A gravity exploration method and variable density terrain correction method thereof

Abstract

The present invention relates to the field of gravity exploration, and the present invention relates to a gravity exploration method and a variable density terrain correction method thereof. The method of the present invention comprises: obtaining density data and elevation DEM data of a target area terrain correction region; establishing a three-dimensional density-terrain model according to the density data and elevation DEM data; replacing the density value in the prism terrain correction value formula in the terrain correction domain calculation method with a lateral variable density value to obtain the lateral variable density terrain correction value of the corresponding elevation in the three-dimensional density-terrain model; obtaining the lateral variable density terrain correction values ​​of multiple elevations involved in the calculation point and the difference between the lateral variable density terrain correction values ​​of adjacent elevations of the same top boundary density; accumulating the difference between the lateral variable density terrain correction values ​​of the adjacent elevations of the same top boundary density to obtain the three-dimensional variable density terrain correction value corresponding to the calculation point. The method of the present invention can improve the accuracy of terrain correction calculation.

Description

Technical Field

[0001] The present invention generally relates to the field of gravity exploration and more particularly to a gravity exploration method and a variable density terrain correction method thereof. Background Art

[0002] In geological exploration, terrain changes have a significant impact on the accuracy of gravity measurement data. Traditional gravity terrain correction methods usually assume that the terrain density is uniform, which can lead to errors in practical applications, especially in areas where the terrain density changes dramatically.

[0003] In order to solve the error of gravity exploration caused by the assumed fixed density value, variable density terrain correction has appeared in the prior art, but there is a lack of specific and universal operation methods. Therefore, in the current gravity exploration, most gravity terrain corrections still use a fixed density value or a commonly used density value to correct the data. In addition, the gravity anomalies corrected with the commonly used density value often contain false anomalies, making it difficult to accurately interpret the relevant properties of the target body. Summary of the invention

[0004] In order to solve the above-mentioned technical problem of false anomalies when using a fixed density value to correct the gravity value, the present invention provides solutions in the following aspects.

[0005] In a first aspect, the present invention provides a variable density terrain correction method for gravity exploration, comprising: obtaining density data and elevation DEM data of a target area terrain correction region, the density data comprising lateral density data and longitudinal density data; establishing a three-dimensional density-terrain model according to the density data and elevation DEM data, the three-dimensional density-terrain model comprising a plurality of plane density contour maps at altitudes; replacing the density value in the prism terrain correction value formula in the terrain correction domain calculation method with a lateral variable density value to obtain a lateral variable density terrain correction value of the corresponding elevation in the three-dimensional density-terrain model; obtaining the lateral variable density terrain correction values ​​of a plurality of elevations involved in the calculation point and the difference between the lateral variable density terrain correction values ​​of adjacent elevations of the same top boundary density; accumulating the difference between the lateral variable density terrain correction values ​​of the plurality of adjacent elevations of the same top boundary density to obtain the three-dimensional variable density terrain correction value corresponding to the calculation point.

[0006] Furthermore, the interval between adjacent elevations is 0.5 to 5 m.

[0007] Furthermore, when the interval between adjacent elevations is 0.5 m, the calculation expression of the three-dimensional variable density terrain correction value is:

[0008]

[0009] In the formula, Δg(x,y) represents the three-dimensional variable density terrain correction value of the calculation point, N is the total number of lateral variable density terrain correction values ​​of multiple adjacent elevations with the same top boundary density involved in the calculation point, max represents the maximum elevation in the elevation DEM data, δg(x,y) max-(i-1)0.5 Indicates the lateral variable density terrain correction value corresponding to the virtual elevation of the calculation point when max-(i-1)0.5 is used, δg(x,y) max-i0.5 Indicates the lateral variable density terrain correction value corresponding to when max-i0.5 is used as the virtual elevation of the calculation point.

[0010] Furthermore, the calculation expression of the lateral variable density terrain correction value is:

[0011]

[0012] In the formula, δg(x, y) represents the lateral variable density terrain correction value of the calculation point, f represents the gravitational constant, Δx and Δy represent the node distance or grid distance, and C ij represents the integration constant, r ij Indicates the distance between node (i, j) and the calculation point, h ij represents the elevation difference between node (i, j) and the calculation point, ρ ij Indicates the corresponding lateral variable density value.

