Airborne gravity measurements over mountainous areas by using a LaCoste & Romberg air‐sea gravity meter

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 807-816 ◽  
Author(s):  
Jérôme Verdun ◽  
Roger Bayer ◽  
Emile E. Klingelé ◽  
Marc Cocard ◽  
Alain Geiger ◽  
...  
Keyword(s):  
Data Reduction ◽  
Classical Method ◽  
Gravity Data ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Vertical Acceleration ◽  
Mountainous Areas ◽  
Free Air ◽  
Gravity Measurements ◽  
Free Air Anomaly

This paper introduces a new approach to airborne gravity data reduction well‐suited for surveys flown at high altitude with respect to gravity sources (mountainous areas). Classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western French Alps by using a LaCoste & Romberg air‐sea gravity meter. The part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra. Beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft. This finding is theoretically argued by solving the equation of the gravimetric system (gravity meter and stabilized platform). The transfer function of the system is derived, and a new formulation of airborne gravity data reduction, which takes care of the sensitive response of spring tension to observable gravity field wavelengths, is given. The resulting gravity signal exhibits a residual noise caused by electronic devices and short‐wavelength Eötvös effects. The use of dedicated exponential filters gives us a way to eliminate these high‐frequency effects. Examples of the resulting free‐air anomaly at 5100‐m altitude along one particular profile are given and compared with free‐air anomaly deduced from the classical method for processing airborne gravity data, and with upward‐continued ground gravity data. The well‐known trade‐off between accuracy and resolution is discussed in the context of a mountainous area.

scholarly journals GRAVIMETRIC GEOID MODELLING OVER PENINSULAR MALAYSIA USING TWO DIFFERENT GRIDDING APPROACHES FOR COMBINING FREE AIR ANOMALY

2019 ◽  
Vol XLII-4/W16 ◽  
pp. 515-522
Author(s):  
M. F. Pa’suya ◽  
A. H. M. Din ◽  
J. C. McCubbine ◽  
A. H. Omar ◽  
Z. M. Amin ◽  
...  
Keyword(s):  
Gravity Data ◽  
Reference Signal ◽  
Digital Terrain Model ◽  
Peninsular Malaysia ◽  
Airborne Gravity ◽  
Geopotential Model ◽  
Gravimetric Geoid ◽  
Geoid Model ◽  
Free Air ◽  
Free Air Anomaly

Abstract. We investigate the use of the KTH Method to compute gravimetric geoid models of Malaysian Peninsular and the effect of two differing strategies to combine and interpolate terrestrial, marine DTU17 free air gravity anomaly data at regular grid nodes. Gravimetric geoid models were produced for both free air anomaly grids using the GOCE-only geopotential model GGM GO_CONS_GCF_2_SPW_R4 as the long wavelength reference signal and high-resolution TanDEM-X global digital terrain model. The geoid models were analyzed to assess how the different gridding strategies impact the gravimetric geoid over Malaysian Peninsular by comparing themto 172 GNSS-levelling derived geoid undulations. The RMSE of the two sets of gravimetric geoid model / GNSS-levelling residuals differed by approx. 26.2 mm. When a 4-parameter fit is used, the difference between the RMSE of the residuals reduced to 8 mm. The geoid models shown here do not include the latest airborne gravity data used in the computation of the official gravimetric geoid for the Malaysian Peninsular, for this reason they are not as precise.

The calculation of deflexions of the vertical from gravity anomalies

1950 ◽  
Vol 204 (1078) ◽  
pp. 374-395 ◽  
Keyword(s):  
Gravity Data ◽  
Gravity Anomalies ◽  
Sources Of Error ◽  
Free Air ◽  
Gravity Measurements ◽  
Standard Deviations ◽  
The Difference ◽  
Different Sources

The theory of the application of gravity measurements to geodetic calculations is discussed, and the errors involved in calculating deflexions of the vertical are estimated. If the gravity data are given as free air anomalies from Jeffreys’s (1948) formula, so thdt the second and third harmonics of gravity are assumed known, the orders of magnitude of the standard deviations of the different sources of error are the following: Single deflexion: neglect of gravity outside 20° 1" Difference of deflexions: neglect of gravity outside 5° 0"·5 Calculation of effects of gravity from 0º·05 to 5° 0"·1 Calculation of effects of gravity within 0º·05 between 0"·1 and 0"·5 Estimates of the deflexions are made for Greenwich, Herstmonceux, Southampton and Bayeux, and the difference between Greenwich and Southampton is compared with the astronomical and geodetic amplitudes.

