MOVING‐BASE GRAVITY GRADIOMETER SURVEYS AND INTERPRETATION

Geophysics ◽  
1978 ◽  
Vol 43 (1) ◽  
pp. 94-101 ◽  
Author(s):  
Stanley K. Jordan
Keyword(s):  
Gulf Coast ◽  
Gravity Anomalies ◽  
Optimal Estimation ◽  
Vehicle Speed ◽  
Gravimetric Survey ◽  
Tensor Quantity ◽  
Moving Base ◽  
Dimensional Gravity ◽  
Vehicle Path ◽  
Speed And Accuracy

Moving‐base gravity gradiometers are currently under development at Bell Aerospace Co., Charles Stark Draper Laboratory, and Hughes Aircraft Co. In principle, these instruments can be mounted on stable platforms in aircraft or marine survey ships. Unlike a conventional gravimeter, the gradiometer is insensitive to vertical (heave) accelerations of the vehicle and does not require an Eötvös correction. Gradiometers thereby offer an overwhelming improvement in the speed and accuracy of gravity surveys. In addition, a gradiometer provides more information than a gravimeter because a tensor quantity is measured, rather than a scalar. How should the gradient data be used? The simplest approach is to convert the gradients into gravity anomalies by integrating along the vehicle path, and then apply conventional interpretation models. This approach is sound if the survey tracks are closely spaced because continuous two‐dimensional gravity anomalies completely define the gravity field outside the earth, according to potential theory. On the other hand, one can widen the survey tracks considerably if a more sophisticated approach is adopted that exploits the extra information in the gradients. In this paper, we compare the “simple” approach and a more elaborate (“optimal”) one that uses the entire gradient tensor. The comparison is based on information theory concepts: How much information is in the gradient data? How much is lost if the gradients are converted to gravity anomalies? Statistical models are fitted to Bouguer residual gravity anomalies from a salt dome field in the Louisiana Gulf Coast, and the interpretation rms errors are evaluated for each approach based on optimal estimation theory. The results show that a gradiometric survey with 18-km spacing contains the same information as a gravimetric survey with 8-km spacing. The sensitivities of the results to the following survey parameters are determined: track spacing, gradiometer noise, vehicle speed, and aircraft altitude.

Three-dimensional gravity modelling applied to the exploration of uranium unconformity-related basement-hosted deposits: the Contact prospect case study, Kiggavik, northeast Thelon region (Nunavut, Canada)

2017 ◽  
Vol 54 (8) ◽  
pp. 869-882 ◽  
Author(s):  
Régis Roy ◽  
Antonio Benedicto ◽  
Alexis Grare ◽  
Mickaël Béhaegel ◽  
Yoann Richard ◽  
...  
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
3D Models ◽  
Low Density ◽  
Uranium Deposits ◽  
Geological Interpretation ◽  
Thelon Basin ◽  
Dimensional Gravity ◽  
Density Values

In unconformity-related uranium deposits, mineralization is associated with hydrothermal clay-rich alteration haloes that decrease the density of the host rock. In the Kiggavik uranium project, located in the eastern Thelon Basin, Nunavut (Canada), basement-hosted shallow deposits were discovered by drilling geophysical anomalies in the 1970s. In 2014, gravity data were inverted for the first time using the Geosoft VOXI Earth ModellingTM system to generate three-dimensional (3D) models to assist exploration in the Contact prospect, the most recent discovery at Kiggavik. A 3D unconstrained inversion model was calculated before drilling, and a model constrained by petrophysical data was computed after drilling. The unconstrained inversion provided a first approximation of the geometry and depth of a low-density body and helped to collar the discovery holes of the Contact mineralization. The constrained inversion was computed using density values measured on 315 core samples collected from 21 drill holes completed between 2014 and 2015. The constrained modelling highlights three shallower and smaller low-density bodies that match the geological interpretation and refines the footprint of the gravity anomalies in relation to the current understanding of the deposit. The 3D inversion of gravity data is a valuable tool to guide geologists in exploration of shallow basement-hosted uranium deposits associated with alteration haloes and to assess the deposit gravity geometry.

