JPH03218485A - Sonar signal processor - Google Patents

Abstract

PURPOSE:To obtain high azimuth resolution by moving a traveling object so that one part of an array composed of parallelly provided photodetectors at equal intervals can be overlapped at the time of reception, and correcting received data by using the information of the overlapped part. CONSTITUTION:At first, the array receives a signal like 2A at certain time and the traveling object receives waves while being turned to a state like 2B by the influence of waves. The reception signals as the outputs from the respec tive receivers at the overlapped part between the two arrays are received with the same sine wave as the transmitted wave as reflected wave at the respective receivers. At the deviated array 2B, the time delay of propagation is generated corresponding to the distance of each receiver. The distance of each receiver is set with the position of the first overlapped receiver as a reference on a lateral axis and the time delay of the receiver on the corresponding array 2A is plotted on a longitudinal axis so as to prepare a linear graph. An equation is calculated from this graph and the time delay of the arbitrary receiver output on the overlapped array 2B to the array 2A is calculated. Then, the already known time delay is corrected to the received signal obtained at each receiver of the overlapped part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for determining the direction of arrival of sound waves, and particularly to a device that obtains high azimuth resolution during wave reception.

[Conventional technology]

Conventionally, a synthetic aperture radar has been put into practical use to achieve high azimuth resolution.

In addition, in the field of sonar, a method using the synthetic aperture method was published in G.S.21, Vol. 54, No. 3 (1973), No. 7.
Pages 99 to 802 (The Journal of A
Coustical Society of Amer
ica VoQ. 5 4NQ3 (1973) pp7
99-802). This is the same principle as synthetic open radar, and the array must be moved accurately in a straight line.

[Problem to be solved by the invention]

The above-mentioned conventional technology requires a technique for accurately moving an array of 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.

The purpose of the present invention is to provide an array in which receivers are lined up to some extent.
The aim is to achieve azimuth resolution similar to the result obtained by receiving waves with a virtual array length approximately equivalent to the distance traveled by the array, even if the array moves away from the straight line. Another object of the present invention is to suppress side ropes.

[Means to solve the problem]

In order to achieve the above object, the sonar signal processing device of the present invention attaches to a moving body an array consisting of receivers lined up at equal intervals, and emits sound waves in the form of burst sine waves, linear FM waves, or encoded pulses. , in a device for detecting the position and direction of an object by receiving the reflected waves, a moving object is moved so that a part of the array overlaps when receiving the waves,
The feature is that beamforming is performed with an array length that roughly corresponds to the distance traveled by the array as a whole by correcting the received wave data of the non-overlapping part using the information of the overlapping part. shall be.

[Effect]

When moving the array and receiving reflected waves from an object to determine the direction of the object, a part of the array is overlapped, and this overlapped part receives waves from the non-overlapping part. Since the signal is corrected, it is possible to obtain a signal similar to the received signal obtained over the distance traveled by the array as a whole, so even if the ship sways to some extent, high azimuth resolution can be obtained.

〔Example〕

Embodiments of the invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

In the present invention, the received signals are acquired without overlapping a part of the array, and the received signals of the non-overlapping part are corrected with the information of the overlapped part. It is possible to have the same effect as receiving waves with. In order to achieve this effect, an input/output interface is required to transfer the data output from each receiver on the array to the signal processing device, and a storage device is required to store the output data. A central processing unit that performs calculations, a signal processing device that calculates the correlation between data obtained in overlapping areas, a fast Fourier transform device that corrects data in non-overlapping areas to determine direction, and calculations. It needs to consist of a display device to display the results. In these devices, if the central processing unit is high-speed, the central processing unit can also perform processing such as correlation and fast Fourier transform.

The physical principle of the present invention will be explained using FIGS. 2 to 4. In the following, it is assumed that a burst sine wave is used as the transmitted wave. first. Suppose that the array receives a signal at a certain time in a state like 2A in Figure 2. 6 Next, the moving object was supposed to move in a straight line, but due to the influence of waves etc.
Suppose that a signal is received in a state like this. here,
If the received waveforms of the outputs of each receiver are measured in the area where the two arrays overlap, the result will be as shown in FIG. 3. That is,
Each receiver receives the same sine wave as the transmitted wave as a reflected wave, and the shifted array 2B has a propagation time delay depending on the distance between each receiver. The time delay of each receiver on this overlapping array 2B is regular, and the horizontal axis represents the distance of each receiver based on the position of the first overlapping receiver, and the vertical axis Array 2A corresponding to the axis
If the time delay with the receiver above is plotted, a straight line graph as shown in Figure 4 will be obtained. This is because the receivers are arranged at equal intervals on the array, and a time delay occurs in the overlapping portion corresponding to the distance between corresponding receivers.