Effects of terrain on borehole gravity data

Geophysics ◽  
1980 ◽  
Vol 45 (2) ◽  
pp. 234-243 ◽  
Author(s):  
J. R Hearst ◽  
J. W. Schmoker ◽  
R. C. Carlson
Keyword(s):  
Gravity Data ◽  
Radial Distance ◽  
Ground Surface ◽  
Absolute Maximum ◽  
Near Surface ◽  
Free Air ◽  
Gravity Measurements ◽  
Terrain Elevation ◽  
Lower Magnitude ◽  
Terrain Features

The effect of terrain on gravity measurements in a borehole and on formation density derived from borehole gravity data is studied as a function of depth in the well, terrain elevation, terrain inclination, and radial distance to the terrain feature. The vertical attraction of gravity [Formula: see text] in a borehole resulting from a terrain element is small at the surface and reaches an absolute maximum at a depth of about one and one‐half times the radial distance to the terrain element, then decreases at greater depths. The effect of terrain on calculated formation density is proportional to the vertical derivative of [Formula: see text] and is maximum at the surface, passes through zero where |[Formula: see text]| is greatest, and reaches a second extremum of opposite sign to the first and of much lower magnitude. Accuracy criteria for borehole‐gravity terrain corrections show that elevation accuracy requirements are most stringent for a combination of nearby terrain features and near‐surface gravity stations. Sensitivity to terrain inclination is also greatest for this combination. The measurement of the free‐air gradient of gravity, commonly made’slightly above the ground surface, is extremely sensitive to topographic irregularities within about 300m of the measurement point. The effect of terrain features 21.9 to 166.7 km from the well [Hammer’s (1939) zone M through Hayford‐Bowie’s (1912) zone O] on calculated formation density is nearly constant with depth. At these distances, the terrain correction will be equivalent to a dc shift of about [Formula: see text] of average elevation above or below the correction datum. The effect of topography beyond 166.7 km is not likely to exceed [Formula: see text].

scholarly journals Regional Seafloor Topography by Extended Kalman Filtering of Marine Gravity Data without Ship-Track Information

2021 ◽  
Vol 14 (1) ◽  
pp. 169
Author(s):  
Lucía Seoane ◽  
Guillaume Ramillien ◽  
Benjamin Beirens ◽  
José Darrozes ◽  
Didier Rouxel ◽  
...  
Keyword(s):  
Gravity Data ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Seafloor Topography ◽  
Single Beam ◽  
Beam Depth ◽  
Marine Gravity ◽  
Gravity Measurements ◽  
Polynomial Series ◽  
Free Air Anomaly

An iterative Extended Kalman Filter (EKF) approach is proposed to recover a regional set of topographic heights composing an undersea volcanic mount by the successive combination of large numbers of gravity measurements at sea surface using altimetry satellite-derived grids and taking the error uncertainties into account. The integration of the non-linear Newtonian operators versus the radial and angular distances (and its first derivatives) enables the estimation process to accelerate and requires only few iterations, instead of summing Legendre polynomial series or using noise-degraded 2D-FFT decomposition. To show the effectiveness of the EKF approach, we apply it to the real case of the bathymetry around the Great Meteor seamount in the Atlantic Ocean by combining only geoid height/free-air anomaly datasets and using ship-track soundings as reference for validation. Topography of the Great Meteor seamounts structures are well-reconstructed, especially when regional compensation is considered. Best solution gives a RMS equal to 400 m with respect to the single beam depth observations and it is comparable to RMS obtained for ETOPO1 of about 365 m. Larger discrepancies are located in the seamount flanks due to missing high-resolution information for gradients. This approach can improve the knowledge of seafloor topography in regions where few echo-sounder measurements are available.

