JPH0693017B2 - Passive ranging system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention receives noise radiated from a target moving in seawater or the like by a plurality of wave receivers, and reduces the radiated noise in the wave receivers. The present invention relates to a passive ranging system that estimates the position of the moving target by estimating the arrival time difference.

(Prior Art) Conventionally, this type of system has been disclosed in Reference 1 “AHQuazi:“ Effects of Signal and Noise Sp
ectral Slopes on Time Delay Estimation in Passive
Localization ", USGovemment Work NUSC." And Document 2 "GC Carter," Passive Ranging Errors due to
Receiving Hydrophone Position ", J.Acoust Soc.Am.Vo
l.62, No.d, 1979. ", and FIGS. 3 to 5 show the simplest case in which the number of receivers N = 3.

In FIG. ₃ , the radiated noise of the moving target received by the wave receivers 1 ₁ , 1 ₂ , 1 ₃ is amplified to a proper level by the amplifiers 2 ₁ , 2 ₂ , 2 ₃ and then subjected to a band limiting filter. Signals S ₁ (t), S ₂ (t), S ₃ (t) limited to an appropriate reception band by 3 ₁ , 3 ₂ , 3 _3.
The cross-correlation function between them is calculated by the cross-correlators 4 ₁ and 4 ₂ . In the example shown in FIG. ₁ , S ₁ (t) and S ₂
The cross-correlation function R _{1, 2} of (t) (τm), the cross-correlator 4 ₂
By the cross-correlation function R of S ₃ (t) and S ₂ (t)
We are looking for _3,2 (τm). Here, τm indicates a discrete time difference obtained by discretizing the time difference region τ with a step size Δτ.

The first maximum point detectors 5 ₁ , 5 ₂ are provided with the cross-correlation function R
The maximum point in the region τm of _1,2 (τm) and R _3,2 (τm) is calculated, and the maximum point is Output as. The interpolators 6 ₁ and 6 ₂ are the first maximum point detector 5
_1, 5 ₂ of output Cross-correlation functions R _1,2 (τ) and R in the vicinity of
_3,2 (τ) is calculated by an interpolation operation from the cross-correlation functions R _1,2 (τm) and R _3,2 (τm) in the discrete time difference region.

The second maximum point detectors 7 ₁ and 7 ₂ detect the cross-correlation function R
The maximum point in the region τ of _1,2 (τ) and R _3,2 (τ) is obtained, and the maximum point is Output as. The target position calculator 8 is based on, for example, the principle of a calculation formula as shown in Document 2, Using the array spacing between the wave receivers 1 ₁ , 1 ₂ and 1 ₃ and the signal propagation speed, the moving target position coordinates Is calculated and output to the output terminal 9.

FIG. 4 shows a first detailed implementation example of the cross-correlator 4 ₁ in FIG. 3, 10 ₁ and 10 ₂ are input terminals, 11 is a fixed delay device, 12 is a variable delay device, and 13 is a multiplication. , 14 is an integrator, and 15 is an output terminal.

Assuming 4 ₁ of FIG. 3 as a cross-correlator, the input terminal 10
₁ and 10 ₂ are the band-limited signals S ₁ (t) and S, respectively.
₂ (t) is input. The fixed delay device 11 gives a fixed time delay amount τ ₀ to the signal S ₂ (t) input from the input terminal 10 ₁ ,
The variable delay unit 12 receives the signal S input from the input terminal 10 _2.
A variable time delay amount τ ₀ + τm is given to ₁ (t). The delayed signals S ₁ (t−τ ₀ −τm) and S ₂ (t−τ ₀ ) are multiplied by a multiplier 13, integrated by an integrator 14, and then cross-correlation function R _{1, 2} (.tau.m) as an output of the cross correlator 4 _1, is output to the output terminal 15.

FIG. 5 shows a second detailed implementation example of the cross-correlator 4 ₁ in FIG. 3, 16 ₁ and 16 ₂ are respective AD converters (ADC), 17 ₁ and 17 ₂
Is each Digital Fourier Transform (DFT), 18 is a multiplier, 1
9 is an inverse digital Fourier transformer (IDFT), and 20 is an accumulator. The AD converters 16 ₁ and 16 ₂ are connected to the band-limited signal S
₁ (t) and S ₂ (t) are sampled at time intervals Ts and converted into digital signals S ₁ (tk) and S ₂ (tk). Digital Fourier transformer 17 ₁ K number of time-series signals S ₁ of the digital signal (tk): k = 1, ..., a digital Fourier transform value X ₁ of the K
(K): k = 1, ..., K is calculated, and the digital Fourier transformer 17 ₂ determines the digital Fourier transform value X ₂ (k): k = 1, of S ₂ (tk): k = 1, ... K. …, K is calculated.

