CN111458761B - Offshore gravity comparison field construction method - Google Patents

Abstract

The invention provides a method for constructing an offshore gravity comparison field. The method includes: determining the stable center position of the measuring ship; installing multiple marine gravimeters as close as possible to the central axis and parallel to the ship's axis, and using the constructed hull coordinate system to accurately measure the position of different types of gravimeters relative to the ship's coordinates; The instrument uses the same set of navigation and positioning signals; data processing is carried out according to the specification requirements, and data quality evaluation is carried out according to the accuracy of the intersection point and the repeating line; the reliability, stability and accuracy of each type of gravimeter are evaluated; Evaluate the results, perform weighted average of repeated survey line data, and construct the standard value of gravity for comparison survey line. The method for constructing an offshore gravity comparison field provided by the present invention can build an offshore gravity comparison field with precise survey lines.

Description

Construction Method of Offshore Gravity Comparison Field

technical field

The invention relates to the technical field of gravity field measurement, in particular to a method for constructing an offshore gravity comparison field.

Background technique

The Earth's gravitational field reflects the composition and distribution of matter in the Earth's interior, and by accurately measuring the Earth's gravitational field, it is possible to invert and estimate the distribution and changes of matter. Therefore, high-precision gravity measurement has important application prospects in the fields of basic geological research, regional gravity survey, geodetic survey, exploration of oil and gas fields and solid mineral resources, and gravity-assisted navigation.

At present, the ocean gravimeters mainly used in my country include Lacoste&Romberg SII, KSS31M, DynamicGravity System and GT-2M. In addition, the CHZ-II, SAG-2M, SGA-WZ and ZL-11A gravimeters independently developed by my country have been gradually put into production and application. The measurement principles of various types of gravimeters are different, the noise level and inherent system noise generated by external influences during the measurement process are different, and the inherent filtering methods of the acquisition system are different (currently, there are mainly FIR filtering based on Blackman window function, Kalman filtering, and Cosine filtering). etc.), resulting in certain differences in the measured gravity anomalies, resulting in certain differences in the quality assessment results such as measurement accuracy and resolution.

In addition to static tests, marine gravimeters need to be tested at sea to verify their performance indicators.

Various scientific research and production units select different test areas for the technical index inspection and self-inspection of marine gravimeters with different measurement principles, and there is no unified national standard, which cannot be objectively evaluated.

At present, there is no survey line similar to the comparison baseline in the airborne gravity survey, and it is urgent to build a marine gravity comparison field.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a method for constructing an offshore gravity comparison field, which can build an offshore gravity comparison field with precise survey lines.

In order to solve the above-mentioned technical problems, the present invention provides a method for constructing an offshore gravity comparison field, the method comprising: determining the position of the stable center of the survey ship; installing multiple marine gravimeters parallel to the ship axis direction, and using the constructed hull coordinates It is used to accurately measure the position and accuracy of different types of gravimeters relative to the ship's coordinates, and is used for the calculation of the measurement results; multiple gravimeters use the same set of navigation and positioning signals, so that each gravimeter can meet the unified position coordinates and time; in accordance with the requirements of the specification Carry out data processing, and evaluate the data quality according to the coincidence accuracy of the intersection point and the coincidence accuracy of the repeated line; The reliability, stability and accuracy of the model gravimeter are evaluated; according to the multi-parameter evaluation results, the repeated survey line data is weighted and averaged, and the comparison survey line gravity standard value is constructed.

In some embodiments, when a plurality of marine gravimeters are installed parallel to the ship axis, the deviation from the central axis is not more than 5m, and the number of marine gravimeters is not less than 5.

In some embodiments, when data processing is performed according to the requirements of the specification, the data processing performed includes: base point comparison, zero drift correction, spatial correction of draft change, Ertworth correction, platform inclination calculation, normal gravity calculation, absolute measurement point Gravity value calculation and space gravity anomaly calculation.

In some embodiments, the method further includes: before performing a weighted average on the repeated survey line data according to the multi-parameter evaluation result and the correlation analysis result, and before constructing the gravity standard value of the comparative survey line, determining the weight of each survey line.

