A magnetic compensation test device and magnetic compensation method for seabed columnar sampling technology

Abstract

The invention relates to the technical field of marine magnetism research, and discloses a magnetic compensation test device for a seabed columnar sampling technology and a magnetic compensation method thereof. The device comprises a rotating table, a seabed sediment columnar sampler can be placed on the top of the rotating table, a magnetic compass is installed on the sampler, and the rotating table can drive the sampler to rotate around itself on a horizontal plane and adjust the placement angle of the sampler on a vertical plane. In view of the shortcomings of a vertical rotating platform such as large volume and weight, high manufacturing cost, and great difficulty in operation and maintenance, the invention proposes an innovative technology of tilting a seabed sediment columnar sampler for magnetic compensation correction based on the working principle of the magnetic compass and experimental data, and accordingly improves an effective and feasible magnetic compensation test scheme. The invention has low manufacturing cost, simple operation and maintenance, safety and reliability, and important value for popularization and application.

Description

Technical Field

[0001] The invention relates to the technical field of marine magnetism research, and more specifically to a magnetic compensation test device for seabed columnar sampling technology and a magnetic compensation method thereof. Background Art

[0002] In marine magnetic research, by collecting seabed sediment samples, measuring the residual magnetism of sediments and collating data, the information on the paleomagnetic field changes recorded during the sedimentation process can be effectively revealed. The general procedure is: first, collect paleomagnetic samples in the field and orient the samples; second, measure the residual magnetism information indoors; finally, restore the recorded information of the paleomagnetic field in the samples by conversion. In land areas, the threshold of the directional technology supporting sample collection is low and easy to implement, so the current land paleomagnetic directional sampling has become a routine technology. However, in the sea area, due to the limitations of seabed directional technology, it is difficult to equip the sampler with a directional azimuth in deep-sea sediment paleomagnetic sampling. Therefore, the current deep-sea sediment paleomagnetic sampling only has up and down directional information, and the marine sediment magnetic research only has information on the change of magnetic inclination with depth. In addition, the magnetic inclination in the mid- and low-latitude sea areas is small and the resolution is low. If there is no magnetic declination information, it will seriously affect the quality of the research results of marine sediment paleomagnetic research, making the research work have regional limitations. Therefore, performing magnetic compensation correction before directional sampling of seabed sediments is crucial to promoting the development of this discipline and solving more scientific problems.

[0003] Traditional orientation equipment is usually divided into two categories: "fiber optic inertial navigation" and "magnetic compass orientation". Among them, fiber optic gyroscope (also known as north finder) technology is not affected by the magnetic and electromagnetic interference of submarine equipment, and the system has high orientation accuracy, but it has a complex structure, high price, high power consumption and large time accumulation error, which makes it difficult to meet the needs of rapid orientation in engineering applications. Vector magnetometer, also known as magnetic compass, is simple and convenient, and can quickly and continuously collect attitude measurement information; but the magnetic compass is easily affected by the environmental magnetic field around the equipment, especially since most submarine equipment is made of ferromagnetic materials. The additional magnetic field generated by the equipment will cause measurement errors (often called compass error), and compass error correction (magnetic compensation) is required to suppress the interference of the additional magnetic field.

[0004] The geological sampling equipment used for paleomagnetism research of seabed sediments is usually a seabed sediment gravity column sampler. Due to the limitations of seabed sampling equipment and technology, the sampling length of the column sampler is generally in the range of several meters to tens of meters, usually within ten meters. If you want to obtain longer cores, there will be special requirements for the size and weight of the column sampler, the breaking force of the geological winch and cable and other technical performance. If you want to obtain information on the posture of the seabed sampling process, you need to install a magnetic compass on the sampling tube or the load-bearing head of the column sampler. Before or after sampling, it is necessary to perform a compass test on the sampling equipment equipped with a magnetic compass, and then perform magnetic compensation correction.

[0005] To perform magnetic compensation correction on a seabed sediment column sampler equipped with a magnetic compass, the following tasks need to be done: 1) Select a weak magnetic or small gradient magnetic environment; 2) Build a platform that can rotate the column sampler equipped with a magnetic compass in an open area; 3) Rotate it several times clockwise and counterclockwise with a high-precision directional device, and simultaneously record the directional measurement information of both. If the gravity sampler equipped with a magnetic compass is corrected in a vertical posture and then rotated several times clockwise or counterclockwise, taking a 6-meter columnar sampling tube as an example, a non-magnetic tower over 7.5 meters high needs to be built (the ratio of the sampling tube length to the tower height is 0.8).

