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.

Sea floor topography modeling by cumulating different types of gravity information

2020 ◽  
Author(s):  
Lucia Seoane ◽  
Benjamin Beirens ◽  
Guillaume Ramillien
Keyword(s):  
New England ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Extended Kalman Filtering ◽  
Sea Floor ◽  
Single Beam ◽  
Free Air ◽  
Free Air Gravity ◽  
Great Meteor Seamount

<p>We propose to cumulate complementary gravity data, i.e. geoid height and (radial) free-air gravity anomalies, to evaluate the 3-D shape of the sea floor more precisely. For this purpose, an Extended Kalman Filtering (EKF) scheme has been developed to construct the topographic solution by injecting gravity information progressively. The main advantage of this sequential cumulation of data is the reduction of the dimensions of the inverse problem. Non linear Newtonian operators have been re-evaluated from their original forms and elastic compensation of the topography is also taken into account. The efficiency of the method is proved by inversion of simulated gravity observations to converge to a stable topographic solution with an accuracy of only a few meters. Real geoid and gravity data are also inverted to estimate bathymetry around the New England and Great Meteor seamount chains. Error analysis consists of comparing our topographic solutions to accurate single beam ship tracks for validation.</p>

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.

Dynamics and navigation of autonomous underwater vehicles for submarine gravity surveying

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. G55-G68 ◽  
Author(s):  
James C. Kinsey ◽  
Maurice A. Tivey ◽  
Dana R. Yoerger
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Gravity Data ◽  
Autonomous Underwater Vehicles ◽  
Free Water ◽  
Cost Effective ◽  
Marine Gravity ◽  
State Estimators ◽  
Gravity Measurements ◽  
Effective Option ◽  
Vertical Accelerations

We investigated the effect of autonomous underwater vehicle (AUV) dynamics and navigation on underway submarine gravimetry. Our research was motivated by the need to obtain spatially dense marine gravity measurements close to the source of subkilometer-scale geologic features in the shallow oceanic crust. Such measurements have been previously obtained, for instance, with piloted submarines and towed sleds; however, the high cost and, in the case of on-bottom measurements, poor spatial sampling preclude routine acquisition of these measurements. Continuous underway gravity surveys with AUVs is a compelling cost-effective option, but this method requires separating the AUV accelerations from the measured gravity. We show that AUVs with a large distance between the center of buoyancy and the center of gravity have lower vertical accelerations than torpedo-shaped AUVs and consequentially are better suited for underway gravity surveys. Furthermore state estimators, which combine sensor measurements and models of the vehicle’s motion, provide superior estimates of the vehicle’s vertical accelerations than methods used in previous underway submarine gravity surveys. We simulated the use of these navigation methods in detecting dike swarms at the East Pacific Rise. Analysis showed that we can shorten filters used in reducing gravity data and consequentially provide improved measurements of the free-water anomaly with a minimal detectable spatial wavelength approximately 65% lower than previously reported results.

scholarly journals A Fast Method for Calculation of Marine Gravity Anomaly

2021 ◽  
Vol 11 (3) ◽  
pp. 1265
Author(s):  
Yuan Fang ◽  
Shuiyuan He ◽  
Xiaohong Meng ◽  
Jun Wang ◽  
Yongkang Gan ◽  
...  
Keyword(s):  
Graphics Processing Unit ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Processing Unit ◽  
Fast Method ◽  
Singularity Problem ◽  
Sequential Method ◽  
Marine Gravity ◽  
Graphics Processing

Gravity data have been playing an important role in marine exploration and research. However, obtaining gravity data over an extensive marine area is expensive and inefficient. In reality, marine gravity anomalies are usually calculated from satellite altimetry data. Over the years, numerous methods have been presented for achieving this purpose, most of which are time-consuming due to the integral calculation over a global region and the singularity problem. This paper proposes a fast method for the calculation of marine gravity anomalies. The proposed method introduces a novel scheme to solve the singularity problem and implements the parallel technique based on a graphics processing unit (GPU) for fast calculation. The details for the implementation of the proposed method are described, and it is tested using the geoid height undulation from the Earth Gravitational Model 2008 (EGM2008). The accuracy of the presented method is evaluated by comparing it with marine shipboard gravity data. Its efficiency is demonstrated through comparison with the conventional sequential method. The tests demonstrate that the proposed method can be employed for accurately calculating marine gravity anomalies and provides an advantage on computational efficiency.