In some embodiments, determining the weight of each survey line includes: calculating the measurement value of each gravimeter with respect to the number of repetitions m of the survey line, the survey points n, and the average value of m and n; calculating the residual term, and considering that there are Sufficient measurement point data makes the average value of the noise to be zero, so as to obtain the noise level of each gravimeter; the weighted average of the measurement results of each gravimeter realizes the construction of the standard value of the comparison line.

In some embodiments, calculating the residual term includes: calculating the residual term according to the following formula:

D _ij =g _ij -g _{i ·} -g _{· j} +g _{· ·} =N _ij -N _{i ·} -N _{· j} +N _{· ·}

Among them, g _ij represents the gravity value measured by a single gravimeter on the repeated line with respect to the measurement value of the jth measurement on the i-th survey line, and g _i represents the gravity value measured by a single gravimeter on the repeated line with respect to the i-th measurement line The average value of the number of repetitions m of a single _gravimeter , g _j represents the average value of the measured gravity anomalies of all measuring points on the jth measurement of a single gravimeter with respect to n, and g represents the gravity measured on the repeated line of a single gravimeter The abnormal value is the average value of the measurement line m and the measurement point n, N _ij represents the measurement noise value of the jth measurement point of the i-th measurement line measured by a single gravimeter on the repeated line, N _{i ·} represents a single gravimeter The average value of the gravity value measured on the repeated line with respect to the number of repetitions m of the survey line, N _{· j} represents the average value of the noise of all measuring points on the jth measurement of a single gravimeter with respect to n, and N _{· ·} represents the repetition of a single gravimeter The noise measured on the line is the average value of line m and point n.

In some embodiments, the method further includes: selecting an offshore operation measurement carrier before determining the center of the measurement vessel.

In some embodiments, the selected marine operation measurement carrier includes: a scientific research vessel over 4500 tons.

In some embodiments, the method further includes: before selecting a measurement carrier for offshore operations, designing a comparison field survey line according to a comparison field survey line design principle, and the length of the survey line is greater than 300 km.

In some embodiments, the method further includes: before designing the comparison field survey line according to the comparison field survey line design principle, selecting an offshore gravity comparison field area, and the selected marine gravity comparison field area includes: continental shelf, continental slope , Slope highlands, seamounts, depressions, uplifts, abnormal gravity fluctuations greater than 50mGal.

After adopting such a design, the present invention has at least the following advantages:

The present invention firstly uses no less than 5 different types of marine gravimeters to operate on the same ship to carry out at least 3 round-trip repeated measurements on the survey line designed in the proposed sea area, and requires the design survey line to have intersections, which is convenient for the overall leveling. Then, the measurement data of each marine gravimeter is processed according to the national standard and standard processing method, and the parameters such as root mean square error, systematic deviation, mutual standard deviation, and correlation are used to evaluate the accuracy; Based on the parameter evaluation results, the gravity standard value of the comparison survey line is constructed by weighted average. The invention can realize the separation of the real gravity signal and the system noise in the shipborne gravity measurement value, obtain the gravity abnormal standard value on the survey line, and can be used for the performance evaluation of the marine gravimeter and the quality evaluation of the shipborne gravity measurement data.

Description of drawings

The above is only an overview of the technical solutions of the present invention. In order to understand the technical means of the present invention more clearly, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

1 is a flowchart of a method for constructing an offshore gravity comparison field provided by an embodiment of the present invention;

2 is a plan view of a construction area of an offshore gravity comparison field provided by an embodiment of the present invention;

FIG. 3 is the noise separation of multiple repeated measurement results provided by an embodiment of the present invention.

Detailed ways

The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, but not to limit the present invention.

FIG. 1 is a flowchart of a method for caching mirror copy data provided by an embodiment of the present invention. Referring to Figure 1, the method for constructing an offshore gravity comparison field includes the following steps:

Step 1: Principles for selection of offshore gravity comparison fields.

The selection of areas for the construction of the offshore gravity comparison field is shown in Figure 2, which includes various geological structures such as continental shelves, continental slopes, highlands on slopes, seamounts, depressions, and uplifts. Fluctuations and changes, abnormal gravity fluctuations greater than 50mGal.

Step 2: Compare the design principles of field survey lines.

The designed survey line should span a variety of different geological structure types, and the survey line length should be greater than 300km.

