JP2003121518A - Magnetometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetometer that does not need compensation, for special movement to determine a compensation factor. SOLUTION: The magnetometer comprises a scalar magnetic sensor 1 detecting terrestrial magnetism, a sensor 5 for airframe information detecting the airframe information, an estimator 6 for a sequential type magnetic compensation factor by system identification which estimates the magnetic compensation factor from the outputs of the scalar magnetic sensor 1 and the sensor 5 for the airframe information, and a magnetic compensator 7 by system identification outputting the magnetic strength of the magnetic field of the terrestrial magnetism, after performing magnetic compensation from the outputs of the scalar magnetic sensor 1 and the sensor 5 for the airframe information, and the output of the estimator 6 for the sequential type magnetic compensation factor by the system identification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a magnetometer for measuring earth magnetism.

[0002]

2. Description of the Related Art Magnetometers are widely used for geological exploration and buried object detection (pipelines of oil facilities, gas pipes, water pipes, various cables, ducts, etc.), as is well known.
A conventional magnetometer will be described with reference to FIG. This magnetometer includes a magnetic compensation coefficient estimator 3 for estimating a magnetic compensation coefficient from the outputs of the scalar magnetic sensor 1 and the triaxial vector magnetic sensor 2, and the output of the scalar magnetic sensor 1 and the triaxial vector magnetic sensor 2. , Scalar magnetic sensor 1
Of the three-axis vector magnetic sensor 2 and the output of the magnetic compensation coefficient estimator 3 to perform magnetic compensation and output the strength of the magnetic field of geomagnetism after magnetic compensation.

A platform such as an aircraft equipped with a magnetic sensor is composed of a magnetic body for generating permanent magnetism, induction magnetism and the like, and a conductor for generating eddy current magnetism.
The maneuver magnetic noise generated by these platforms will be described. The magnetic field NM created by the magnetic substance of the platform and the eddy current at the magnetic sensor position can be expressed by Equation 1 using parameters such as T, L, V, and TT which are constants that do not change with time.

[0004]

[Equation 1]

Here, Hx, Hy, and Hz are three-axis orthogonal components of the geomagnetic vector H, and dHx, dHy, and dHz are time derivatives of Hx, Hy, and Hz, respectively. The first term on the right side of Equation 1 is permanent magnetism, the second term is induction magnetism, and the third term is eddy current magnetic component. However, the formulation according to Equation 1 is premised on that the relative positions of the magnetic substance of the platform and the eddy current magnetism generating source and the magnetic sensor remain unchanged. That is, it is assumed that the platform is rigid.

The strength of the magnetic field observed by the scalar magnetic sensor 1 in the earth's magnetism is the scalar value of the vector sum of the geomagnetic vector H and the magnetic field vector NM created by the platform magnet and the eddy current magnetism at the position of the scalar magnetic sensor 1. ｜ H + NM
| In the field of magnetic anomaly detection, pre-processing of a high pass filter (HPF) or a band pass filter (BPF) is performed in order to avoid the influence of extremely low frequency geomagnetic variations. Therefore, as shown in Equation 2, the maneuver magnetic noise N
Is approximated by the projection component of the magnetic field NM produced by the platform magnetic body and the eddy current magnetism at the position of the scalar magnetic sensor 1 onto the geomagnetic vector H.

[0007]

[Equation 2]

Here, | H | >> | NM | and the intensity of geomagnetism | H | are static or extremely low frequencies, and HPF
Is assumed to be suppressed by. Note that this assumption is a condition that can be sufficiently satisfied in the magnetic anomaly detection problem by the magnetic sensor mounted on a platform such as an aircraft.

Further, if the NM given by the equation 1 is substituted into the equation 2, the maneuver magnetic noise N is given by the geomagnetism H as shown in the equation 3.
Of the unit vector (u, v, w) and its time derivative (du, dv, dw).

[0010]

[Equation 3]

Here, since it is possible to assume that the magnitude of the geomagnetism is spatially and temporally constant in the data section in which the parameter estimation is performed, equations 4 and 5 are given.
I put it.

