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Clark R Wilson - One of the best experts on this subject based on the ideXlab platform.
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assessment of degree 2 zonal gravitational changes from grace Earth Rotation climate models and satellite laser ranging
IAG International Symposium on "Gravity Geoid and Earth Observation 2008", 2010Co-Authors: Jianli Chen, Clark R WilsonAbstract:Four independent time series of degree-2 zonal gravitational variations ΔC20 are compared for the period April 2002 to February 2008. We examine estimates from the Gravity Recovery and Climate Experiment (GRACE), Earth Rotation variations, climate models (AOW), and satellite laser ranging (SLR). At the annual period, all ΔC20 estimates agree remarkably well, and good correlation is found among these time series at nonseasonal time scales as well. SLR and AOW ΔC20 time series show the best agreement in a broad band of frequencies with the maximum cross-correlation coefficient of 0.86 at nonseasonal time scales. GRACE monthly ΔC20 estimates are subject to significant aliasing effects due to errors in high-frequency tide models, especially the S2 and K2 tides. Correctly removing winds and ocean currents and other motion related excitations from length-of-day (LOD) observations plays a key role in estimating ΔC20 from LOD, especially at interannual or longer time scales.
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low degree gravity changes from grace Earth Rotation geophysical models and satellite laser ranging
Journal of Geophysical Research, 2008Co-Authors: Jingyi Chen, Clark R WilsonAbstract:[1] Several independent time series of variations ΔC 21 , ΔS 21 , and ΔC 20 in Earth's gravity field are compared for the period April 2002 to May 2007. We examine estimates from the Gravity Recovery and Climate Experiment (GRACE), Earth Rotation variations, climate models, and satellite laser ranging (SLR). Recently released GRACE solutions show significant improvement relative to earlier results, especially for ΔC 21 and ΔS 21 . At the annual period, all estimates agree remarkably well, and good correlation is found among time series at intraseasonal periods. In general, Earth Rotation values for ΔC 21 and ΔS 21 , and SLR values for ΔC 20 agree best with GRACE estimates. GRACE ΔC 20 time series are contaminated by aliased ocean tide model errors. SLR ΔC 21 and ΔS 21 time series have been reported without an ocean pole tide (OPT) correction and with an older Solid Earth Pole Tide (SEPT) model. After correcting for OPT and SEPT deficiencies, SLR ΔC 21 and ΔS 21 time series show improved agreement with other estimates.
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low degree gravitational changes from Earth Rotation and geophysical models
Geophysical Research Letters, 2003Co-Authors: Jianli Chen, Clark R WilsonAbstract:[1] Spherical harmonic degree 2 gravitational variations ΔC21, ΔS21, and ΔC20 are estimated from accurately measured Earth Rotational changes and compared with predictions from atmospheric, oceanic, and hydrological models. Earth Rotation-derived changes agree very well with model predictions over a broad frequency band, and particularly well at intraseasonal and seasonal time scales. The agreement is significantly better compared to previous studies, due mainly to improved oceanic and hydrological models. An independent determination of degree 2 changes serves as an important constraint for satellite-based estimates such as those of the Gravity Recovery and Climate Experiment (GRACE) mission.
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the global geophysical fluids center ggfc of the international Earth Rotation and reference systems service
ITN, 2003Co-Authors: Ben F Chao, Veronique Dehant, R S Gross, R D Ray, D A Salstein, H P Plag, T Van Dam, T Van Hoolst, M M Watkins, Clark R WilsonAbstract:The International Earth Rotation Service established a Global Geophysical Fluids Center (GGFC) in 1998, as one if its product centers. The purpose is to better support, facilitate, and provide services to the worldwide research community, in areas related to the variations in Earth Rotation, gravity field and geocenter that are caused by mass transport in the geophysical fluids including the atmosphere, ocean, solid Earth, and core, and geophysical processes associated with tides, mass loading, and hydrological cycles. These services are administered through GGFC’s Special Bureaus (SB). Today there are eight SBs worldwide; they are SB Atmosphere, SB Oceans, SB Tides, SB Hydrology, SB Mantle, SB Core, SB Gravity/Geocenter, and SB Loading. They maintain individual data archive and services.
