Absolute relative gravimeter combined measurement method

Abstract

The invention discloses an absolute relative gravimeter combined measurement method. The method comprises the following steps: S1, taking a drift error of a strapdown relative gravimeter, a change rate of the strapdown relative gravimeter, other errors of the strapdown relative gravimeter, a change rate of the other errors of the strapdown relative gravimeter, and an error of an atomic interference absolute gravimeter and a change rate of the atomic interference absolute gravimeter as system states; s2, taking the difference of gravity anomalies measured by the two gravimeters as measurement, and constructing a combined measurement model; and S3, predicting a reliable error state through robust Kalman filtering based on a maximum entropy criterion. According to the method, the characteristics of an atom interference absolute gravimeter and a strapdown gravimeter are combined to complement each other, the precision and reliability of open sea gravity measurement are effectively improved, and the method is practical and has wide application prospects. The problems of strapdown relative gravimeter drift error accumulation and poor dynamic performance of an atomic interference absolute gravimeter during open sea measurement are effectively solved, through combined measurement of the strapdown relative gravimeter and the atomic interference absolute gravimeter, it is avoided that the relative gravimeter needs to return at regular time for drift error calibration, and the gravity measurement precision is improved.

Description

Technical Field

[0001] The invention relates to the technical field of gravity measurement, and in particular to an absolute relative gravimeter combined measurement method. Background Art

[0002] The ocean, which occupies about 71% of the earth's area, is rich in minerals, biological resources and other resources. The measurement of the ocean gravity field will help people further understand, explore and develop the ocean. As one of the main components of the ocean gravity field, ocean gravity anomaly plays an important role in the mapping of ocean gravity background fields, marine resource detection, underwater matching navigation and other fields. Currently, commonly used gravity measurement equipment includes strapdown relative gravimeters, atomic interferometer absolute gravimeters, spring relative gravimeters, etc. Among them, strapdown gravimeters have attracted widespread attention in the measurement field due to their superior dynamic performance and atomic gravimeters due to their drift-free characteristics.

[0003] The strapdown gravimeter is based on Newton's laws of motion and uses the specific force, attitude, displacement and other data provided by the global navigation satellite system (GNSS) or other devices that can provide location information and the strapdown inertial navigation system (SINS) to extract relative gravity. The integration, miniaturization, temperature control, gravity extraction and other technologies related to the strapdown gravimeter are relatively mature, and there is no need for the assistance of a stable platform or vibration isolation system. The degree of integration is high, and shipborne gravity measurements can be performed under any sea conditions. However, due to the inherent properties of the device itself, there is a drift accumulated over time. This limitation requires the strapdown gravimeter to return to the previous calibration site for zero drift error correction after sailing for a period of time, which also makes it difficult for the strapdown gravimeter to perform long-distance measurements.

[0004] The atomic interferometer absolute gravimeter is based on optics, using magneto-optical wells to cool trapped atoms and make them fall freely. Atomic interference is then achieved using matter waves, and gravity information is extracted from the interference pattern. Since there is no mechanical wear during operation, the atomic interferometer absolute gravimeter has the advantages of no drift and strong static stability. However, the preparation and vertical fall of the atomic cluster must be maintained at all times during the measurement process. Therefore, the atomic gravimeter has extremely high requirements for the environment in which it is located. It must rely on the assistance of a temperature control system, a stable platform, and a vibration isolation system. The dynamic performance is poor. In offshore measurements, it is difficult to withstand interference from wind and waves, and it is easy to introduce gross errors. This is the key to restricting the atomic gravimeter from conducting offshore measurements.

[0005] In view of the problems and defects of the above two gravity measurement methods, we proposed an absolute relative gravimeter combined measurement method to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings in the prior art and to propose an absolute relative gravimeter combined measurement method.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] An absolute relative gravimeter combined measurement method comprises the following steps:

[0009] S1. The drift error and its changing rate of the strapdown relative gravimeter, the remaining errors and their changing rates, and the error and its changing rate of the atomic interferometer absolute gravimeter are taken as the system state;

[0010] S2, using the difference between the gravity anomalies measured by the two gravimeters as the measurement, a combined measurement model is constructed;

[0011] S3, predicting reliable error states through robust Kalman filtering based on the maximum entropy criterion;

[0012] S4. Compensate for the gravity anomaly of the strapdown relative gravimeter to obtain more accurate gravity information.

