JPH04125487A - Detecting method for position of object - Google Patents

Abstract

PURPOSE:To obtain a high azimuth resolution by performing synthesis by overlapping while shifting an array position when obtaining an azimuth where an object exists by receiving a reflected wave. CONSTITUTION:An array 2 of a specified length where a transmitter/receiver 3 is arranged is mounted to a moving body 1 and the reflection wave is received, thus enabling azimuth and distance of the object to be detected. At this time, transmission of signal which is obtained by combining verses of a certain frequency and frequencies which are different from it is repeated for a plurality of times. Then, one part of the array 2 which received the reflection wave previously is shifted by overlapping it with one part of the next array 2, the received data is compensated for as if it is received on an extension of the previous array 2, and then the amount of shift is detected by a virtual array length which nearly corresponds to the length obtained by adding the amount of shift to the specified length of the array 2 at least once. Therefore, a high azimuth resolution can be obtained even if the shifting body 1 where the array 2 is mounted swings more or less.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for determining the direction of arrival of sound waves, electromagnetic waves, etc., and in particular, a method for detecting the position of an object suitable for obtaining high azimuth resolution when receiving waves. Regarding.

[Conventional technology]

A conventional device using two pulse signals with different frequencies, as described in Japanese Patent Application Laid-Open No. 57-34507, obtains water depth information regarding an object placed underwater, and is used for beamforming. There was nothing.

[Problem to be solved by the invention]

The conventional method for detecting the position of an object using the aperture method requires a technique for accurately moving an array of wave receivers in a straight line. In reality, in the case of underwater sonar, the array cannot be moved accurately in a straight line because the ship on which it is mounted shakes due to the effects of waves and other factors.

On the other hand, even when synthetic aperture radar is used in the atmosphere, it is extremely sensitive to vibrations of the airplane and fluctuations in the atmosphere, making it difficult to accurately move an array of antennas in a straight line. For this reason, accurate received signals could not be obtained, resulting in noise when determining direction, and high azimuth resolution could not be achieved.

The purpose of the present invention is to obtain the result that even if the array in which the receivers are lined up moves away from the straight line, the wave is received with a virtual long array length that is added with a length approximately equivalent to the distance the array has moved. An object of the present invention is to provide a method and apparatus for detecting the position of an object that achieves azimuth resolution similar to that of the present invention. When forming a virtual long array, the present invention requires information on the distance between two receivers. When measuring this distance, a received signal is used, but when the received signal is a sine wave, the following problem occurs. When calculating the correlation function of the received signal and calculating the distance from its maximum value, if a sine wave is used, multiple maximum values of the correlation function may appear.

In such cases, the maximum value cannot be uniquely determined. Therefore, the exact distance is uncertain. In order to solve this problem, the present invention uses two pulse signals with different frequencies. By using such a signal, the maximum value of the correlation function can be uniquely determined. In addition, the distance between two points can be calculated by calculating the phase difference between two corresponding pulses, which can significantly reduce the amount of calculation compared to using correlation coefficients. It also has some characteristics.

Other objects of the present invention are to significantly improve azimuth resolution, increase array gain, suppress side lobes (subpoles), improve target detection sensitivity, and improve received signal-to-noise.

[Means to solve the problem]

In order to achieve the above object, the method and device for detecting the position of an object according to the present invention includes mounting an array of a predetermined length in which transducers are arranged on a moving body, and receiving the reflected waves to determine the direction and distance. In a method for detecting the position of an object, a signal combining a burst sine wave of a certain frequency and a burst sine wave of a different frequency is transmitted multiple times,
The reception signal of the array that received the reflected wave first and the part of the array that receives the wave from the second time onward overlaps a part of the previous array, and receives the reflected wave, making each array overlap. The positional relationship between the two arrays is determined based on the signals from the corresponding receivers, and the second and subsequent received signals are corrected so that the received signal is received by a virtual long array that is an extension of the first received array. However, the present invention is characterized in that the detection is performed with a virtual array length approximately corresponding to the length obtained by adding the amount of movement at least once to the predetermined length of the array.

[Effect]

According to the method for detecting the position of an object of the present invention, when the direction in which the object exists is determined by receiving reflected waves from the object while moving the array, the arrays are shifted in position, overlapped, and synthesized. Since different sine waves are transmitted successively, the maximum value of the correlation function can be uniquely determined, and as a result, the positional relationship of the arrays can be determined, and the received signals of the overlapping arrays can be corrected. can name. Overall, a signal similar to the received signal obtained with the array length obtained by adding the distance traveled by the array is obtained. Even if the moving object on which the array is mounted, such as a ship or an airplane, shakes a little, high azimuth resolution can be obtained.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 8.

