Method for removing striping in the direction of the line of an airborne geophysical data

Abstract

This invention relates to a noise reduction method for removing stripes along the survey line direction in airborne geophysical data, comprising the following steps: a. gridding the airborne geophysical data; b. performing curvelet transform on the gridded airborne geophysical data; c. calculating the direction coefficient indices to be processed at each scale; d. thresholding, setting all direction coefficients to be processed calculated in step c to zero; e. performing inverse curvelet transform on the curvelet coefficients after thresholding; f. discretizing the inverse curvelet transform results into airborne geophysical data. This invention can quickly and effectively remove stripes along the survey line direction while retaining anomaly information, thus improving the processing efficiency of airborne geophysical data. This invention is mainly applied to airborne geophysical exploration for mineral exploration, searching for metallic minerals, oil and gas, and radioactive minerals. It can also be applied to tasks such as emergency airborne monitoring without upper crystal nuclei, airborne geophysical exploration, and environmental monitoring.

Description

Technical Field

[0001] This invention relates to a method for processing airborne geophysical data, specifically a noise reduction method for removing stripes along the survey line direction in airborne geophysical data. Background Technology

[0002] Airborne geophysical exploration is a geophysical exploration technique that integrates multiple new technologies, characterized by high efficiency, speed, and economy. The main airborne geophysical methods include airborne magnetic surveying, airborne radiometric surveying, airborne gravity surveying, and airborne electromagnetic surveying. Initially, airborne geophysical work primarily focused on airborne magnetic and radiometric surveying to locate magnetic deposits, radioactive deposits, and oil and gas fields. Later, its applications expanded to include geological mapping, tectonic studies, radioactive environmental measurement, and nuclear accident emergency monitoring.

[0003] Due to the complexity of airborne geophysical surveys, stripes exist along the survey line in the data. These stripes represent noise in the data, and without processing, they will affect the accuracy. Currently, the methods for processing these stripes along the survey line are mostly line-by-line leveling or fine-tuning techniques. Line-by-line leveling is very time-consuming and labor-intensive, and in practical applications, due to tight schedules, it is rarely used unless the survey area is very small and there are few survey lines. The disadvantage of fine-tuning is that it can only level stripes of one width at a time. For complex stripes with multiple widths, not only is multiple leveling required, but it is also prone to losing anomaly information, resulting in a situation where stripe-free data and local anomalies cannot be obtained simultaneously. Furthermore, fine-tuning technology is integrated into foreign airborne geophysical survey software, which also raises copyright issues.

[0004] Therefore, there is an urgent need for a method to process airborne geophysical data that can effectively remove stripes along the survey line while retaining anomalies, so as to achieve the result of both stripe-free data and local anomalies. Summary of the Invention

[0005] The purpose of this invention is to provide a noise reduction method for removing strips along the survey line direction in airborne geophysical data, so as to solve the problems of time-consuming and labor-intensive methods and easy loss of abnormal information when using line-by-line leveling or fine-tuning techniques for existing strips.

[0006] The present invention is implemented as follows: a noise reduction method for removing stripes along the survey line direction in airborne geophysical data, comprising the following steps.

[0007] a. Grid-based data processing of airborne geophysical survey results.

[0008] b. Set the coefficient type, transformation type, transformation scale, and the number of angles for the second scale to perform curvelet transformation on the gridded airborne geophysical data.

[0009] c. Calculate the direction coefficient index to be processed at each scale. The calculation formula is as follows:

[0010]

[0011] y1 = y0 + 16 g(m);

[0012] In the formula, y0 is the index of the first direction coefficient to be processed;

[0013] y1 is the index of the second directional coefficient that needs to be processed;

[0014] f(n) is an angle function: f(n) = 360 - n, 0 < n ≤ 360;

[0015] n is the angle of the survey line direction, and its value ranges from 0 to 180.

[0016] g(m) is the scaling function:

[0017]

[0018] m is the scale series after the curvelet transform, and its value is an integer ranging from 5 to 8;

[0019] p is the number of angles in the second scale, p is a multiple of 4, and must be greater than 16.

[0020] d. Threshold processing: Set all the direction coefficients that need to be processed calculated in step c to zero.

[0021] e. Perform inverse curvelet transform on the curvelet coefficients after thresholding.

[0022] f. Discretize the results of the inverse curve transform into airborne geophysical data.

[0023] For the noise reduction method of removing strips along the survey line direction of airborne geophysical data according to the present invention, in step a, after the airborne geophysical data is gridded, a two-dimensional data M*N is formed, and the minimum value of M and N should be greater than 256.

