individual condominium units within multiunit structures, have significant effects on the property values of units within a condominium project. The results indicate that, when cost is not prohibitive, both appraisers and underwriters should take intra-project externalities and layout variables into consideration when estimating property values or underwriting residential mortgages for condominium properties.

Static and Kinematic Absolute GPS Positioning and Satellite Clock Error Estimation

This report was prepared by Shin-Chan Han, a graduate student, Department Civil and Environmental Engineering and Geodetic Science, under the supervision of Professor Christopher Jekeli. This research was supported by the National Imagery and Mapping Agency under Air Force Phillips Laboratory contracts F19628-95-K-0020 and F19628- 96-C-0169.This report was also submitted to the Graduate School of Ohio State University as a thesis in partial fulfillment of the requirements for the Master of Science degree.This study presents the results of investigations to determine accurate position coordinates using the Global Positioning System in the absolute (point) positioning mode. The most common method to obtain accurate positions with GPS is to apply doubledifferencing procedures whereby GPS satellite signals are differenced at a station and these differences are again differenced with analogous differences at other stations. The differencing between satellites eliminates the receiver clock errors, while the betweenstation differences eliminate the satellite clock errors (as well as other errors, such as orbit error). However, only coordinate differences can be determined in this way and the accuracy depends on the baseline length between cooperating stations. The strategy with accurate point positioning is to estimate GPS satellite clock errors independently, thus obviating the between-station differencing. The clock error estimates are then used in an application of a single-difference (between-satellite) positioning algorithm at any site to determine the coordinates without reference to any other site. Using IGS (International GPS Service) orbits and station coordinates, the GPS clock errors were estimated at 30- second intervals and these estimates were compared to values determined by JPL (Zumberge et al., 1998). The agreement was at the level of about 0.1 nsec (3 cm). The absolute positioning technique was tested in an application of a single-differenced (between-satellite) positioning algorithm in static and kinematic modes. For the static case, an IGS station was selected and the coordinates were estimated. The estimated absolute position coordinates and the published values had a mean difference of up to 18 cm with standard deviation less than 2 cm. For the kinematic case, data (every second) obtained from a GPS buoy were tested and the result from the absolute positioning was compared to a DGPS solution. The mean difference between the two algorithms is less than 40 cm and the standard deviation is less than 23 cm. It was proved that a higher rate (less than 30 sec.) of satellite clock determination and a good tropospheric delay model are required to do absolute kinematic positioning to better than 10 cm accuracy

Sea Level Rise in the Samoan Islands Escalated by Viscoelastic Relaxation After the 2009 Samoa-Tonga Earthquake

The Samoan islands are an archipelago hosting a quarter million people mostly residing inthree major islands, Savai'i and Upolu (Samoa), and Tutuila (American Samoa). The islands haveexperienced sea level rise by 2-3 mm/year during the last half century. The rate, however, has dramaticallyincreased following the Mw 8.1 SamoaTonga earthquake doublet (megathrust + normal faulting) inSeptember 2009. Since the earthquake, we found largescale gravity increase (0.5 Gal/year) around theislands and ongoing subsidence (8-16 mm/year) of the islands from our analysis of Gravity Recovery AndClimate Experiment gravity and GPS displacement data. The postseismic horizontal displacement is faster inSamoa, while the postseismic subsidence rate is considerably larger in American Samoa. The analysis oflocal tide gauge records and satellite altimeter data also identified that the relative sea level rise becomesfaster by 7-9 mm/year in American Samoa than Samoa. A simple viscoelastic model with a Maxwellviscosity of 2310(exp 18) Pa s for the asthenosphere explained postseismic deformation at nearby GPS sites aswell as Gravity Recovery And Climate Experiment gravity change. It is found that the constructiveinterference of viscoelastic relaxation from both megathrust and normal faulting has intensified thepostseismic subsidence at American Samoa, causing ~5 times faster sea level rise than the global average.Our model indicates that this trend is likely to continue for decades and result in sea level rise of 30-40 cm,which is independent of and in addition to anticipated climaterelated sea level rise. It will worsen coastalflooding on the islands leading to regular nuisance flooding

