A method for obtaining continuous magnetic declination

Abstract

The present invention provides a method for obtaining continuous magnetic declination. First, a first geomagnetic theodolite is set up in the target area, and the voltage-time series data is stored in real time through a continuous data acquisition board. Then, the initial reading of the horizontal dial is set, the horizontal dial is finely adjusted and left stationary after fine adjustment, and the difference between the reading after each fine adjustment and the initial reading, the corresponding voltage value, and the corresponding time before and after fine adjustment and stationary are recorded. The magnetic declination grid value is calculated, and the continuous magnetic declination sequence data is calculated and generated. Finally, the second geomagnetic theodolite set up in the target area is used for absolute measurement of magnetic declination, and the generated magnetic declination sequence data is calibrated according to the measurement results. The present invention collects the voltage signal that can represent the magnetic signal and calibrates it through the measured data. The calibrated continuous magnetic declination data obtained can accurately reflect the magnetic declination value at any time, successfully solving the current situation of difficult or inaccurate acquisition of magnetic declination diurnal variation information due to the shortage of geomagnetic stations.

Description

Technical Field

[0001] The present invention relates to a method for obtaining a continuous magnetic declination, belonging to the technical field of geomagnetic element measurement. Background Art

[0002] Magnetic declination refers to the angle between the projection of the magnetic induction intensity vector in the horizontal direction and the true north direction, that is, the angle between magnetic north and true north, and it is usually stipulated that eastward deviation is positive. Measuring magnetic declination can provide a reliable azimuth reference for military (civilian) navigation and aviation activities, especially when navigation satellites are unavailable and when it is impossible to use star orientation during the day; in addition, measuring magnetic declination can also provide data or technical support for research and applications in many fields such as geophysical exploration, earthquake prediction, space weather forecasting, mine engineering, tunnel engineering, underwater navigation, indoor and underground navigation, etc.

[0003] At present, the measurement of magnetic declination can be carried out based on fixed electromagnetic stations for long-term continuous tracking observations. However, the site selection and infrastructure construction standards of geomagnetic stations are very high, and the number of stations is limited. Due to the strong time-varying characteristics of the geomagnetic field, the magnetic declination observation results usually need to be corrected for daily variation according to the data of nearby geomagnetic stations. The number of stations in the current International Geomagnetic Reference Field (INTERMAGNET) has exceeded 150, and the number of stations worldwide is increasing year by year. However, due to the regional variation characteristics of the geomagnetic field, with an average spacing of 1000 kilometers (if ocean areas are considered, the average spacing will exceed 2000 kilometers), it is always difficult to meet the high-precision daily variation correction requirements in any region.

[0004] In the domestic situation, as of April 2020, the China Earthquake Administration has built a geomagnetic reference network including 46 reference stations (with an average spacing of more than 600 kilometers), a geomagnetic basic network including 97 basic stations (with an average spacing of more than 200 kilometers), and a geomagnetic mobile network including 1385 mobile stations (with an average spacing of more than 70 kilometers). However, in the western region or the far sea area of China, such a distribution is still difficult to meet the requirements of high-precision continuous measurement.

[0005] In addition, accurate magnetic declination can be obtained through a geomagnetic theodolite. However, to obtain high-precision continuous measurement results in this way requires staff to continuously observe for a long time, which does not conform to the actual operation situation and is difficult to achieve. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for obtaining a continuous magnetic declination to solve the problem of difficult acquisition of high-precision continuous magnetic declination at present.

[0007] The present invention proposes a method for obtaining a continuous magnetic declination, and the method includes the following steps:

[0008] 1) Set up the first geomagnetic theodolite within the target area, connect a continuous data acquisition board at the geomagnetic zero detector end to convert the magnetic signal into an electrical signal and store it in real time to obtain voltage-time series data;

[0009] 2) Adjust the vertical circle of the geomagnetic theodolite to 90° or 270°; set the initial reading of the horizontal circle, finely adjust the horizontal circle and then let it stand still each time. Record the difference between the horizontal circle reading and the initial reading after each fine adjustment, the corresponding voltage value, and the corresponding time at the start and after the fine adjustment and standing still each time;

[0010] 3) Calculate the magnetic declination grid value based on the obtained difference, corresponding voltage value, and the time at the start and after the fine adjustment and standing still each time for each fine adjustment;

[0011] 4) Calculate and generate continuous magnetic declination sequence data according to the calculated magnetic declination grid value and the obtained voltage-time series data;

[0012] 5) Set up the second geomagnetic theodolite within the target area, conduct absolute magnetic declination measurement according to the set measurement interval to obtain the absolute magnetic declination measurement result, and calibrate the generated continuous magnetic declination sequence data according to the absolute magnetic declination measurement result so that the calibrated continuous magnetic declination sequence is aligned with the absolute magnetic declination measurement result at the same moment.

