CN112285787A - System and method for detecting extremely low frequency magnetic field of underwater target from air - Google Patents

System and method for detecting extremely low frequency magnetic field of underwater target from air Download PDF

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CN112285787A
CN112285787A CN202011163619.6A CN202011163619A CN112285787A CN 112285787 A CN112285787 A CN 112285787A CN 202011163619 A CN202011163619 A CN 202011163619A CN 112285787 A CN112285787 A CN 112285787A
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magnetic field
low frequency
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underwater vehicle
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CN112285787B (en
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张宁
常明
程锦房
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Naval University of Engineering PLA
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Abstract

The invention provides a system and a method for detecting a very low frequency magnetic field of an underwater target from the air, wherein the system comprises a magnetic field sensor, a signal conditioning circuit and a data acquisition module; the magnetic field sensor is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the data acquisition module, and the data acquisition module is connected with an external computer; the magnetic field sensor is used for collecting magnetic field signals and transmitting the magnetic field signals to the signal conditioning circuit; the signal conditioning circuit comprises an amplifying circuit and a filtering circuit, and the signal conditioning circuit is used for processing the magnetic field signal and transmitting the processed magnetic field signal to the data acquisition module and the computer. The system and the method for detecting the extremely low frequency magnetic field of the underwater target from the air realize effective and accurate detection of the extremely low frequency magnetic field of the underwater vehicle in the air, have wide application range, and can be applied to fixed platforms at seasides, aircrafts and the like.

Description

System and method for detecting extremely low frequency magnetic field of underwater target from air
Technical Field
The invention relates to the field of magnetic field detection of underwater vehicles, in particular to a system and a method for detecting an extremely low frequency magnetic field of an underwater target from air.
Background
When the underwater vehicle sails, on one hand, a hull generates corrosion current in surrounding seawater, a cathode protection system used for preventing the hull from being corroded also generates anticorrosion current, and the periodic change of the resistance of a propeller-main shaft-hull loop generates periodic current for corrosion and anticorrosion current modulation, the current can generate a very low frequency magnetic field, and the fundamental frequency is about 1-7 Hz. On the other hand, a rotating magnetic field formed by the presence of nonuniform magnetization or remanence of components such as the main shaft and the propeller is also a very low frequency magnetic field.
The magnetic anomaly detection is the most mature magnetic detection means at present, and the application of the magnetic anomaly detection is generally divided into three aspects, namely a mine magnetic fuze, underwater magnetic target monitoring such as an electromagnetic buoy and an underwater monitoring net, and aviation magnetic detection. The extremely low frequency magnetic field of the underwater vehicle can be used as a signal source for detecting the underwater vehicle. When the magnetic probe is used for magnetic detection of an aviation airplane, high-speed maneuvering detection can be performed on a large-area sea area, and the search efficiency is very high. However, degaussing techniques and degaussing techniques are continuously developed, and the signal source of the target becomes weaker. Therefore, there is a need for an improvement to the existing magnetic anomaly latency detection method to improve the latency detection capability.
Disclosure of Invention
In order to solve the above problems, the present invention provides a system and a method for detecting a very low frequency magnetic field of an underwater target from air.
A detection system of a very low frequency magnetic field of an underwater vehicle in the air comprises a magnetic field sensor, a signal conditioning circuit and a data acquisition module; the magnetic field sensor is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the data acquisition module, and the data acquisition module is connected with an external computer;
the magnetic field sensor is used for collecting magnetic field signals and transmitting the magnetic field signals to the signal conditioning circuit; the signal conditioning circuit comprises an amplifying circuit and a filtering circuit, and the signal conditioning circuit is used for processing the magnetic field signal and transmitting the processed magnetic field signal to the data acquisition module and the computer.
In some embodiments, an instrumentation amplifier AD624 is adopted in the amplifying circuit; the magnetic field sensor adopts a three-axis fluxgate sensor Mag-13 or an inductive magnetic field sensor LEMI-120; the data acquisition module adopts an NIUSB-6216 acquisition card.
In some embodiments, the filter circuit is a band-pass filter formed by connecting a second-order high-pass active filter and a fourth-order low-pass active filter in series.
In some embodiments, the filtering circuit is an adaptive filter based on an LMS adaptive algorithm.