A LEAST‐SQUARES PROCEDURE FOR GRAVITY INTERPRETATION

Geophysics ◽  
1965 ◽  
Vol 30 (2) ◽  
pp. 228-233 ◽  
Author(s):  
Charles E. Corbató
Keyword(s):  
Least Squares ◽  
High Speed ◽  
Gravity Anomalies ◽  
The Body ◽  
Two Dimensional ◽  
Partial Derivatives ◽  
Dimensional Gravity ◽  
Gravity Interpretation ◽  
Relationship Of ◽  
Derivatives Of

A procedure suitable for use on high‐speed digital computers is presented for interpreting two‐dimensional gravity anomalies. In order to determine the shape of a disturbing mass with known density contrast, an initial model is assumed and gravity anomalies are calculated and compared with observed values at n points, where n is greater than the number of unknown variables (e.g. depths) of the model. Adjustments are then made to the model by a least‐squares approximation which uses the partial derivatives of the anomalies so that the residuals are reduced to a minimum. In comparison with other iterative techniques, convergence is very rapid. A convenient method to use for both the calculation of the anomalies and the adjustments is the two‐dimensional method of Talwani, Worzel, and Landisman, (1959) in which the outline of the body is polygonized and the anomalies and the partial derivatives of the anomaly with respect to the depth of a vertex on the body can be expressed as functions of the coordinates of the vertex. Not only depths but under certain circumstances regional gravity values may be evaluated; however, the relationship of the disturbing body to the gravity information may impose certain limitations on the application of the procedure.

scholarly journals Gravimetric survey and modeling of the basement morphology in the sedimentary thickness characterization, NE portion of Paraná Sedimentary Basin - Brazil

2017 ◽  
Vol 47 (2) ◽  
pp. 249-260 ◽  
Author(s):  
Maximilian Fries ◽  
Walter Malagutti Filho ◽  
João Carlos Dourado ◽  
Mariana Aparecida Fernandes
Keyword(s):  
Sedimentary Basin ◽  
3D Visualization ◽  
Sedimentary Rocks ◽  
Gravity Anomalies ◽  
Forward Modeling ◽  
Surrounding Area ◽  
Gravimetric Survey ◽  
Paraná Sedimentary Basin ◽  
Structural High ◽  
Sedimentary Layer

ABSTRACT: The northeast portion of the Paraná Sedimentary Basin is distinguished by structural highs as the known Pitanga Dome, an uplifted structure identified in the last century. It represents a geological and evolutionary evidence of the Paraná Sedimentary Basin and has undergone inspired studies and intense exploration surveys. This study consists of a gravimetric survey in the Pitanga Dome area, State of São Paulo, Brazil. The Bouguer gravity anomalies have been identified and related to the structural high, sedimentary thickness, and the basement morphology. Processing and enhancement techniques were used for forward modeling based on previous studies. The three models from profiles sectioning the dome have a sedimentary thickness varying from 200 to 1.250 meters. The adopted methodology has provided important results determining that the Pitanga Dome can be understood through rational 3D visualization. The area can be interpreted as an undulating basement with thinning of sedimentary rocks related to deep features (structures) in the crust/mantle limit (Moho uplift). This characteristic is confirmed by the sedimentary layer thickening present throughout the surrounding area. The results also offer important insights and support for further studies concerning the genesis and evolution of this and other uplifted structures of the Paraná Sedimentary Basin.

A Simple Vehicle Model for Path Prediction During Evasive Maneuvers and a Stochastic Analysis on the Crash Probability

2007 ◽  
Author(s):  
Taewung Kim ◽  
Kyukwon Bang ◽  
Hyun-Yong Jeong ◽  
Stephen Decker
Keyword(s):  
Test Data ◽  
Stochastic Analysis ◽  
False Positive Rate ◽  
False Negative ◽  
False Negative Rate ◽  
Vehicle Speed ◽  
Vehicle Model ◽  
Moment Arms ◽  
Heading Angle ◽  
Vehicle Path