[0012]

[Equation 4]

[0013]

[Equation 5]

Thus, the maneuver magnetic noise N is 16
This is a quadratic model that includes unknown parameters. However, for example, when the Y axis of the magnetic sensor mounted platform is the heading direction, the Z axis is the downward direction, and the rolling direction is eastward, the rolling sway is T, V,
Eight parameters of TT, VT, tt, tv, vt, and vl can be estimated, but other parameters are not excited and are difficult to estimate. In order to estimate all parameters, it is necessary to have data measured in the azimuths of north, south, east, west, and sway in the azimuth, north, east, and west of the magnetic sensor platform. Thus, quadratic compensation (16-term magnetic compensation) requires a special compensatory flight with severe air movement for parameter estimation. As described above, the maneuver magnetic noise N included in the output of the scalar magnetic sensor 1 is compensated based on the equation 3 using the vector magnetic field (Hx, Hy, Hz) from the triaxial vector magnetic sensor 2.

The magnetic compensation coefficient estimator 3 calculates the magnetic compensation coefficient from the output of the scalar magnetic sensor 1 and the output of the triaxial vector magnetic sensor 2. The magnetic compensator 4 performs magnetic compensation using the output of the magnetic compensation coefficient estimator 3, the output of the scalar magnetic sensor 1 and the output of the triaxial vector magnetic sensor 2, and outputs the magnetic field strength HC of the geomagnetism.

[0016]

When the conventional magnetometer as described above is mounted on an aircraft or the like, the magnetic compensating function requires compensating flight for performing a special motion in order to obtain a compensating coefficient. There was a problem that the crew was burdened.

The present invention has been made in order to solve the above problems, and an object thereof is to obtain a magnetometer which does not require a compensating flight to perform a special motion for obtaining a compensation coefficient.

[0018]

A magnetometer according to a first aspect of the present invention is a scalar magnetic sensor for detecting geomagnetism, a body information sensor for detecting motion information of a body, an output of the scalar magnetic sensor and the body information sensor. From the output of, the sequential magnetic compensation coefficient estimator by system identification for estimating the magnetic compensation coefficient, the output of the scalar magnetic sensor and the output of the airframe information sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification , And a magnetic compensator by system identification that performs magnetic compensation and outputs the strength of the geomagnetic field after magnetic compensation.

The magnetometer according to the second aspect of the present invention obtains a magnetic compensation coefficient from the scalar magnetic sensor and the triaxial vector magnetic sensor for detecting the geomagnetism, and the output of the scalar magnetic sensor and the output of the triaxial vector magnetic sensor. The magnetic compensation is performed by magnetic field compensation from the output of the scalar magnetic sensor, the output of the three-axis vector magnetic sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification. And a magnetic compensator by system identification for outputting the strength of the magnetic field of the geomagnetism after compensation.

The magnetometer according to the third aspect of the invention comprises a scalar magnetic sensor for detecting the earth's magnetism and a three-axis vector magnetic sensor, and a body information sensor for detecting motion information of the body.
A sequential magnetic compensation coefficient estimator by system identification for estimating a magnetic compensation coefficient from the output of the scalar magnetic sensor, the output of the three-axis vector magnetic sensor, and the output of the airframe information sensor; the output of the scalar magnetic sensor; By system identification that performs magnetic compensation from the output of the three-axis vector magnetic sensor, the output of the airframe information sensor, and the output of the sequential magnetic compensation coefficient estimator based on the system identification, and outputs the magnetic field strength of the geomagnetism after magnetic compensation. And a magnetic compensator.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 shows Embodiment 1 of the present invention. In the figure, 1 is the same as that shown in FIG. A machine body information sensor 5 detects machine body information. Reference numeral 6 denotes a system identification sequential magnetic compensation coefficient estimator which estimates the magnetic identification coefficient by system identification from the output of the scalar magnetic sensor 1 and the output of the machine body information sensor 5. Reference numeral 7 denotes a magnetic compensator based on system identification, which performs magnetic compensation by system identification from the output of the scalar magnetic sensor 1 and the output of the airframe information sensor 5 and the output of the sequential magnetic compensation coefficient estimator 6 based on system identification, and after magnetic compensation. Outputs the strength of the geomagnetic field of.