[0024] In the noise reduction method for removing strips along the survey line direction of airborne geophysical data according to the present invention, in step b, the transformation type of the curve transform is a real-value transformation.

[0025] In the noise reduction method for removing strips along the survey line direction of airborne geophysical data according to the present invention, in step b, the transformation coefficient type of the curve transform is curve.

[0026] In the noise reduction method for removing strips along the survey line direction of airborne geophysical data according to the present invention, in step c, the direction coefficient sequence number to be processed at scale 1 is not calculated.

[0027] This invention removes stripes along the survey line direction through curvelet transform, thresholding, and inverse curvelet transform. It accurately calculates the direction coefficient indices associated with the stripes along the survey line direction and then sets these indices to zero through thresholding, thereby removing the stripes. The formula provided by this invention can calculate the direction coefficient indices associated with the stripes along the survey line direction for different survey line direction angles and different curvelet transform scales. Each set of survey line direction angles and curvelet transform scales corresponds to two direction coefficient indices that need to be processed.

[0028] This invention can quickly and effectively remove stripes along the survey line while retaining anomaly information, thus improving the efficiency of airborne geophysical data processing. This invention is primarily used in airborne geophysical exploration for mineral exploration, searching for metallic minerals, oil and gas, and radioactive minerals. It can also be applied to tasks such as emergency airborne monitoring without upper crystal nuclei, airborne geophysical exploration, and environmental monitoring. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention.

[0030] Figure 2 This is a raw data map of the airborne geophysical survey results for a certain survey area at 315° along the survey line direction.

[0031] Figure 3 yes Figure 2 The aerial geophysical survey results image after stripe removal using the method of this invention.

[0032] Figure 4 This is a raw data map of the airborne geophysical survey results for a certain survey area at a 285° survey line direction.

[0033] Figure 5 yes Figure 4 The aerial geophysical survey results image after stripe removal using the method of this invention. Detailed Implementation

[0034] like Figure 1 As shown, the present invention is a noise reduction method for removing stripes along the survey line direction in airborne geophysical data, comprising the following steps.

[0035] a. Grid-based data processing of airborne geophysical survey results.

[0036] Airborne geophysical survey data typically includes aeromagnetic ΔT, total aeromagnetic emissions, aeromagnetic potassium, uranium, thorium content, and airborne Bouguer gravity data. When gridding the data, an appropriate grid spacing is selected. After gridding, the airborne geophysical survey data forms a two-dimensional dataset M*N, where the minimum value of M and N should be greater than 256.

[0037] b. Perform curvelet transform on the gridded airborne geophysical data, with the transform scale being on the order of m.

[0038] Four parameters need to be set when performing curvelet transform. The first parameter is the type of coefficients, including complex-valued transform or real-valued transform, that is, whether the data type after the transform is real or complex, which is selected according to the purpose and effect of processing; the second parameter is the type of transform, curvelet or wavelet, that is, the method used to transform spatiotemporal domain data into frequency domain data; the third parameter is the number of levels of the transform scale, that is, how many levels the data is divided into; the fourth parameter is the number of angles in the second scale, which determines the number of angles in all subsequent scales.

[0039] The specific parameters are set as follows: the first coefficient type is real-valued transformation; the second transformation type is curvelet; the third transformation scale level is m levels, where m ranges from 5 to 8; the fourth second scale angle number is p, where p is a multiple of 4 and must be greater than 16.

[0040] The number of angles p in the second scale is generally set to 16 or 32, depending on the area of ​​the airborne geophysical survey data. The larger the area, the greater the number of angles needs to be.

[0041] c. Calculate the direction coefficient index to be processed at each scale. The calculation formula is as follows:

[0042]

[0043] y1 = y0 + 16 g(m);

[0044] In the formula, y0 is the index of the first direction coefficient to be processed;

[0045] y1 is the index of the second directional coefficient that needs to be processed;

[0046] f(n) is an angle function: f(n) = 360 - n, 0 < n ≤ 360;

[0047] n is the angle of the survey line direction, and its value ranges from 0 to 180.

[0048] g(m) is the scaling function:

[0049]

[0050] m is the scale series after the curvelet transform, and its value is an integer ranging from 5 to 8;

[0051] p is the number of angles in the second scale, p is a multiple of 4, and must be greater than 16.

[0052] The above formula can be used to obtain the two direction coefficients y0 and y1 that need to be processed for each set of survey line direction angles and curve transformation scales.