Step 3: Selection of measurement carrier for offshore operations.

The measurement carrier for the construction of the offshore gravity comparison field shall be a scientific research vessel above 4,500 tons.

Step 4: Determine the center of the measuring ship, that is, the cabin with the smallest horizontal acceleration caused by the rolling and pitching of the ship, avoid mechanical vibration interference and areas with frequent personnel activities, and build a ship-borne coordinate system.

Step 5: Install multiple marine gravimeters parallel to the ship's axis at the position of the ship's center in step 4. According to the internal structural characteristics of the surveying ship, install them as close as possible to the center axis, and the deviation from the center axis should not exceed 5m. Use the constructed hull coordinates The system accurately measures the position of different types of gravimeters relative to the ship's coordinates, and is used to calculate the position of the measurement results.

Step 6: Multiple gravimeters use the same set of navigation and positioning signals, so that each gravimeter satisfies the unity of position coordinates and time.

Step 7: Ship-borne gravity measurement data processing: Data processing is carried out according to the requirements of the regulations, including base point comparison, zero drift correction, draft change space correction, Utterworth correction, platform inclination calculation, normal gravity calculation, and absolute gravity value of measuring points Calculation and space gravity anomaly calculation, and perform data quality evaluation according to the intersection accuracy and repeating line coincidence accuracy.

Step 8: According to the multi-parameter evaluation system composed of the root mean square error, mutual difference, mutual standard deviation and correlation results of the measurement results, comprehensively evaluate the reliability, stability and accuracy of each type of gravimeter.

Step 9: According to the multi-parameter evaluation results, weighted average of the repeated survey line data to construct the standard value of the comparison survey line gravity. Among them, the selection rules of weights are as follows:

It is considered that the gravity value processed by the shipborne gravity data is the sum of the standard gravity value _Pi of the measuring point and the noise _Ni , namely:

g _ij =P _i +N _ij (1)

Among them: N _ij — is the noise size of the i-th observation on the j-th repeated measurement on the repeated line.

Calculate the measurement value of each gravimeter with respect to the number of repetitions of the measuring line m (m≥3), the measuring point n, and the average value of m and n. The specific formula is as follows:

g _{i ·} =P _i +N _{i ·} (2)

g _{· j} =P _· +N _.j (3)

g _.. =P _. +N _.. (4)

in:

g _i ——the average value of the gravity value measured by a single gravimeter on the repeated line with respect to the number of repetitions m of the measuring line.

N _i· —the average value of the gravity value measured by a single gravimeter on the repeated line with respect to the number of repetitions m of the survey line.

g _j —the average value of the measured gravity anomalies of all measuring points on the jth measurement of a single gravimeter with respect to n.

N _·j —the average value of the noise of all measuring points with respect to n in the jth measurement of a single gravimeter.

P _· —The average value of the true gravity outliers of all measuring points on the repeating line with respect to n.

g _{· ·} —The average value of the gravity anomaly measured on the repeated line of a single gravimeter with respect to the measuring line m and the measuring point n.

N _{· ·} —The average value of the noise measured on the repeated line of a single gravimeter with respect to the measurement line m and the measurement point n.

Combining the above formula, the residual term is calculated, and the expression is as follows:

D _ij =g _ij -g _{i ·} -g _{· j} +g _{· ·} =N _ij -N _i. -N _.j +N _.. (5)

According to the requirement of measuring line length greater than 300km, it is considered that there is enough measuring point data to make the average value of the noise term zero, then the noise level of each gravimeter itself is:

D _ij ≈N _ij (6)

Figure 3 shows the measurement anomalies, theoretical anomalies and noise levels of each survey line in the actual measurement. Use the ratio of the root mean square error value σ _i of each survey line to its corresponding gravimeter noise variance var(D _ij ) to determine the weight of each survey line, and perform a weighted average of the measurement results of each gravimeter to achieve a comparison test. Construction of line standard values.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Those skilled in the art make some simple modifications, equivalent changes or modifications by using the technical contents disclosed above, all of which fall within the scope of the present invention. within the scope of protection of the invention.

