Gravimetric terrain corrections in western Canada

1983 ◽  
Vol 20 (2) ◽  
pp. 259-265 ◽  
Author(s):  
J. A. R. Blais ◽  
G. D. Lodwick ◽  
R. Ferland
Keyword(s):  
Western Canada ◽  
Gravimetric Measurements ◽  
Optimal Technique ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Theoretical Results

Terrain corrections for gravimetric measurements have been studied in terms of accuracy requirements and automated computations. Geodetic and geophysical applications in western Canada have been considered specifically because of complications arising from the rugged topography. Comparing the computation methods of Nagy and Mathisen in relation to the theoretical results, the former is shown to be more reliable with simulated accidented topography. Other approaches are also briefly discussed and general recommendations are made for an optimal technique to compute gravimetric terrain corrections in western Canada.

Improvement of the conic prism model for terrain correction in rugged topography

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1054-1056 ◽  
Author(s):  
Raymond J. Olivier ◽  
Réjean G. Simard
Keyword(s):  
Gravity Anomalies ◽  
Terrain Correction ◽  
Field Calculation ◽  
Bouguer Gravity ◽  
New Model ◽  
Gravity Station ◽  
Rugged Terrain ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Prism Model

Terrain corrections for Bouguer gravity anomalies are generally obtained from topographic models represented by flat‐topped compartments of circular zones, utilizing the so‐called Hayford‐Bowie (1912), or Hammer’s (1939) method. Some authors have introduced improved relief models for taking uniform slope into consideration (Sandberg, 1958; Kane, 1962; Takin and Talwani, 1966; Campbell, 1980). We present a new model that increases the accuracy of the calculation of terrain correction close to the gravity station in rugged terrain, especially when conventional templates with few zones are used in field calculation.

PROSPECTING FOR CHROMITE WITH GRAVIMETER AND MAGNETOMETER OVER RUGGED TOPOGRAPHY IN EAST TURKEY

Geophysics ◽  
1956 ◽  
Vol 21 (2) ◽  
pp. 433-454 ◽  
Author(s):  
Sulhi Yüngül
Keyword(s):  
Major Part ◽  
Promising Technique ◽  
Magnetic Susceptibilities ◽  
Chromite Ore ◽  
Ore Body ◽  
Gravity And Magnetic ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Made In

From 1952 to 1954 gravity and magnetic surveys were made in Turkey over the concessions of the Eastern Chromite Works to discover new chromite reserves in a region of rugged topography and complicated geology. As a result of these surveys a new chromite ore body of 250,000 tons was discovered at the bottom of an open cut beneath a thin horizontal sheet of chromite. It is shown that gravity prospecting is a more promising technique for locating relatively large chromite masses, even over rugged topography, than might have been expected. The terrain corrections, which constitute the major part of the computations, must be simplified and it is important that the correct surface densities be employed. In addition, difficulties arizing from the high and variable magnetic susceptibilities in serpentines must be surmounted. The mass of chromite estimated from the gravity results agrees well with the amount found by subsequent drilling.

GRAVIMETER OPERATIONS IN THE FOOTHILLS BELT OF ALBERTA, CANADA

Geophysics ◽  
1945 ◽  
Vol 10 (4) ◽  
pp. 526-534
Author(s):  
W. K. Hastings
Keyword(s):  
Rocky Mountain ◽  
Reduced Gravity ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Conventional Methods ◽  
Methods Of Operation

As part of a gravimeter survey in western Alberta, Canada, the work was extended into quite rugged areas of the Rocky Mountain Foothills belt. This paper outlines the general methods of operation, carried out on horseback from a movable camp, which were employed where conventional methods, using trucks, were impossible. Gravity observations were made with a new, small type Gulf gravimeter which, complete with batteries and other accessories, weighs about forty‐eight pounds. The reduced gravity results were quite smooth and regular in spite of rugged topography and terrain corrections running up to 7 milligals.

scholarly journals Gravity terrain correction for mainland territory of Vietnam

2017 ◽  
Vol 17 (4B) ◽  
pp. 145-150
Author(s):  
Pham Nam Hung ◽  
Cao Dinh Trieu ◽  
Le Van Dung ◽  
Phan Thanh Quang ◽  
Nguyen Dac Cuong
Keyword(s):  
Gravity Data ◽  
Computing Time ◽  
Terrain Correction ◽  
Bouguer Gravity ◽  
Mountainous Region ◽  
Terrain Effect ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Gravity Map

Terrain corrections for gravity data are a critical concern in rugged topography, because the magnitude of the corrections may be largely relative to the anomalies of interest. That is also important to determine the inner and outer radii beyond which the terrain effect can be neglected. Classical methods such as Lucaptrenco, Beriozkin and Prisivanco are indeed too slow with radius correction and are not extended while methods based on the Nagy’s and Kane’s are usually too approximate for the required accuracy. In order to achieve 0.1 mGal accuracy in terrain correction for mainland territory of Vietnam and reduce the computing time, the best inner and outer radii for terrain correction computation are 2 km and 70 km respectively. The results show that in nearly a half of the Vietnam territory, the terrain correction values ≥ 10 mGal, the corrections are smaller in the plain areas (less than 2 mGal) and higher in the mountainous region, in particular the correction reaches approximately 21 mGal in some locations of northern mountainous region. The complete Bouguer gravity map of mainland territory of Vietnam is reproduced based on the full terrain correction introduced in this paper.