[0013] Preferably, according to step S2, the combined measurement model is as follows:

[0014]

[0015] The model status is ap and is the relative gravimeter drift error and its variation, ao and is the remaining error of the relative gravimeter and its variation, be and are the absolute gravimeter error and its variation, x k-1 is the state value at the previous moment, x k Current state value

[0016] State transition matrix That is, from the state at time k-1 to the state at time k

[0017] System noise η k-1 The corresponding system noise matrix is ​​Q k-1 , Z k For measurement, Z k =δg xd -δg jd , δ gxd is the gravity anomaly measured by the relative gravimeter, δg jd The gravity anomaly provided by the absolute gravimeter is measured by the transfer matrix H k =[1 0 1 0 -10], measurement noise ξ k The corresponding system noise matrix is ​​R k .

[0018] Preferably, according to step S3, the Kalman filter algorithm involves the following steps:

[0019]

[0020] in, Status x The predicted value at the previous moment, for x The one-step prediction value at the current moment, P k-1 The previous state The error covariance matrix, P k,k-1 One-step prediction The error covariance matrix of For measurement prediction Relative to state prediction The covariance matrix of is the error covariance matrix of measurement prediction, Kk is the filter gain, is the state prediction value at time k, Pk for The corresponding error covariance matrix.

[0021] Preferably, according to step S4, after calculating the error covariance of the measurement prediction according to the Kalman filter formula in step S3, After that, the measurement information is calculated, that is,

[0022]

[0023] Then construct the judgment test value:

[0024]

[0025] The detection criteria are as follows:

[0026]

[0027] Among them, χ 2 (α) is the preset fault chi-square threshold value, and its value can correspond to a certain false alarm rate. From the chi-square distribution table, we can get χ 2 (α) and the corresponding relationship between the false alarm rate, when normal, according to the formula The normal Kalman filter algorithm is used to calculate the filter gain, state prediction value and update covariance. When an abnormality occurs, the maximum entropy Kalman filter is used, that is,

[0028]

[0029] ψ k =diag[k σ (Ek,i )]

[0030]

[0031] In the formula, E k is the maximum entropy factor of the construction, ψ k is the maximum entropy weight matrix, k σ (·) is the maximum entropy kernel function, is the measurement noise matrix after maximum entropy correction, are the corrected measurement prediction error covariance matrix and filter gain respectively.

[0032] The present invention aims to provide an atomic interferometer absolute gravimeter-strapdown relative gravimeter combined measurement method, aiming to solve the problem of the drift of the strapdown relative gravimeter and the susceptibility of the atomic interferometer absolute gravimeter to high maneuverability during offshore measurement.

[0033] The method of the present invention combines the characteristics of the atomic interferometer absolute gravimeter and the strapdown gravimeter, takes advantage of their strengths and makes up for their weaknesses, effectively improves the accuracy and reliability of offshore gravity measurement, and is practical and effectively solves the problems of drift error accumulation of the strapdown relative gravimeter and poor dynamic performance of the atomic interferometer absolute gravimeter during offshore measurement. Through the combined measurement of the two, it also avoids the need for the relative gravimeter to return regularly for drift error calibration, thereby improving the efficiency of offshore measurement and the accuracy of gravity measurement during the period of accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the working flow chart of the strapdown relative gravimeter.

[0035] Figure 2 This is the working flow chart of the atomic interferometer absolute gravimeter.

[0036] Figure 3 This is the principle block diagram of the atomic interferometer absolute gravimeter-strapdown relative gravimeter combined measurement method.

[0037] Figure 4 This is a reference gravity simulation diagram in the simulation experiment conducted in the present invention.

[0038] Figure 5 This is a simulation diagram of the strapdown gravity measurement results in the simulation experiment conducted in the present invention.

