RU2327193C2 - Device to determine horizontal gradient of 2nd-order pull of gravity - Google Patents

Abstract

FIELD: mechanics.

SUBSTANCE: invention relates to the device made up of three parts, i.e. a top, medium and bottom parts, wherein the medium part is made in the form of the rotating plate the edge of which has a seat to locate a casing with one twisting system. Note that the plate diameter is larger that that of the casing. Thanks to the rotating plate there are three points of observation, that is, the corners of an equiangular triangle lying in one horizontal plane.

EFFECT: simpler device design, higher accuracy of measurement of the horizontal gradient of the second-order pull of gravity.

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Description

The invention relates to geophysical instrumentation, and in particular to devices for measuring higher derivatives of the potential υ gravity

и

and

These derivatives are also called the second horizontal gradients of gravity or the third derivatives of the potential of gravity and are denoted as υ _zxx , υ _zyy , υ _{zxy, respectively} .

Measuring Instruments

и

and

gravitational field: variometers and gradiometers usually consist of three coaxial parts: the upper one is the device itself, which includes the torsion system, the middle one is the rotating device for transferring the device from azimuth to azimuth and the lower one is the fixed base (V. Mironov Gravity prospecting course. - L. : Subsoil. - 1980. - P.274). Due to the complexity of designing devices for measuring second horizontal gradients of gravity in an industrial environment, they are not used.

When processing materials from geophysical observations, for example, obtained using a gravimeter, these values are obtained by numerical differentiation. However, the computational procedure is an unstable operation and can lead to a sharp accumulation of errors, and the results will be dependent. In addition, a sufficiently dense network and high accuracy of gravity measurements are required.

Closest to the proposed device is a device equipped with two torsion systems for measuring the horizontal gradient of gravity, spaced horizontally at such a distance that eliminates their mutual gravitational influence (Balabushevich I.A. Higher derivatives of the potential of gravity and the possibility of their use in geological Gravimetry. - Kiev: From the Academy of Sciences of the Ukrainian SSR. - 1983. - P.259).

Derivatives

и

and

obtained by dividing the magnitude of the increment of the gravity gradients by the distance - the base between the suspension points of two torsion systems.

A disadvantage of the known device is the need to use two identical torsion systems. In addition, it is necessary to exclude their mutual influence, which requires an increase in the size of the device.

The purpose of the invention is to simplify the design of the device and improve the accuracy of measuring the horizontal gradient of the gravity of the second order.

This goal is achieved by the fact that the middle part of the device for determining the horizontal gradient of gravity of the second order is made in the form of a rotating disk, on the edge of which there is a slot for holding the body with one torsion system, and the diameter of the disk is larger relative to the diameter of the body. The removable housing, in addition to the torsion system, contains optical, lighting, measuring and others, as well as other systems that ensure the performance of observations at the point. The azimuth of the torsion system is changed either by the corresponding rotation of the housing or its rearrangement, for which special pins are used.

Comparative analysis with the prototype allows us to conclude that the claimed device for determining the highest derivatives of the potential of gravity differs in that its middle part is made in the form of a rotating disk, on the edge of which there is a socket for holding the body with one torsion system, and the diameter of the disk is larger relative to the diameter of the housing. Thus, the claimed technical solution meets the criterion of "novelty."

As a result of the patent information research, no technical solutions were found with similar significant distinguishing features in the inventive device for determining higher derivatives of the potential of gravity. Therefore, the proposed technical solution meets the criterion of "significant differences".

The proposed design of the device consists of one torsion system, in addition, due to the averaging of values, the accuracy increases, because the determined higher derivatives of the potential of gravity depend on the horizontal coordinates of two vertices. It is the design of the device that allows the applied measurement technology and the processing graph to be considered as a filtering type of smoothing. Filtering is a two-dimensional transformation. It includes averaging at a triangular polygon (low-pass filtering) and calculation of finite differences (high-pass filtering).

Thus, the goal of the invention is achieved - simplifying the design and improving the accuracy of measuring the horizontal gradient of gravity of the second order.

Therefore, we can conclude that the proposed invention meets the criterion of "positive effect".

Figure 1 schematically shows the design of the device. The device has a fixed base - stand 1, rotating disk 2, and the diameter of the disk is 2-3 times the diameter of the device itself, socket 3 for holding the housing 4 with a torsion system, tripod 5. On the upper surface of the rotating disk 2 marks 6 are made in -120 °, and also a degree scale can be applied. The rotating disk 2 using locking devices (not shown in the drawing) is fixed in one of three positions.

и

связаны соотношениемThe main parameters of the device, primarily the disk, are calculated as follows. The second horizontal gradient of gravity and the gradient of gravity, respectively

and

are related by

- расстояние (база) между точками 1 и 2.where υ _zl (2) and υ _zl (1) are the magnitudes (modulus) of the horizontal gradient of gravity;

- distance (base) between points 1 and 2.