Optimization in gravimetric terrain corrections

1984 ◽  
Vol 21 (5) ◽  
pp. 505-515 ◽  
Author(s):  
J. A. R. Blais ◽  
R. Ferland
Keyword(s):  
Computer Software ◽  
Point Of View ◽  
Test Results ◽  
Computational Problem ◽  
Gravimetric Measurements ◽  
Terrain Corrections

Terrain corrections for gravimetric measurements require topographical data of appropriate accuracy and density. The situation is clearly dependent on the ruggedness of the topography and the accuracy specifications for the terrain corrections. From the optimization point of view, this computational problem has been investigated and computer software developed for the near, intermediate, and distant zones surrounding the gravity stations. Test results indicate that the general accuracy objective of 1.0–1.5 mGal (10–15 μm s−2) for the gravimetric terrain corrections is easily achievable in practice with appropriate topographical data. For geophysical applications, higher accuracies are certainly achievable with the method, even in rugged areas.

A sloping wedge technique for calculating gravity terrain corrections

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 1061-1063 ◽  
Author(s):  
L. J. Barrows ◽  
J. D. Fett
Keyword(s):  
High Precision ◽  
Field Data ◽  
Open Space ◽  
Gravity Station ◽  
Topographic Features ◽  
Original Field ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Wedge Technique

Gravity terrain corrections account for the upward pull of topographic features which are higher than a gravity station (hills) and the lack of downward pull from open space which is lower than the station (valleys). In areas of rugged topography or in high precision surveys, the magnitude of the terrain corrections can be comparable to the anomalies being sought and the uncertainties in the terrain corrections can limit the accuracy of the survey. Also, calculating the corrections can require more time and effort than gathering the original field data. Even if terrain corrections are not made, it is necessary to show that their omission does not compromise the integrity of the survey.

Gravimetric terrain corrections by triangular‐element method

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 232-238 ◽  
Author(s):  
X. Zhou ◽  
B. Zhong ◽  
X. Li
Keyword(s):  
Simple Formula ◽  
Gravity Data ◽  
High Accuracy ◽  
Rectangular Prism ◽  
Triangular Element ◽  
Volume Integral ◽  
Correction Process ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Element Method

Terrain corrections for gravity data are a critical concern in rugged topography, because the magnitude of the corrections may be large relative to the anomalies of interest. The terrain‐correction process, however, is very tedious. At present, rectangular prism and fan‐shaped prism methods are commonly used for the corrections; but these methods assume elements have horizontal tops, an assumption which does not reflect true topography, especially near the station. A triangular‐element method which allows dipping surfaces has been developed using a Gaussian formulation to improve the correction process. This method involves a simple formula employing a surface rather than a volume integral for computing the terrain corrections with high accuracy.

GRAVITY TERRAIN CORRECTIONS USING MULTIQUADRIC EQUATIONS

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 266-275 ◽  
Author(s):  
Douglas H. Krohn
Keyword(s):  
Linear System ◽  
Numerical Integration ◽  
Digital Computer ◽  
Digital Terrain Model ◽  
Computer Method ◽  
Gravity Station ◽  
Terrain Model ◽  
Digital Terrain ◽  
Rugged Topography ◽  
Terrain Corrections

A digital computer method of making gravity station terrain corrections has been developed that uses a linear system of multiquadric equations. This system is fitted to the points defined by square topographic compartments and the point defined by the station itself to give a mathematically described surface. The surface is a better model of the actual topography than the digital terrain model, especially near the station. Terrain correction of this surface is calculated using a simple and fast numerical integration. A theoretical example shows that the multiquadric equation method is potentially more accurate than a hand chart method for near‐station terrain corrections. Field examples in an area of rugged topography show that the method can be successfully used for actual gravity stations.

Generation of Correlated Logistic-Normal Random Variates for Medical Decision Trees

1998 ◽  
Vol 37 (03) ◽  
pp. 235-238 ◽  
Author(s):  
M. El-Taha ◽  
D. E. Clark
Keyword(s):  
Monte Carlo ◽  
Decision Trees ◽  
Computer Algebra ◽  
Taylor Series ◽  
Computer Algebra System ◽  
Random Variable ◽  
Monte Carlo Analysis ◽  
Normal Random Variable ◽  
Medical Decision ◽  
Theoretical Results

AbstractA Logistic-Normal random variable (Y) is obtained from a Normal random variable (X) by the relation Y = (ex)/(1 + ex). In Monte-Carlo analysis of decision trees, Logistic-Normal random variates may be used to model the branching probabilities. In some cases, the probabilities to be modeled may not be independent, and a method for generating correlated Logistic-Normal random variates would be useful. A technique for generating correlated Normal random variates has been previously described. Using Taylor Series approximations and the algebraic definitions of variance and covariance, we describe methods for estimating the means, variances, and covariances of Normal random variates which, after translation using the above formula, will result in Logistic-Normal random variates having approximately the desired means, variances, and covariances. Multiple simulations of the method using the Mathematica computer algebra system show satisfactory agreement with the theoretical results.

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