[0006] Given the limitations of factors such as the weight of the columnar sampler itself and the strength of engineering plastic materials, when building a rotating platform on a tower, issues such as manufacturing difficulty, operation and maintenance difficulty, cost, and safety hazards must be considered. Summary of the invention

[0007] In view of the problems existing in the prior art, the primary purpose of the present invention is to provide a safe, reliable, simple to manufacture, low-cost magnetic compensation test device for seabed columnar sampling technology, so as to overcome the problems of high cost and high operation and maintenance difficulty of the rotating platform in the prior art.

[0008] The above-mentioned purpose of the present invention is achieved through the technical solution of the following device:

[0009] A magnetic compensation test device for seabed sediment columnar sampling technology, the device comprises a rotating table, a seabed sediment columnar sampler is placed on the top of the rotating table, the seabed sediment columnar sampler comprises a sampling tube, a bearing head and a sampling port in sequence along the length extension direction, a magnetic azimuth meter is installed at the front end of the sampling tube, the rotating table can drive the seabed sediment columnar sampler to rotate around itself on a horizontal plane, and adjust the placement angle of the seabed sediment columnar sampler on a vertical plane.

[0010] As a further optimization scheme of the device of the present invention, the rotating table comprises, from bottom to top, a rotating platform, a base for raising the sampler, and a swing frame for adjusting the placement angle of the sampler. The rotating platform is used to drive the base and the swing frame thereon to rotate along itself. The swing frame is rotatably connected to the base, and can adjust the inclination angle of the seabed sediment columnar sampler when it is placed.

[0011] As a further optimization scheme of the device of the present invention, the rotating platform is provided with an upper base plate and a lower base plate which are parallel to each other, and the two base plates are movably connected by a rotating shaft. A plurality of guide rollers are installed on the bottom wall of the upper base plate along the circumference of the rotating shaft, and the lower wheel surface of the guide roller abuts against the top wall of the lower base plate, thereby realizing the mutual rotation of the two base plates.

[0012] As a further optimization solution of the device of the present invention, the lower base plate is penetrated by a plurality of downward leveling bolts, and the leveling bolts are evenly distributed along the circumference of the rotating shaft and are used for level correction of the rotating table.

[0013] As a further optimization scheme of the device of the present invention, the bottom of the base is connected to the top surface of the upper base plate, and the base is an upright square frame structure with the swing frame placed inside. The two parallel side walls of the base are provided with base through holes distributed along the same axis near the top area, and the swing frame is aligned with the base through holes through its corresponding hole positions and pivotally connected; the top surface of the swing frame is provided with more than two grooves arranged in a straight line, and the load-bearing head is placed in the groove, and the axis of the groove is perpendicular to the axis of the base through hole, so that the sediment column sampler can swing up and down around the through hole of the base.

[0014] As a further optimization scheme of the device of the present invention, a fiber optic compass is fixedly installed on the rotating platform, and the magnetic azimuth meter is internally configured with a three-component fluxgate magnetometer sensor and an inclination sensor, and the 0° pointing of the fiber optic compass and the magnetic azimuth meter are consistent; wherein the fiber optic compass gives a reference value of the heading angle of the rotating platform, the three-component fluxgate magnetometer sensor is used to measure the three-axis components and the magnetic heading angle in the carrier coordinate system where the magnetic azimuth meter is located, and the inclination sensor is used to measure the rock angle and pitch angle of the magnetic azimuth meter, and the above data are used to calculate the heading angle of the magnetic azimuth meter in the magnetic geographic coordinate system after magnetic compensation.

[0015] Secondly, the second object of the present invention is to provide a magnetic compensation correction method using the device of the present invention, which is achieved by the following method and technical solution:

[0016] A magnetic compensation method for directional measurement of seabed sediment columnar sampling technology, using the aforementioned magnetic compensation test device, comprises the following steps:

[0017] (1) The magnetic compensation test device is placed in the designated test site, and the optical fiber compass and magnetic azimuth meter are horizontally calibrated using the rotating table. The heading angle of the optical fiber compass and the magnetic field vector and attitude information of the magnetic azimuth meter are collected respectively, and the heading angle of the magnetic azimuth meter before compass compensation is calculated;

[0018] (2) performing a compass error compensation calculation, including calculating the optical fiber compass measurement data obtained in step (1) to obtain a compass error compensation coefficient;

[0019] (3) The heading angle of the magnetic azimuth instrument before compass compensation calculated in step (1) and the compass compensation coefficient calculated in step (2) are calculated to obtain the heading angle information of the magnetic azimuth instrument after compass compensation; after the magnetic declination correction, the heading angle measured by the magnetic azimuth instrument can be converted into the heading angle in the geographic coordinate system.