The invention also provides a method for detecting the air middle-pole low-frequency magnetic field of the underwater vehicle, which adopts the detection system of the air middle-pole low-frequency magnetic field of the underwater vehicle and comprises the following steps:
s1, establishing an extremely low frequency magnetic field model and a magnetic interference compensation model of the underwater vehicle in the air in computer software;
s2, collecting magnetic field signals through the magnetic field sensor, and transmitting the magnetic field signals to the signal conditioning circuit;
s3, amplifying the magnetic field signal through the signal conditioning circuit, filtering out part of interference signals in the magnetic field signal, and transmitting the processed magnetic field signal to the data acquisition module and the computer;
and S4, further processing the data of the data acquisition module through the underwater vehicle in-air extremely low frequency magnetic field model and the magnetic interference compensation model to calculate the underwater vehicle in-air extremely low frequency magnetic field.
In some embodiments, in step S1, the step of modeling the magnetic field of the underwater vehicle at the very low frequency in the air includes: the method comprises the steps of taking a horizontal electric dipole and a vertical electric dipole as equivalent sources of a very low frequency magnetic field generated by the underwater vehicle, respectively modeling the very low frequency magnetic field generated by the horizontal electric dipole and the vertical electric dipole in an air layer, modeling the very low frequency magnetic field generated by the rotation of a magnetic dipole, and combining the three to serve as a very low frequency magnetic field model of the underwater vehicle in the air.
Compared with the prior art, the system and the method for detecting the extremely low frequency magnetic field of the underwater target from the air, provided by the invention, realize the effective and accurate detection of the extremely low frequency magnetic field of the underwater vehicle in the air, have wide application range, and can be applied to fixed platforms at sea, aircrafts and the like.
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Fig. 1 is a schematic diagram of an underwater vehicle when detecting with a detection system of a very low frequency magnetic field in the air.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without any inventive step, are within the scope of protection of the invention.
Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.
The invention provides a detection system for a very low-frequency magnetic field of an underwater vehicle in the air, which comprises a magnetic field sensor, a signal conditioning circuit and a data acquisition module, wherein the signal conditioning circuit is connected with the magnetic field sensor; the magnetic field sensor is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the data acquisition module, and the data acquisition module is connected with an external computer; the magnetic field sensor is used for collecting magnetic field signals and transmitting the magnetic field signals to the signal conditioning circuit; the signal conditioning circuit comprises an amplifying circuit and a filtering circuit, and the signal conditioning circuit is used for processing the magnetic field signal and then transmitting the magnetic field signal to the data acquisition module and the computer.
In a specific embodiment, an instrumentation amplifier AD624 is adopted in the amplifying circuit; the magnetic field sensor adopts a three-axis fluxgate sensor Mag-13 or an inductive magnetic field sensor LEMI-120; the data acquisition module adopts an NIUSB-6216 acquisition card. The filter circuit can adopt a band-pass filter formed by connecting a second-order high-pass active filter and a fourth-order low-pass active filter in series.
Preferably, the filter circuit employs an adaptive filter based on an LMS adaptive algorithm. The LMS adaptive algorithm has the advantages that under the condition that reference noise is not known in advance, a time delay form of a measurement signal can be used as a reference signal, parameters can be continuously adjusted, the requirement on initial parameters is low, an embedded system is easy to realize, the instantaneity is high, broadband noise can be effectively inhibited under the condition of low signal-to-noise ratio, and the line spectrum of a target extremely-low frequency magnetic field signal is enhanced.
The invention also provides a method for detecting the air middle-pole low-frequency magnetic field of the underwater vehicle, which adopts the detection system of the air middle-pole low-frequency magnetic field of the underwater vehicle and comprises the following steps:
s1, establishing an extremely low frequency magnetic field model and a magnetic interference compensation model of the underwater vehicle in the air in computer software;
s2, collecting magnetic field signals through the magnetic field sensor, and transmitting the magnetic field signals to the signal conditioning circuit;
s3, amplifying the magnetic field signal through the signal conditioning circuit, filtering out part of interference signals in the magnetic field signal, and transmitting the processed magnetic field signal to the data acquisition module and the computer;
and S4, further processing the data of the data acquisition module through the underwater vehicle in-air extremely low frequency magnetic field model and the magnetic interference compensation model to calculate the underwater vehicle in-air extremely low frequency magnetic field.
