Graphical Terrane Correction for Gravity Gradient Page: 6
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6 GRAPHICAL TERRANE CORRECTION FOR GRAVITY GRADIENT
The octants are taken one at a time and the elevations for the octant
plotted on the chart; a smooth curve for each zone is then drawn or
visualized through the points, and the number of the 0.1 E rectangles
included between the curve and the axis of zero elevation is counted
and entered without regard to sign in the proper space in line A
of Figure 4.
I II III IV V VI VII VIII-
N. NE. E. SE. S. SW. W. NW.
-4.7 A Chart values.
2. 3 - B Sp.gr.
S2.8 . __
-10. 8 -- -
- 5.6C AXB.
Vc - -- -_ - - VIIc .---------
-IIc ---1 46 --------IIc -16. 4
-VIIIc ....... VIIIc
IVc --IVc ---------
VIc -------- VIc --
0.707X -16. 4 -11.6 0.707X -16. 4 -11.6
dxdz -11.6 dd--11. 6
FIG. 4.-Suggested form for calculation
The values entered in line A of Figure 4 are normally uncorrected
for specific gravity and are for a specific gravity of 1.0; they must
therefore be multiplied respectively by the specific gravity estimated
to be most probable for the particular octants. The products are
entered in their respective spaces in line B. The total effect is:
2 = - I - VB -- 0.707(- IIB - VIIB I IVB - -VIB) (6)
-- I:IIs+ VIIP, +0.707(- IIB+IV-i VI,+ VIII). (7)
The resulting values are then subtracted from the respective observed
FLEXIBILITY OF IVIETHOD
1. If the terrane is too irregular to allow a single radial line of
elevations down the axis of an octant to give a reasonably accurate
representation of the terrane.
(a) Any octant may be divided into two equal sectors or into four
sectors whose widths are in the ratio of 53: 47: 47: 53. The levels
should be run along the radial axis of each subsector. The effect
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Barton, Donald C. Graphical Terrane Correction for Gravity Gradient, report, 1929; [Washington D.C.]. (digital.library.unt.edu/ark:/67531/metadc66454/m1/8/: accessed May 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.