[0013] Furthermore, a three-dimensional density-terrain model is established according to the density data and the elevation DEM data, including: drawing density profiles of the terrain correction area of ​​the target area according to the density data and the elevation DEM data according to the set grid spacing; setting multiple virtual section lines for the density profile according to the altitude, and setting multiple nodes on the virtual section lines; generating spatial data of each node, the spatial data including: density value, two-dimensional coordinates and elevation; generating a plane density contour map according to the spatial data of each node of the virtual section line at the same altitude; and obtaining plane density contour maps corresponding to different altitudes.

[0014] Furthermore, a plurality of virtual profile lines are set for the density profile according to the altitude, including: starting from the maximum altitude of the density profile, virtual profile lines are set according to preset intervals until the minimum altitude of the density profile.

[0015] Furthermore, the preset interval is 0.5 to 5 m; when performing prism terrain correction calculation, the preset interval is further interpolated with plane variable density data at a spacing of 0.5 m.

[0016] Furthermore, the distance between adjacent nodes is 5m.

[0017] In a second aspect, the present invention provides a gravity exploration method, comprising: performing gravity exploration of a terrain correction area of ​​a target area using any of the variable density terrain correction methods for gravity exploration described in the first aspect.

[0018] The beneficial effect of the present invention is that the present invention realizes the calculation of terrain correction using variable density by establishing a three-dimensional density-terrain model and performing terrain correction calculation based on the three-dimensional density-terrain model, which includes not only the variable density correction calculation in the horizontal direction, but also the variable density correction calculation in the vertical direction, thereby avoiding false anomalies caused by using a uniform density value for terrain correction calculation, thereby improving the accuracy of terrain correction calculation, and further improving the reliability of gravity exploration results. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0020] Figure 1 is a flowchart schematically illustrating variable density terrain correction according to an embodiment of the present invention;

[0021] Figure 2 is a schematic diagram schematically showing a grid cross-hatching line according to an embodiment of the present invention;

[0022] Figure 3 is a schematic diagram schematically showing a density profile according to an embodiment of the present invention;

[0023] Figure 4 is a schematic diagram schematically showing a density profile according to an embodiment of the present invention;

[0024] Figure 5 Is for Figure 4 Schematic diagram of density profile after setting virtual section line;

[0025] Figure 6 Is for Figure 5 Schematic diagram of density profile after setting nodes for virtual profile lines in ;

[0026] Figure 7 is a planar density contour diagram schematically illustrating an embodiment of the present invention;

[0027] Figure 8 Schematically shows a three-dimensional density model and a schematic diagram of a vertical rectangular parallelepiped with variable density according to an embodiment of the present invention;

[0028] Fig. 9Schematic diagram schematically showing the range of a three-dimensional density-terrain model involved in calculation points according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0030] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0031] Figure 1 FIG. 4 is a flowchart schematically showing a variable density terrain correction process according to an embodiment of the present invention.

[0032] In a first aspect, the present invention provides a variable density terrain correction method for gravity exploration, specifically, by Figure 1 It can be seen that the variable density terrain correction method of the present invention includes:

[0033] S101, obtaining density data and elevation DEM data of the terrain correction area of ​​the target area.

[0034] The terrain correction area is the area after the target area (working area) is expanded according to the terrain correction radius.

[0035] Since geological exploration work is a gradual process from large to small, from coarse to fine. According to the "Specifications for Large-Scale Gravity Exploration", large-scale gravity exploration is a detailed or more specific exploration work based on the previous survey. Therefore, through the work in various stages of the previous stage, geological results such as geological maps of different scales in the terrain correction area, deep stratigraphic framework, mineralization and ore-forming factors of major minerals and mineralization models have generally been formed. In addition, a certain amount of density data of related lithology has also been formed in the previous geological, geophysical and drilling work. The density data includes horizontal density data and vertical density data. Therefore, the density data obtained from these preliminary works are used as the density data required to establish a three-dimensional density-terrain model in the terrain correction area. Elevation DEM data can be obtained by collecting existing elevation DEM data or by measuring the terrain correction area of ​​the target area.

[0036] S102: Establish a three-dimensional density-terrain model according to the density data and the elevation DEM data.

