CN114236519A - Signal processing method combining parallel multi-beam and dynamic aperture - Google Patents

Abstract

The invention relates to a signal processing method combining parallel multi-beam with dynamic aperture, which introduces dynamic aperture technology based on multi-beam, namely, the aperture size of a transducer array is variable in the echo signal receiving process, and comprises the following steps: array elements in the center of the array are in an open state, and other array elements are in a closed state; calculating to obtain the corresponding required beam widths of the focused beams completely covering the area between two adjacent scanning lines at different distances; calculating the aperture size; and controlling the gradual opening speed of the receiving array element channel. The signal processing method of the invention realizes high-speed dragging and distance full coverage by using a mode of combining multi-beam and dynamic aperture; wherein the high-speed dragging is mainly realized by increasing the number of sub-apertures, namely the number of beams; while distance full coverage is by dynamic aperture techniques.

Description

Signal processing method combining parallel multi-beam and dynamic aperture

Technical Field

The invention relates to a high-speed dragging side-scan sonar design technology, in particular to a signal processing method combining parallel multi-beams and a dynamic aperture.

Background

Conventional single beam side-scan sonar systems have a limit on the maximum towing speed Vmax when they do not leak-scan any seafloor region within the operating range. In addition, although the traditional multi-beam side-scan sonar system ensures higher towing speed, the traditional multi-beam side-scan sonar system only covers a medium and long distance target in an all-around way, and the phenomenon of missing scanning often occurs when a target in a short distance is scanned at a high speed, so that the design target with full distance coverage cannot be reached.

Disclosure of Invention

Therefore, the technical problem to be solved by the invention is to overcome the problem that the short-distance target is always missed to be scanned when a single-beam side-scan sonar system carries out high-speed scanning measurement on the short-distance target in the prior art, so that a signal processing method combining parallel multi-beams and dynamic apertures is provided, which can support high-speed dragging and can meet the requirement of full distance coverage.

In order to solve the above technical problem, the signal processing method of the present invention that combines parallel multi-beams with dynamic aperture introduces dynamic aperture technology based on multi-beams, that is, the aperture size of a transducer array is variable during echo signal receiving, includes the following steps:

step S1: the dynamic aperture technology is that only the array element at the center of the array is in an open state and other array elements are in a closed state when the echo signal is received;

step S2: according to the number of transducer array elements, carrying out uniform region segmentation on the acoustic image, and calculating to obtain the corresponding required beam widths of the focused beams completely covering the region between two adjacent scanning lines at different distances;

step S3: reversely deducing the aperture size required under the depth according to the beam widths of different detection distances;

step S4: controlling the gradual opening speed of a receiving array element channel to enable the beam width formed by the transmitting signal to be b1, b2, … and bm at the focal points F1, F2, … and Fm in sequence;

step S5: and normalizing the amplitude value of the synthesized beam according to the main maximum direction of the beam.

In an embodiment of the present invention, in step S3, if the size of the dynamic aperture needs to be obtained, the design curvature radius is R, the array element interval is d, m receiving focuses F1, F2, …, and Fm are provided on the scan line, the depth corresponding to each focus is Z1, Z2, …, and Zm, and each depth corresponds to a convex array description with a beam width of b1, b2, …, and bm.

In one embodiment of the present invention, the dynamic aperture technique combines the convex array parameters and the graph to obtain:

in one embodiment of the invention, the transducers have normalized directivity functions with respect to the discrete matrix:

in an embodiment of the present invention, the normalization result in step S5 is to combine the normalized directivity function with the dynamic aperture technique, that is, D (0, z) ═ 1(0dB), so as to obtain the number of open array elements:

in the formula:

the complex amplitude of the response of the ith array element of the discrete array;

calculating the acoustic phase difference between the point and the focus for the ith array element, wherein k is 1,2, …, m; n is a radical of_kIs a distance z_kThe number of the corresponding array elements is started.

Compared with the prior art, the technical scheme of the invention has the following advantages: the signal processing method combining the parallel multi-beam and the dynamic aperture realizes high-speed dragging and distance full coverage by using a mode of combining the multi-beam and the dynamic aperture; wherein the high-speed dragging is mainly realized by increasing the number of sub-apertures, namely the number of beams; while distance full coverage is by dynamic aperture techniques.

Drawings

In order that the present disclosure may be more readily and clearly understood, reference will now be made in detail to the present disclosure, examples of which are illustrated in the accompanying drawings.