Differentiating formula (2) and replacing the differentials with absolute limit errors, we obtain

- ошибка определения второго горизонтального градиента силы тяжести;

- ошибка измерения приращения горизонтального градиента силы тяжести;

- ошибка измерения длины базы

Where

- error in determining the second horizontal gradient of gravity;

- error in measuring the increment of the horizontal gradient of gravity;

- error measuring the length of the base

теоретически можно обеспечить на уровне 1·10^-12 ед. СГС (Маловичко А.К., Тарунина О.Л. Использование высших производных при обработке и интерпретации результатов геофизических наблюдений. - М.: Недра, 1981. - C.101-102). Практически достаточно иметь чувствительность на порядок ниже, т.е. 1·10^-11 ед. СГС. При этом будут обнаруживаться плотностные неоднородности в виде массы 5÷10 кг вблизи устройства.Sensitivity of the measuring device

theoretically, it is possible to provide at the level of 1 · 10 ^-12 units. GHS (Malovichko AK, Tarunina OL. The use of higher derivatives in the processing and interpretation of the results of geophysical observations. - M .: Nedra, 1981. - C.101-102). It is practically enough to have a sensitivity an order of magnitude lower, i.e. 1 · 10 ^-11 units GHS. In this case, density inhomogeneities in the form of a mass of 5 ÷ 10 kg near the device will be detected.

Assuming the maximum sensitivity of the gradiometer is 1 · 10 ^-9 units. GHS, on the basis of formula (2) we get

This calculated value justifies the diameter of the rotating disk. Based on the sizes of the known devices: gravity variometers E-60, Z-40, S-20 and gradiometer GRBM-2, the diameter of the rotating disk will be 2 ÷ 3 times the diameter of these devices, which is one of the distinguishing features of the proposed device.

редко превышает значение 100·10^-9 ед. СГС и принимая

и

по формуле (3) получимGiven that during exploration work, the value

rarely exceeds the value of 100 · 10 ^-9 units GHS and taking

and

by the formula (3) we get

Thus, the diameter of the rotating disk has a size of the order of 1 m. Depending on the content of the problem being solved and the necessary accuracy of observations, it is advisable to use interchangeable disks of different diameters.

Based on measurements with the proposed device, the higher derivatives of the potential of gravity in the coordinate system, the beginning of which is combined with the center of the disk depicted in figure 2, is calculated by the following formulas.

We have

where x ₁ ; at ₁ ; x ₂ ; y ₂ ; x ₃ ; ₃ - the coordinates of the vertices of a triangle on the disk, with the y axis pointing north, the x axis east; υ _zx , υ _zy - values of gradients - modules obtained at three positions of the disk.

The full second horizontal gradient of gravity is calculated by the formula

The azimuth of υ _{zss is} found from the ratio:

In this case, the angle θ is measured in directions from the y axis: to the right - positive, to the left - negative.

так называемого второго смешанного градиента силы тяжести, является новым свойством, реализуемым при помощи предлагаемого устройства. Эта величина, получаемая из двух серий наблюдений, во-первых, может служить для контроля и, во-вторых, расширяет возможности геологической гравиметрии.The possibility of obtaining a value

the so-called second mixed gradient of gravity is a new property implemented using the proposed device. This value, obtained from two series of observations, firstly, can serve as a control and, secondly, expands the possibilities of geological gravimetry.

The device operates as follows.

Install the device at the observation point, for example on the earth's surface, and using the levels (not shown in the drawing), rotate the disk in a horizontal position. Then fix the upper part of the device - the body - in the slot for holding it and orient the rotating disk along one of the marks in the north direction along the astronomical meridian. Using the locking device, the disk is fixed relative to the base and measurements are taken with the device in this position. Next, turn the disk 120 ° and perform measurements: then rotate the disk again 120 ° and perform measurements υ _zx and υ _zy . For control, it is advisable to re-measure at the initial, north-oriented position of the disk.

Measurement processing is carried out in accordance with formulas (4) - (9). In this case, the increments along the horizontal coordinate axes for the disk will be constant.

Thanks to the use of a rotating disk in the observation process at the point, three measurement points are involved - the vertices of an equilateral triangle located at the same horizontal level. This eliminates the need for additional topographic and geodetic work, as required by field differential observation systems in geophysics (Kashik A.S. Informational sufficiency of differential observation systems in geophysics // Izv. Universities Geol. And exploration. - 1986. - 12. - P.152 -153).

The proposed device is designed to study density inhomogeneities of small size and low intensity at relatively shallow depths from several to tens and hundreds of meters.

Claims (1)

A device for determining a horizontal gradient of second order gravity, containing three parts: the upper one is a sensitive system for measuring the horizontal gradient of the first order, the lower one is a tripod, and the middle one is movable relative to the tripod, characterized in that, in order to simplify the design and increase the accuracy of measurement, the middle movable part is made in the form of a rotating disk, on the edge of which there is a socket for holding the upper part of the housing with a sensitive system containing one torsion system, when The disk diameter is larger than the case diameter.

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