Gary D Egbert - One of the best experts on this subject based on the ideXlab platform.
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reply to comments by s r dickman on fortnightly Earth Rotation ocean tides and mantle anelasticity
Geophysical Journal International, 2013Co-Authors: Richard D Ray, Gary D EgbertAbstract:Dickman argues that our model of the Mf ocean tide is unrealistic and that this invalidates conclusions regarding mantle anelasticity. His evidence is based on comparison with his own ocean modelling experiments and on his physical intuition regarding near-equilibrium tides. That evidence is unconvincing. Simple physical arguments alone are enough to rebut his main points. Furthermore, we test here his suggestion of increasing bottom-friction dissipation by a factor of 100 over our preferred solution, and we show that this results in unacceptable polar motion and poor agreement with independent tide-gauge data. In contrast, tests against independent data lend support to the realism of our Mf tide model and give confidence that our estimates of mantle anelasticity are reliable within stated error bounds.
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fortnightly Earth Rotation ocean tides and mantle anelasticity
Geophysical Journal International, 2012Co-Authors: Richard D Ray, Gary D EgbertAbstract:SUMMARY This study of the fortnightly Mf tide comprises three main topics: (1) a new determination of the fortnightly component of polar motion and length of day (LOD) from a multidecade time-series of observed space-geodetic data; (2) the use of the polar motion determination as one constraint in the development of a hydrodynamic ocean model of the Mf tide and (3) the use of these results to place new constraints on mantle anelasticity at the Mf tidal period. Our model of the Mf ocean tide assimilates more than 14 years of altimeter data from the Topex/Poseidon and Jason-1 satellites. Because the Mf altimetric signal-to-noise ratio is very small, it is critical that altimeter data not be overweighted. The polar motion data, plus tidegauge data and independent altimeter data, give useful additional information, with only the polar motion putting constraints on tidal current velocities. The resulting ocean-tide model, plus the dominant elastic body tide, leaves a small residual in observed LOD caused by mantle anelasticity. The inferred effective tidal Q of the anelastic body tide is 90 and is in line with a ω α frequency dependence with α in the range 0.2–0.3.
Richard D Ray - One of the best experts on this subject based on the ideXlab platform.
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reply to comments by s r dickman on fortnightly Earth Rotation ocean tides and mantle anelasticity
Geophysical Journal International, 2013Co-Authors: Richard D Ray, Gary D EgbertAbstract:Dickman argues that our model of the Mf ocean tide is unrealistic and that this invalidates conclusions regarding mantle anelasticity. His evidence is based on comparison with his own ocean modelling experiments and on his physical intuition regarding near-equilibrium tides. That evidence is unconvincing. Simple physical arguments alone are enough to rebut his main points. Furthermore, we test here his suggestion of increasing bottom-friction dissipation by a factor of 100 over our preferred solution, and we show that this results in unacceptable polar motion and poor agreement with independent tide-gauge data. In contrast, tests against independent data lend support to the realism of our Mf tide model and give confidence that our estimates of mantle anelasticity are reliable within stated error bounds.
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fortnightly Earth Rotation ocean tides and mantle anelasticity
Geophysical Journal International, 2012Co-Authors: Richard D Ray, Gary D EgbertAbstract:SUMMARY This study of the fortnightly Mf tide comprises three main topics: (1) a new determination of the fortnightly component of polar motion and length of day (LOD) from a multidecade time-series of observed space-geodetic data; (2) the use of the polar motion determination as one constraint in the development of a hydrodynamic ocean model of the Mf tide and (3) the use of these results to place new constraints on mantle anelasticity at the Mf tidal period. Our model of the Mf ocean tide assimilates more than 14 years of altimeter data from the Topex/Poseidon and Jason-1 satellites. Because the Mf altimetric signal-to-noise ratio is very small, it is critical that altimeter data not be overweighted. The polar motion data, plus tidegauge data and independent altimeter data, give useful additional information, with only the polar motion putting constraints on tidal current velocities. The resulting ocean-tide model, plus the dominant elastic body tide, leaves a small residual in observed LOD caused by mantle anelasticity. The inferred effective tidal Q of the anelastic body tide is 90 and is in line with a ω α frequency dependence with α in the range 0.2–0.3.