[0039] Figure 6 This is a simulation diagram of the absolute gravity measurement results of atomic interference in the simulation experiment conducted in the present invention.

[0040] Figure 7 The figure is a comparison chart of the gravity measurement results of the three measurement methods performed in the present invention.

[0041] Figure 8 This is a simulation diagram of relative gravimeter drift in the semi-physical simulation experiment conducted in the present invention.

[0042] Fig. 9 The inner coincidence curve diagram after introducing simulated drift into the relative gravimeter measurement results in the semi-physical simulation experiment conducted in the present invention.

[0043] Fig.10 This is an inner coincidence curve diagram of the measurement results of the atomic interferometer absolute gravimeter in the semi-physical simulation experiment conducted in the present invention after high maneuvering interference is introduced.

[0044] Fig.11 It is an internal coincidence curve diagram of the atomic interferometer absolute gravimeter-strapdown relative gravimeter combined measurement method in the semi-physical simulation experiment conducted in the present invention. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0046] Reference Figure 1-11

[0047] 1 Basic principles and characteristics of strapdown relative gravity measurement and atomic interferometry absolute gravity measurement

[0048] The commonly used coordinate systems of strapdown relative gravimeters include navigation coordinate system (n-system), carrier coordinate system (b-system), geographic coordinate system (c-system), Earth-centered Earth-fixed coordinate system (e-system), inertial coordinate system (i-system), etc. Because people are accustomed to using longitude, latitude and altitude to represent the navigation information of the carrier, the geographic coordinate system with the direction of "east-north-sky" is recorded as the navigation coordinate system. Corresponding to the n-system, the direction of the b-system is expressed as "right-front-up". The navigation coordinate system and carrier coordinate system with calculation errors are called n'-system and b'-system respectively. Gravity measurement is carried out in the n-system.

[0049] In the strapdown gravity measurement based on SINS / GNSS, the direct difference method is the most commonly used. According to Newton's laws of motion and Einstein's general theory of relativity, the carrier motion acceleration in the specific force information is deducted to obtain gravity information. Gravity, gravity anomaly and other information are related to the position. Since the position is usually expressed in longitude, latitude and altitude, gravity measurement is often performed in n The specific measurement principle is as follows.

[0050]

[0051] In the formula, g n Represents the Earth's gravity at a certain point, also known as true gravity. and Represent the three-axis acceleration and velocity of the carrier respectively. It is the specific force of the accelerometer after integrated navigation compensation. It is the specific force information with error, measured by the accelerometer. is the angular velocity with error, measured by the gyroscope. represents the rotation matrix of the n-system relative to the b-system. represents the angular velocity of the Earth's rotation in the n-frame. is the angular velocity of the connection. Representation Matrix of the opposition to this matrix.

[0052] Gravity disturbance is the difference between true gravity and normal gravity. Disturbed gravity is:

[0053] δg n =g n -γ n (2)

[0054] In the formula, γ n It is normal gravity, which can be calculated by WGS-84, CGCS2000, etc.

[0055] The gravity generally referred to is actually the vertical component of equation (2), that is, the gravity anomaly. Expanding equation (2) in matrix form, the gravity anomaly is:

[0056]

[0057] Where L and h represent the latitude and altitude of the carrier respectively. M and R N The radius of the meridian and meridian of the earth is ω. ie is the Earth's rotation angular velocity It is called Eotovs correction. is the correction for vertical acceleration in the sky. for The celestial component, for n -The relative strength of the system,

[0058] γ=978032.53349(1+0.00530244sin 2 L-0.00000582sin 2 L)-0.3086H (4)

[0059] Where H is the ellipsoid height of the calculation point.

[0060] If the height at the measuring point cannot be accurately obtained, the corresponding normal gravity formula is as follows.