Claims (10)

1. a method for constructing an offshore gravity comparison field, is characterized in that, comprising: Determine the stable center of the surveying vessel; Multiple marine gravimeters are installed parallel to the ship's axis, and the constructed hull coordinate system is used to accurately measure the position of different types of gravimeters relative to the ship's coordinates, which is used to calculate the position of the measurement results; Multiple gravimeters use the same set of navigation and positioning signals, so that each gravimeter satisfies the unity of position coordinates and time; Data processing is carried out according to the specification requirements, and data quality evaluation is carried out according to the intersection accuracy and repeating line accuracy; According to the multi-parameter evaluation system composed of the root mean square error, mutual difference, mutual standard deviation and correlation results of the measurement results, the reliability, stability and accuracy of each type of gravimeter are comprehensively evaluated; Use the ratio of the root mean square error value σ _i of each survey line to its corresponding gravimeter noise variance var(D _ij ) to determine the weight of each survey line, and perform a weighted average of the measurement results of each gravimeter to achieve a comparison test. Construction of line standard values. 2. The method for constructing an offshore gravity comparison field according to claim 1, is characterized in that, when multiple marine gravimeters are installed parallel to the ship axis direction, the deviation from the central axis is no more than 5m, and the number of marine gravimeters is no less than 5 m. tower. 3. The method for constructing an offshore gravity comparison field according to claim 1, characterized in that, when performing data processing according to specification requirements, the data processing performed comprises: base point comparison, zero drift correction, draft change space correction, Erte Warsh correction, platform tilt calculation, normal gravity calculation, absolute gravity value calculation of measuring point and space gravity anomaly calculation. 4. offshore gravity comparison field construction method according to claim 1, is characterized in that, also comprises: According to the multi-parameter evaluation results, the weighted average of the repeated survey line data is carried out to construct the gravity standard value of the comparison survey line, and the weight of each survey line is determined. 5. The method for constructing an offshore gravity comparison field according to claim 4, wherein determining the weight of each survey line, comprising: Calculate the measurement value of each gravimeter with respect to the number of repetitions of the measuring line m, the measuring point n, and the average value of m and n; Calculate the residual term, and consider that there are enough measuring points to make the average value of the noise to be zero, so as to obtain the noise level of each gravimeter; The weighted average of the measurement results of each gravimeter realizes the construction of the standard value of the comparison line. 6. The method for constructing an offshore gravity comparison field according to claim 5, wherein calculating the residual term comprises: The residual term is calculated according to the following formula: D _ij =g _ij -g _{i ·} -g _{· j} +g _.. =N _ij -N _{i ·} -N _{· j} +N _{· ·} Among them, g _ij represents the gravity value measured by a single gravimeter on the repeated line with respect to the measurement value of the jth measurement on the i-th survey line, and g _i represents the gravity value measured by a single gravimeter on the repeated line with respect to the i-th measurement line The average value of the repetition times m of a measurement line, g _j represents the average value of the gravity anomalies measured at all measuring points on the jth measurement of a single gravimeter with respect to n, g _.. represents the gravity measured on the repeated line of a single gravimeter The abnormal value is the average value of the measurement line m and the measurement point n, N _ij represents the measurement noise value of the jth measurement point of the i-th measurement line measured by a single gravimeter on the repeated line, N _{i ·} represents a single gravimeter The average value of the _gravity value measured on the repeated line with respect to the number of _repetitions m of the line The noise measured on the line is the average value of line m and point n. 7. The method for constructing an offshore gravity comparison field according to claim 1, further comprising: Before determining the stable center of the survey ship, select the survey carrier for offshore operations. 8 . The method for constructing an offshore gravity comparison field according to claim 7 , wherein the selected marine operation measurement carrier comprises: a scientific research vessel of 4500 tons or more. 9 . 9. The method for constructing an offshore gravity comparison field according to claim 7, further comprising: Before selecting the measurement carrier for offshore operations, according to the design principle of the comparison field measurement line, the comparison field measurement line is designed, and the length of the measurement line is greater than 300km. 10. The method for constructing an offshore gravity comparison field according to claim 9, further comprising: According to the design principle of the comparison field survey line, before designing the comparison field survey line, select the offshore gravity comparison field area. Uplift, the abnormal gravity fluctuation is greater than 50mGal.

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