With such a configuration, the strength of the geomagnetic field (scalar magnetic field) H output from the scalar magnetic sensor 1
Is sent to the system-identified iterative magnetic compensation coefficient estimator 6 and the system-identified magnetic compensator 7. On the other hand, the airframe information sensor 5 monitors airframe information that causes magnetic noise affecting the magnetometer, and sends its output to the sequential magnetic compensation coefficient estimator 6 by system identification and the magnetic compensator 7 by system identification. .

Next, the sequential magnetic compensation coefficient estimator 6 based on system identification estimates the magnetic compensation coefficient based on the system identification from the output of the scalar magnetic sensor 1 and the output of the machine body information sensor 5, and outputs the estimated magnetic compensation coefficient based on the system identification. Send to the magnetic compensator 7. The magnetic compensation coefficient by system identification is obtained by calculating the coefficient of a noise model in which the output of the machine body information sensor 5 is input and the output of the scalar magnetic sensor 1 is output. Since the scalar magnetic field H contains maneuver noise, magnetic noise occurs due to the platform swaying even in the uniform geomagnetism. On the other hand, a band pass filter (BPF) is applied to the scalar magnetic field H in order to suppress low frequency components and high frequency components of the earth's magnetism. A general mathematical method for estimating magnetic compensation coefficients by system identification and for magnetic compensation by system identification is presented in the document "Theory of Digital Signal Processing 3: Estimating and Adaptive Signal Processing", Takashi Tanihagi, Corona Publishing. ing. Here, as an example, a bandpass filter (BPF) process is performed on the scalar magnetic field H that is the output of the scalar magnetic sensor 1 and the outputs (p (pitch), r (roll), y (yaw)) of the machine body information sensor 5. Here, the body information at the time t after the bandpass filter processing is (pf (t), rf
(T), yf (t)) and the scalar magnetic field are represented as Hf (t). Assuming that pf (t), rf (t), and yf (t) are specific input data for the noise model to be estimated and the output is Hf (t), the input / output relational expression of the system (noise model) is It is represented by a difference equation such as.

[0024]

[Equation 6]

Here, bi, ci and di are magnetic compensation coefficients, n is the order of the noise model, and e (t) is noise.
Rewriting equation 6 gives equation 7.

[0026]

[Equation 7]

Here, equations 8, 9 and 10 are given.

[0028]

[Equation 8]

[0029]

[Equation 9]

[0030]

[Equation 10]

At this time, equation 11 holds.

[0032]

[Equation 11]

Here, Equation 12, Equation 13, Equation 14, and Equation 15
Is.

[0034]

[Equation 12]

[0035]

[Equation 13]

[0036]

[Equation 14]

[0037]

[Equation 15]

An evaluation function for estimating the parameter G is given by Expression 16.

[0039]

[Equation 16]

Here, it is assumed that W is an N × N positive definite symmetric matrix. If N is chosen large enough and Equation 17 is assumed, J
The optimum estimated value GH that minimizes is obtained from Eq.

[0041]

[Equation 17]

[0042]

[Equation 18]

When the magnetic compensation parameter estimated value GH is obtained off-line, N can be selected to be sufficiently large and Equation 18 can be used. In this paper, we describe an iterative estimation algorithm for online parameter estimation using newly observed data. Now, if the estimated value of G obtained by observing the input / output data up to time t is represented by GH (t), GH is calculated in the successive estimation.
It is desirable that (t + 1) be obtained using GH (t). In order to make an online iterative estimation, W
Let (t + 1) be a (t + 1) × (t + 1) positive definite value diagonal matrix and be set to Expressions 19 to 23.

[0044]

[Formula 19]

[0045]

[Equation 20]

[0046]

[Equation 21]

[0047]

[Equation 22]

[0048]

[Equation 23]

From Expression 18, Expression 24 is established.

[0050]

[Equation 24]

Here, the number 25 is replaced by the number 26.

[0052]

[Equation 25]

[0053]

[Equation 26]

From Expression 26, Expression 27 is established.

[0055]

[Equation 27]

Here, the numbers 28 and 29 are given.

[0057]

[Equation 28]

[0058]

[Equation 29]

Here, I is an identity matrix. Since Equation 25 is defined when Equation 30 is satisfied, at least t ≧ 2n−1
is necessary.