[0013] The present invention proposes a method for obtaining continuous magnetic declination. By using the first geomagnetic theodolite set up within the target area, the voltage signal that can represent the magnetic signal is collected; then, the magnetic declination grid value is calculated based on the difference and voltage value during multiple fine adjustments of the horizontal circle, and then the continuous magnetic declination sequence data is calculated according to the collected voltage signal and the magnetic declination grid value; finally, according to the absolute magnetic declination measurement result obtained by measuring with the second geomagnetic theodolite within the target area, the continuous magnetic declination sequence data is calibrated to generate accurate continuous magnetic declination data, successfully solving the current situation of difficult or inaccurate acquisition of magnetic declination diurnal variation information due to the shortage of geomagnetic stations.

[0014] Further, in order to accurately calculate the magnetic declination grid value, in step 3), the voltage value obtained needs to be corrected for diurnal variation before calculating the magnetic declination grid value. The calculation formula is:

[0015]

[0016]

[0017] In the formula, U i is the voltage value at the i-th fine adjustment, δU i is the diurnal variation correction of the voltage, is the voltage value after diurnal variation correction, n is the number of fine adjustments and is an odd number, T (i) qis the corresponding time when the i-th fine-tuning starts, T (i) z is the corresponding time after the i-th fine-tuning and standing still.

[0018] Furthermore, the calculation formula for the magnetic declination grid value in step 3) is:

[0019]

[0020] In the formula, k is the magnetic declination grid value, ΔD i is the difference between the horizontal circle reading and the initial reading during the i-th fine-tuning, is the voltage value after daily variation correction, and n is the total number of fine-tuning times and is an odd number.

[0021] Furthermore, in order to ensure the accuracy of the magnetic declination grid value calculation, the circle readings of the horizontal circle after fine-tuning in step 2) need to be distributed on both sides of the initial reading, and the difference between the horizontal circle reading after each fine-tuning and the initial reading needs to be within 1′ to 30′.

[0022] Furthermore, in order to simplify the calculation of the magnetic declination variation, the initial reading in step 2) is the horizontal circle reading when the voltage reading of the zero detector is 0.

[0023] Furthermore, in order to ensure the accuracy of continuous magnetic declination data calibration, the set measurement interval time in step 5) needs to be less than 12 hours.

[0024] Furthermore, in order to ensure the consistency of the data measured by two electromagnetic theodolites at the same moment and avoid signal interference caused by too close a distance, the distance between the second geomagnetic theodolite and the first geomagnetic theodolite in step 5) needs to be within 3 to 5 meters.

[0025] Furthermore, in order to avoid inaccurate measurement caused by too long or too short standing still time, the standing still time after each fine-tuning in step 2) is within 1′ to 1′30″.

[0026] Furthermore, in order to facilitate the calculation of the magnetic declination variation at any time, step 4) also needs to eliminate outliers from the generated magnetic declination sequence data and perform fitting based on the magnetic declination sequence data after elimination to obtain the relationship between the magnetic declination variation and time.

[0027] Furthermore, in order to quickly obtain accurate magnetic declination sequence data, the calibration process in step 5) is: vertically translate the magnetic declination sequence data according to the measured absolute magnetic declination measurement result. Description of the Drawings

[0028] Figure 1 is the specific flowchart for obtaining continuous magnetic declination of the present invention;

[0029] Figure 2 It is the continuous magnetic declination sequence diagram after abnormal signals are removed in the embodiments of the present invention;

[0030] Figure 3 It is the signal frequency spectrum diagram of the continuous magnetic declination sequence in the embodiments of the present invention;

[0031] Figure 4 It is the continuous magnetic declination sequence diagram after calibration in the embodiments of the present invention;

[0032] Figure 5 It is the relationship diagram among the true azimuth, magnetic azimuth, and magnetic declination. Specific Embodiments