[0053] d. Thresholding: Set all the orientation coefficients that need to be processed at each scale calculated in step c to zero.

[0054] After curve processing, each directional coefficient at each scale is a matrix. In this invention, the matrix with the lowest number of directional coefficients is 16 at the second scale, 32 at the third and fourth scales, and 64 at the fifth and sixth scales. Based on the calculation results in step c, the matrix that needs to be processed is found, and all its coefficients are set to zero.

[0055] e. Perform inverse curvelet transform on the curvelet coefficients after thresholding.

[0056] When the number of angles in the second scale is set to 16 and the number of transformation scale levels is set to 7, there are a total of 337 coefficient matrices after the curve wave transformation. Six directional coefficients need to be thresholded. This step is to perform a curve wave inverse transformation on the six thresholded directional coefficients and the remaining 331 unprocessed coefficient matrices, that is, to transform all the data in the frequency domain into data in the spatiotemporal domain.

[0057] f. Discretize the results of the inverse curve transform into airborne geophysical data.

[0058] Since the curve wave transform processes gridded data, the processed data will also be gridded. However, due to the needs of airborne geophysical surveys, planographic maps and other forms of results are also required, which necessitate a result data format (data in the form of survey lines). Therefore, the data processed by the curve wave transform must be discretized into result data (data in the form of survey lines).

[0059] This invention removes stripes along the survey line direction through curvelet transform, thresholding, and inverse curvelet transform. It accurately calculates the direction coefficient indices associated with the stripes along the survey line direction and then sets these indices to zero through thresholding, thereby removing the stripes. The formula provided by this invention can calculate the direction coefficient indices associated with the stripes along the survey line direction for different survey line direction angles and different curvelet transform scales. Each set of survey line direction angles and curvelet transform scales corresponds to two direction coefficient indices that need to be processed.

[0060] To verify the correctness of this method, thorium content data for a certain testing area was processed using the method described in this patent. The testing area's measurement line direction was 315°. Figure 2 To facilitate the processing of the initial data, the stripes are more distinct along the survey line direction. Figure 3 The processed data shows that all stripes along the measurement line direction have been removed. To verify that measurement line data in other directions can be processed, the total count rate data from a CiBr crystal flight of a certain UAV was also processed, with the measurement line direction at 285°. Figure 4 Before processing the data, the stripes along the survey line are obvious. Figure 5The processed data does not contain stripes along the survey line direction. The processing of the two survey areas above corroborates the correctness of this method.

[0061] This invention can quickly and effectively remove stripes along the survey line while retaining anomaly information, thus improving the efficiency of airborne geophysical data processing. This invention is primarily used in airborne geophysical exploration for mineral exploration, searching for metallic minerals, oil and gas, and radioactive minerals. It can also be applied to tasks such as emergency airborne monitoring without upper crystal nuclei, airborne geophysical exploration, and environmental monitoring.

Claims

1. A noise reduction method for removing stripes along the survey line direction in airborne geophysical data, characterized in that, Includes the following steps: a. Grid the airborne geophysical survey data; after gridding, the airborne geophysical survey data will form two-dimensional data M×N, and the minimum value of M and N should be greater than 256; b. Set the coefficient type, transformation type, transformation scale, and the number of angles at the second scale to perform curvelet transformation on the gridded airborne geophysical data; c. Calculate the direction coefficient index to be processed at each scale. The calculation formula is as follows: In the formula, y0 is the index of the first direction coefficient to be processed; y1 is the index of the second directional coefficient that needs to be processed; f(n) is an angle function: f(n) = 360 - n, where n is the angle of the survey line direction, and its value ranges from 0 to 180. g(m) is the scaling function: m is the scale series after the curvelet transform; p is the number of angles in the second scale, p is a multiple of 4, and must be greater than 16; d. Threshold processing: Set all the direction coefficients that need to be processed calculated in step c to zero; e. Perform inverse curvelet transform on the curvelet coefficients after thresholding; f. Discretize the results of the inverse curve transform into airborne geophysical data.

2. The noise reduction method for removing stripes along the survey line direction in airborne geophysical data according to claim 1, characterized in that, In step b, the transformation type is a real-valued transformation.

3. The noise reduction method for removing stripes along the survey line direction in airborne geophysical data according to claim 1, characterized in that, In step b, the coefficient type is curve wave.

4. The noise reduction method for removing stripes along the survey line direction in airborne geophysical data according to claim 1, characterized in that, In step c, the direction coefficient sequence number to be processed at the first scale is not calculated.

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