Patent GB-985510-A (GB)
Title: Method and system for producing a record of averaged gravity profiles
IPC: G01V7/06
Filed: 1963-08-01
Abstract: 985, 510. Gravitational surveys. SOCONY MOBIL OIL CO. Inc. Aug. 1, 1963 [Aug. 6, 1962], No. 30564/63. Heading G1W. Relates to methods of and means for transforming gravitational potentials existing along a profile into a form which accentuates anomalies and provides information as to the depths of masses giving rise to them. General. A graph or profile is prepared from measured values of gravity potential along a line of exploration. After correction for changes in elevation along and near this profile 101 (Fig. 8) there are generated therefrom a plurality of averaged profiles 102 to 108 (Fig. 8) each differing from the other by reason of the use of a different averaging operator, each successively longer than the last. The generated profiles are then subtracted from one another to generate difference profiles 112 to 117 (Fig. 9), on which the anomalies e.g. 112a, 112b, appear in turn in enhanced form. The enhancement, the distinctive character of the anomalies all appear as functions of the depth of the sources of the anomalies. The mid-points of the wavelets e.g. 112a (Fig. 9) are then plotted with distance for abscissae and depth as ordinates (Fig. 11 not shown) making it possible to draw the outline of the assumed total anomaly. The nature of residual effects of gravity can be ascertained and with the arrangement of the apparatus of Fig. 7 and Fig. 10 (not shown) a set of smoothed residuals of gravity potential are obtained (Fig. 12 not shown). Apparatus. Analogue or digital procedures may be used to perform the averaging. In an analogue means Fig. 7 and Fig.10 (not shown), the curve (101 Fig. 8 not shown) plotted from observed data is converted into a variable area record 20s on a photographic film (or alternatively a magnetic tape) 30. The film is driven at constant speed and light passing therethrough is received by a photo responsive cell 32 which thereby transmits a signal which is amplified and passed to an integrator 36. From thence the signal passes through a recording head 37 to magnetic tape on a motor driven drum 38. Associated with the drum are circumferentially adjustable pick up heads 41-47 connected respectively to amplifiers 51-57 and each spaced from its immediate neighbour by an interval T. Only two heads 41, 43 may be utilized since they are circumferentially adjustable, although in practice a multiplicity of heads are used. The heads 41, 43 are separated by a smoothing interval 2T and the amplified outputs therefrom are passed to a summing amplifier 63 and from thence to a potential divider 64 and by suitable adjustment thereof the signal output at line 65 will be the output of the amplifier 63 modified by the expression 1/2T. The line 65 is connected to a recording head 67 and as the drum 38 is rotated there will be concurrently recorded on a magnetic tape on a drum 38a by recorder head 67 and heads 68 to 73 &c. averaged gravity profiles each averaged with a different smoothing interval. The subtraction of one averaged gravity profile from another is accomplished by means of a summing amplifier 82 which receives signals from pick up heads 75, 76 (in practice a plurality of heads feed a plurality of amplifiers) and passes an amplified signal to a recording head 90 and thence to a recording drum 91. The difference gravity profile is reproduced by a pick up head 92, amplified, and applied to control the rotation of a motor M which position a recording pen 96 laterally of a recording chart 98. Thus is recorded the profiles of Fig. 8. The difference gravity potential 112 Fig. 9 is the result of subtracting curve 103 of Fig. 8 from the curve 102 and so on. Means are described whereby the curves of smoothed residual gravity potential Fig. 12 can be obtained using the apparatus.