Kerry Vahala - One of the best experts on this subject based on the ideXlab platform.
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Earth Rotation measured by a chip-scale ring laser gyroscope
Nature Photonics, 2020Co-Authors: Yu-kun Lu, Boqiang Shen, Qi-fan Yang, Ki Youl Yang, Jiang Li, Heming Wang, Kerry VahalaAbstract:A Sagnac gyroscope based on Brillouin ring lasers on a silicon chip is presented. The stability and sensitivity of this on-chip planar gyroscope allow measurement of the Earth’s Rotation, with an amplitude sensitivity as small as 5 deg h^−1 for a sinusoidal Rotation, an angle random walk of 0.068 deg h^−1/2 and bias instability of 3.6 deg h^−1. Optical gyroscopes are among the most accurate Rotation measuring devices and are widely used for navigation and accurate pointing. Since the advent of photonic integrated components for communications, and with their increasing complexity, there has been interest in the possibility of chip-scale optical gyroscopes^ 1 . Besides the potential benefits of integration, such solid-state systems would be robust and resistant to shock. Here, we report a gyroscope using Brillouin ring lasers on a silicon chip. Its stability and sensitivity enable measurement of Earth’s Rotation, representing a major milestone for this new class of gyroscope.
André Gebauer - One of the best experts on this subject based on the ideXlab platform.
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a laser gyroscope system to detect the gravito magnetic effect on Earth
Physics, 2012Co-Authors: M Allegrini, Jacopo Belfi, Alex Virgilio, Nicolo' Beverini, F Bosi, B Bouhadef, G Carelli, G Cella, M Cerdonio, André GebauerAbstract:Ring lasers are inertial sensors for angular velocity based on the Sagnac effect. In recent years they have reached a very high sensitivity and accuracy; the best performing one, the ring Laser G in Wettzell (Germany), a square ring with 16 m perimeter, has reached a sensitivity of 12prad/s very close to the shot noise limit inferred from ring-down time measurements. On this basis it is expected that an array of six square ring lasers of 36 m perimeter, can perform a 1% accuracy test for the measurement of the Lense-Thirring frame dragging after 2 years of integration time. Essential for this measurement is the comparison between the Earth angular velocity and orientation in space measured with the ring array and compared to the measurement series maintained by the International Earth Rotation and Reference System Service (IERS), which measures Earth Rotation and pole position with respect to remote quasars. It has been shown that the accuracy of G in Wettzell is limited by the low frequency motion of the near surface laboratory, which is of the order of several prad/s, roughly 100 times larger than the Lense-Thirring contribution. For this reason the entire experiment should be placed in a quite underground laboratory, where these perturbations are reduced. The feasibility to properly place such a device inside the GranSasso INFN National Laboratory has been investigated.
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how to detect the chandler and the annual wobble of the Earth with a large ring laser gyroscope
Physical Review Letters, 2011Co-Authors: K U Schreiber, J P R Wells, Thomas Klügel, Robert B Hurst, André GebauerAbstract:We demonstrate a $16\text{ }\text{ }{\mathrm{m}}^{2}$ helium-neon ring laser gyroscope with sufficient sensitivity and stability to directly detect the Chandler wobble of the rotating Earth. The successful detection of both the Chandler and the annual wobble is verified by comparing the time series of the ring laser measurements against the ``C04 series'' of Earth Rotation data from the International Earth Rotation and Reference System Service.