The multiplier 18 calculates the Fourier transform values X ₁ (k) and X ₂ (k).
Product of And the inverse digital Fourier transformer 19 calculates the signal Y
(K): The inverse digital Fourier transform values of k = 1, ..., K are obtained, and the averaging operation is further performed by the accumulator 20 and then the cross-correlation function R
Output to output terminal 15 as _1,2 (τm).

(Problems to be Solved by the Invention) In the method shown in FIGS. 3 to 5, the interpolators 6 ₁ , 6 ₂ shown in FIG. 3 are used.
In order to estimate the true maximum point of the cross-correlation function by the interpolation operation, the cross-correlation functions R _1,2 (τm), R _3,2 (τm) calculated by the cross-correlators 4 ₁ , 4 ₂ are used. Since there is a constraint that the step width Δτ of τm of τm must be selected so that the interpolation theorem holds, let c be the center frequency of the band limiting filter and W be the bandwidth. Need to choose like. Therefore, when there is no prior information about the position or direction of the moving target, the array interval of the receivers is long, and the maximum value of the arrival time difference between the receiver signals is large, the cross-correlation correlators 4 ₁ , 4 ₂ There is a drawback that the number of cross-correlation functions that need to be calculated increases and the amount of processing required increases.

The above problems will be described in more detail. FIG. 6 shows the arrangement intervals of the receivers d _1,2 , d _3,2 and the arrival time differences τ _1,2 , τ _3,2 of the target when the number N of the receivers is N = 3. It is a diagram showing the relationship, 20 shows the moving target, X, Y is the origin of the receiver 1
₂ every, Y axis orthogonal coordinate system chosen so as to pass through the receiving transducer 1 _1, [theta] y is the direction cosine angle of the target 20 in the Y-axis, r is the distance of the target 20 from the receivers 1 _2. From FIG. 6, it is assumed that the propagation velocity of the signal is C when the distance r is sufficiently larger than the receiver array spacing d _1,2. Therefore, if there is no prior information on the position or direction of the moving target 20, τ _1,2 is It is necessary to calculate the cross-correlation function as if it exists in any of Since the same can be said for τ _3,2 , when there is no incident information regarding the position or direction of the moving target 20, the points that need to be calculated by the cross-correlators 4 ₁ and 4 ₂ are as follows. Become.

Where λmin is the maximum frequency in the reception frequency band Shows the wavelength of.

Therefore, when d _1,2 and d _3,2 are larger than the wavelength λ min, M ₁ and M ₂ are large, and the required processing amount is increased. For example, if c = 5.5 kHz, W = 10 kHz, C = 1500 m / sec (sound velocity in seawater), and d _1,2 = d _3,2 = 2,000 m, It becomes the order of.

On the other hand, as shown in the document, the estimation accuracy of the position of the target 20 in the passive ranging is such that the larger c and W, the larger the receiver array spacing d _1,2 , d _3,2 ,
Ie The higher is the higher. Therefore, the higher the accuracy in passive ranging, the greater the increase in the number of calculation points.

Therefore, the present invention does not have the aforesaid prior information on the position or direction of the moving target,
It must be assumed that the target exists in all directions, and the receiver array spacing is the maximum frequency of the reception band.
The problem of increasing the required number of calculation points in the cross-correlator, which is a problem when the wavelength is larger than max wavelength λmin, is eliminated, and the position estimation accuracy is reduced even if the reception bandwidth increases and the spacing of the receiver array increases. It is an object of the present invention to provide a passive ranging method that can reduce the increase in the number of calculation points without doing so.