In the present invention, as shown in FIG. 1, an array 2 having a predetermined length U in which receivers 3 are arranged is mounted on a moving body 1 such as a ship, and a burst sine wave of a certain frequency and a burst sine wave of a different frequency are transmitted. In a method for detecting the position of an object in which the direction and distance are detected by repeatedly transmitting a signal that is a combination of burst sine waves multiple times and receiving the reflected wave, at least once,
Move a part of the array so that it overlaps with a part of the previous array, correct the received data as if it were received on an extension of the previous array, and add the amount of movement to a predetermined length U of the array. The array is configured to detect a virtual array length that approximately corresponds to the length added at least once.

An array 2 of a predetermined length U in which the receivers are arranged is mounted on the moving body 1, and a storage device 9 that captures the received signals and stores the signals, and a central processing unit (CPU) that processes the signals.
The input/output device 5, which inputs and outputs the received signal to and from the signal processing device 4, includes a display device 10 that displays the result of signal processing.
stores the signal received by array 2, moves the moving body l at least once so that a part of this array overlaps, stores the received signal in the storage device, and stores the received signal in the storage device. Based on the wrapped information, the signal received from the second time onwards is corrected, and the length obtained by adding the amount of movement at least once to the predetermined length U of array 2 is detected with an array length equivalent to &K. The structure shall be equipped with means.

FIG. 1 is a diagram showing an example of the entire apparatus for realizing the method of the present invention. In the present invention, when performing the synthetic aperture method realized in synthetic aperture radar etc., instead of simply connecting arrays on an extension of the array, the arrays are overlapped when shifting their positions, and the In order to obtain a virtual long array length by connecting the array on the extension of the array without correcting the received wave data,
High azimuth resolution can be achieved using more accurate received wave data.

In order to realize this, an input/output device 5 is provided which transfers the data of the output of each receiver on the array to the signal processing device 4, and a storage device 9 which stores the output data. A central processing unit that performs calculations (
CPU)6. 4. A signal processing device that corrects the received signal based on information on the movement of the ship. Fast Fourier Transform (FFT) to find the bearing using the corrected signal7. It is necessary to configure the display device 10 and the like that display the calculation results. In these devices, if the central processing unit 6 is high-speed, the central processing unit 6 can perform any fast Fourier transform processing.

First, a synthetic aperture method that improves lateral resolution will be described. The synthetic aperture method uses a finite-length array several times to realize a long virtual array. As a premise for performing this synthetic aperture method, it is necessary that the following two points hold true.

(1) The moving object must be able to move accurately in a straight line. (2) The target must remain stationary while the synthetic aperture is being performed. In Figure 2, the reflected wave was first received in the state shown in ■. shall be.

Next, the moving object moves to ■ as an extension of ■, transmits waves, and receives reflected waves. Suppose that the variable moving object moves to position (■), transmits waves, and receives waves in the same way. I repeated sending and receiving waves five times, but if the target was stationary, every reflected wave should return exactly the same. Therefore, this operation is the same as receiving the data of the virtual long array shown in FIG. 2 by dividing it into five sections. For this reason, it is not possible to perform beamforming by connecting each piece of data received in five sections, which is the same as performing beamforming on a long virtual array. As a result, high lateral resolution can be obtained.

Next, the principle of the present invention will be explained with reference to FIGS. 3 to 6. Assume that a transmission consisting of two burst sine waves as shown in FIG. 3 is performed, and the first angular frequency is ω1 and the second angular frequency is ω2. In response to this transmission, the array receives the sound wave at a certain time, and after a certain period of time (as the ship moves) the wave transmission and reception are repeated. At this time, the same array receives the sound wave by partially overlapping the array that received the wave last time. Here, it is assumed that the moving object was supposed to travel in a straight line, but a deviation occurred due to the influence of waves and the like. This state is shown in FIG. The deviation in Fig. 4 is considered not to be so large unless the waves are high. A sound wave consisting of two burst sine waves was received three times by the same array, the first one being array A, and the second one being array B. In FIG. 4, array B is not an extension of array A. For this reason, it is impossible to obtain high lateral resolution using the synthetic aperture method.

In Figure 4, the overlapping receivers on array A are designated as ai, the overlapping receivers on array B are designated as bi, the remaining receivers on array B are designated as bj, and array A
Let cj be a virtual receiver corresponding to bj on the extension of
Let the array consisting of cj be array C. The same reflected waves are incident on ai and bi, but the difference between them is the arrival time difference τ of the reflected waves, as shown in FIG. The arrival time difference τ of this reflected wave increases in proportion to the distance to the corresponding receiver, and it is thought that this relationship also exists between bj and cj. Therefore, by using the received data of bj and correcting it by τ, the received data of cj can be obtained. Below, cj
This section describes how to obtain the received data.