[0033] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0034] The present invention proposes a method for obtaining a continuous magnetic declination, and the specific process is as Figure 1 shown. First, set up a first geomagnetic theodolite in the target area, connect a continuous data acquisition board at the geomagnetic zero detector end to store the voltage-time series data in real time; set the initial reading of the horizontal dial, finely adjust the horizontal dial and let it stand still after fine adjustment, record the difference between the horizontal dial reading after each fine adjustment and the initial reading, the corresponding voltage value, the corresponding time during and after fine adjustment, and calculate the magnetic declination grid value; then calculate and generate continuous magnetic declination sequence data based on the obtained voltage sequence data and magnetic declination grid value; finally, use the second geomagnetic theodolite set up in the target area to perform absolute magnetic declination measurement at a set interval, and calibrate the generated magnetic declination sequence data according to the obtained absolute magnetic declination measurement result, so that the calibrated continuous magnetic declination sequence is aligned with the absolute magnetic declination measurement result at the same moment. The present invention collects the voltage signal that can represent the magnetic signal and calibrates it with the measured data. The calibrated continuous magnetic declination data obtained can accurately reflect the magnetic declination value at any moment, successfully solving the current situation of difficult or inaccurate acquisition of magnetic declination diurnal variation information due to the shortage of geomagnetic stations.

[0035] Step 1. Obtain continuous voltage-time series data

[0036] Set up a geomagnetic theodolite in the target area. The geomagnetic zero detector can convert the magnetic signal obtained by the fluxgate into an electrical signal. In the present invention, a continuous data acquisition board is connected at the geomagnetic zero detector end to store the voltage value output by the fluxgate in real time and generate voltage-time series data.

[0037] Before data acquisition, it is necessary to carry out measuring point layout and true azimuth calculation first. According to the maps, images and other data of the target area, initially plan the erection position of the first geomagnetic theodolite; use the first geomagnetic theodolite as a diurnal variation station to obtain voltage time series data through long-term observation; conduct on-site survey according to the actual characteristics of the area and the magnetic distribution of ground objects to layout the specific diurnal variation station. For example, the layout needs to be in an open area without obstruction and avoid high-voltage, power supply, water supply pipelines and other places; finally, at the selected diurnal variation station position, erect the first geomagnetic theodolite, center and level it, and conduct data observation.

[0038] In this embodiment, the MAG-01H geomagnetic theodolite is used as the first geomagnetic theodolite. Assuming a certain airport as the target area, according to the above requirements for measuring point layout, the geomagnetic theodolite is erected at the selected measuring point position, and the magnetic declination diurnal variation data of a certain airport is continuously measured for 48 hours to obtain the voltage time series data in this area.

[0039] Step 2. Fine-tune the horizontal dial to obtain corresponding data

[0040] In order to convert the obtained voltage sequence data into corresponding magnetic declination sequence data, it is necessary to calculate the magnetic declination grid value first. For this purpose, record the data required for calculating the magnetic declination grid value by fine-tuning the horizontal dial. The fine-tuning process is as follows:

[0041] First, adjust the vertical dial of the geomagnetic theodolite and set it to 90° or 270°; rotate the sighting part of the geomagnetic theodolite horizontally until the reading of the zero detector is zero, record the time and the horizontal dial reading, and take the horizontal dial reading at this time as the initial reading;

[0042] Then, fine-tune the horizontal dial n times to make the dial readings equal to different readings in turn, and record the difference between the horizontal dial reading after each fine-tuning and the initial reading; after each fine-tuning, let it stand for a period of time, record the corresponding time during and after each fine-tuning. After n fine-tunings, adjust the horizontal dial back to the initial reading, and then let it stand until the entire measurement activity ends. Among them, in order to ensure the accuracy of the magnetic declination grid value calculation, when fine-tuning the horizontal dial, the dial readings should be symmetrically distributed on both sides of the initial reading, and the reading difference should be controlled within the range of 1′ to 30′. Generally, n is an odd number; the standing time after each fine-tuning should not be too short or too long, and should be controlled within 1′ to 1′30″.