[0020] As a further optimization scheme of the method of the present invention, in the step (1), there are special requirements for the test site. The background geomagnetic field of the site should be centered on the placement of the test site equipment. The horizontal gradient of the total intensity F is uniformly distributed on the cross lines of 10 m in the east-west and north-south directions, and is not greater than 5 nT / m; within the range of 2 m above, the vertical gradient of the total intensity F is not greater than 5 nT / m.

[0021] As a further optimization scheme of the method of the present invention, in the step (2), the method for measuring and calculating the compass compensation coefficient of the seabed sediment columnar sampler is as follows: select a test site, transport the seabed sediment columnar sampler and the rotating platform equipment to the pre-selected site, level the rotating platform and rotate it clockwise along the horizontal plane for two circles, with a sampling interval of 2s, and pause for recording every 15° rotation to obtain clockwise recorded data; then rotate the rotating platform counterclockwise for 2 circles, and collect data in the same way as in the clockwise direction; when the fiber optic compass and magnetic azimuth are When the instruments work synchronously, two sets of data are generated: the first set of data is the numerical value of the azimuth and attitude information of the magnetic azimuth meter changing with time, and the second set of data is the data of the heading angle of the fiber optic compass changing with time; each set of data is screened and the average value is calculated as the measurement result, and several sets of measurement time, fiber optic compass reference value and magnetic azimuth meter measurement value are obtained; the data obtained by the fiber optic compass and the magnetic azimuth meter are averaged, a set of data is extracted every 15° and averaged to obtain 24 sets of calculated values, and then the compass error compensation coefficient of the operating site is obtained through the magnetic compensation algorithm.

[0022] As a further optimization scheme of the method of the present invention, the specific method of obtaining the compass error compensation coefficient of the operating site and the magnetic field value after eliminating the compass error by the magnetic compensation algorithm is as follows:

[0023] The first step is to establish a coordinate system on the device where the magnetic compass is installed as the carrier coordinate system; when the magnetic compass is in a certain state, the rock angle measured by the inclination sensor is θ, the pitch angle is Φ, and the magnetic field vector under the fluxgate sensor carrier coordinate system XYZ is X', Y', Z', then the heading angle of the magnetic compass before compass compensation is The calculation process is as follows:

[0024]

[0025]

[0026] in:

[0027]

[0028] In actual measurement operations, due to the presence of additional magnetic fields in the working environment, the heading angle output by the magnetic azimuth instrument needs to be Make compass corrections;

[0029] The second step is to substitute the sorted fiber optic compass heading angle data into the error equation formula (1) and the matrix formula (2), and solve the equation group to obtain the compass error compensation coefficient matrix C. Here, A, B, C, D, and E are calculated as the compass error compensation coefficients;

[0030]

[0031]

[0032] in:

[0033]

[0034] The third step is to use the compass compensation obtained in the first step to compensate the heading angle of the magnetic azimuth , and the compass compensation coefficient obtained in the second step are substituted into formula (3) to calculate the total compass error:

[0035]

[0036] The fourth step is to use formula (4) to obtain the heading angle of the magnetic azimuth after compass compensation: :

[0037]

[0038] in, For the total Luocha, The output heading value of the magnetic azimuth instrument before compass compensation, The actual magnetic azimuth in the magnetic geographic coordinate system after compass compensation; the measured data of the magnetic azimuth instrument installed on the seabed sediment column sampler Subtract the total difference , that is, the heading angle value of the magnetic azimuth instrument after compass compensation correction in the magnetic geographic coordinate system can be obtained .

[0039] It should be noted that there is a magnetic declination between the obtained magnetic coordinate north and south poles and the geographic north and south poles, as shown in Figure 6 (b). Only after the local magnetic declination correction can the magnetic azimuth heading angle in the magnetic geographic coordinate system be converted into the heading angle in the geographic coordinate system.

[0040] As a further optimization scheme of the method of the present invention, during the directional sampling process, the inclination angle of the seabed sediment column sampler relative to the horizontal plane must be greater than 15°.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] In the process of seabed sediment column sampling, the sediment column sampler needs to be inserted into the seabed sediment, usually in a vertical or nearly vertical posture, that is, the posture information monitored by the magnetic compass installed on the sampler is also vertical or nearly vertical. If the compass test of the magnetic compensation correction of the column sampler is similar to the posture of the column sampler during actual field operations, then the rotating platform will be built quite high, greatly increasing the production and operation and maintenance costs.

[0043] In view of this technical drawback, the present invention proposes a technical solution for tilting a seabed sediment column sampler at a certain angle for magnetic compensation correction, that is, placing the sediment column sampler with a magnetic azimuth installed on a rotating table. Driven by the rotating table, the sampling instrument can rotate clockwise and counterclockwise in situ, thereby realizing planar compensation correction of magnetic interference; in addition, the sampling instrument can also be tilted relative to the rotating table base and the placement angle can be adjusted, and compensation correction in the tilted state can be realized.