[0061] γ=978032.53349(1+0.00530244sin 2 L-0.00000582sin 2 L) (5)

[0062] According to equations (3)-(5), the process of gravity measurement based on SINS / GNSS is shown in the attached Figure 1 In the figure, The carrier speeds measured by SINS and GNSS, respectively. are the positions output by SINS and GNSS respectively. The parameters are calculated from the navigation information provided by SINS. n '-system. After combined navigation suppression, these parameters have no errors. It is generally believed that the speed and position provided by GNSS are accurate and have no errors. represents the vertical acceleration correction term, given by Eotovs and γ represent the Eotovs correction and normal gravity values ​​calculated based on the velocity and position provided by GNSS.

[0063] In the atomic interferometer absolute gravimeter, in order to measure the gravitational acceleration, a three-dimensional magneto-optical trap is used to cool and trap atoms in a stable environment of vacuum and constant temperature, and the atoms are further cooled to the micro-open (μ)K level through polarization gradient cooling. After that, the light field is turned off to allow the atoms to fall freely under the action of gravity. Then, the falling cold atoms are split, reflected, and combined using three π / 2-π-π / 2 laser beams and their opposing laser pulses formed by the reflector to achieve MZ interference and transfer the acceleration information of the atoms relative to the reflector to the interference fringes. The phase difference of the two path atomic interference is Δφ=k eff ·gT 2 ,in, is the effective wave vector of Raman light, k1 and k2 are the wave vectors of two Raman light beams, λ is the wavelength of laser, and T is the time interval between the two Raman light beams.

[0064] In order to compensate for the Doppler frequency shift during the free fall of the atoms, the frequency difference between the two Raman beams needs to be linearly chirped. At this time, the interference phase difference can be expressed as

[0065] Δφ=(k eff ·g-2πα)T 2 (6)

[0066] When the chirp rate α = k effWhen g / 2π, the phase shift of Raman light is exactly the same as the phase shift due to gravity.

[0067] During the Raman light action, the internal state of the atom changes. At the initial moment, the atom is in | g > state, after the first π / 2 Raman light, some atoms transition to the |e> state, after the second π Raman light, atoms in |g> transition to |e>, atoms in |e> transition to |g>, after the third Raman light, the atomic wave packet beams interfere. The population number P of atoms in the |e> state after interference is measured by a photodetector, and its relationship with the gravitational phase shift Δφ is

[0068]

[0069] Where P0 is the fringe offset and C is the contrast. Under static conditions, since the measured gravity value remains unchanged or changes very little, multiple interference fringes can be fitted by changing the chirp rate α and the Raman light interval time T. The gravity value corresponding to the fringe center α0 is the local gravity value:

[0070]

[0071] It can be seen that strapdown gravity measurement is based on SINS, so it has high dynamic measurement performance, but due to the presence of mechanical devices, there is inevitably a zero drift problem. These problems may lead to a decrease in the accuracy of the measurement results, so it is necessary to return these instruments to the standard reference point regularly for error calibration and calibration. For long-term offshore measurement missions, the need for regular calibration has become a limiting factor because accurate calibration in the offshore environment is often more difficult and time-consuming. Thanks to its non-mechanical working method, the atomic gravimeter uses an optical device based on atomic interference, which does not require mechanical alignment and is basically fully automatic, thus avoiding the problem of mechanical wear. In addition, it is a sealed vacuum system inside, which does not require external force to evacuate, and there are no moving parts inside, which further enhances its stability and avoids zero drift. However, due to the high environmental requirements of optical devices, the atomic gravimeter will face more complex environmental factors such as temperature, vibration, and electromagnetics when conducting shipboard measurements compared to the laboratory environment. These factors will introduce more measurement noise and errors. However, it can be seen that the characteristics of the two gravimeters are actually complementary.

[0072] 2 Establishment of combined measurement model

[0073] In order to overcome the shortcomings of two gravimeters and realize the acquisition of accurate gravity information during offshore measurement. Based on the characteristics of strapdown relative gravimeter and atomic interferometer absolute gravimeter, the present invention designs an atomic interferometer absolute gravimeter-strapdown relative gravimeter combined measurement method for the offshore. The method uses the drift error and its change rate of the strapdown relative gravimeter, the remaining errors and their change rates, and the error and its change rate of the atomic interferometer absolute gravimeter as the system state, and uses the difference in gravity anomalies measured by the two gravimeters as the measurement to construct a combined measurement model. Then, a reliable error state is estimated through a robust Kalman filter based on the maximum entropy criterion, and the gravity anomaly of the strapdown relative gravimeter is compensated for error to obtain more accurate gravity information.