Further, in step S1, the step of establishing a model of the magnetic field of the underwater vehicle at the extremely low frequency in the air includes: the method comprises the steps of taking a horizontal electric dipole and a vertical electric dipole as equivalent sources of a very low frequency magnetic field generated by the underwater vehicle, respectively modeling the very low frequency magnetic field generated by the horizontal electric dipole and the vertical electric dipole in an air layer, modeling the very low frequency magnetic field generated by the rotation of a magnetic dipole, and combining the three to serve as a very low frequency magnetic field model of the underwater vehicle in the air.
In one embodiment, the specific process of modeling is as follows:
when the underwater vehicle is sailing, on the one hand, the hull generates corrosion currents in the surrounding sea water, the cathodic protection system used to prevent hull corrosion also generates corrosion protection currents, and the periodic variation of the resistance of the propeller-main shaft-hull circuit generates periodic currents that generate a very low frequency magnetic field, in addition to the corrosion and corrosion protection currents that are modulated by the current. On the other hand, a rotating magnetic field formed by the presence of nonuniform magnetization or remanence of components such as the main shaft and the propeller is also a very low frequency magnetic field. Thus, the present invention models the current associated with corrosion of an underwater vehicle.
The alternating current formed after the corrosion-related current is modulated by the main shaft generally has two equivalent methods, namely an electric dipole model and a current section model. The current section describes the current IL between the propeller and the anode of the cathodic protection system (I is the time-harmonic current intensity and L is the length of the current section). When L is smaller, the current segment model is simplified into an electric dipole model. Experience has shown that when measuring distances greater than twice the length of the current segments, the current segments can be equated with an electrical dipole and the calculations are relatively simple. Therefore, the invention adopts the electric dipole model and models the extremely low frequency magnetic fields generated by the horizontal electric dipole and the vertical electric dipole in the air layer respectively.
From the basic theory of electromagnetic fields, it is known that a time-varying current necessarily generates a time-varying magnetic field. A horizontal electric dipole or a vertical electric dipole is used as an equivalent source of an underwater vehicle low-frequency magnetic field generation model, and a schematic diagram of the underwater vehicle low-frequency magnetic field generation model under shallow sea conditions is shown in FIG. 1. The positive direction of the X axis corresponds to the direction of a boat bow of the underwater vehicle, the Y axis refers to the starboard direction, and the Z axis is vertically downward.
In fig. 1, the harmonic horizontal electric dipole and the vertical electric dipole are considered in the three-layer model composed of medium 0, medium 1, and medium 2. In practice, these three models correspond to air, sea water and sea bottom, respectively, and the electric dipoles are located in the sea water layer, so that Maxwell equation sets in a time-harmonic form can be obtained:
Figure BDA0002745053970000041
wherein: j. the design is a squaresIs the current density of the electric dipole; hiAnd BiMagnetic field intensity vector and magnetic induction intensity vector; eiAnd DiRespectively representing an electric field strength vector and an electric displacement vector; assuming that all three media are isotropic linear homogeneous media, σi，μi，εiThe electrical conductivity, magnetic permeability and dielectric constant, i ═ 0,1,2 denote field numbers, respectively.
Introducing vector magnetic potential A, scalar potential phi and Lorentz specification
Figure BDA0002745053970000051
The Helmholtz equation for vector magnetic potential can be derived from equations (1) and (2):
Figure BDA0002745053970000052
wherein k is a propagation constant, and k2＝-jωμσ+ω2με。
The method for establishing the horizontal electric dipole model comprises the following steps:
in FIG. 1, the horizontal electric dipole has the coordinate of (x)0，0，z0) The vector magnetic potential in the sea water layer is generated by a primary source and a secondary source, which can be expressed as A1＝A1p+A1sWherein A is1pAnd A1sVector magnetic potential generated by primary source and secondary source, vector magnetic potential A of air layer and sea bottom layer0And A2Is generated by a secondary source, which can be represented as A0sAnd A2s. The vector magnetic potential generated by the primary source of the horizontal electric dipole only has a component in the X direction, and the vector magnetic potential generated by the secondary source has two components in the X direction and the Z direction. The vector magnetic potential expression of each field region can be obtained firstly based on a Sommerfeld basic formula, and then each magnetic field is solved by utilizing the boundary condition of the electromagnetic field.
