Validation of GOCE Gravitational Gradients in Satellite Track Cross-Overs

<p>The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was the first mission which carried a novel instrument, gradiometer, which allowed to measure the second-order directional derivatives of the gravitational potential or gravitational gradients with uniform quality and a near-global coverage. More than three years of the outstanding measurements resulted in two levels of data products (Level 1b and Level 2), six releases of global gravitational models (GGMs), and several grids of gravitational gradients (see, e.g., ESA-funded GOCE+ GeoExplore project or Space-wise GOCE products). The grids of gravitational gradients represent a step between gravitational gradients measured&#160;directly along the GOCE orbit and data directly from GGMs. One could use grids of gravitational gradients for geodetic as well as for geophysical applications. In this contribution, we are going to validate the official Level 2 product GRD_SPW_2 by terrestrial gravity disturbances and GNSS/levelling over two test areas located in Europe, namely in Norway and former Czechoslovakia (now Czechia and Slovakia). GRD_SPW_2 product contains all six gravity gradients at satellite altitude from the space-wise approach computed only from GOCE data for the available time span (r-2, r-4, and r-5) and provided on a 0.2 degree grid. A mathematical model based on a least-squares spectral weighting will be developed and the corresponding spectral weights will be presented for the validation of gravitational gradients grids. This model allows us to continue downward gravitational gradients grids to an irregular topographic surface (not to a mean sphere) and transform them into gravity disturbances and/or geoidal heights in one step. Before we compared results obtained by spectral downward continuation, we had to remove the high-frequency part of the gravitational signal from terrestrial data because in gravitational gradients measured at GOCE satellite altitude is attenuated. To do so we employ EGM2008 up to d/o 2160 and the residual terrain model correction (RTC) has been a) interpolated from ERTM2160 gravity model, b) synthesised from dV_ELL_Earth2014_5480_plusGRS80, c) calculated from a residual topographic model by forward modelling in the space domain. &#160;</p>

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Dynamic behavior of coalbed methane flow along the annulus of single-phase production

International Journal of Coal Science & Technology ◽

10.1007/s40789-019-00276-1 ◽

2019 ◽

Vol 6 (4) ◽

pp. 547-555 ◽

Cited By ~ 2

Author(s):

Xinfu Liu ◽

Chunhua Liu ◽

Guoqiang Liu

Keyword(s):

Water Column ◽

Dynamic Behavior ◽

Coalbed Methane ◽

Single Phase ◽

Compressibility Factor ◽

Production Performance ◽

Flow Rates ◽

Pressure Drops ◽

Bottom Hole ◽

Gravitational Gradients

Abstract Dynamic behavior of coalbed methane (CBM) flow will provide the theoretical basis to optimize production performance for a given well. A mathematical model is developed to simulate flowing pressures and pressure drops of CBM column from well head to bottom hole. The measured parameters and independent variables of flow rates, flowing pressures and temperatures are involved in CBM producing process along the annulus. The developed relationships are validated against full-scale measured data in single-phase CBM wellbores. The proposed methodology can analyze the dynamic behavior in CBM reservoir and process of CBM flow with an overall accuracy of 2%. The calculating process of flowing pressures involves friction factor with variable Reynolds number and CBM temperature and compressibility factor with gravitational gradients. The results showed that the effect of flowing pressure on CBM column was more obvious than that on CBM and water column accompanied by an increase of dynamic water level. The ratios of flowing pressure on increment of CBM column to the whole column increased with the declined flow rates of water column. Bottom-hole pressure declined with the decreased flowing pressure of CBM column along the annulus. It will lead to the results of the increased pressure drop of CBM column and CBM flow rate in single-phase CBM wellbores.

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Daily generation of a footward fluid shift attenuates ocular changes associated with head-down tilt bed rest

Journal of Applied Physiology ◽

10.1152/japplphysiol.00250.2020 ◽

2020 ◽

Vol 129 (5) ◽

pp. 1220-1231

Author(s):

Justin S. Lawley ◽

Gautam Babu ◽

Sylvan L. J. E. Janssen ◽

Lonnie G. Petersen ◽

Christopher M. Hearon ◽

...

Keyword(s):

Negative Pressure ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Lower Body ◽

Fluid Shift ◽

Gravitational Gradients ◽

Ocular Changes

Choroid measurements appear to be sensitive to changes in gravitational gradients, as well as periods of head-down tilt (HDT) bed rest, suggesting that they are potential indicators of early ocular remodeling and could serve to evaluate the efficacy of countermeasures for SANS. Eight hours of lower body negative pressure (LBNP) daily attenuates the choroid expansion associated with 3 days of strict −6° HDT bed rest, indicating that LBNP may be an effective countermeasure for SANS.