[0043] In this embodiment, rotate the sighting part of the horizontal rotation geomagnetic theodolite until the reading of the zero detector is zero, record the time and the horizontal dial reading, and assume that the horizontal dial reading at this time is C0; finely adjust the horizontal dial so that the dial readings are successively equal to C0 + 1′, C0 + 2′, C0 + 5′, C0 + 10′, C0 + 20′, C0, C0 - 1′, C0 - 2′, C0 - 5′, C0 - 10′, C0 - 20′, for a total of 11 fine adjustments. Record the difference between the horizontal dial reading after the i-th fine adjustment and C0 as ΔD i and the corresponding voltage value U i , then the differences between the horizontal dial readings after each fine adjustment and the initial reading are 1′, 2′, 5′, 10′, 20′, 0, -1′, -2′, -5′, -10′, -20′; the standing time after each fine adjustment is within 1′ to 1′30″, and record the corresponding time (T (i) q (i = 1, 2, …, 11)) at the start of each fine adjustment and the corresponding time (T (i) z (i = 1, 2, …, 11)) after standing after the fine adjustment. After 11 fine adjustments are completed, adjust the dial back to C0, and then stand still until the entire measurement activity ends.

[0044] Step 3. Calculation of magnetic declination grid value

[0045] Calculate the magnetic declination grid value according to the differences, corresponding voltage values, and corresponding times at the start of fine adjustment and after standing recorded in Step 2. Among them, the formula (1) and formula (2) need to be used to perform daily variation correction on the obtained voltage values first.

[0046]

[0047]

[0048] In the formula, U i is the voltage value at the i-th fine adjustment, δU i is the daily variation correction of the voltage, is the voltage value after daily variation correction, n is the number of fine adjustments and is odd, T (i) q is the corresponding time at the start of the i-th fine adjustment, T (i) z is the corresponding time after standing for the i-th fine adjustment.

[0049] Assume that the magnetic declination change is ΔD i ', and there is an approximate relationship between the voltage and the magnetic declination change:

[0050]

[0051] From this, the magnetic declination grid value can be calculated:

[0052]

[0053] Where k is the magnetic declination grid value, ΔD i is the difference between the horizontal disk reading and the initial reading during the i-th fine-tuning.

[0054] In this embodiment, the voltage value after daily variation correction is solved according to formula (1) and formula (2), and ΔD is obtained. i and The relationship is shown in Table 1. According to formula (4), the magnetic declination grid value k = 8.8667 × 10 3 , that is, for every 0.001V change in voltage, the corresponding magnetic declination changes by 8.8667'; that is, for every 1' change in magnetic declination, the voltage changes by 1.128×10 -4 V.

[0055] Table 1:

[0056]

[0057] Step 4. Generate a continuous magnetic declination sequence

[0058] According to the calculated magnetic declination grid value k, combined with the voltage time series data recorded by the board, the voltage time series data can be converted into continuous magnetic declination sequence data by corresponding multiplication, and the abnormal values ​​therein are eliminated to ensure the accuracy of the continuous magnetic declination sequence data obtained. In addition, since the continuous magnetic declination sequence data obtained has a certain periodicity, in order to facilitate the calculation of the magnetic declination change at any time, the magnetic declination sequence data after elimination is fitted to obtain the relationship between the magnetic declination change and time. In this embodiment, the Fourier transform analysis method is used to extract the periodic signal of the magnetic declination sequence, and the magnetic declination change function model is constructed according to the Fourier series, and the functional relationship between the magnetic declination change ΔD and the time t is obtained as follows:

[0059]

[0060] In the formula, time t is calculated from the time when the first geomagnetic theodolite is completely stationary, A0 is the fitting constant term, and A j (j=1,2,…,m) and B j (j=1,2,…,m) is the fitting coefficient, m is the series of the Fourier function; substituting time into formula (5), the magnetic declination value at the corresponding time can be calculated.

[0061] In this embodiment, the voltage time series data of a certain airport for 48 hours is multiplied by the calculated magnetic declination grid value, and the abnormal values ​​are eliminated to obtain the continuous magnetic declination sequence data as follows: Figure 2As shown, the variation of magnetic declination at different times is obtained; the Fourier transform analysis method is used to extract the periodic signal of the magnetic declination sequence, and the result is as shown in Figure 3 ; a magnetic declination variation function model is constructed using a Fourier series with the highest order of 6, and the functional relationship between the magnetic declination variation ΔD and time t is as shown in formula (6), and the finally obtained fitting curve is as shown in Figure 4 .

[0062]

[0063] In the formula, A j (i = 0, 1, …, 6), B j (j = 1, 2, …, 6) are fitting coefficients, and the specific values are shown in Table 2.