For medium 1, the vector magnetic bits can be expressed as:
Figure BDA0002745053970000053
and A is0、A1sAnd A2All satisfy the homogeneous Helmholtz equation
Figure BDA0002745053970000054
The general solution can be expressed as:
Figure BDA0002745053970000055
wherein, i is 0,2,
Figure BDA0002745053970000056
φ＝arctan(y(x-x0))，
Figure BDA0002745053970000057
Jm(ρ ξ) is an m-th order Bessel function of the first kind. Also known from the Euler equation, ejmφCosm phi + jsinum phi, and a (rho, phi, z) is a (rho, -phi, z) in the coordinate system (rho, phi, z), so e is obtainedjmφCosm phi. Combining equation (4) and equation (5), one can obtain:
Figure BDA0002745053970000061
from the infinity boundary condition: when z approaches plus or minus infinity, A0And A2Should be of limited value. Then there is c0(ξ,m)＝0，d0(ξ,m)＝0，a2(ξ,m)＝0，b2(xi, m) ═ 0, then a in formula (6)0And A2Can be written as:
Figure BDA0002745053970000062
the electromagnetic field air-seawater boundary conditions are as follows:
Figure BDA0002745053970000063
the electromagnetic field seawater-seabed boundary conditions are as follows:
Figure BDA0002745053970000064
the parameters of the vector magnetic potential are solved using the boundary conditions.
The method comprises the following steps: using a third equation in the boundary conditions [ A ]1x-A0x]z＝00 and [ A2x-A1x]z＝d＝0。
First, using [ A ]1x-A0x]z＝0The derivation is 0, then there is,
Figure BDA0002745053970000071
the two equations are equal, and due to the existence of Bessel function, the equation a is combined with the electromagnetic field uniqueness theorem0(ξ,m)，a1(xi, m) and c1M in (xi, m) can only take 0, and the formula (10) can be written as,
Figure BDA0002745053970000072
a parametric equation is obtained for the measured values,
Figure BDA0002745053970000073
then, using [ A2x-A1x]z＝dThe derivation is 0, then there is,
Figure BDA0002745053970000074
the above two equations are equal, and the same principle as in the push-type equations (11) and (12) is to be understood as that of c2(ξ,m)，a1(xi, m) and c1M in (xi, m) can only take 0, formula (13) can be written as,
Figure BDA0002745053970000075
then a parametric equation can be derived that,
Figure BDA0002745053970000076
step two, utilizing a fourth equation in the boundary condition
Figure BDA0002745053970000081
And
Figure BDA0002745053970000082
first of all utilize
Figure BDA0002745053970000083
To deduce, in the following,
Figure BDA0002745053970000084
the two equations are equal, and a parameter equation can be obtained by combining the uniqueness theorem of the electromagnetic field,
Figure BDA0002745053970000085
secondly, then, again by
Figure BDA0002745053970000086
The derivation is carried out in such a way that,
Figure BDA0002745053970000087
the two formulas are equal, and a parameter equation can be obtained in the same way,
Figure BDA0002745053970000088
the united type (12), (15), (17) and (19) obtains the following equation systemSolving for a0(ξ,0)，a1(ξ,0)， c1(xi, 0) and c2(ξ,0)。
Figure BDA0002745053970000089
Step three: using the first equation in the boundary conditions
Figure BDA0002745053970000091
And
Figure BDA0002745053970000092
first, utilize
Figure BDA0002745053970000093
To derive.
For the
Figure BDA0002745053970000094
Wherein:
Figure BDA0002745053970000095
it is possible to write out,
Figure BDA0002745053970000096
and is also provided with
Figure BDA0002745053970000097
Wherein the content of the first and second substances,
Figure BDA0002745053970000098
it is possible to write out,
Figure BDA0002745053970000099
combinations (23) and (24) of
Figure BDA0002745053970000101
A parametric equation can be obtained that,
Figure BDA0002745053970000102
the formula contains Bessel function, and combines with electromagnetic field uniqueness theorem, thereby obtaining b0(ξ,m)、 b1(xi, m) and d1In (xi, m), m can only take 1, the parameter equation (25) can be simplified,
Figure BDA0002745053970000103
secondly, utilize
Figure BDA0002745053970000104
To derive.