[0044] Due to the flexible structural characteristics of the device of the present invention and the magnetic compensation method under the inclined state, the present invention obtains horizontal orientation information and three-dimensional attitude measurement information in the magnetic geographic coordinate system in the directional sampling of deep-sea sediments. The present invention is also suitable for the situation where the magnetic inclination is small in mid- and low-latitude sea areas, and can effectively obtain magnetic declination information in various sea areas, which to a certain extent promotes the quality and scope of application of paleomagnetic research results of marine sediments.

[0045] The invention has an ingenious design and a simple structure, can reduce the required height and occupied volume of the platform for building, is safe and reliable, and greatly reduces the cost of use. It has a vital and enlightening significance in the technical direction of directional sampling of seabed sediments in the field of marine magnetic research and has significant value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0047] Figure 1 It is the general assembly diagram of the magnetic compensation test device of the present invention;

[0048] Figure 2 It is a structural schematic diagram of the sediment column sampler of the present invention;

[0049] Figure 3 is a schematic structural diagram of the base of this embodiment;

[0050] Figure 4 Schematic diagram of the structure of the swing frame of this embodiment;

[0051] FIG5 (a) is a perspective view of the rotary platform of this embodiment;

[0052] FIG5( b ) is a top view of the rotary platform of this embodiment;

[0053] FIG5( c ) is a partial cross-sectional view of the rotary platform of this embodiment;

[0054] FIG6 (a) is a schematic diagram showing the relationship between the cylindrical sampler coordinate system and the magnetic coordinate system;

[0055] Figure 6 (b) is a schematic diagram of the relationship between the geomagnetic pole and the geographic North Pole;

[0056] Figure 7 This is the comparison curve of the fiber optic compass and magnetic azimuth meter before magnetic compensation;

[0057] Figure 8 is the measurement deviation curve before magnetic compensation;

[0058] Fig. 9 This is the comparison curve of the fiber optic compass and magnetic azimuth meter after magnetic compensation;

[0059] Fig.10 is the measurement deviation curve after magnetic compensation;

[0060] In the figure, 1-rotating table; 11-slewing platform; 111-upper bottom plate; 112-lower bottom plate; 113-rotating shaft; 114-guide roller; 115-leveling bolt; 12-base; 121-base through hole; 122-avoidance groove; 13-swing frame; 131-groove; 132-swing frame through hole; 2-sediment columnar sampler; 21-sampling tube; 22-weight-bearing head; 23-sampling port; 24-magnetic azimuth instrument; 3-fiber optic compass. DETAILED DESCRIPTION

[0061] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0062] like Figure 1 , 2 As shown, this embodiment provides a magnetic compensation test device for a seabed columnar sampling technology, comprising a rotating platform 1, a seabed sediment columnar sampler 2 is arranged on the top of the rotating platform 1, the seabed sediment columnar sampler 2 comprises a sampling tube 21, a bearing head 22 and a sampling port 23 in sequence along the length extension direction, and a magnetic azimuth meter 24 is installed at the front end of the sampling tube 21; the rotating platform 1 comprises a rotating platform 11, a base 12 for raising the sampler, and a swing frame 13 for adjusting the placement angle of the seabed sediment columnar sampler 2 in sequence from bottom to top;

[0063] The OCTANCE fiber optic compass 3 is rigidly mounted on the rotating platform 11 using a non-magnetic copper screw, and the magnetic azimuth meter 24 is internally configured with a three-component fluxgate magnetometer sensor and a MEMS inclination sensor (not shown in the figure), and the 0° pointing of the fiber optic compass 3 and the magnetic azimuth meter must be consistent; the fiber optic compass 3 gives a reference value of the heading angle of the rotating platform 11, the three-component fluxgate magnetometer sensor is used to measure the three-axis components and the magnetic heading angle in the carrier coordinate system where the magnetic azimuth meter 24 is located, and the inclination sensor is used to measure the rock angle and pitch angle of the magnetic azimuth meter 24;

[0064] The rotating platform 11 of the rotating table 1 can drive the seabed sediment column sampler 2 to rotate clockwise and counterclockwise in situ, thereby realizing the plane compensation correction of magnetic interference. The swing frame 13 of the rotating table 1 can also adjust the tilt angle of the seabed sediment column sampler 2 when it is placed, and realize magnetic compensation correction in the tilted state.