Active safety systems are being developed in automotive industry, and an analytical vehicle model is needed in such systems to predict vehicle path to assess the crash probability. However, the bicycle model cannot result in a good correlation with test data and ADAMS simulation results, and other analytical vehicle models which have 8 or 14 degrees of freedom need more computation time. Therefore, in this study a simple analytical vehicle model was proposed to predict vehicle path especially during evasive maneuvers. The analytical vehicle model can predict a vehicle’s path based on the given vehicle speed and steering angle. In the analytical vehicle model, two different moment arms were used for inboard and outboard wheels, and lateral and longitudinal load transfers were taken into account. In addition, the magic formula tire model was used to estimate the lateral force. The analytical vehicle model has been validated with a sophisticated ADAMS model, and it resulted in a good correlation with test data. Using the simple analytical model, a stochastic analysis was conducted to analyze the effect of the initial offset amount and the heading angle on the crash probability. Another stochastic analysis was also conducted to analyze the effect of a sensing error on the false negative rate (FNR) and the false positive rate (FPR). It was found that the initial offset amount and the heading angle played a key role in the crash probability, and only FPR was affected noticeably by a sensing error.

TECHNIQUE FOR IMPROVED CONVERGENCE IN ITERATIVE ANALYSIS OF GRAVITY ANOMALY PROFILES

Geophysics ◽  
1973 ◽  
Vol 38 (3) ◽  
pp. 500-506 ◽  
Author(s):  
K. P. Fournier ◽  
S. F. Krupicka
Keyword(s):  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Computer Time ◽  
Two Dimensional ◽  
Profile Data ◽  
Plate Method ◽  
Modeling Process ◽  
Iterative Analysis ◽  
Dimensional Gravity ◽  
Number Of Iterations

Narrow two‐dimensional gravity anomalies are difficult to interpret iteratively by the relatively simple flat‐plate method suggested by Bott (1960) and employed by others. In this report Bott’s formula is modified empirically after a number of iterations have proceeded. The process is repeated until satisfactory convergence is obtained. The results can be applied to other profiles across the anomaly of interest and thus save substantial computer time by requiring fewer iterations. The technique is applied to two Bouguer anomaly profiles. Analysis of adjoining anomaly profile data with similar amplitudes and widths can be used to speed the convergence in the iterative modeling process.

Designing Crossing Islands for Speed Control and Intersection Safety on Two-Lane Collectors and Arterials

2021 ◽  
pp. 036119812110049
Author(s):  
Peter G. Furth ◽  
Milad Tahmasebi ◽  
Sepehr (Steve) Shekari ◽  
Jay Jackson ◽  
Zhao (Howie) Sha ◽  
...  
Keyword(s):  
Geometric Analysis ◽  
Speed Control ◽  
Original Data ◽  
Vehicle Speed ◽  
Left Turn ◽  
School Buses ◽  
Lane Width ◽  
Road Geometry ◽  
Vehicle Path ◽  
Pedestrian Crossing

Crossing islands at unsignalized intersections, in addition to their pedestrian crossing safety benefits, can also serve as speed control chicanes by forcing vehicles to make a reverse curve. A method is developed for determining the chicane length (and thus, parking setback) needed for a two-lane road for a given lane width, island width, and target speed, based on models of the relationship between road geometry vehicle path radius, and speed. New data on the speed–radius relationship is presented. The concept of “informal flare” is also introduced; it is a common approach geometry that allows a left-turning vehicle to wait for a gap in opposing traffic without blocking through traffic behind it. Using informal flares can make it possible to prevent left-turn blockage without sacrificing a crossing island for a left-turn lane. Curb continuation lines at median openings are presented as a means to enhance informal flare function. Original data are presented relating informal flare function (the tendency of through vehicles to bypass a waiting left-turner) to a road’s half-width. Geometric analysis shows that intersections with crossing islands can fit on roads with right of way as narrow as 60 ft, and with curb-to-curb width as narrow as 40 ft, while still accommodating turning school buses and bike facilities and preventing left-turn blockage. Various performance measures are used to evaluate intersection geometry, including measures related to through vehicle speed, turning vehicles, and pedestrians. With crossing islands, pedestrian safety with respect to left-turning vehicles is substantially improved as the turning path becomes square to the crosswalks, making the vehicle path more predictable and reducing vehicle speed, conflict area size, and pedestrian exposure distance.

Sign in / Sign up

Export Citation Format

Share Document