[0060]

[Equation 30]

However, since the calculation of the inverse matrix is not necessary in Equations 27 to 29, GH (t) (t = 1, 2, ...) Can be easily obtained if GH (0) and P (0) are given. Can be calculated to Usually, the initial value is given by Equations 31 and 32 with α being a sufficiently large positive number.

[0062]

[Equation 31]

[0063]

[Equation 32]

If α> 0, the asymptotic property of the estimated value does not change depending on how to select the initial value. If α is set to a sufficiently large positive number and the initial values are given by Equations 31 and 32, GH can be obtained by repeatedly using Equations 27 to 29.
(T) (t = 1, 2, ...) Can be obtained.
From the above, the magnetic compensation coefficient which is the output of the successive magnetic compensation coefficient estimator 6 by system identification is obtained. Although not shown here, it is easy to extend the method of weighting observation data and reducing the weight of past data.

The magnetic compensator 7 based on the system identification uses the outputs of the scalar magnetic sensor 1 and the body information sensor 5 and the magnetic compensation coefficient which is the output of the sequential magnetic compensation coefficient estimator 6 based on the system identification, Outputs the magnetic field strength HC of the geomagnetism after magnetic compensation.

[0066]

[Expression 33]

In Equation 33, the estimated magnetic compensation parameter is used immediately, but it is also possible to add a time delay if the system state changes slowly. As described above, it becomes possible to obtain a magnetometer capable of magnetic compensation without the need for compensating flight for performing a special motion for obtaining a compensation coefficient.

Embodiment 2. FIG. 2 shows a second embodiment of the present invention. In the figure, reference numerals 1, 6 and 7 are the same as those shown in FIG. 2 is the same as that shown in FIG.

With this configuration, the intensity of the geomagnetism (scalar magnetic field) H output from the scalar magnetic sensor 1 is
It is sent to the system-identified iterative magnetic compensation coefficient estimator 6 and the system-identified magnetic compensator 7. On the other hand, 3
The axis vector magnetic sensor 2 monitors information that causes magnetic noise that affects the magnetometer, and sends its output to a sequential magnetic compensation coefficient estimator 6 by system identification and a magnetic compensator 7 by system identification.

The operations of the system-identified iterative magnetic compensation coefficient estimator 6 and the system-identified magnetic compensator 7 are the same as those in the first embodiment. The operation of the triaxial vector magnetic sensor 2 is similar to that of the conventional example. As described above, it becomes possible to obtain a magnetometer capable of magnetic compensation without the need for compensating flight for performing a special motion for obtaining a compensation coefficient.

Third Embodiment FIG. 3 shows Embodiment 3 of the present invention. In the figure, 1, 5 to 7 are the same as those shown in FIG. 2 is the same as that shown in FIG.

With such a configuration, the intensity of the geomagnetism (scalar magnetic field) H output from the scalar magnetic sensor 1 is
It is sent to the system-identified iterative magnetic compensation coefficient estimator 6 and the system-identified magnetic compensator 7. On the other hand, 3
The axial vector magnetic sensor 2 and the airframe information sensor 5 monitor information that causes magnetic noise affecting the magnetometer, and the outputs thereof are used as a sequential magnetic compensation coefficient estimator 6 by system identification and a magnetic compensator by system identification. Send to 7.

The operations of the machine body information sensor 5, the sequential magnetic compensation coefficient estimator 6 by system identification, and the magnetic compensator 7 by system identification are the same as those in the first embodiment. The operation of the triaxial vector magnetic sensor 2 is similar to that of the conventional example. As described above, it becomes possible to obtain a magnetometer capable of magnetic compensation without the need for compensating flight for performing a special motion for obtaining a compensation coefficient.

[0074]

According to the first aspect of the present invention, the scalar magnetic sensor for detecting the earth's magnetism, the body information sensor for detecting the motion information of the body, the output of the scalar magnetic sensor and the output of the body information sensor, Magnetic compensation is performed from the output of the scalar magnetic sensor, the output of the airframe information sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification by the system identification that estimates the compensation coefficient. Since the magnetic compensator based on the system identification that outputs the strength of the magnetic field of the geomagnetism after the magnetic compensation is provided, there is an effect that the magnetic compensation that does not require the compensating flight for performing the special motion for obtaining the compensation coefficient can be performed.