[0074] The working block diagram of combined measurement is attached. Figure 3 ,The combined measurement model is as follows.

[0075]

[0076] The model status is ap and is the relative gravimeter drift error and its variation, a o and is the remaining error of the relative gravimeter and its variation, b e and are the absolute gravimeter error and its variation respectively. k-1 is the state value at the previous moment, x k is the current state value.

[0077] State transition matrix That is, it changes from the state at time k-1 to the state at time k.

[0078] System noise η k-1 The corresponding system noise matrix is ​​Q k-1 .

[0079] z k For measurement, z k =δg xd -δg jd ,δg xd is the gravity anomaly measured by the relative gravimeter, δg jd Gravity anomaly provided for absolute gravimeter.

[0080] Measurement transfer matrix H k =[1 0 1 0 -1 0].

[0081] Measurement noise ξ k The corresponding system noise matrix is ​​R k .

[0082] Through this measurement model, the combined measurement of the strapdown relative gravimeter and the atomic interferometer absolute gravimeter can be realized. With the help of the drift-free characteristic of the absolute gravimeter, the drift error of the relative gravimeter can be estimated in real time, thereby reducing its impact, realizing drift-free measurement in the open sea during long voyages, and eliminating the need for the relative gravimeter to return for calibration, thereby improving the efficiency and accuracy of deep sea gravity measurements.

[0083] 3 Robust Kalman Filter

[0084] However, when measuring in the open sea, it is often affected by factors such as waves and wind, which in turn causes the absolute gravimeter to vibrate and produce disturbances, resulting in abnormal measurement information of the combined measurement, thereby affecting the accuracy of the combined measurement. In order to avoid this situation, a robust strategy based on the maximum entropy criterion is introduced into the Kalman filter to obtain a robust Kalman filter, which improves the robustness of data fusion.

[0085] 3.1 Kalman Filter

[0086] The Kalman filter algorithm involves the following steps

[0087]

[0088] in, is the predicted value of state x at the previous moment, is the one-step predicted value of x at the current moment. k-1 The previous state The error covariance matrix, P k,k-1 One-step prediction The error covariance matrix of . For measurement prediction Relative to state prediction The covariance matrix of . K is the error covariance matrix of measurement prediction. k is the filter gain. is the state prediction value at time k. k for The corresponding error covariance matrix.

[0089] Kalman filtering performs well in dealing with Gaussian noise by using only the second-order moment information of the error. However, its performance is reduced in the face of non-Gaussian noise environments (such as vibration). In order to overcome this limitation, the present invention introduces the maximum correlation entropy criterion to integrate the second-order and higher-order moment information of the error, so that the Kalman filter can provide more accurate state estimation performance under non-Gaussian noise conditions.

[0090] 3.2 Robust Kalman Filtering Based on Maximum Entropy and Chi-Square Test

[0091] Since the probability of abnormal information appearing during navigation is not too high, in order to make full use of the robust strategy, the chi-square test is first introduced to construct the judgment criteria. When an abnormal situation is detected, the maximum entropy robustness is performed, otherwise the normal Kalman filter is performed.

[0092] After calculating the error covariance of the measurement prediction according to the Kalman filter formula After that, calculate the measurement information, that is,

[0093]

[0094] Then construct the judgment test value:

[0095]

[0096] The detection criteria are as follows:

[0097]

[0098] Among them, χ 2 (α) is the preset fault chi-square threshold value, and its value can correspond to a certain false alarm rate. From the chi-square distribution table, we can get 2 (α) and the corresponding relationship between the false alarm rate.