[0065] Specifically, as shown in FIG. 5 (a), (b), and (c), the rotary platform 11 is provided with an upper base plate 111 and a lower base plate 112 which are parallel to each other, wherein the lower base plate 112 is penetrated with a plurality of downwardly-pointing leveling bolts 115, and the leveling bolts 115 are evenly distributed along the circumference of the rotating shaft 113 and are used for leveling the rotary table. Before the magnetic compensation test, the user can adjust the screwing length of the leveling bolts 115 appropriately with a leveler or other calibration instrument, so as to achieve the position adjustment of the rotary platform 11. The upper bottom plate 111 and the lower bottom plate 112 are both disc-shaped with the same size, and the two are movably connected at the center of the circle by a rotating shaft 113. A plurality of guide rollers 114 are installed on the bottom wall of the upper bottom plate 111 along the circumference of the rotating shaft 113, and the lower wheel surface of the guide roller 114 abuts against the top wall of the lower bottom plate 112, thereby realizing the smooth rotation of the upper bottom plate 111 relative to the lower bottom plate 112, providing a basis for the magnetic field plane calibration movement of the seabed sediment columnar sampler 2 above the rotating platform 11.

[0066] It is additionally noted that, for a relatively small sampling device, it can also be directly placed on the rotary platform 11 to perform a magnetic compensation correction test.

[0067] like Figure 3 , Figure 4 As shown, in this embodiment, the base 12 is an upright frame structure, in which the swing frame 13 is placed, the bottom of the base 12 is connected to the upper bottom plate 111, and the two parallel side walls of the base 12 are provided with base through holes 121 distributed along the same axis near the top area, and the swing frame 13 is aligned with the base through hole 121 through its corresponding swing frame through hole 132 and pivotally connected to achieve a rotational connection; the top surface of the swing frame 13 is provided with more than two grooves 131 arranged in a straight line, and the load-bearing head 22 is placed in the groove 131, and the axis of the groove 131 is perpendicular to the axis of the base through hole 121, so that the seabed sediment column sampler 2 can swing up and down around the base through hole 121.

[0068] The configuration of the base 12 and the swing frame 13 is a key factor in the present invention to achieve the tilted placement and effective sampling of the seabed sediment columnar sampler 2. The design principle of the lever is referred to, and the load-bearing head 22 is placed on the swing frame 13, that is, the heaviest component in the sampler is placed at the rotation point of the lever mechanism. The structural composition of the seabed sediment columnar sampler 2 itself also makes the arm lengths on both sides of the swing frame 13 differ greatly, forming the advantageous effects that the sampling tube 21 is less stressed on the long arm and easy to adjust the tube body angle, and the load-bearing head 22 is more stressed on the short arm and easy to stabilize the orientation.

[0069] It should be noted that, during the magnetic compensation correction process, the inclination angle of the sampling tube 21, that is, the magnetic compass 24, relative to the horizontal plane must be greater than 15°, preferably 20°. This is because the magnetic compass 24 calculates the heading angle by integrating the measurement data of the three-component fluxgate magnetometer sensor and the inclination sensor. As shown in FIG6 (a), when the magnetic compass 24 is in a certain state, the rock angle measured by the inclination sensor is θ, the pitch angle is Φ, and the magnetic field vector in the three-component fluxgate magnetometer sensor carrier coordinate system (XYZ) is X', Y', Z'. Then the heading angle of the magnetic compass before compass compensation is The calculation process is as follows:

[0070]

[0071]

[0072] in:

[0073]

[0074] Then when θ≈π / 2:

[0075]

[0076] At this time, although the magnetic azimuth meter 24 still has output, H y1 The projection of Y' is no longer included, that is, the measured navigation angle cannot reflect the actual heading angle. In other words, the error of heading measurement is mainly related to the size of the rock angle θ. The larger the rock angle θ, the greater the heading measurement error. When the seabed sediment columnar sampler 2 is placed horizontally, the magnetic azimuth meter 24 cannot even give the actual heading angle, that is, the more inclined it is placed, the smaller the measurement error.

[0077] According to the above principle, in a weak magnetic experimental environment, the applicant compared the measured values ​​of the magnetic compass 24 at multiple placement angles. The results showed that when the rock angle θ of the magnetic compass 24 was kept at no more than 75°, even the measured heading angle When θ is approximately 0° (the sampler is in a vertical state), the deviation between the measured heading angles is less than 1°. Of course, this error will increase with the intensity of the environmental magnetic disturbance.

[0078] Based on the above theoretical principles and experimental data, this technical solution proposes: in order to ensure the accuracy of the magnetic compensation parameter test, during the compass test of the magnetic compensation correction of the seabed sediment column sampler 2, the inclination angle of the seabed sediment column sampler 2 placed on the rotating platform 11 should be greater than 15°.

[0079] In this embodiment, in order to ensure the effective swing of the seabed sediment columnar sampler 2 on the vertical plane, it is recommended that the base 12 is provided with a corresponding avoidance groove 122 on the side wall facing the groove 131. Of course, the top surface of the swing frame 13 can also be set to be higher than the top surface of the base 12 by a certain distance, which can also basically play the role of avoidance, so the avoidance form of the base is not specifically limited here.