Figure BDA0002745053970000105
Wherein:
Figure BDA0002745053970000106
then there is
Figure BDA0002745053970000107
Herein, the formula (22) was derived
Figure BDA0002745053970000108
The method comprises the following steps of (1) preparing,
Figure BDA0002745053970000111
is formed by combining a compound of formula (28) and a compound of formula (29)
Figure BDA0002745053970000112
Can derive b1(ξ,m)、d1(xi, m) and d2M in xi, m can only take the value of 1, and a parameter equation is provided by combining the electromagnetic field uniqueness theorem,
Figure BDA0002745053970000113
step four: using a second equation in the boundary conditions
Figure BDA0002745053970000114
And
Figure BDA0002745053970000115
according to the previous derivation, the simplified vector magnetic potential equation set is,
Figure BDA0002745053970000116
first, at
Figure BDA0002745053970000117
In the formula (I), the following expression is shown,
Figure BDA0002745053970000121
combining with the uniqueness theorem of the electromagnetic field to obtain a parameter equation,
Figure BDA0002745053970000122
secondly, in
Figure BDA0002745053970000123
In the following, there areThe expression is that the expression is used,
Figure BDA0002745053970000124
combining the uniqueness theorem of the electromagnetic field to obtain a parameter equation:
Figure BDA0002745053970000125
synthesizing the third and fourth Chinese formulas (26), (30), (34) and (35) to obtain a parameter equation set,
Figure BDA0002745053970000126
in conjunction with equations (20) and (36), the eight parameters of the vector magnetic potential can be solved. Therefore, the vector magnetic potential in the air can be obtained as,
Figure BDA0002745053970000131
wherein:
Figure BDA0002745053970000132
b0(ξ,1)＝b1(ξ,1)+d1(ξ,1)，
Figure BDA0002745053970000133
Figure BDA0002745053970000134
Figure BDA0002745053970000135
Figure BDA0002745053970000136
Figure BDA0002745053970000137
Figure BDA0002745053970000138
Figure BDA0002745053970000139
Figure BDA00027450539700001310
and then in formula (2)
Figure BDA00027450539700001311
The magnetic field of the horizontal electric dipole in the air can be respectively obtained,
Figure BDA0002745053970000141
the method for establishing the vertical electric dipole model comprises the following steps:
the magnetic field generated by the vertical electric dipole with the same strength in the air layer is smaller than that generated by the horizontal electric dipole, and the vertical electric dipole only has vector magnetic potential in the vertical direction in each horizontal layered space[84]Thus A is0、 A1And A2Can be expressed as:
Figure BDA0002745053970000142
according to the Euler equation, ejmφCosm phi + jsinum phi, andin the coordinate system (ρ, Φ, z), a (ρ, Φ, z) ═ a (ρ, - Φ, z) is obtained, and therefore e is obtainedjmφCosm phi. From the infinity boundary condition: when z approaches plus or minus infinity, A0And A2Is of limited value. Then there is d0(xi, m) ═ 0 and b2(xi, m) ═ 0, equation (39) can be simplified to:
Figure BDA0002745053970000143
Figure BDA0002745053970000151
since the vector magnetic bit has only the z-component, the electromagnetic field boundary conditions can be simplified as follows.