(Means for Solving Problems) The present invention corresponds to a plurality of wave receivers (1) that receive noise radiated from a moving target and each wave receiver, as in the conventional passive ranging system. First filter means (21), which has a center frequency of fc and a band of W and which limits the band of the signal received by the receiver.
The cross-correlation function R _{i, j} (τ) between the two band-limited received signals with the outputs of the two first filter means as inputs
m) is calculated for each predetermined step width of the time difference, and a plurality of first cross-correlation means (23) and a time difference that gives the maximum cross-correlation function are detected based on the output of each first cross-correlation means.
First detecting means (25) for outputting the maximum point and first interpolating means for detecting the cross-correlation function R _{i, j} (τ) in the vicinity of the first maximum point detected by each of the first detecting means by interpolation operation. (27), second detecting means (29) for detecting a time difference that gives the maximum cross-correlation function based on the output of each first interpolating means and outputting it as a second maximum point, and a plurality of these second maximum points. It has a target position calculating means (8) for calculating an estimated value of the target position based on the second maximum point output from the two detecting means.

In addition to the above-mentioned structure, the present invention is provided corresponding to each wave receiver and has a center frequency fc 'and a band W', which limits the received signal by the wave receiver. Control means (24, 26) corresponding to the two filter means (22) and each first cross-correlation means and outputting the control information of the second maximum point to the corresponding first cross-correlation 1 means (23). , 28, 30) and are provided.

Further, the center frequency and band in the second filter 2 means of the present invention are set so as to satisfy the relationship of fc '+ W' / 2 <fc + W / 2.

Further, each control means of the present invention includes two second filters 2
Calculating the cross-correlation function R'i _{, j} (τm ') between the two band-limited received signals with the output of the means as an input for each step size which is larger than the step size and which satisfies the interpolation theorem. Two cross-correlation means (24), and a third detection means (26) for detecting a time difference giving a maximum cross-correlation function based on the output of each second cross-correlation means and outputting it as a first maximum point.
Based on the second interpolating means (28) for detecting the cross-correlation function R ′ _{i, j} (τ) in the vicinity of the first maximum point detected by the third detecting means by interpolation operation, and the output of the second interpolating means. Give the maximum cross-correlation function Detecting means (30) for detecting and outputting as the second maximum point
And have.

Furthermore, the first cross-correlation correlation means of the present invention limits the time difference range for calculating the cross-correlation function R _{i, j} (τm) to the vicinity of the second maximum point given as control information from the control means. It is what is done.

(Operation) The cross-correlation function _{^{▲ R 'i, j ▼ (}} ▲ τ' m ▼) of tau
The step size of the area By reducing the number of calculation points of ▲ R ^' _{i, j} ▼ (▲ τ ^' _m ▼), the calculation range of the cross-correlation function R _{i, j} (τm) in the τ region can be reduced. By reducing the number of calculation points of R _{i, j} (τm) by limiting to the vicinity of, the total number of calculation points of the cross-correlation function can be reduced.

(Embodiment) FIG. 1 is a functional block diagram showing an embodiment of the present invention, in which 21 ₁ , 21 ₂ and 21 ₃ are band limiting filters B, 22 ₁ , 22 ₂ and 22 _{3 respectively.}
Is each band-limiting filter A, 23 ₁ and 23 ₂ are each cross-correlator B, 2
4 ₁ and 24 ₂ are each cross-correlator A, 25 ₁ and 25 ₂ are each first maximum point detector B, 26 ₁ and 26 ₂ are each first maximum point detector A, 27 ₁ and 27 ₂ are The interpolators B, 28 ₁ and 28 ₂ are the interpolators A, the 29 ₁ and 29 ₂ are the second maximum point detectors B, and the 30 ₁ and 30 ₂ are the second maximum detectors A, respectively.

As shown in FIG. ₂ , the band limiting filters B21 ₁ , 21 ₂ and 21 ₃ and the band limiting filters A22 ₁ , 22 ₂ and 22 ₃ of this embodiment are ▲ ^′ _c
Select as ▼ + W '/ 2 <c + W / 2. That is, the band limiting filters A22 ₁ , 22 ₂ and 22 ₃ have the bandwidth of the first reception band '
Signals ▲ S ^′ ₁ ▼ (t), ▲ S ^′ ₂ ▼ (t), ▲ S ^′ ₃
(T) is output, and the band limiting filters B21 ₁ , 21 ₂ , and 21 ₃ output signals S ₁ (t), S ₂ (t), and S ₃ (t) having the second reception bandwidth W.