[0037] Specifically, the three-dimensional density-terrain model building includes the following steps:

[0038] S1201, drawing density profiles of the target area terrain correction area according to the density data and the elevation DEM data at a set grid distance.

[0039] Specifically, according to the range of terrain correction in the work area (for example, the terrain correction radius is 20 km) and the acquired density data, a grid spacing of 1 km × 1 km (such as Figure 2 As shown in the figure, the density profiles with actual terrain are drawn respectively (as shown in the figure Figure 3 and Figure 4 As shown in Figure 2, further, when drawing the density profile, the profile extends downward from the maximum elevation of the terrain correction area to the minimum elevation of the terrain correction area. If the set grid line does not pass through the maximum elevation within the terrain correction area, a grid line numbered X0 or Y0 passing through the maximum elevation should be added perpendicular to the direction of the geological elements in the area.

[0040] Specifically, Figure 2 The X1, X2, X3, X4, Y1, Y2, Y3 and Y4 marked at both ends of the grid lines indicate the grid line numbers. Figure 3 It represents the density profile of the target area terrain correction area drawn along the grid line X1 direction. Figure 4 It represents the density profile of the target area terrain correction area drawn along the grid line Y1 direction. Among them, the Z axis represents the elevation axis, Figure 3 and Figure 4 The numbers in represent the density values ​​of the area. It can be understood that density profiles drawn along the grid lines X2, X3, X4, Y2, Y3 and Y4 are also drawn.

[0041] S1202: setting a plurality of virtual section lines for the density profile according to the altitude, and setting a plurality of nodes on the virtual section lines.

[0042] Specifically, the maximum and minimum elevations within the terrain correction range are first determined, and multiple virtual profile lines (such as Figure 5 As shown), and the setting of the virtual section line does not exceed the drawn area. Specifically, Figure 5 As shown, a virtual profile line is set starting from the maximum altitude in the density profile, and the next virtual profile line is set according to a preset interval, and the setting ends at the minimum altitude. In one embodiment, the preset interval can be 0.5 to 5m, and further, can be an integer multiple of 0.5m, such as 0.5m, 2m, etc., but not more than 5m.

[0043] In this embodiment, the preset interval is set to 5m. This is because the density value data of each altitude in the vertical direction explored may be incomplete. If it is set to 0.5m, there may be unknown density values ​​within the terrain correction range, so it is impossible to draw an accurate density contour map. In other optional embodiments, those skilled in the art can set it according to actual conditions. For example, if the density values ​​obtained at each altitude are relatively complete within the terrain correction range, it can be set to 0.5m to improve the accuracy of subsequent terrain correction calculations. Furthermore, for unknown density, it can be obtained by linear interpolation.

[0044] It should be noted that when determining the maximum altitude and the minimum altitude, the actual maximum altitude and the minimum altitude are determined based on a position accuracy of 0.5m. For example, if the actual maximum altitude is 567.38m, the maximum altitude is determined to be 567.5m; if the actual maximum altitude is 567.11m, the maximum altitude is determined to be 567.0m. Similarly, the minimum altitude is determined in the same way.

[0045] Furthermore, nodes are set along the horizontal axis with a step length of 5m on the virtual section line (such as Figure 6 As shown), specifically, the nodes can be set starting from the Z axis. In other optional embodiments, those skilled in the art can select different step sizes to set the nodes.

[0046] S1203: Generate a plane density contour map based on the spatial data of each node on the virtual profile line at the same altitude.

[0047] Generate spatial data of each node on each virtual profile line, the spatial data including the two-dimensional coordinates, density value and elevation. Further, generate corresponding plane density contour map according to the spatial data of the nodes on the virtual profile line at the same altitude in different density profiles. Similarly, generate plane density contour map corresponding to other altitudes according to the above process, thereby obtaining plane density contour map of different altitudes in the target area terrain correction area (such as Figure 7 shown).

[0048] S1204. Establish a three-dimensional density-terrain model based on multiple planar density contour maps.

[0049] The obtained multiple plane density contour maps are modeled according to the altitude. Among them, the altitude spacing between adjacent plane density contour maps is 5m, which is the preset interval when setting the virtual section line. Furthermore, in order to improve the accuracy of terrain correction, the model is linearly interpolated with a step value of 0.5m to obtain the final three-dimensional density-terrain model.