If the equation of this straight line is determined using the straight line graph in FIG. 4, it becomes possible to determine the time delay of any receiver output on the overlapping array 2B with respect to the array 2A. Therefore, once the time delay is known, if the known time delay is corrected for the received signal obtained by each receiver in the non-overlapping portion, the 7-ray 2
This is the same as receiving the wave on the extension of A, that is, at the position indicated by the dotted line.

Here, the accuracy of calculating the equation of the straight line in Figure 4 using the information of the overlapped part directly affects the accuracy of calculating the time delay of each receiver in the non-overlapping part. . As a result, the accuracy of time delay correction for non-overlapping portions is affected. Therefore, it is necessary to obtain the equation of the straight line shown in FIG. 4 with high accuracy. Since each corresponding receiver in the overlapped area receives the same reflected wave, the cross-correlation function of the time signal waveforms received by the corresponding receivers is as shown in FIG. The maximum value of the obtained cross-correlation function becomes the time delay between corresponding receivers.

When calculating the equation of the straight line in FIG. 4, in order to reduce the amount of calculation, the receiver outputs are used at regular intervals for every set or more of corresponding sets of receivers in the overlapped part. That is, find the cross-correlation function of the receiver output signals sampled at regular intervals.

The time delay is determined from the maximum value of this cross-correlation function.

The equation of the straight line shown in FIG. 4 is estimated using the least squares method from each time delay obtained. Since the least squares method minimizes the square error, it has good accuracy in fitting a straight line.

Above, we explained the burst sine wave as a transmission wave, but
The same applies to the transmission of linear FM waves and coded sequences.

A linear FM wave is a wave whose frequency is linearly modulated within the transmission pulse width. Figure 5 shows an example of a wave whose frequency is gradually increased. A pulse compression effect is performed by transmitting a wave as shown in Fig. 5 and passing it through a matched filter having a linear frequency vs. delay time characteristic as shown in Fig. 6. Therefore, an output having an envelope waveform as shown in Fig. 7 is obtained. The position showing the maximum value in Figure 7 represents the time delay between the corresponding receivers. In this way, if we find the time delay between corresponding receivers in the overlapped part and find the equation of the straight line in Figure 4 using the least squares method, we can find the time delay of each non-overlapping receiver. can be known. An example of a coded sequence wave is as follows when a wave consisting of an M sequence is used for transmission. The autocorrelation function of the M series is the 8th
As shown in the figure, it is sufficient to transmit waves within one cycle.

Among the various methods described above, an example of an algorithm when a sine wave is used for transmission and the data of every other set of receivers is used in each set of receivers in the overlapped part. is shown in Figure 9.

〔Effect of the invention〕

According to the present invention, the ship equipped with the array can accurately obtain a virtual long array length even if the ship is only slightly shaken.
It has the effect of achieving high lateral resolution. In addition, since beamforming can be performed using the data of a virtual long array length, it is possible to reduce the sagittal droop.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the essential parts of Fig. 1 with an overlapping array, and Figs. A graph showing the relationship between position and time delay, Fig. 5 is a graph of an example of a linear FM wave, Fig. 6 is a graph showing the characteristics of a linear FM wave,
Fig. 7 is a graph showing the Pagas compression, Fig. 8 is a graph showing the self-phase I function of the M series, and Fig. 9 is an embodiment of the present invention σ.
It is a flowchart.

Claims (1)

[Claims] 1. A device that detects the position and direction of an object by attaching an array consisting of equally spaced receivers to a moving object, emitting burst sine wave sound waves, and receiving the reflected waves. In this step, the moving object is moved so that a part of the array overlaps when receiving waves, and the received wave data of the non-overlapping part is corrected by using the information of the overlapped part. A sonar signal processing device characterized in that beamforming is performed with an array length approximately corresponding to the moving distance of the array as a whole.