The cross-correlators A24 ₁ and 24 ₂ are the signals of the first reception band ▲ S ^'
₁ ▼ (t) and ▲ S ^' ₂ ▼ (t) and ▲ S ^' ₃ ▼ (t) and ▲ S ^' ₂ ▼ (t) are cross-correlators, and the cross-correlation function ▲ R ^' _1,2 ▼ (▲ τ ^′ _m ▼) and ▲ R ^′ _3,2 ▼
(▲ τ _^'m ▼) is calculated. In order for the interpolation theorem to hold in the interpolation operation of the phase compensators 28 ₁ and 28 ₂ , ▲ τ ^′ _m
▼ step size Δτ ′ is So that ▲ τ ^′ _m ▼ is Choose to cover all ranges of. Therefore, the calculation points ∇M ^' ₁ ▼ and ∇M ^' ₂ ▼ of the cross-correlation function are respectively given as follows.

However, ▲ lambda _^'min ▼ maximum frequency of the first reception band ▲
_^'Max ▼ wavelength C / ^▲' _max ▼ shows a.

First maximum point detector A26 _1, 26 _2, the maximum point detector 5 ₁ of the first of the FIG. 3, 5 ₂ similarly to the ▲ R _^'1,2 ▼ (▲ τ
_^'M ▼) and _{^{▲ R' 3,2 ▼ (▲ τ}} 'm ▼) takes the maximum value ▲ ^tau' _m ▼ value, The interpolators 28 ₁ and 28 ₂ are the same as the interpolators 6 ₁ and 6 ₂ shown in FIG. In the vicinity of the _{^{▲ R '1,2 ▼ (▲ τ}} ' m ▼) and ▲ ^{R '
_{3,2 ▼ (▲ τ 'm ▼}} ) complement correlation value ▲ ^R' _1,2 ▼ (τ) and ▲
R ^′ _3,2 ▼ (τ) is calculated, and the second maximum detector A 30 ₁ , 30 ₂
, The third same as the maximum point detector 7 _1, 7 ₂ of the second view, the R _1,2 (τ) and R _3,2 (tau) is the value of tau takes the maximum value Ask for.

The cross-correlators B23 ₁ , 23 ₂ are The cross-correlation function R _1,2 within the delay time width T centered on
Calculate (τm) and R _3,2 (τm). That is, the calculation points M ₁ and M ₂ of the cross-correlation function are approximately Becomes The time width T is at least Estimation error of It is necessary to select a size larger than the order of the interpolation function used in the interpolation calculation.

The first maximum point detector B25 ₁ , 25 ₂ has a τm value at which R _1,2 (τm) and R _3,2 (τm) have maximum values, And the interpolators 27 ₁ and 27 ₂ In the vicinity of, the interpolated values R _1,2 (τ) and R _3,2 (τ) of R _1,2 (τm) and R _3,2 (τm) are calculated, and the second maximum point detector 29 ₁ , 29 ₂ is a τ value at which R _1,2 (τ) and R _3,2 (τ) take the maximum value, Then, the estimated value is calculated by the target position calculator 8,
Similar to FIG. 3, the position coordinates of the moving target 20 Is output to the output terminal 9.

According to this embodiment, for example, c = 5.5 kHz, W = 10 kHz
When z, d _1,2 = d _2,3 = 2,000m and C = 1,500m / sec, ▲
_{^{'C ▼ = 1kHz, W'}} = If you choose to 1kHz, It becomes the order of. If the order of T = 10 × Δτ ′ is selected, the calculation points M ₁ and M ₂ of the cross-correlators 23 ₁ and 23 ₄ are ΔτΔτ ′ / 10 in this example, so M ₁ = M ₂ 100 ( 10).

Therefore, the total calculation score of the cross-correlation function is about 1.6.
The order of × 10 ⁴ or more is obtained, and the order of the calculation points by the conventional method is the order of 10 × 10 ⁴ from the above formula (3). Therefore, according to the present embodiment, the calculation point of about 1/6 is enough. Become.

(Effects of the Invention) As described above in detail, according to the present invention, the reception band is divided into the first reception band having the center frequency of ^{′ ′} _c ▼ and the bandwidth of W ′ and the center band having the center frequency of c. It is divided into a second reception band having a width of W, and ▲ ^′ _max ▼ = ▲ ^′ _c ▼ + W ′ / 2
By choosing smaller than max = c + W / 2,
The cross-correlation function is calculated using the signal in the reception band of The cross-correlation function is calculated using the signal in the second reception band only in the vicinity of Therefore, even if there is no prior information on the position or direction of the moving target, there is an advantage that the calculation amount can be significantly reduced without lowering the position estimation accuracy.