Fig. 1 is a schematic diagram of beam positions of a conventional single-beam side-scan sonar;

fig. 2 is a schematic diagram of the beam positions of a multi-beam side-scan sonar;

fig. 3 is a schematic diagram of beam positions of the signal processing method combining parallel multi-beams and dynamic aperture of the present invention, wherein 3a is a schematic diagram of beam positions for long-distance coverage and 3b is a schematic diagram of beam positions for short-distance coverage;

fig. 4 is a schematic diagram of the change process after beam-on of the signal processing method combining the parallel multi-beam and the dynamic aperture according to the present invention;

FIG. 5 is an implementation schematic of a dynamic aperture technique;

FIG. 6 shows the number of open array channels N_kA relational data points table as a function of depth.

Detailed Description

The embodiment provides a signal processing method combining parallel multi-beams and dynamic apertures, where the signal processing method introduces a dynamic aperture technology based on multi-beams, that is, in an echo signal receiving process, an aperture size of a transducer array is variable, and the method includes the following steps:

step S1: the dynamic aperture technology is that only the array element at the center of the array is in an open state and other array elements are in a closed state when the echo signal is received; further, as shown in fig. 4, as time goes on, more and more array elements open the channel, and the receiving aperture gradually increases;

step S2: according to the number of transducer array elements, carrying out uniform region segmentation on the acoustic image, and calculating to obtain the corresponding required beam widths of the focused beams completely covering the region between two adjacent scanning lines at different distances;

step S3: reversely deducing the aperture size required under the depth according to the beam widths of different detection distances;

step S4: controlling the gradual opening speed of a receiving array element channel to enable the beam width formed by the transmitting signal to be b1, b2, … and bm at the focal points F1, F2, … and Fm in sequence;

step S5: and normalizing the amplitude value of the synthesized beam according to the main maximum direction of the beam.

Further, as shown in fig. 4, when callback data of a target at a short distance is received, only a small number of array elements are opened, so that the aperture is small, the main lobe of the beam is wide, and more areas can be covered, thereby achieving the purpose of short-distance coverage. When the long-distance target is detected, all the receiving array elements are opened, the receiving aperture is enlarged, and therefore, when the long-distance target is detected, the main lobe of the wave beam is narrowed, and the resolution ratio is increased.

And the calculation of the maximum drag speed limit is determined by the specific survey requirements. The number of irradiation targets specified according to the appropriate detection probability in a particular case will determine the maximum towing speed. The calculation formula is as follows:

V＝L×C/2×1.94/(R×H) (1)

wherein: l is the target length; c is the sound velocity in water, generally about 1500 m/s; h is the target irradiation times; r is the distance in meters; v is the towing speed in knots.

The survey requirements here are 1m for L, 3 times for H, and 150m for R long distance.

As shown in the beam position diagram of the conventional single-beam side-scan sonar shown in fig. 1, the maximum towing speed V is calculated according to equation (1) and is 1 × 1500/2 × 1.94/(150 × 3): section 3.2.

The beam position diagram of the multi-beam side-scan sonar of fig. 2 has a 5-beam number, so the maximum towing speed is increased by a factor of 4 compared to a single-beam side-scan sonar. The formula (1) becomes the following form:

V＝M×L×C/2×1.94/(R×H) (2)

m is the number of beams, which can also be considered as the number of sub-apertures for synthetic aperture sonar.

At this time, the maximum towing speed V is 5 × 3.2 — 16 knots. The towing speed is far higher than that of the single-beam side-scan sonar, but the single-beam side-scan sonar only covers a long-distance target, and as shown in fig. 2, the coverage rate of the short-distance target is very low, and the blind scanning area is also very large, so that the traditional multi-beam side-scan sonar only solves the problem of low towing speed of the single beam, and cannot simultaneously cover the short-distance target and the long-distance target.

At this time, the maximum towing speed V is 5 × 3.2 — 16 knots. The towing speed is far higher than that of the single-beam side-scan sonar, but the single-beam side-scan sonar only covers a long-distance target, and as shown in fig. 2, the coverage rate of the short-distance target is very low, and the blind scanning area is also very large, so that the traditional multi-beam side-scan sonar only solves the problem of low towing speed of the single beam, and cannot simultaneously cover the short-distance target and the long-distance target.

According to the problem that the traditional multi-beam side-scan sonar only improves the towing speed and does not realize the coverage of a short-distance target, the invention introduces a dynamic aperture technology on the basis of the traditional multi-beam, and aims at the difference of the aperture sizes of a long-distance target scanning array and a short-distance target scanning array, so as to achieve the effect of full coverage.