[0050] It is understandable that in the three-dimensional density-terrain model, the elevation difference between the two plane density contour maps changes from 5m to 0.5m after linear interpolation. By setting the linear interpolation with a step size of 0.5m, a more complete and accurate density value between different altitudes in the vertical direction is obtained, thereby improving the precision and accuracy of terrain correction calculation.

[0051] Figure 8 is a three-dimensional space density model, Figure 8 It can be seen that the three-dimensional density-terrain model can be regarded as composed of small cubes at the microscopic level. The plane composed of the top surfaces of the cubes at the same altitude is the density contour map corresponding to the altitude of the top surface, and the plane composed of the bottom surfaces is the density contour map corresponding to the altitude of the bottom surface. The positions of the cubes correspond to the positions in the density contour map one by one. Furthermore, each cube is correspondingly set with a body unit density value, which is the density value of the corresponding position in the density contour line corresponding to the top surface of the cube. The above body unit density values ​​are used to perform variable density terrain correction calculations at the microscopic level. For example, in Figure 8 , calculate the first cube (i.e. Figure 8 When calculating the three-dimensional variable density terrain correction value of the cube labeled 1 in the figure, the volume unit density value (i.e., the top boundary density) is 2.6; when calculating the second cube (i.e., Figure 8 When calculating the three-dimensional variable density terrain correction value of the cube (the cube with label 2), the volume unit density value (i.e., the top boundary density) is 2.63; similarly, the third, fourth, or other cubes are calculated in the same way.

[0052] S103, performing variable density terrain correction calculation according to the three-dimensional density-terrain model.

[0053] Specifically, according to "H.2.2 Terrain Correction Domain Calculation Method" in Appendix H of the "Large Scale Gravity Survey Specifications", the density value in the prismatic terrain correction value calculation formula is replaced with the laterally variable density value to obtain the laterally variable density terrain correction value of the corresponding elevation in the three-dimensional density-terrain model.

[0054] Specifically, the calculation expression of the lateral variable density terrain correction value is:

[0055]

[0056] In the formula, δg(x, y) represents the lateral variable density terrain correction value of the calculation point (measurement point), f represents the gravitational constant, Δx and Δy represent the node distance or grid distance, and C ij represents the integration constant, r ij Indicates the distance between node (i, j) and the calculation point, h ijrepresents the elevation difference between node (i, j) and the calculation point, ρ ij Indicates the density value of the corresponding top interface (i.e. the corresponding lateral variable density value).

[0057] According to the calculation expression of the lateral variable density terrain correction value, the elevation of the calculation point and the lateral variable density terrain correction values ​​of multiple elevations involved in the terrain correction range of the calculation point (measurement point) are obtained. Among them, within the terrain correction range of the calculation point, the maximum elevation value z in the elevation DEM data can be used. max , minimum elevation value z min The distance D between adjacent elevations determines the total number N of lateral variable density terrain correction values ​​of multiple adjacent elevations with the same top boundary density involved in the calculation point.

[0058] Specifically, there are:

[0059] Therefore, the spacing D between adjacent elevations is different, and the total number of lateral variable density terrain correction values ​​involved in the calculation points is also different, where D can be set to 0.5~5m.

[0060] For example, suppose Fig. 9 To calculate the lateral variable density terrain correction values ​​of multiple elevations involved in the terrain correction range (part of the established three-dimensional density-terrain model), Fig. 9 Multiple planes are shown in the figure (i.e., the part involved in the calculation point in the plane density contour map). The elevation difference between adjacent planes is 5m, and the elevation corresponding to the top layer is z max , the elevation corresponding to the bottom layer is z min , there are N+1 planes in total, and a 5m thick interlayer is formed between the two planes, where It can be understood that the spacing D between adjacent elevations is the elevation difference between two adjacent plane density contour maps. Therefore, in this embodiment, the spacing D between adjacent elevations before linear interpolation is 5m, and the spacing D between adjacent elevations after linear interpolation becomes 0.5m.

[0061] It should be noted here that the elevation of the calculation point and the maximum elevation value z max , minimum elevation value z min They are all obtained based on a positioning accuracy of 0.5m; when performing terrain correction calculations, interpolation can be performed between two adjacent plane density contour maps with a spacing of D (for example, 5m) with a step value of 0.5m to allow the elevation of the calculation point to coincide with the altitude corresponding to a plane density contour map in the three-dimensional density-terrain model.