Gravity measurements in an airplane using state‐of‐the‐art navigation and altimetry

Geophysics ◽  
1982 ◽  
Vol 47 (5) ◽  
pp. 832-838 ◽  
Author(s):  
Lucien LaCoste ◽  
James Ford ◽  
Robert Bowles ◽  
Keith Archer
Keyword(s):  
Gravity Data ◽  
Sampling Rate ◽  
Personal Communication ◽  
Systematic Errors ◽  
Inertial System ◽  
Vertical Acceleration ◽  
Radar Altimeter ◽  
Preliminary Results ◽  
Pressure Surface ◽  
Gravity Measurements

In 1976 the U. S. Naval Oceanographic Office made experimental gravity measurements over the Atlantic in an airplane using a LaCoste and Romberg shipboard gravity meter, a Honeywell electrostatic gyro inertial system, a Rosemont pressure port altimeter, a Honeywell radar altimeter, Loran C and other electronic navigational aids. Preliminary results were reported at the 47th Annual International SEG Meeting in Calgary, Canada, in 1977. These preliminary results were compared with sea gravity data furnished by the Naval Oceanographic Office and were found to be in general agreement. However, there were some unexplained systematic errors of about 15 mgal and the airplane gravity profiles were considerably more noisy than helicopter gravity profiles reported by William Gumert (1977, personal communication). After the paper was given, we found that corrections for Schuler oscillations in the inertial system significantly reduced the systematic errors. We also found that by making full use of a half‐second sampling rate of the radar altimeter, we could make meaningful vertical acceleration corrections relative to sea level as well as relative to an atmospheric pressure surface. A comparison of the two corrections showed that variations in the isobaric surfaces were the main cause of the noise in the airplane gravity profiles. It also became apparent that the noise could be reduced by flying slower or making successive flights at different speeds.

scholarly journals New Bouguer Gravity Maps of Venezuela: Representation and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Javier Sanchez-Rojas
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Geodetic Reference System ◽  
Bouguer Gravity ◽  
Free Air ◽  
Data Compilation ◽  
Regional Tectonic ◽  
Moho Depths ◽  
Free Air Anomaly ◽  
Gravity Map

A new gravity data compilation for Venezuela was processed and homogenized. Gravity was measured in reference to the International Gravity Standardization Net 1971, and the complete Bouguer anomaly was calculated by using the Geodetic Reference System 1980 and 2.67 Mg/m3. A regional gravity map was computed by removing wavelengths higher than 200 km from the Bouguer anomaly. After the anomaly separation, regional and residual Bouguer gravity fields were then critically discussed in term of the regional tectonic features. Results were compared with the previous geological and tectonic information obtained from former studies. Gravity and topography data in the spectral domain were used to examine the elastic thickness and depths of the structures of the causative measured anomaly. According to the power spectrum analysis results of the gravity data, the averaged Moho depths for the massif, plains, and mountainous areas in Venezuela are 42, 35, and 40 km, respectively. The averaged admittance function computed from the topography and Free-Air anomaly profiles across Mérida Andes showed a good fit for a regional compensation model with an effective elastic thickness of 15 km.

scholarly journals Quasi Geoid and Geoid Modeling with the Use of Terrestrial and Airborne Gravity Data by the GGI Method—A Case Study in the Mountainous Area of Colorado

2021 ◽  
Vol 13 (21) ◽  
pp. 4217
Author(s):  
Marek Trojanowicz ◽  
Magdalena Owczarek-Wesołowska ◽  
Yan Ming Wang ◽  
Olgierd Jamroz
Keyword(s):  
Gravity Data ◽  
Research Work ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
Geoid Model ◽  
Data Inversion ◽  
Gravimetric Quasigeoid ◽  
The Mean ◽  
Grid Points