Fig. 3 is a schematic diagram of beam positions of the signal processing method according to the present invention, in which the parallel multi-beam and the dynamic aperture are combined, and the number of the sub-apertures is 5, so that the maximum towing speed is calculated according to the formula (2) to obtain V ═ 16 knots. Meanwhile, after the upper dynamic aperture technology is used, the coverage of a close-distance target is realized, and compared with the traditional multi-beam design of a left image, the close-distance coverage range is larger and the blind area is smaller.

The selection of the number of the sub-apertures is generally calculated according to the navigational speed substituting formula (2).

In step S3, the size of the dynamic aperture needs to be obtained, and the implementation process of the dynamic aperture technology is illustrated by taking a convex matrix as an example, as shown in fig. 5, a design curvature radius is R, an array element interval is d, m receiving focuses F1, F2, …, and Fm are provided on a scan line, a depth corresponding to each focus is Z1, Z2, …, and Zm, and a beam width corresponding to each depth is b1, b2, …, and bm.

The dynamic aperture technology combines convex array parameters and graphs to obtain:

the transducer has normalized directivity function of discrete matrix:

the normalization result in step S5 is to combine the normalized directivity function with the dynamic aperture technique, that is, D (0, z) ═ 1(0dB), so as to obtain the number of open array elements:

in the formula:

the complex amplitude of the response of the ith array element of the discrete array;

calculating the acoustic phase difference between the point and the focus for the ith array element, wherein k is 1,2, …, m; n is a radical of_kIs a distance z_kThe number of the corresponding array elements is generally solved by a computer iteration method.

Further, taking an actual convex array probe as an example, the related calculation parameters are set as follows:

the ultrasonic sound speed c is 1500 m/s;

the array element distance d is 0.78 mm;

the curvature radius R of the probe is 60 mm;

center frequency f of the pulse_c＝3.5MHz；

The detection depth range is within 20-200 mm;

uniformly taking 10 calculated depths Z on a focusing scanning line₁＝20，Z₂＝40，…，Z₁0-200 in mm.

The number N of the array element channels can be obtained by calculation of the formula (5)_kThe relationship with depth is shown in fig. 6.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.

Claims (5)

1. A signal processing method combining parallel multi-beam with dynamic aperture, the signal processing method introduces dynamic aperture technology based on multi-beam, that is, the aperture size of a transducer array is variable in the echo signal receiving process, characterized by comprising the following steps:

step S1: the dynamic aperture technology is that only the array element at the center of the array is in an open state and other array elements are in a closed state when the echo signal is received;

step S2: according to the number of transducer array elements, carrying out uniform region segmentation on the acoustic image, and calculating to obtain the corresponding required beam widths of the focused beams completely covering the region between two adjacent scanning lines at different distances;

step S3: reversely deducing the aperture size required under the depth according to the beam widths of different detection distances;

step S4: controlling the gradual opening speed of a receiving array element channel to enable the beam width formed by the transmitting signal to be b1, b2, … and bm at the focal points F1, F2, … and Fm in sequence;

step S5: and normalizing the amplitude value of the synthesized beam according to the main maximum direction of the beam.

2. The method of signal processing combining parallel multi-beams with dynamic apertures according to claim 1, characterized in that: in step S3, if the size of the dynamic aperture needs to be obtained, the design curvature radius is R, the array element spacing is d, m receiving focuses F1, F2, …, and Fm are provided on the scan line, the depth corresponding to each focus is Z1, Z2, …, and Zm, and each depth corresponds to a convex array description with the beam width of b1, b2, …, and bm.

3. The method of signal processing combining parallel multi-beams with dynamic apertures according to claim 2, characterized in that: the dynamic aperture technology combines convex array parameters and graphs to obtain:

4. the method of signal processing combining parallel multi-beams with dynamic apertures according to claim 1, characterized in that: the transducer has normalized directivity function of discrete matrix:

5. the method of signal processing combining parallel multi-beams with dynamic apertures according to claim 4, characterized in that: the normalization result in step S5 is to combine the normalized directivity function with the dynamic aperture technique, that is, D (0, z) ═ 1(0dB), so as to obtain the number of open array elements:

in the formula:

the complex amplitude of the response of the ith array element of the discrete array;

calculating the acoustic phase difference between the point and the focus for the ith array element, wherein k is 1,2, …, m; n is a radical of_kIs a distance z_kThe number of the corresponding array elements is started.

Images