Quantum advantage through the magic pentagram problem

Through the two specific problems, the 2D hidden linear function problem and the 1D magic square problem, Bravyi et al. have recently shown that there exists a separation between $\mathbf{QNC^0}$ and $\mathbf{NC^0}$, where $\mathbf{QNC^0}$ and $\mathbf{NC^0}$ are the classes of polynomial-size and constant-depth quantum and classical circuits with bounded fan-in gates, respectively. In this paper, we present another problem with the same property, the magic pentagram problem based on the magic pentagram game, which is a nonlocal game. In other words, we show that the problem can be solved with certainty by a $\mathbf{QNC^0}$ circuit but not by any $\mathbf{NC^0}$ circuits.Comment: 10 pages, 5 figure

Global Characteristics of the Correlation and Time Lag Between Solar and Ionospheric Parameters in the 27-day Period

The 27-day variations of topside ionosphere are investigated using the in-situ electron density measurements from the CHAMP planar Langmuir probe and GRACE K-band ranging system. As the two satellite systems orbit at the altitudes of approx. 370 km and approx. 480 km, respectively, the satellite data sets are greatly valuable for examining the electron density variations in the vicinity of F2-peak. In a 27-day period, the electron density measurements from the satellites are in good agreements with the solar flux, except during the solar minimum period. The time delays are mostly 1-2 day and represent the hemispherical asymmetry. The globally-estimated spatial patterns of the correlation between solar flux and in-situ satellite measurements show poor correlations in the (magnetic) equatorial region, which are not found from the ground measurements of vertically-integrated electron content. We suggest that the most plausible cause for the poor correlation is the vertical movement of ionization due to atmospheric dynamic processes that is not controlled by the solar extreme ultraviolet radiation

Serum cytokine profiles in healthy young and elderly population assessed using multiplexed bead-based immunoassays

<p>Abstract</p> <p>Background</p> <p>Lipid metabolites and cytokines, including chemokines and growth factors, are the key regulators of immune cell function and differentiation, and thus, dysregulation of these regulators is associated with various human diseases. However, previous studies demonstrating a positive correlation of cytokine levels with aging may have been influenced by various environmental factors and underlying diseases. Also, data regarding cytokine profiling in the elderly are limited to a small subset of cytokines.</p> <p>Methods</p> <p>We compared the profiles of 22 cytokines, including chemokines and growth factors, in a case-controlled study group of a gender-matched, healthy cohort of 55 patients over the age of 65 and 55 patients under the age of 45. Assessment of serum cytokine concentrations was performed using commercially-available multiplex bead-based sandwich immunoassays.</p> <p>Results</p> <p>Soluble CD40 ligand (sCD40L) and transforming growth factor alpha (TGF-α) levels were significantly higher in the elderly patients, whereas granulocyte colony-stimulating factor (G-CSF), granulocyte-monocyte colony-stimulating factor (GM-CSF), and monocyte chemoattractant protein-1 (MCP-1) levels were significantly lower in the elderly patients. The partial correlation analysis demonstrating the correlation between cytokine levels when controlled for gender, systolic blood pressure, total cholesterol, HDL cholesterol, triglyceride, and serum creatinine levels further demonstrated that G-CSF, GM-CSF, and MCP-1 had significant negative correlations with age, whereas sCD40L and TGF-α had significant positive correlations.</p> <p>Conclusions</p> <p>Future studies will focus on examining the significance of these age-related changes in circulating cytokines and other biological markers and their potential contribution to the development of different age-associated diseases.</p

CubeSat GPS Observation of Traveling Ionospheric Disturbances After the 2022 Hunga-Tonga Hunga-Ha'apai Volcanic Eruption and Its Potential Use for Tsunami Warning

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