This article concerns the development of gravimetric quasigeoid and geoid models using the geophysical gravity data inversion technique (the GGI method). This research work was carried out on the basis of the data used in the Colorado geoid experiment, and the mean quasigeoid (ζm) and mean geoid (Nm) heights, determined by the approaches used in the Colorado geoid experiment, were used as a reference. Three versions of the quasigeoid GGI models depending on gravity data were analyzed: terrestrial-only, airborne-only, and combined (using airborne and terrestrial datasets). For the combined version, which was the most accurate, a model in the form of a 1′×1′ grid was calculated in the same area as the models determined in the Colorado geoid experiment. For the same grid, the geoid–quasigeoid separation was determined, which was used to build the geoid model. The agreement (in terms of the standard deviation of the differences) of the determined models, with ζm and Nm values for the GSVS17 profile points, was ±0.9 cm for the quasigeoid and ±1.2 cm for the geoid model. The analogous values, determined on the basis of all 1′×1′ grid points, were ±2.3 cm and ±2.6 cm for the quasigeoid and geoid models, respectively.

scholarly journals Improvement of Downward Continuation Values of Airborne Gravity Data in Taiwan

2018 ◽  
Vol 10 (12) ◽  
pp. 1951 ◽  
Author(s):  
Qilong Zhao ◽  
Xinyu Xu ◽  
Rene Forsberg ◽  
Gabriel Strykowski
Keyword(s):  
Tibetan Plateau ◽  
Gravity Data ◽  
Parametric Method ◽  
Downward Continuation ◽  
Airborne Gravity ◽  
Mountainous Area ◽  
The Tibetan Plateau ◽  
Random Errors ◽  
Airborne Gravity Survey ◽  
The Difference

An airborne gravity survey was carried out to fill gaps in the gravity data for the mountainous areas of Taiwan. However, the downward continuation error of airborne gravity data is a major issue, especially in regions with complex terrain, such as Taiwan. The root mean square (RMS) of the difference between the downward continuation values and land gravity was approximately 20 mGal. To improve the results of downward continuation we investigated the inverse Poisson’s integral, the semi-parametric method combined with regularization (SPR) and the least-squares collocation (LSC) in this paper. The numerically simulated experiments are conducted in the Tibetan Plateau, which is also a mountainous area. The results show that as a valuable supplement to the inverse Poisson’s integral, the SPR is a useful approach to estimate systematic errors and to suppress random errors. While the LSC approach generates the best results in the Tibetan Plateau in terms of the RMS of the downward continuation errors. Thus, the LSC approach with a terrain correction (TC) is applied to the downward continuation of real airborne gravity data in Taiwan. The statistical results show that the RMS of the differences between the downward continuation values and land gravity data reduced to 11.7 mGal, which shows that an improvement of 40% is obtained.

scholarly journals Gravity anomaly to identify Walanae fault using second vertical derivative method

2018 ◽  
Vol 2 (1) ◽  
pp. 34
Author(s):  
Marsellei Justia ◽  
Muhammad Fikri H Hiola ◽  
Nur Baiti Febryana S
Keyword(s):  
Gravity Data ◽  
Moving Average ◽  
Normal Fault ◽  
Reverse Fault ◽  
The South ◽  
Vertical Derivative ◽  
The North ◽  
Free Air ◽  
Free Air Anomaly ◽  
Fault Mechanism

<p class="Abstract">Research has been conducted to identify the Walanae Fault, coordinates 4–6 S and 118-120 E using anomalous gravity data. This research uses data measurement of Topography and the Free Air Anomaly from the TOPEX/Poseidon satellite. Then the authors processed to obtain the bouguer anomalies and made modeling by using the Surfer 10. The authors used the Second Vertical Derivative (SVD) with filter Elkins of Moving Average then analyze the graph of the SVD. The results shows the value of the residual anomaly in the north of fault is 25.21 mGal, in the middle occur range 17.67 mGal to 24.98 mGal and 30,376 mGal in the south of fault. The authors indicates the existence of a difference between the gravity between the Walanae Fault with surrounding geologic. From these results also show that Walanae Fault has a reverse fault mechanism in the northern part and the normal fault mechanism in the middle to the south, the authors conclude that the Walanae Fault is divided into two segments, that is the northern and the southern segment.</p>

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