Air-seawater boundary conditions:
Figure BDA0002745053970000152
sea water-sea bed boundary conditions:
Figure BDA0002745053970000153
the method comprises the following steps: using a second equation in the boundary conditions
Figure BDA0002745053970000154
And
Figure BDA0002745053970000155
the system of equations can be found:
Figure BDA0002745053970000156
b in the formula (43) by combining the electromagnetic field uniqueness theorem due to the Bessel0(ξ,m)、b1(ξ,m)、 d1(ξM) and d2M in (xi, m) can only take 0, so that the process can be simplified to
Figure BDA0002745053970000157
Further, equation (40) can be written as,
Figure BDA0002745053970000161
step two: using the first equation of the boundary conditions
Figure BDA0002745053970000162
And
Figure BDA0002745053970000163
then there is a change in the number of,
Figure BDA0002745053970000164
by
Figure BDA0002745053970000165
And
Figure BDA0002745053970000166
a simplified parametric equation can be obtained,
Figure BDA0002745053970000167
summary parametric equations (44) and (47) having
Figure BDA0002745053970000168
Solving the system of equations can obtain four parameters of the vector magnetic potential, therefore, the vector magnetic potential in the air can be obtained as,
Figure BDA0002745053970000171
wherein:
Figure BDA0002745053970000172
Figure BDA0002745053970000173
Figure BDA0002745053970000174
Figure BDA0002745053970000175
Figure BDA0002745053970000176
Figure BDA0002745053970000177
by
Figure BDA0002745053970000178
The magnetic field of the vertical electric dipole in the air can be solved,
Figure BDA0002745053970000179
the method for establishing the extremely-low-frequency magnetic field model generated by the rotation of the magnetic dipole comprises the following steps:
the inhomogeneous magnetization of the shafting of the underwater vehicle and the residual magnetism of the propeller can be equivalent to a uniform magnetic dipole at a longer distance. Magnetic hypothesisThe initial position of the dipole is the original point and is on the axis of the main shaft, the X axis points to the bow direction of the boat, the Y axis is the starboard direction, and the Z axis is vertically downward. Magnetic moment M ═ Mx·ex+my·ey+mz·ezWherein e isx、eyAnd ezUnit vectors, m, of the X, Y, Z axes, respectivelyx、myAnd mzThe components of the magnetic dipole at the X, Y, Z axis, respectively. The magnetic dipole makes uniform rotation motion around the X axis at an angular velocity omega.
The total magnetic moment of the magnetic dipole at time t is M'x·ex+m'y·ey+m'z·ezThe magnetic moment components in each direction are respectively,
Figure BDA0002745053970000181
then for any point in space (x, y, z), the magnetic field distribution of the magnetic dipole at the origin at time t is
Figure BDA0002745053970000182
Wherein mu0The magnetic permeability is vacuum permeability, r is the vector diameter of a magnetic dipole pointing measuring point, and r is x.ex+y·ey+z·ez。
Writing formula (52) in three-component form, having
Figure BDA0002745053970000183
Wherein the content of the first and second substances,
Figure BDA0002745053970000184
is the distance from the center of the magnetic dipole to the measurement point.
As the diameter of a main shaft and a propeller of the underwater vehicle is larger, the center of an equivalent magnetic dipole deviates from the axis of the main shaft due to nonuniform magnetization, which is equivalent to the fact that the center of the magnetic dipole moves around a circle, the diameter of the main shaft and the propeller of the underwater vehicle is larger than that of the equivalent magnetic dipoleThis can be modified for equation (53). The connecting center of the propeller and the shaft is used as an original point, and the central position of the residual magnetic moment of the shafting is assumed to be away from the original point R and form an included angle with the negative direction of the Y shaft
Figure BDA0002745053970000185
Then the magnetic dipole initial position x0＝0，
Figure BDA0002745053970000186
Figure BDA0002745053970000187
。
The real-time position of the magnetic dipole can be written,
Figure BDA0002745053970000188
the magnetic field generated by the rotation of the magnetic dipole can be written,
Figure BDA0002745053970000189
wherein the content of the first and second substances,
Figure BDA00027450539700001810
in addition, in step S1, the specific steps of establishing the magnetic interference compensation model are as follows:
firstly, respectively establishing a residual magnetic model, an induction magnetic field model and an eddy current magnetic field model of a background magnetic field, and combining the residual magnetic model, the induction magnetic field model and the eddy current magnetic field model to be used as a total magnetic interference compensation model.