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Modeling Earth's gravitational gradients for GPS-free navigation

2013 American Control Conference ◽

10.1109/acc.2013.6580064 ◽

2013 ◽

Author(s):

Troy C. Welker ◽

Richard E. Huffman ◽

Meir Pachter

Keyword(s):

Gravitational Gradients

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Effects of 18 days of bed rest on leg and arm venous properties

Journal of Applied Physiology ◽

10.1152/japplphysiol.00835.2003 ◽

2004 ◽

Vol 96 (3) ◽

pp. 840-847 ◽

Cited By ~ 21

Author(s):

M. W. P. Bleeker ◽

P. C. E. De Groot ◽

J. A. Pawelczyk ◽

M. T. E. Hopman ◽

B. D. Levine

Keyword(s):

Orthostatic Intolerance ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Venous Occlusion ◽

Stress Index ◽

Orthostatic Tolerance ◽

Venous Compliance ◽

Venous Flow ◽

Gravitational Gradients ◽

Small Change

Venous function may be altered by bed rest deconditioning. Yet the contribution of altered venous compliance to the orthostatic intolerance observed after bed rest is uncertain. The purpose of this study was to assess the effect of 18 days of bed rest on leg and arm (respectively large and small change in gravitational gradients and use patterns) venous properties. We hypothesized that the magnitude of these venous changes would be related to orthostatic intolerance. Eleven healthy subjects (10 men, 1 woman) participated in the study. Before (pre) and after (post) 18 days of 6° head-down tilt bed rest, strain gauge venous occlusion plethysmography was used to assess limb venous vascular characteristics. Leg venous compliance was significantly decreased after bed rest (pre: 0.048 ± 0.007 ml·100 ml-1·mmHg-1, post: 0.033 ± 0.007 ml·100 ml-1·mmHg-1; P < 0.01), whereas arm compliance did not change. Leg venous flow resistance increased significantly after bed rest (pre: 1.73 ± 1.08 mmHg·ml-1·100 ml·min, post: 3.10 ± 1.00 mmHg·ml-1·100 ml·min; P < 0.05). Maximal lower body negative pressure tolerance, which was expressed as cumulative stress index (pressure·time), decreased in all subjects after bed rest (pre: 932 mmHg·min, post: 747 mmHg·min). The decrease in orthostatic tolerance was not related to changes in leg venous compliance. In conclusion, this study demonstrates that after bed rest, leg venous compliance is reduced and leg venous outflow resistance is enhanced. However, these changes are not related to measures of orthostatic tolerance; therefore, alterations in venous compliance do not to play a major role in orthostatic intolerance after 18 days of head-down tilt bed rest.

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Effect of Gravitational Gradients on Cardiac Filling and Performance

Journal of the American Society of Echocardiography ◽

10.1016/j.echo.2017.08.005 ◽

2017 ◽

Vol 30 (12) ◽

pp. 1180-1188 ◽

Cited By ~ 23

Author(s):

Kazuaki Negishi ◽

Allen G. Borowski ◽

Zoran B. Popović ◽

Neil L. Greenberg ◽

David S. Martin ◽

...

Keyword(s):

Gravitational Gradients ◽

Cardiac Filling ◽

And Performance

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Relationships between regional ventilation and vascular and extravascular volume in supine humans

Journal of Applied Physiology ◽

10.1152/jappl.1994.76.3.1195 ◽

1994 ◽

Vol 76 (3) ◽

pp. 1195-1204 ◽

Cited By ~ 24

Author(s):

L. H. Brudin ◽

C. G. Rhodes ◽

S. O. Valind ◽

T. Jones ◽

B. Jonson ◽

...

Keyword(s):

Left Lung ◽

Vertical Direction ◽

Vertical Gradient ◽

Quiet Breathing ◽

Alveolar Volume ◽

Positron Emission ◽

Significant Linear Correlation ◽

Horizontal Variation ◽

Gravitational Gradients ◽

Extravascular Volume

With the use of positron emission tomography, alveolar ventilation (VA), lung density, and pulmonary blood volume (VB) were measured regionally in eight nonsmokers in the supine posture and one nonsmoker in the prone posture during quiet breathing in a transaxial thoracic section at midheart level. Regional values of alveolar volume (VA) and extravascular tissue volume (VEV) were derived from the inherent relationships between different compartments in the lung. Ratios proportional to gas volume (VA/VEV) and ventilation (VA/VEV) per alveolar unit, respectively, were calculated. No differences between right and left lung were found. Variations in the vertical direction could explain approximately 65% of the total within-group variation in VA, VB, and ln (VA), whereas the corresponding value for horizontal variation was only 3–9% (right lung, supine subjects). Similar gravitational gradients were found in the single prone subject. There was a significant linear correlation between VA and ln (VA). When VA and VA are related to a given number of alveolar units (VEV), the data are consistent with a linear relationship between VA/VEV and VA/VEV, indicating that ventilation might be explained by the elastic properties of lung tissue according to Salazar and Knowles (J. Appl. Physiol. 19: 97–104, 1964). Regional VB was closely associated with the gradient of regional alveolar volume (VA/VEV) (by virtue of weight of blood and competition for space) and therefore, indirectly, closely associated with the vertical gradient of ventilation.

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