A simple objective method for minimizing crossover errors in marine gravity data

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 1070-1083 ◽  
Author(s):  
Roger A. Prince ◽  
Donald W. Forsyth
Keyword(s):  
Least Squares ◽  
Gravity Data ◽  
Original Data ◽  
Free Air ◽  
Percent Confidence Level ◽  
Individual Segment ◽  
Marine Gravity ◽  
Anomaly Map ◽  
Free Air Anomaly ◽  
The Right

A method is presented which does not require a model for the source of crossover errors in marine gravity data in order to minimize them. The cruises are divided up into straight line segments and the assumption is made that whatever the sources of error, their net effect will be constant over the length of the track segment. A least‐squares approach is used where the crossover differences in the original data are the observations which it is desired to match. The desired set of constant corrections, one for each segment, is that which will minimize the sum of the squares of the residual crossover errors. This method has the advantage of reducing the crossover errors while simultaneously preserving the relative gravity anomalies along individual ship’s profiles. A data set consisting of gravity measurements made on nine cruises in the region of the Vema fracture zone in the equatorial Atlantic is used as a case study. The resulting least squares solution reduces the root mean square (rms) of 298 crossover errors from 10.3 mGals in the original data to 2.9 mGals after the calculated segment corrections are made. An F‐test shows that the reduced rms deviation from the mean is statistically significant at the 99 percent confidence level. A least‐squares fit was also done to find the best single cruise corrections for each of the 9 cruises for the 204 crossings between cruises. The original rms error is reduced from 11.4 to 7.8 mGals and the improvement is again significant at the 99 percent confidence level. An analysis of the variances shows that 37.5 percent of the total variance can he explained by constant corrections to each of the 9 cruises, while an additional 49.5 percent of the total variance can be explained by individual segment corrections. A linear regression analysis of the segment corrections as a function of elapsed time in the cruise suggests that for two of the cruises, drift of the gravity meter was not properly corrected for in the original data. Analysis of the segment corrections as a function of ship’s heading suggests that for two other cruises, cross‐coupling effects were not properly corrected. Eötvös corrections caused by navigational errors are the most likely explanation for many of the remaining individual segment corrections. After the calculated corrections were made, a free‐air anomaly map of the region was drawn. A comparison with an earlier published, free‐air anomaly map of the right half of this region shows that the contours are similar, but that the new map is shifted by a few mGals relative to the older map. This discrepancy between the old and new maps is a consequence of matching the data between the left and right sides of the new map and does not arise if the right side is considered alone with the least‐squares technique.

scholarly journals Evaluation of the BGM-3 sea gravity meter system onboard R/V Conrad

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1480-1493 ◽  
Author(s):  
Robin E. Bell ◽  
A. B. Watts
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Test Range ◽  
Free Air ◽  
Marine Gravity ◽  
Abrupt Changes ◽  
Spring Type ◽  
Free Air Gravity ◽  
Free Air Anomaly

The first Bell Aerospace BGM-3 Marine Gravity Meter System available for academic use was installed on R/V Robert D. Conrad in February, 1984. The BGM-3 system consists of a forced feedback accelerometer mounted on a gyrostabilized platform. Its sensor (requiring no cross‐coupling correction) is a significant improvement over existing beam and spring‐type sea gravimeters such as the GSS-2. A gravity survey over the Wallops Island test range together with the results of subsequent cruises allow evaluation of the precision, accuracy, and capabilities of the new system. Over the test range, the BGM-3 data were compared directly to data obtained by a GSS-2 meter onboard R/V Conrad. The rms discrepancy between free‐air gravity anomaly values at intersecting ship tracks of R/V Conrad was ±0.38 mGal for BGM-3 compared to ±1.60 mGal for the GSS-2. Moreover, BGM-3’s platform recovered from abrupt changes in ship’s heading more rapidly than did the platform of GSS-2. The principal factor limiting the accuracy of sea gravity data is navigation. Over the test range, where navigation was by Loran C and transit satellite, a two‐step filtering of the ship’s velocity and position was required to obtain an optimal Eötvös correction. A spectral analysis of 1 minute values of the Eötvös correction and the reduced free‐air gravity anomaly determined the filter characteristics. To minimize the coherence between the Eötvös and free‐air anomaly, it was necessary to prefilter the ship’s position and velocity. Using this procedure, reduced free‐air gravity anomalies with wavelengths as small as a few kilometers can be resolved.

scholarly journals Gravity observations on Santorini island (Greece): Historical and recent campaigns

2021 ◽  
Vol 51 (1) ◽  
pp. 1-24
Author(s):  
Melissinos PARASKEVAS ◽  
Demitris PARADISSIS ◽  
Konstantinos RAPTAKIS ◽  
Paraskevi NOMIKOU ◽  
Emilie HOOFT ◽  
...  
Keyword(s):  
Gravity Anomaly ◽  
Bronze Age ◽  
Gravity Data ◽  
Absolute Gravity ◽  
Bouguer Gravity ◽  
Near Surface ◽  
Bouguer Gravity Anomaly ◽  
Minoan Eruption ◽  
Marine Gravity ◽  
Gravity Measurements

Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age “Minoan” eruption that may have been responsible for the decline of the great Minoan civilization on the island of Crete. To use gravity to probe the internal structure of the volcano and to determine whether there are temporal variations in gravity due to near surface changes, we construct two gravity maps. Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) carried out terrestrial gravity measurements in December 2012 and in September 2014 at selected locations on Thera, Nea Kameni, Palea Kameni, Therasia, Aspronisi and Christiana islands. Absolute gravity values were calculated using raw gravity data at every station for all datasets. The results were compared with gravity measurements performed in July 1976 by DSO/NTUA and absolute gravity values derived from the Hellenic Military Geographical Service (HMGS) and other sources. Marine gravity data that were collected during the PROTEUS project in November and December 2015 fill between the land gravity datasets. An appropriate Digital Elevation Model (DEM) with topographic and bathymetric data was also produced. Finally, based on the two combined datasets (one for 2012–2014 and one for the 1970s), Free air and complete Bouguer gravity anomaly maps were produced following the appropriate data corrections and reductions. The pattern of complete Bouguer gravity anomaly maps was consistent with seismological results within the caldera. Finally from the comparison of the measurements made at the same place, we found that, within the caldera, the inner process of the volcano is ongoing both before, and after, the unrest period of 2011–2012.

scholarly journals Comparison of Marine Gravity Measurements from Shipborne and Satellite Altimetry in the Arctic Ocean

2021 ◽  
Vol 14 (1) ◽  
pp. 41
Author(s):  
Zilong Ling ◽  
Lihong Zhao ◽  
Tao Zhang ◽  
Guojun Zhai ◽  
Fanlin Yang
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
Wavelength Range ◽  
Satellite Altimetry ◽  
Gravity Data ◽  
The Arctic ◽  
Significant Information ◽  
Marine Gravity ◽  
The Arctic Ocean ◽  
Gravity Measurements

To understand the influence of sea ice on shipborne gravity measurements and the accuracy of the satellite-altimetry-derived gravity field in the Arctic Ocean, we compared shipborne gravity measurements with those obtained from satellite altimetric gravity measurements. The influence of sea ice on the shipborne gravity measurements was mainly concentrated in the 0–6 km wavelength range, and the standard deviation of the noise amplitudes was 2.62 mGal. Compared to ice-free regions, the accuracies in the region with floating ice were reduced by 13% for DTU21 and 6% for SV31. Due to the influence of sea ice, satellite altimetric gravity data lose significant information in the 9–12 km wavelength range. The coherence curve of the shipborne gravity with bathymetry was nearly the same as that of the satellite altimetric gravity. The satellite data contain nearly all of the significant information that is present in the shipborne data. The differences between the shipborne and satellite gravity data are small and can be used to study the crustal structure of the Arctic.

scholarly journals Forty-three years of absolute gravity observations of the Fennoscandian postglacial rebound in Finland

2021 ◽  
Vol 95 (2) ◽  
Author(s):  
Mirjam Bilker-Koivula ◽  
Jaakko Mäkinen ◽  
Hannu Ruotsalainen ◽  
Jyri Näränen ◽  
Timo Saari
Keyword(s):  
Gravity Data ◽  
Gravity Change ◽  
Global Navigation Satellite Systems ◽  
Absolute Gravity ◽  
Data Sets ◽  
Postglacial Rebound ◽  
Land Uplift ◽  
Satellite Systems ◽  
Gravity Measurements ◽  
Global Navigation Satellite

AbstractPostglacial rebound in Fennoscandia causes striking trends in gravity measurements of the area. We present time series of absolute gravity data collected between 1976 and 2019 on 12 stations in Finland with different types of instruments. First, we determine the trends at each station and analyse the effect of the instrument types. We estimate, for example, an offset of 6.8 μgal for the JILAg-5 instrument with respect to the FG5-type instruments. Applying the offsets in the trend analysis strengthens the trends being in good agreement with the NKG2016LU_gdot model of gravity change. Trends of seven stations were found robust and were used to analyse the stabilization of the trends in time and to determine the relationship between gravity change rates and land uplift rates as measured with global navigation satellite systems (GNSS) as well as from the NKG2016LU_abs land uplift model. Trends calculated from combined and offset-corrected measurements of JILAg-5- and FG5-type instruments stabilized in 15 to 20 years and at some stations even faster. The trends of FG5-type instrument data alone stabilized generally within 10 years. The ratio between gravity change rates and vertical rates from different data sets yields values between − 0.206 ± 0.017 and − 0.227 ± 0.024 µGal/mm and axis intercept values between 0.248 ± 0.089 and 0.335 ± 0.136 µGal/yr. These values are larger than previous estimates for Fennoscandia.

Sediment Stripping Correction to Marine Gravity Data

2014 ◽  
Vol 37 (4) ◽  
pp. 419-439 ◽  
Author(s):  
Wenjin Chen ◽  
Robert Tenzer ◽  
Xiang Gu
Keyword(s):  
Gravity Data ◽  
Marine Gravity
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