[0064] Table 2:

[0065]

[0066]

[0067] Step 5. Calibration of magnetic declination data

[0068] In the target area, according to the principle of measuring point layout in step 1, the positions of the second geomagnetic theodolite (with the same model as the first one as much as possible) and the target are laid out; the second geomagnetic theodolite is used as an absolute measurement station to measure the absolute value of the magnetic declination for data calibration. At the selected absolute measurement station position, the fixed solution of the geodetic coordinates here is obtained using the GNSS RTK measurement technology, and the second geomagnetic theodolite (with the same model as the first geomagnetic theodolite) is set up and centered and leveled; at the selected target position, the fixed solution of the geodetic coordinates here is obtained using the GNSS RTK measurement, and the prism is set up and centered and leveled; the true azimuth angle from the absolute measurement station to the target is solved using the obtained geodetic coordinates.

[0069] Using the second geomagnetic theodolite, absolute measurement of the magnetic declination is carried out according to the set measurement interval, and the absolute measurement result of the magnetic declination is obtained. The generated continuous magnetic declination sequence data is calibrated according to the absolute measurement result of the magnetic declination. By vertically translating the continuous magnetic declination sequence data, the calibrated continuous magnetic declination sequence data is aligned with the absolute measurement result of the magnetic declination at the same time. To ensure the consistency of the data measured by the two electromagnetic theodolites at the same time and avoid signal interference caused by too close a distance, the distance between the second geomagnetic theodolite and the first geomagnetic theodolite needs to be within 3 - 5 meters. Among them, the measurement interval needs to be controlled within 12 hours. At the same time, to ensure the accuracy of the measurement, the number of measurement rounds for each magnetic declination measurement should be 2 - 3 rounds. As other implementation manners, the measurement interval and the number of measurement rounds can be determined according to the specific measurement implementation situation.

[0070] In this embodiment, a second geomagnetic theodolite is set up at a position 3 meters away from the first geomagnetic theodolite. The magnetic declination is measured in two sets of observations every 12 hours, and the measurement time is recorded. According to the measurement results and the true azimuth A from the absolute measurement station to the target measured by RTK, the magnetic declination at the corresponding moment is calculated. The relationship between the reading of the magnetic north direction on the horizontal dial of the geomagnetic theodolite, the true azimuth from the absolute measurement station to the target, and the magnetic declination is as Figure 5 shown. The specific steps for measuring the magnetic declination are as follows:

[0071] (1) Observation of the horizontal angle in the target direction. The observation sequence is left disk → right disk → right disk → left disk, and the horizontal dial readings are read and recorded (assuming the left-disk reading is C L1 、C L2 , and the right-disk reading is C R1 、C R2 );

[0072] (2) Observation of the magnetic north direction. The observation sequence is:

[0073] i Set the vertical dial of the geomagnetic instrument to 90° and brake the vertical dial;

[0074] ii Place the fluxgate sensor above the telescope and point the telescope approximately eastward; adjust the horizontal direction of the telescope so that the display reading is zero. Immediately record the time (T1) and read and record the horizontal dial reading of the theodolite (C EU );

[0075] iii Horizontally rotate the telescope by approximately 180°; adjust the horizontal direction of the telescope. When the null detector reading is zero, read and record the horizontal dial reading (C WU );

[0076] iv Vertically rotate the telescope by 180°, set the vertical dial to 270° and brake it; adjust the horizontal direction of the telescope. When the null detector reading is zero, read and record the horizontal dial reading (C WD );

[0077] v Horizontally rotate the telescope by approximately 180°; adjust the horizontal reading of the telescope. When the null detector reading is zero, immediately record the time (T2) and read and record the horizontal dial reading (C ED );

[0078] (3) Closed observation of the horizontal angle in the target direction. The observation sequence is left disk → right disk → right disk → left disk, and the horizontal dial readings are read and recorded (assuming the left-disk reading is C L3 、C L4 , and the right-disk reading is C R3 、C R4 ).

[0079] The reading MM of the magnetic north direction on the horizontal dial of the geomagnetic theodolite can be obtained:

[0080]

[0081] Combining the observation record times T1 and T2, and the true azimuth A from the absolute measurement station to the target obtained by RTK measurement, the magnetic declination D at the moment of (T1 + T2) / 2 can be obtained. 1,2 It is:

[0082]

[0083] In this embodiment, the magnetic declination observation values at three moments are obtained through observation, and two measurement rounds are carried out at each moment, as Figure 4 shown by the positions of the circles. The generated continuous magnetic declination sequence data is translated up and down by the calculated absolute magnetic declination value, so that the calibrated continuous magnetic declination sequence data is aligned with the absolute measurement result of the magnetic declination at the same moment, and the accurate continuous magnetic declination sequence data in this area is obtained. Finally, the calibrated continuous magnetic declination sequence data is as Figure 4 shown. By comparing Figure 4 and Figure 2 it can be seen that the calibrated continuous magnetic declination sequence data is aligned with the absolute measurement result of the magnetic declination at the same moment.