Specifically, in step S1, the step of establishing the residual magnetism model includes:
the remanence is expressed as: hp＝{p1 p2 p3}
Then the projection in the direction of the geomagnetic vector at the measurement point is:
Figure BDA0002745053970000191
wherein u isi＝cosθiDirection cosine of the geomagnetic vector;
the step of establishing the induced magnetic field model comprises the following steps:
the vector of the induced magnetic field at the measurement point is represented as:
Figure BDA0002745053970000192
the projection in the direction of the geomagnetic vector is:
Figure BDA0002745053970000193
wherein:
Figure BDA0002745053970000194
when i is not equal to j
a11＝(i11-i33)B
a22＝(i22-i33)B
Let a33When it is equal to 0
Figure BDA0002745053970000201
The step of establishing an eddy current magnetic field model comprises the following steps:
the vector of the induced magnetic field at the measurement point is represented as:
Figure BDA0002745053970000202
according to the property of directional cosine, there are:
Figure BDA0002745053970000203
u1u′1+u2u′2+u3u′3＝0
order:
Figure BDA0002745053970000204
the projection of the eddy magnetic field in the direction of the geomagnetic vector can be expressed as:
Figure BDA0002745053970000205
thus, the overall magnetic disturbance compensation model is:
Figure BDA0002745053970000206
it can be understood that after the extremely low frequency magnetic field model of the underwater vehicle in the air and the background magnetic interference compensation model are established, a simulation test method can be used for generating a regression equation set related to model parameters, and then each parameter in the model is solved, so that the method is applied to actual underwater vehicle detection. In addition, before practical application, the underwater vehicle model can be tested in a sea water pool, and model parameters are improved according to test results so as to further improve the detection capability of the underwater vehicle model.
In conclusion, the system and the method for detecting the extremely low frequency magnetic field of the underwater target from the air provided by the invention realize the effective and accurate detection of the extremely low frequency magnetic field of the underwater vehicle in the air, have wide application range and can be applied to fixed platforms at seaside, aircrafts and the like.
The above-described embodiments are intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above-described embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be within the scope of the present invention.

Claims (6)

1. A detection system for a very low frequency magnetic field of an underwater vehicle in the air is characterized by comprising a magnetic field sensor, a signal conditioning circuit and a data acquisition module; the magnetic field sensor is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the data acquisition module, and the data acquisition module is connected with an external computer;
the magnetic field sensor is used for collecting magnetic field signals and transmitting the magnetic field signals to the signal conditioning circuit; the signal conditioning circuit comprises an amplifying circuit and a filtering circuit, and the signal conditioning circuit is used for processing the magnetic field signal and transmitting the processed magnetic field signal to the data acquisition module and the computer.
2. The system for detecting the extremely low frequency magnetic field in the air of the underwater vehicle as claimed in claim 1, wherein an instrumentation amplifier AD624 is adopted in the amplifying circuit; the magnetic field sensor adopts a three-axis fluxgate sensor Mag-13 or an inductive magnetic field sensor LEMI-120; the data acquisition module adopts an NI USB-6216 acquisition card.
3. The system for detecting the extremely low frequency magnetic field in the air of the underwater vehicle as claimed in claim 1, wherein the filter circuit is a band-pass filter formed by connecting a second-order high-pass active filter and a fourth-order low-pass active filter in series.
4. The system for detecting the extremely low frequency magnetic field in the air of an underwater vehicle as recited in claim 1, wherein said filter circuit is an adaptive filter based on the LMS adaptive algorithm.
5. A method for detecting a very low frequency magnetic field in the air of an underwater vehicle, which is characterized in that the detection system of the very low frequency magnetic field in the air of the underwater vehicle according to any one of claims 1 to 4 is adopted, and the method comprises the following steps:
s1, establishing an extremely low frequency magnetic field model and a magnetic interference compensation model of the underwater vehicle in the air in computer software;
s2, collecting magnetic field signals through the magnetic field sensor, and transmitting the magnetic field signals to the signal conditioning circuit;
s3, amplifying the magnetic field signal through the signal conditioning circuit, filtering out part of interference signals in the magnetic field signal, and transmitting the processed magnetic field signal to the data acquisition module and the computer;
and S4, further processing the data of the data acquisition module through the underwater vehicle in-air extremely low frequency magnetic field model and the magnetic interference compensation model to calculate the underwater vehicle in-air extremely low frequency magnetic field.
6. The method for detecting the airborne extremely low frequency magnetic field of the underwater vehicle as recited in claim 5, wherein the step of modeling the airborne extremely low frequency magnetic field of the underwater vehicle in step S1 comprises: the method comprises the steps of taking a horizontal electric dipole and a vertical electric dipole as equivalent sources of a very low frequency magnetic field generated by the underwater vehicle, respectively modeling the very low frequency magnetic field generated by the horizontal electric dipole and the vertical electric dipole in an air layer, modeling the very low frequency magnetic field generated by the rotation of a magnetic dipole, and combining the three to serve as a very low frequency magnetic field model of the underwater vehicle in the air.
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