[0099] When normal, the normal Kalman filter algorithm is performed according to formulas (14)-(16), that is, the filter gain, state prediction value and updated covariance are calculated. When abnormal, the maximum entropy Kalman filter is performed, that is,

[0100]

[0101] ψ k =diag[k σ (E k,i )] (twenty one)

[0102]

[0103] In the formula, E k is the maximum entropy factor of the construction, ψ k is the maximum entropy weight matrix, k σ (·) is the maximum entropy kernel function. is the measurement noise matrix after maximum entropy correction. are the corrected measurement prediction error covariance matrix and filter gain respectively.

[0104] Robust Kalman can avoid the impact of absolute gravimeter measurement anomalies caused by high maneuvers, vibrations and other disturbances during offshore measurements, thereby improving the robustness of the combined measurement.

[0105] 4. Implementation steps of the present invention in shipboard experiments

[0106] The experimental verification method of the present invention for the open sea atomic interferometer absolute gravimeter-strapdown relative gravimeter combined measurement method specifically comprises the following steps.

[0107] 1) Obtain the measurement data of the strapdown relative gravimeter and the atomic interferometer absolute gravimeter. Figure 1 and attached Figure 2 The measurement data of the two gravimeters are obtained through the measurement steps.

[0108] 2) Establish a combined measurement model. Figure 3 The combined measurement steps of , and the models of 2 and 3 and the robust Kalman filter are used for combined measurement.

[0109] 3) Simulation experiment. Carry out shipborne combined navigation experiment to compare the performance of the proposed method with the strapdown relative gravimeter and atomic interferometer absolute gravimeter. In the simulation experiment, first simulate a gravity benchmark, and use it as a standard to compare and evaluate the accuracy of relative gravity anomaly and absolute gravity anomaly, that is, to serve as prior data in the external coincidence accuracy assessment, as shown in the attached figure. Figure 4 As shown. Then the relative gravimeter measurement results and the absolute gravimeter measurement results are simulated. The relative gravimeter has high dynamic performance, but due to device reasons, it inevitably has zero drift problems. According to its performance characteristics, the corresponding simulation measurement results are shown in the attached Figure 5 The absolute gravimeter is susceptible to sudden changes due to environmental influences such as vibration and high maneuverability. According to its characteristics, the simulation measurement results are shown in the attached Figure 6 Then a combined measurement is performed based on the results of the two gravimeters.

[0110] In this experiment, the simulation parameters for combined measurement are set as follows.

[0111] System noise matrix:

[0112] Q k-1 =diag([0.1m Gal 0.004m Gal 0.2m Gal 0.005m Gal 0.1m Gal 0.002mGal]) 2

[0113] Measurement noise matrix: R k =diag([1m Gal]) 2

[0114] The initial error covariance matrix is ​​as follows:

[0115] P0=diag([0.1m Gal 0.003m Gal 0.04m Gal 0.001m Gal 0.1m Gal 0.002mGal]) 2

[0116] Initial state: x0 = [0 0 0 0 0 0] T .

[0117] The combined measurement results are shown in the attached Figure 7 The external accuracy is shown in Table 1. It can be seen from the results that the combined measurement results after robust filtering have the highest accuracy, indicating that the deviation between the combined gravity and the reference gravity is the smallest and the accuracy is the highest.

[0118] Table 1 External conformity accuracy of each method in simulation experiment

[0119]

[0120] 4) Semi-physical simulation. A sea trial was conducted using an experimental strapdown gravimeter and an atomic ocean gravimeter, with a total of four survey lines, using internal compliance accuracy as the evaluation standard. However, the sea trial was short, the strapdown gravimeter had no drift, and the atomic gravimeter had a stable measurement environment. Therefore, with the help of this data, a measurement lasting about one month was simulated. First, the above data was expanded to a data volume of about one month. Then, the relative gravimeter drift was simulated, and its drift was introduced into the expanded relative gravimeter data. The relative gravimeter drift is shown in the attached figure. Figure 8 shown.

[0121] Parameter settings of the combined measurement model in this experiment:

[0122] System noise matrix:

[0123] Q k-1 =diag([0.1mGal 0.003mGal 0.04mGal 0.001mGal 0.1mGal 0.002mGal]) 2

[0124] Measurement noise matrix: R k =diag([0.5m Gal]) 2

[0125] The initial error covariance matrix is ​​as follows:

[0126] P0=diag([0.1mGal 0.003mGal 0.04mGal 0.001mGal 0.1mGal 0.002mGal]) 2

[0127] Initial state: x0 = [0 0 0 0 0 0] T .