[0062] Further, the difference of the lateral variable density terrain correction values ​​of the adjacent elevations of the same top boundary density involved in the terrain correction range of the calculation point is obtained; specifically, from the maximum elevation value z max To begin with, use the height z max 、z max-D As the virtual elevation of the calculation point, the corresponding lateral variable density terrain correction value δg(x,y) is calculated according to the calculation expression of the lateral variable density terrain correction value mentioned above. max ,δg(x,y) max-D , and then make a difference, according to the above process, obtain the difference of the lateral variable density terrain correction value of other adjacent elevations with the same top boundary density, where D is the step value of linear interpolation. For example, if D is 0.5m, it is equivalent to Fig. 9 Nine virtual planes are formed in the interlayer between the two planes in , and each virtual plane corresponds to one virtual elevation value.

[0063] Then, the differences between the lateral variable density terrain correction values ​​of adjacent elevations with the same top boundary density are accumulated to obtain the three-dimensional variable density terrain correction value corresponding to the calculation point (measurement point).

[0064] Furthermore, when the interval D between adjacent elevations is 0.5 m (equivalent to Fig. 9 The three-dimensional density-terrain model in is linearly interpolated with a step value of 0.5m), and the corresponding calculation expression of the three-dimensional variable density terrain correction value is:

[0065]

[0066] In the formula, Δg(x, y) represents the three-dimensional variable density terrain correction value of the calculation point, N is the total number of lateral variable density terrain correction values ​​of multiple adjacent elevations with the same top interface density involved in the calculation point, and max represents the maximum elevation in the elevation DEM data (i.e., z max ),δg(x,y) max-(i-1)0.5 Indicates the lateral variable density terrain correction value corresponding to the virtual elevation of the calculation point when max-(i-1)0.5 is used, δg(x,y) max-i0.5 Indicates the lateral variable density terrain correction value corresponding to when max-i0.5 is used as the virtual elevation of the calculation point.

[0067] It can be understood that the above-mentioned three-dimensional variable density terrain correction calculation involves lateral and longitudinal density changes. Therefore, when the longitudinal lithology density does not change (or the change is very small and can be regarded as unchanged), the three-dimensional variable density terrain correction of the present invention is converted into a lateral variable density terrain correction.

[0068] For example, in gravity exploration, when the dip angles of all strata below the surface are 90° (the sedimentary strata are inverted and upright due to the regional geological structure), the vertical stratum (lithology) density within the working area remains unchanged, and only the lateral stratum (lithology) density changes. The three-dimensional variable density terrain used in the present invention for terrain correction calculation is essentially a lateral variable density terrain correction calculation. Further, when only the density data of the lateral (surface) strata / lithology can be collected in the working area, and the density data corresponding to the vertical strata cannot be collected, or there are only sporadic longitudinal density data, since the acquired density data cannot support the three-dimensional variable density terrain correction, the lateral variable density terrain correction can be performed through the three-dimensional variable density terrain correction calculation of the present invention.

[0069] Furthermore, the three-dimensional variable density terrain correction value of the calculated calculation point is summed with the gravity observation value to obtain the corrected gravity value.

[0070] By using variable density in the horizontal and vertical directions for terrain correction calculations, the errors caused by using a uniform density value when performing terrain correction are avoided, and false gravity anomalies can be weakened to the greatest extent, thereby improving the accuracy of terrain correction and the reliability of the results obtained from gravity exploration.

[0071] In a second aspect, the present invention further provides a gravity exploration method, which uses the variable density terrain correction method for gravity exploration as described in the first aspect to perform gravity exploration in a target area terrain correction area.

[0072] In summary, those skilled in the art can directly establish a three-dimensional density-terrain model based on density data and elevation DEM data, and the model can be applied to gravity exploration in the fields of hydrology, engineering, environment, and disaster address investigation, and has strong universality. Furthermore, since the three-dimensional density-terrain model is used to perform terrain correction calculations using variable density values, the problem of false anomalies caused by the existing three-dimensional address model using constant density values ​​for terrain correction calculations is solved, thereby improving the reliability of the work results obtained from gravity exploration.