[0080] In this embodiment, in order to achieve the above-mentioned strong supporting effect and avoid causing geomagnetic interference in the site, the rotating platform 11, the base 12 and the swing frame 13 are all made of high-strength engineering plastics, and the installation parts such as the leveling bolts 115 are made of non-magnetic materials such as copper and copper alloy.

[0081] In addition, the present embodiment also relates to a magnetic interference compensation method using the above device to comprehensively and accurately obtain magnetic compensation test data for directional measurement of seabed sediment columnar sampling. The method mainly includes two steps: directional measurement magnetic compensation correction test and magnetic interference soft compensation processing:

[0082] Step 1: Conduct magnetic compensation correction test on seafloor sediment columnar sampling directional measurement technology

[0083] 1.1 Select a site with a small magnetic field gradient. According to the requirements for the selection of observation sites for mobile geomagnetic observation networks in the "Technical Requirements for Seismic Network Design - Geomagnetic Observation Network" in the Seismic Industry Standard of the People's Republic of China (DB / T37-2010), the test site should be selected with a flat ground, uniform soil coverage, no buildings and metal garbage piles around, and no buildings and water conservancy facilities around. In addition, with the test site equipment placement as the center, the background geomagnetic field of the site meets the requirements that the horizontal gradient of the total intensity F is evenly distributed on the cross survey line of 10 m in the east-west and north-south directions, and is not greater than 5 nT / m; the vertical gradient of the total intensity F within the range of 2 m above is not greater than 5 nT / m.

[0084] 1.2 Transport the seabed sediment column sampler 2, rotating table 1 and other equipment to the pre-selected test site; place the rotating platform 11 on the flat ground and screw the leveling bolts 115 to adjust it to a horizontal level, hang the seabed sediment column sampler 2 on the swing frame 13, adjust the inclination angle of the seabed sediment column sampler 2 to be greater than 15°, and adjust the center of gravity of the equipment at the same time.

[0085] 1.3 Install the fiber optic compass 3 on the rotary platform 11, wherein the pointer of the fiber optic compass 3 and the pointer of the magnetic azimuth meter 24 must be in the same direction.

[0086] 1.4 Start the power of the fiber optic compass 3 and the magnetic azimuth meter 24, and allow the equipment to stabilize for 30 minutes.

[0087] 1.5 Push the rotary platform 11 to rotate two circles in the clockwise direction, with a sampling interval of 2 s. The recording time for each 15° rotation is not less than 60 s. The first and last records are repeated three times, with a total of 25 records; then rotate it counterclockwise for 2 circles, and the data collection method is the same as the clockwise direction. After screening each set of data, the average value is calculated as the measurement result. In this experiment, a total of 50 sets of measurement time, reference value of fiber optic compass 3 and measurement value of magnetic azimuth 24 are obtained. The azimuth data is averaged, and a set of data (the heading angle of fiber optic compass 3 and the pitch angle, rock angle, and magnetic field vector of magnetic azimuth 24) is extracted every 15° for average calculation to obtain 24 sets of calculated values, and the specific measurements are organized into a table.

[0088] Step 2: Soft compensation for magnetic compensation correction test of seabed sediment columnar sampling directional measurement

[0089] 2.1 A coordinate system is established on the device where the magnetic compass 24 is installed as the carrier coordinate system, wherein a schematic diagram of the relationship between the columnar sampler coordinate system and the magnetic coordinate system is shown in FIG6 (a): The three-component fluxgate magnetometer sensor carrier is selected as the origin of the magnetic compass coordinate system. In step 1.5, the rock angle and the pitch angle obtained by the inclination sensor are θ and Φ, respectively. The magnetic field vectors under the three-component fluxgate magnetometer sensor carrier coordinate system (XYZ) are X', Y', and Z'. Then the heading angle of the magnetic compass before compass compensation is The calculation process is as follows:

[0090]

[0091]

[0092] in:

[0093]

[0094] 2.2 Substitute the 24 sets of fiber optic compass heading angle data measured in step 1.5 into the error equation such as formula (1) and matrix formula (2), and solve the equation group to obtain the compass compensation coefficient C. Here, the compass compensation coefficients are calculated as A, B, C, D, and E;

[0095]

[0096]

[0097] in:

[0098]

[0099] 2.3 The output heading angle of the magnetic azimuth instrument 24 before the compass compensation calculated in step 2.1 is Find the average and substitute it together with the compass compensation coefficient calculated in step 2.2 into formula (3) to calculate the total compass error:

[0100]

[0101] 2.4 Use formula (4) to obtain the magnetic heading angle after compass compensation: :

[0102]

[0103] in, For the total Luocha, The output heading value of the magnetic azimuth instrument before compass compensation, is the actual magnetic azimuth in the magnetic geographic coordinate system after compass compensation; the measured data of the magnetic azimuth meter 24 installed on the seabed sediment columnar sampler 2 Subtract the total difference , that is, the heading angle value after compass compensation correction of the magnetic geographic coordinate system can be obtained .