[0084] According to the above steps, accurate continuous magnetic declination sequence data in the target area can be obtained, without the need for long-term manual magnetic declination measurement, and the problem of difficult or inaccurate acquisition of magnetic declination daily variation information caused by the shortage of geomagnetic stations is successfully solved, ensuring that continuous magnetic declination data in the required area can be obtained, which can provide effective data support for the research and application in many fields such as earthquake prediction, mine engineering, tunnel engineering, indoor and underground navigation, etc.

Claims

1. A method for obtaining a continuous magnetic declination, characterized in that The method includes the following steps: 1) Set up the first geomagnetic theodolite in the target area, connect a continuous data acquisition board to the geomagnetic zero detector end to convert the magnetic signal into an electrical signal and store it in real time, obtaining voltage-time series data; 2) Adjust the vertical circle of the geomagnetic theodolite to 90° or 270°; set the initial reading of the horizontal circle, finely adjust the horizontal circle and let it stand still after each fine adjustment, record the difference between the horizontal circle reading and the initial reading after each fine adjustment, the corresponding voltage value, and the corresponding time at the start and after the fine adjustment and standing still; 3) Calculate the magnetic declination grid value based on the obtained difference, corresponding voltage value, and the time at the start and after the fine adjustment and standing still for each fine adjustment; The calculation formula for the magnetic declination grid value is: where k is the magnetic declination grid value, and ΔD i is the difference between the horizontal dial reading and the initial reading during the i-th fine adjustment, is the voltage value after daily variation correction, and n is the total number of fine adjustments and is an odd number; 4) Calculate and generate continuous magnetic declination sequence data based on the calculated magnetic declination grid value and the obtained voltage-time series data; 5) Set up the second geomagnetic theodolite in the target area, conduct absolute magnetic declination measurement according to the set measurement interval, obtain the absolute magnetic declination measurement result, and calibrate the generated continuous magnetic declination sequence data according to the absolute magnetic declination measurement result, so that the calibrated continuous magnetic declination sequence is aligned with the absolute magnetic declination measurement result at the same moment.

2. The method for obtaining a continuous magnetic declination according to claim 1, wherein Before calculating the magnetic declination grid value in step 3), the daily variation correction needs to be performed on the obtained voltage value, and the calculation formula is: Where, U i is the voltage value at the i-th fine adjustment, δU i is the daily variation correction of the voltage, is the voltage value after the daily variation correction, n is the total number of fine adjustments and is an odd number, T (i) q is the corresponding time when the i-th fine adjustment starts, T (i) z is the corresponding time after the i-th fine adjustment stands still.

3. The method for obtaining a continuous magnetic declination according to claim 1, wherein In step 2), the dial readings after the fine adjustment of the horizontal circle should be distributed on both sides of the initial reading, and the difference between the horizontal circle reading and the initial reading after each fine adjustment should be within 1′ - 30′.

4. The method for obtaining a continuous magnetic declination according to claim 1 or 3, characterized in that In step 2), the initial reading is the horizontal circle reading when the voltage reading of the zero detector is 0.

5. The method for obtaining a continuous magnetic declination according to claim 1, characterized in that In step 5), the set measurement interval should be less than 12 hours.

6. The method for obtaining a continuous magnetic declination according to claim 1, wherein In step 5), the distance between the second geomagnetic theodolite and the first geomagnetic theodolite should be within 3 - 5 meters.

7. The method for obtaining a continuous magnetic declination according to claim 1, characterized in that, In step 2), the standing still time of the horizontal circle after the fine adjustment is within 1′ - 1′30″.

8. The method for obtaining a continuous magnetic declination according to claim 1, characterized in that, In step 4), outliers also need to be removed from the generated magnetic declination sequence data, and fitting is performed according to the magnetic declination sequence data after the removal to obtain the relationship between the magnetic declination change amount and time.

9. The method for obtaining a continuous magnetic declination according to claim 1, characterized in that The calibration process in step 5) is: translate the magnetic declination sequence data up and down according to the measured absolute magnetic declination measurement result.

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