According to the second aspect of the invention, the magnetic compensation coefficient is estimated from the scalar magnetic sensor and the triaxial vector magnetic sensor for detecting the geomagnetism, the output of the scalar magnetic sensor and the output of the triaxial vector magnetic sensor. Magnetic compensation is performed from the output of the scalar magnetic sensor, the output of the three-axis vector magnetic sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification. Since the magnetic compensator based on the system identification for outputting the strength of the magnetic field of the earth's magnetic field is provided later, there is an effect that the magnetic compensation that does not require the compensating flight for performing the special motion for obtaining the compensation coefficient can be performed.

According to the third invention, the scalar magnetic sensor and the 3-axis vector magnetic sensor for detecting the earth's magnetism, the machine information sensor for detecting the motion information of the machine, the output of the scalar magnetic sensor and the 3-axis. From the output of the vector magnetic sensor and the output of the three-axis vector magnetic sensor,
Sequential magnetic compensation coefficient estimator by system identification for estimating magnetic compensation coefficient, output of the scalar magnetic sensor, output of the three-axis vector magnetic sensor, output of the machine body information sensor, and sequential magnetic compensation coefficient by the system identification A magnetic compensator based on system identification that performs magnetic compensation from the output of the estimator and outputs the magnetic field strength of the geomagnetism after magnetic compensation is provided, so compensatory flight for performing special motion to obtain the compensation coefficient is unnecessary. There is an effect that various magnetic compensation can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a magnetometer according to the present invention.

FIG. 2 is a diagram showing a second embodiment of a magnetometer according to the present invention.

FIG. 3 is a diagram showing Embodiment 3 of the magnetometer according to the present invention.

FIG. 4 is a diagram showing a conventional magnetometer.

[Explanation of symbols]

1 scalar magnetic sensor, 2 3 axis vector magnetic sensor,
3 Magnetic compensation coefficient estimator, 4 Magnetic compensator, 5 Airframe information sensor, 6 Sequential magnetic compensation coefficient estimator by system identification, 7 Magnetic compensator by system identification.

Claims (3)

[Claims] 1. A magnetometer mounted on a movable body, a scalar magnetic sensor for detecting geomagnetism, a body information sensor for detecting motion information of the body, an output of the scalar magnetic sensor and the body information sensor. From the output of
Magnetic compensation is performed from the sequential magnetic compensation coefficient estimator by system identification for estimating the magnetic compensation coefficient, the output of the scalar magnetic sensor, the output of the airframe information sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification. A magnetometer equipped with a magnetic compensator by system identification that outputs the strength of the earth's magnetic field after performing magnetic compensation. 2. A magnetometer mounted on a movable airframe, wherein a magnetic field is detected from a scalar magnetic sensor and a triaxial vector magnetic sensor for detecting geomagnetism, and an output of the scalar magnetic sensor and an output of the triaxial vector magnetic sensor. From the output of the scalar magnetic sensor, the output of the three-axis vector magnetic sensor, and the output of the sequential magnetic compensation coefficient estimator by the system identification, the magnetic compensation is performed by the system identification for estimating the compensation coefficient. And a magnetic compensator by system identification that outputs the strength of the geomagnetic field after magnetic compensation. 3. A magnetometer mounted on a movable body, comprising a scalar magnetic sensor and a 3-axis vector magnetic sensor for detecting geomagnetism, a body information sensor for detecting motion information of the body, and the scalar magnetic sensor. A sequential magnetic compensation coefficient estimator by system identification for estimating a magnetic compensation coefficient from the output, the output of the three-axis vector magnetic sensor and the output of the machine body information sensor, the output of the scalar magnetic sensor and the three-axis vector magnetic sensor And the output of the airframe information sensor and the output of the iterative magnetic compensation coefficient estimator based on the system identification, and a magnetic compensator based on the system identification that performs magnetic compensation and outputs the magnetic field strength of the geomagnetism after magnetic compensation. Equipped magnetometer.