[0104] Of course, it should be understood that, as shown in Figure 6 (b), since there is a magnetic declination between the magnetic coordinate north and south poles of the magnetic compensation test point and the geographic north and south poles, the heading angle value under the magnetic geographic coordinates can only be obtained after being corrected by the local magnetic declination.

[0105] After the soft compensation of magnetic interference, the accuracy of the magnetic azimuth meter 24 needs to be evaluated. The specific method is to use the measured value of the reference device as the reference value (i.e. the measured value of the optical fiber compass 3) and the measured data after compensation calculation as the reference value. The difference between the reference value and the compass value can be used to calculate the system error value after compass compensation, including the maximum and minimum errors and their error range.

[0106] In order to demonstrate the effect of the present invention, this embodiment uses a sediment columnar sampler including a 6-meter sampling tube and a 1.5-meter bearing head, with an inclination angle of 20 degrees and a rotating table height of about 2.3 meters, and compares the measurement errors before and after magnetic compensation. The specific data can be seen in the attached Figure 7-10 Graph of the curve.

[0107] in Figure 7 and Fig. 9 The comparison curves of the fiber optic compass 3 and the magnetic azimuth meter before and after magnetic compensation are shown respectively (the solid curve is the heading angle curve of the fiber optic compass 3, and the hollow curve is the heading angle curve of the magnetic azimuth meter); Figure 8 and Fig.10 The measurement deviation (compass) curves before and after magnetic compensation are shown respectively.

[0108] The results show that: through the magnetic compensation correction method of the present invention, the measurement value obtained by the tilted magnetic azimuth instrument is almost equal to that of the horizontally placed optical fiber compass 3, the measurement curves are close to overlap, and there is no obvious measurement error. That is, the magnetic compensation correction method of the present invention can overcome the magnetic interference of the seabed sediment columnar sampler, and the tilted magnetic compensation correction method does not affect the technical effect of the sampler.

[0109] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the scope of protection of the present invention.