[0128] Finally, two data mutations caused by vibration, high maneuverability, etc. were introduced into the expanded absolute gravimeter measurement data. Finally, the internal coincidence curves of the relative gravimeter with drift and the absolute gravimeter with mutation were obtained, as shown in the attached figure. Figure 9-11 The internal accuracy is shown in Table 2. The experimental results show that the combined gravity measurement data has the smallest discreteness, the best consistency and repeatability, and the highest reliability.

[0129] Table 2 Internal accuracy of each method in semi-physical simulation experiment

[0130]

[0131] 5) Overall analysis shows that the present invention effectively solves the problems of drift error accumulation of strapdown relative gravimeters and poor dynamic performance of atomic interferometer absolute gravimeters during offshore measurements. Through the combined measurement of the two, it also avoids the need for the relative gravimeter to return regularly for drift error calibration, thereby improving the efficiency and accuracy of offshore measurements.

[0132] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An absolute relative gravimeter combined measurement method, characterized in that: The following steps are involved: S1. The drift error and its changing rate of the strapdown relative gravimeter, the remaining errors and their changing rates, and the error and its changing rate of the atomic interferometer absolute gravimeter are taken as the system state; S2, using the difference between the gravity anomalies measured by the two gravimeters as the measurement, a combined measurement model is constructed; S3, predicting reliable error states through robust Kalman filtering based on the maximum entropy criterion; S4. Compensate for the gravity anomaly of the strapdown relative gravimeter to obtain more accurate gravity information.

2. The absolute relative gravimeter combined measurement method according to claim 1, characterized in that: According to step S2, the combined measurement model is as follows: The model status is a p and is the relative gravimeter drift error and its variation, a o and is the remaining error of the relative gravimeter and its variation, b e and are the absolute gravimeter error and its variation, x k-1 is the state value at the previous moment, x k Current state value State transition matrix That is, from the state at time k-1 to the state at time k System noise η k-1 The corresponding system noise matrix is ​​Q k-1 , Z k For measurement, Z k =δg xd -δg jd ,δg xd is the gravity anomaly measured by the relative gravimeter, δg jd The gravity anomaly provided by the absolute gravimeter is measured by the transfer matrix H k =[1 0 1 0 -1 0], measurement noise ξ k The corresponding system noise matrix is ​​R k .

3. The absolute relative gravimeter combined measurement method according to claim 1, characterized in that: According to step S3, the Kalman filter algorithm involves the following steps: in, is the predicted value of state x at the previous moment, is the one-step prediction value of x at the current moment, P k-1 The previous state The error covariance matrix, P k,k-1 One-step prediction The error covariance matrix of For measurement prediction Relative to state prediction The covariance matrix of is the error covariance matrix of measurement prediction, K k is the filter gain, is the state prediction value at time k, P k for The corresponding error covariance matrix.

4. The absolute relative gravimeter combined measurement method according to claim 1, characterized in that: According to step S4, after calculating the error covariance of the measurement prediction according to the Kalman filter formula in step S3, After that, the measurement information is calculated, that is, Then construct the judgment test value: The detection criteria are as follows: Among them, χ 2 (α) is the preset fault chi-square threshold value, and its value can correspond to a certain false alarm rate. From the chi-square distribution table, we can get χ 2 (α) and the corresponding relationship between the false alarm rate, when normal, according to the formula The normal Kalman filter algorithm is used to calculate the filter gain, state prediction value and update covariance. When an abnormality occurs, the maximum entropy Kalman filter is used, that is, ψ k =diag[k σ (E k,i )] In the formula, E k is the maximum entropy factor of the construction, ψ k is the maximum entropy weight matrix, k σ (·) is the maximum entropy kernel function, is the measurement noise matrix after maximum entropy correction, are the corrected measurement prediction error covariance matrix and filter gain respectively.

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