As described above, according to the present invention, the wavelength d of the receiver array and the wavelength λmin of the maximum frequency max in the reception frequency band are used.
Is effective when the ratio d / λmin is large, that is, when highly accurate passive ranging needs to be realized. For example, when c = 5.5 kHz, W = 10 kHz, and d = 2,000, ▲
^{If ′} _c ▼ = 1 kHz and W ′ = 1 kHz are selected, the calculation amount can be reduced to about 1/6 or more.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of characteristics of band limiting filters A and B in FIG. 1,
3 to 5 are explanatory views of the prior art, and FIG. 6 is an explanatory view of problems to be solved. 21 ₁ , 21 ₂ and 21 ₃ are each band limiting filters B, 22 ₁ , 22 ₂ and 22 ₃ are each band limiting filters A, 23 ₁ and 23 ₂ are each cross correlators B, 24 ₁ and 2
4 ₂ is each cross-correlator A, 25 ₁ and 25 ₂ are each first maximum point detector B, 26 ₁ and 26 ₂ are each first maximum point detector A, 27 ₁ and 27 ₂ are each interpolator B, 28 ₁ and 28 ₂ are interpolators A, 29 ₁ and 29 ₂ are second maximum point detectors B, and 30 ₁ and 30 ₂ are second maximum point detectors A. S ₁ (t), S ₂ (t), S ₃ (t) ... Received signal band-limited by the band-limiting filter B, ▲ S ^' ₁ ▼ (t), ▲ S ^' ₂ ▼ (t), ▲ S _^'3 ▼
(T) the received signal is band-limited by ...... band limiting filter A, τ, τm, ▲ τ 'm ▼ ...... time _{difference, R 1,2 (τm), R} 3,2 (τm), ▲ R' 1 _{, 2} ▼ (▲ τ ^′ _m
▼), ▲ R ^′ _3,2 ▼ (▲ τ ^′ _m ▼) …… Cross-correlation function, …… The value of τ _m , ▲ τ ^′ _m ▼ where the cross-correlation function takes the maximum value, R _1,2 (τ), R _3,2 (τ), ▲ R ^′ _1,2 ▼ (τ), ▲ R ^′
_3,2 ▼ (τ) …… Interpolated value near the maximum value, …… The value of τ for which the interpolated value takes the maximum value.

Claims (1)

[Claims] 1. A plurality of wave receivers for receiving noise radiated from a moving target, a wave receiver provided corresponding to each wave receiver, and having a center frequency fc and a band W. A first filter means for band-limiting the signal received by the wave receiver and an output of the two first filter means are input, and a cross-correlation function between the two received signals is calculated for each predetermined step size of the time difference. A plurality of first cross-correlation means, a first detection means for detecting a time difference which gives a maximum cross-correlation function based on the output of each first cross-correlation means, and outputting it as a first maximum point, and each first detection means. The first interpolating means for detecting the cross-correlation function in the vicinity of the first maximum point detected by the first interpolating operation, and the time difference that gives the maximum cross-correlation function based on the output of each first interpolating means are detected. Second output as maximum point Fc ′ + W ′ / 2 in the passive ranging system having a detection means and a target position calculation means for calculating an estimated value of the target position based on the second maximum points output from the plurality of second detection means. A second filter means having a center frequency fc 'and a band W', which satisfies the relationship <fc + W / 2, and limits the band of the signal received by the receiver; and the corresponding first mutual filter. And a control means for outputting the control information of the second maximum point to the correlation 1 means, and each control means receives the output of the two second filter 2 means as an input and a cross-correlation function between the two received signals. Is calculated for each step size that is larger than the step size and that satisfies the interpolation theorem.
Cross-correlation means, third detection means for detecting the time difference that gives the maximum cross-correlation function based on the output of each second cross-correlation means, and outputting it as the first maximum point, and third detection means detected by each third detection means. Second interpolating means for detecting a cross-correlation function in the vicinity of the one maximum point by interpolation operation, and a time difference which gives the maximum cross-correlation function based on the output of the second interpolating means is detected and output as the second maximum point. And a fourth detecting means, wherein the first cross-correlation means limits the time difference range for calculating the cross-correlation function to the vicinity of the second maximum point given by the control means. This is a passive ranging system.