First, the arrival time difference of corresponding overlapping receivers is determined. This calculates the cross-correlation function of the receiver output,
All you have to do is find the maximum value (Figure 6). When only a burst sine wave is used for transmission, this maximum value is determined to be a - point when the maximum value of the correlation function of the sine wave occurs periodically as shown in FIG. 7. Therefore, the maximum value can be determined more reliably than when a burst sine wave is used for transmission. This operation for determining the maximum value is performed for all overlapped parts. Then, a graph as shown in FIG. 8 is drawn, with the horizontal axis representing the position from the receiver that started the overlap, and the vertical axis representing the maximum value of each cross-correlation function. Since the straight line on this graph indicates the slope of array B, in order to obtain this straight line with high accuracy, it is determined by the method of least squares. From the obtained straight line, the difference in arrival time of sound waves between array B in the non-overlapping portion and array C on the extension of array A is determined. The non-overlapping received signals of array B are
The received signal of array C is corrected by this arrival time difference. The received wave data of array A and array C may be used for beam forming in the process of determining the direction of the sound wave.

The above algorithm is shown in FIG.

To reduce the amount of calculation required to calculate the slope of the array,
It is sufficient to obtain the correlation functions of several sets of corresponding receivers among the receivers in the overlapped portion, and to obtain a straight line equation for these using the least squares method. Furthermore, in order to minimize the amount of calculation, it is sufficient to select two representative numbers and obtain a linear equation by linear interpolation as shown in FIG. After finding the inclination of array B using each method, find the arrival time difference of the sound waves in the same way, correct the received signals in the non-overlapping part by this arrival time difference, and calculate the arrival time difference of the virtual array C. It is sufficient to perform beamforming by combining the received signal with the signal of array A.

When using wave transmission as shown in FIG. 3, the following processing can also be considered. This is a method of determining the time delay from the phase difference of the same frequency. Angular frequency ω1. The ω2 sine wave occurs after the same time delay.

The phase of ω1 is 2nπ+01, the phase of ω2 is 2mπ+02
If so, the following formula holds true.

2nπ+01=τω1...(1)2
mπ+02=τω2 (2) Here, by subtracting equation (2) from equation (1), equation (3) is obtained, and τ can be determined.

τ=(2nz+01-2nπ+02)/(ωl-ω2)
(3) This operation may be performed for all overlapping sets of receivers, and a straight line may be estimated by the least squares method. Alternatively, a straight line may be determined by taking out several sets of corresponding receivers and using least squares or the like. Alternatively, each τ may be determined using two representative sets of receivers, and a straight line may be determined by linear interpolation. In any of the above methods, the relationship between the arrays becomes clear.

Once the relationship between the arrays is clear, the bj signal can be corrected to obtain cj received data.

Thus, a virtual long array is obtained.

Although the above-mentioned embodiments have been described with respect to sound waves, exactly the same functions and effects can be obtained when an antenna array using electromagnetic waves is mounted on an airplane or on an artificial satellite.

〔Effect of the invention〕

According to the present invention, even if a ship carrying an array or an airplane carrying an antenna shakes a little, a virtually long array length can be accurately obtained, and high azimuth resolution can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of the synthetic aperture method, Fig. 3 is a waveform diagram used for wave transmission, and Fig. 4 is an array showing the main parts of Fig. 1. Explanatory diagram with misalignment, 5th
The figure is an explanatory diagram showing the arrival time difference of received signals between receiver ai of array A and receiver bi of array B.
Figure 7 is an explanatory diagram of the correlation function of a sine wave, and Figure 8 is a diagram of the waveform obtained by calculating the cross-correlation function with i. FIG. 9 is a flowchart of an embodiment of the present invention, and FIG. 1o is an explanatory diagram for estimating a straight line.

Claims (1)

[Claims] 1. In an object position detection method in which an array of transducers of a predetermined length is mounted on a moving body and the reflected waves are received to detect the direction and distance, a burst sine wave of a certain frequency and a burst sine wave of a certain frequency are used. Transmission of a signal combining burst sine waves of different frequencies is repeated multiple times, and the received signal of the array that first received the reflected wave and the part of the array that receives the reflected wave from the second time onwards are different from the previous one. The reflected wave is received by overlapping a part of the array, and the positional relationship between the two arrays is determined based on the signal from the corresponding overlapped receiver of each array, and the array that received the wave first is The second and subsequent received signals are corrected so that the received signal is received by a virtual long array on the extension of A method for detecting the position of an object characterized by detecting the position using a virtual array length.