[0073] In the description of this specification, “plurality” means at least two, such as two, three or more, etc., unless otherwise clearly and specifically defined.

[0074] Although this specification has shown and described a number of embodiments of the present invention, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art will conceive of many modifications, changes and alternatives without departing from the ideas and spirit of the present invention. It should be understood that in the practice of the present invention, various alternatives to the embodiments of the present invention described herein may be employed.

Claims

1. A variable density terrain correction method for gravity exploration, characterized in that: include: Obtaining density data and elevation DEM data of a terrain correction area of ​​a target area, wherein the density data includes lateral density data and longitudinal density data; Establishing a three-dimensional density-terrain model according to the density data and the elevation DEM data, wherein the three-dimensional density-terrain model includes a plurality of plane density contour maps at altitudes; Replacing the density value in the prism terrain correction value formula in the terrain correction domain calculation method with the lateral variable density value to obtain the lateral variable density terrain correction value corresponding to the elevation in the three-dimensional density-terrain model; Obtain the difference between the lateral variable density terrain correction values ​​of multiple elevations involved in the calculation point and the lateral variable density terrain correction values ​​of adjacent elevations with the same top boundary density; The differences between the lateral variable density terrain correction values ​​of the adjacent elevations of the same top boundary density are accumulated to obtain the three-dimensional variable density terrain correction value corresponding to the calculation point.

2. The variable density terrain correction method for gravity exploration according to claim 1, characterized in that: The interval between the adjacent elevations is 0.5 to 5 m.

3. The variable density terrain correction method for gravity exploration according to claim 2, characterized in that: When the interval between adjacent elevations is 0.5m, the calculation expression of the three-dimensional variable density terrain correction value is: In the formula, Δg(x,y) represents the three-dimensional variable density terrain correction value of the calculation point, N is the total number of lateral variable density terrain correction values ​​of multiple adjacent elevations with the same top boundary density involved in the calculation point, max represents the maximum elevation in the elevation DEM data, δg(x,y) max-(i-1)0.5 Indicates the lateral density terrain correction value corresponding to the virtual elevation of the calculation point when max-(i-1)0.5 is used, δg(x,y) max-i0.5 Indicates the lateral variable density terrain correction value corresponding to when max-i0.5 is used as the virtual elevation of the calculation point.

4. The variable density terrain correction method for gravity exploration according to claim 1, characterized in that: The calculation expression of the lateral variable density terrain correction value is: In the formula, δg(x, y) represents the lateral variable density terrain correction value of the calculation point, f represents the gravitational constant, Δx and Δy represent the node distance or grid distance, and C ij represents the integration constant, r ij Indicates the distance between node (i, j) and the calculation point, h ij represents the elevation difference between node (i, j) and the calculation point, ρ ij Indicates the corresponding lateral variable density value.

5. The variable density terrain correction method for gravity exploration according to claim 1, characterized in that: A three-dimensional density-terrain model is established according to the density data and the elevation DEM data, including: drawing density profiles of the terrain correction area of ​​the target area according to the density data and the elevation DEM data according to the set grid spacing; setting multiple virtual profile lines for the density profile according to the altitude, and setting multiple nodes on the virtual profile lines; generating spatial data of each node, the spatial data including: density value, two-dimensional coordinates and elevation; generating a plane density contour map according to the spatial data of each node of the virtual profile line at the same altitude; and obtaining plane density contour maps corresponding to different altitudes.

6. The variable density terrain correction method for gravity exploration according to claim 5, characterized in that: The density profile is provided with a plurality of virtual profile lines according to the altitude, including: starting from the maximum altitude of the density profile, the virtual profile lines are provided according to preset intervals until the minimum altitude of the density profile.

7. The variable density terrain correction method for gravity exploration according to claim 6, characterized in that: The preset interval is 0.5 to 5 m. When performing prism terrain correction calculation, the preset interval is further interpolated with plane variable density data at a spacing of 0.5 m.

8. The variable density terrain correction method for gravity exploration according to claim 1, characterized in that: The distance between adjacent nodes is 5m.

9. A gravity exploration method, characterized in that: include: A gravity survey of the terrain correction area of ​​the target area is carried out using the variable density terrain correction method for gravity survey as described in any one of claims 1 to 8.

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