Claims

1. A magnetic compensation method for directional measurement using a seabed columnar sampling technique, using a magnetic compensation test device using a seabed columnar sampling technique, characterized in that: The magnetic compensation test device of the seabed columnar sampling technology comprises a rotating platform, a seabed sediment columnar sampler is placed on the top of the rotating platform, the seabed sediment columnar sampler comprises a sampling tube, a bearing head and a sampling port in sequence along the length extension direction, a magnetic azimuth meter is installed at the front end of the sampling tube, and the rotating platform can drive the seabed sediment columnar sampler to rotate around itself on the horizontal plane and adjust the placement angle of the seabed sediment columnar sampler on the vertical plane; The rotating platform is composed of a rotating platform, a base for raising the sampler, and a swing frame for adjusting the sampler placement angle from bottom to top. The rotating platform is used to drive the base and the swing frame thereon to rotate along itself. The swing frame is rotatably connected to the base to adjust the tilt angle of the seabed sediment columnar sampler when it is placed. The optical fiber compass is fixedly installed on the rotary platform, and the magnetic azimuth meter is internally provided with a three-component fluxgate magnetometer sensor and an inclination sensor, and the 0° pointing of the optical fiber compass and the magnetic azimuth meter are consistent; The fiber optic compass gives a reference value of the heading angle of the slewing platform, the three-component fluxgate magnetometer sensor is used to measure the three-axis components and the magnetic heading angle in the carrier coordinate system where the magnetic compass is located, and the inclination sensor is used to measure the rock angle and pitch angle of the magnetic compass. The above data are used to calculate the heading angle of the magnetic compass after magnetic compensation in the magnetic geographic coordinate system; The method comprises the following steps: (1) The magnetic compensation test device is placed in the designated test site, and the optical fiber compass and magnetic azimuth meter are horizontally calibrated using the rotating table. The heading angle of the optical fiber compass and the magnetic field vector and attitude information of the magnetic azimuth meter are collected respectively, and the heading angle of the magnetic azimuth meter before compass compensation is calculated; (2) performing a compass error compensation calculation, including calculating the optical fiber compass measurement data obtained in step (1) to obtain a compass error compensation coefficient; (3) Calculating the heading angle of the magnetic azimuth instrument before compass compensation obtained in step (1) and the compass compensation coefficient calculated in step (2) to obtain the heading angle information of the magnetic azimuth instrument after compass compensation; after the magnetic declination correction, the heading angle measured by the magnetic azimuth instrument can be converted into the heading angle in the geographic coordinate system; In the step (2), the method for measuring and calculating the compass compensation coefficient of the seabed sediment column sampler is as follows: select a test site, transport the seabed sediment column sampler and the rotating platform to the pre-selected site, level the rotating platform and rotate it clockwise along the horizontal plane for two circles, and the sampling interval is 2 s, pause and record every 15° rotation, and obtain the clockwise recorded data; then rotate the rotating platform counterclockwise for 2 circles, and the data collection method is the same as the clockwise direction; when the fiber optic compass and the magnetic azimuth meter work synchronously, two sets of data are produced: the first set of data is the value of the azimuth and attitude information of the magnetic azimuth meter changing with time, and the second set of data is the data of the heading angle of the fiber optic compass changing with time; each set of data is screened and the average value is calculated as the measurement result, and several sets of measurement time, fiber optic compass reference value and magnetic azimuth meter measurement value are obtained; the data obtained by the fiber optic compass and the magnetic azimuth meter are averaged, a set of data is extracted every 15° and averaged, 24 sets of calculated values ​​are obtained, and then the compass error compensation coefficient of the operating site is obtained through the magnetic compensation algorithm; The specific method for obtaining the compass error compensation coefficient of the operating site and the magnetic field value after eliminating the compass error by the magnetic compensation algorithm is as follows: The first step is to establish a coordinate system on the device where the magnetic compass is installed as the carrier coordinate system; when the magnetic compass is in a certain state, the rock angle measured by the inclination sensor is θ, the pitch angle is Φ, and the magnetic field vector under the fluxgate sensor carrier coordinate system XYZ is X', Y', Z', then the heading angle of the magnetic compass before compass compensation is The calculation process is as follows: ； ； in: ； The second step is to substitute the sorted fiber optic compass heading angle data into the error equation formula (1) and the matrix formula (2), and solve the equation group to obtain the compass error compensation coefficient matrix C. Here, A, B, C, D, and E are calculated as the compass error compensation coefficients; ； ； in: ； The third step is to use the compass compensation obtained in the first step to compensate the heading angle of the magnetic azimuth , and the compass compensation coefficient obtained in the second step are substituted into formula (3) to calculate the total compass error: ； The fourth step is to use formula (4) to obtain the heading angle of the magnetic azimuth after compass compensation: : ； in, For the total Luocha, The output heading value of the magnetic azimuth instrument before compass compensation, The actual magnetic azimuth in the magnetic geographic coordinate system after compass compensation; the measured data of the magnetic azimuth instrument installed on the seabed sediment column sampler Subtract the total difference , that is, the heading angle value of the magnetic azimuth instrument after compass compensation correction in the magnetic geographic coordinate system can be obtained .

2. The magnetic compensation method for directional measurement of seabed columnar sampling technology according to claim 1, characterized in that: The revolving platform is provided with an upper base plate and a lower base plate which are parallel to each other. The two base plates are movably connected by a rotating shaft. A plurality of guide rollers are installed on the bottom wall of the upper base plate along the circumference of the rotating shaft. The lower wheel surface of the guide roller abuts against the top wall of the lower base plate, thereby realizing the mutual rotation of the two base plates.

3. The magnetic compensation method for directional measurement of seabed columnar sampling technology according to claim 2 is characterized in that: The lower base plate is penetrated by a plurality of downward leveling bolts, and the leveling bolts are evenly distributed along the circumference of the rotating shaft and are used for leveling the rotating table.

4. The magnetic compensation method for directional measurement of seabed columnar sampling technology according to claim 2, characterized in that: The bottom of the base is connected to the top surface of the upper base plate. The base is an upright square frame structure with the swing frame placed inside. The two parallel side walls of the base are provided with base through holes distributed along the same axis near the top area. The swing frame is aligned with the base through holes through its corresponding hole positions and pivotally connected. The top surface of the swing frame is provided with more than two grooves arranged in a straight line. The load-bearing head is placed in the grooves. The axis of the groove is perpendicular to the axis of the base through hole, so that the sediment column sampler can swing up and down around the through hole of the base.

5. The magnetic compensation method for directional measurement of seabed columnar sampling technology according to claim 1, characterized in that: In step (1), the test environment should be such that the background geomagnetic field of the test site is centered on the equipment placement, and the horizontal gradient of the total intensity F is uniformly distributed along the cross lines of 10 m in the east-west and north-south directions, and is not greater than 5 nT / m; within the range of 2 m above, the vertical gradient of the total intensity F is not greater than 5 nT / m.

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