CN109655834B - Multi-beam sonar sounding method and system based on constant false alarm detection - Google Patents

Abstract

The invention relates to a multi-beam sonar sounding method and a multi-beam sonar sounding system based on constant false alarm detection. The invention discloses a constant false alarm detection-based multi-beam sonar sounding method, which comprises the following steps of: s1, emitting a multi-beam sounding sonar beam, and receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected; s2, pre-detecting a signal to be detected through VI-CFAR to obtain an echo time interval with the amplitude larger than a first threshold value in the signal to be detected; s3, sequentially obtaining time intervals of continuous echo time intervals, and combining the echo time intervals when the time intervals are smaller than a second threshold value so as to finally obtain a complete echo time interval of the detection target; and S4, acquiring the accurate position of the detection target through a bottom detection method. The implementation of the invention can improve the detection effectiveness and stability and realize the accurate detection of multiple targets.

Description

Multi-beam sonar sounding method and system based on constant false alarm detection

Technical Field

The invention relates to the technical field of multi-beam sonar sounding, in particular to a multi-beam sonar sounding method and system based on constant false alarm detection.

Background

The multi-beam sounding sonar widely uses a Mills cross arrangement technology, and completes the acquisition of a plurality of direction beam signals through a transmitting and receiving beam forming technology. And through a bottom detection algorithm, dozens of to hundreds of depth values can be measured at one time, and the method is widely applied to surveying and mapping of underwater terrains. The bottom detection algorithm is a linkage process of detection and estimation, wherein the detection is to determine whether the bottom exists in the received echo signal, the estimation is to accurately estimate the arrival time TOA and the arrival angle DOA of the submarine topography on the basis of the detection result, and the depth of the submarine topography to be detected is determined by combining the known sound velocity. At present, the traditional bottom detection technologies, such as WMT, energy center convergence method, split sub-array method, multi-sub-array method, etc., can only detect one of two kinds of targets in water and submarine topography, and cannot meet the mapping requirements in complex marine environments. In order to improve the detection capability of the multi-beam sounding sonar on the water target position on the basis of ensuring the reliable bottom detection capability, a pre-detection link can be added before bottom detection, the echo intervals of the water target and the seabed are obtained in advance, and then the accurate water target position and the seabed terrain depth are obtained simultaneously through a bottom detection algorithm.

The existing pre-detection method based on a fixed threshold is influenced by uneven background noise, and the detection stability and effectiveness need to be improved. The CFAR (Constant False Alarm Rate) detector calculates a detection threshold value based on a background noise estimation unit, the threshold value is adaptively adjusted along with the fluctuation of the background, constant False Alarm probability is kept, and the CFAR detector is widely applied to radar and sonar signal detection. Existing CFAR detection methods, such as a cell average CFAR (CA-CFAR) detector, an order statistics CFAR (OS-CFAR) detector, and a clear average CFAR (CCA-CFAR) detector, generally have better detection performance in a specific environment, and have larger detection loss in other environments. In addition, due to fluctuation and broadening of multi-beam sounding sonar echoes, a detection result of a target echo may be discrete, and the method cannot be effectively used for a multi-beam sounding sonar bottom detection algorithm.

Disclosure of Invention

The invention aims to solve the technical problem of providing a multi-beam sonar depth sounding method and system based on constant false alarm detection aiming at partial technical defects in the prior art.

The technical scheme adopted by the invention for solving the technical problems is as follows: a multi-beam sonar depth sounding method based on constant false alarm detection is constructed, and the method comprises the following steps:

s1, emitting a multi-beam sounding sonar beam, and receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected;

s2, pre-detecting the signal to be detected through VI-CFAR to obtain an echo time interval with the amplitude larger than a first threshold value in the signal to be detected;

s3, sequentially obtaining time intervals of continuous echo time intervals, and combining the echo time intervals when the time intervals are smaller than a second threshold value so as to finally obtain a complete echo time interval of the detection target;

and S4, acquiring the accurate position of the detection target through a bottom detection method.

Preferably, the detection target includes a plurality of detection targets, and the second threshold includes a plurality of second thresholds respectively corresponding to the plurality of detection targets;

in step S3, the merging the echo time intervals to obtain a complete echo time interval of the detection target includes:

and respectively obtaining complete echo time intervals corresponding to the detection targets according to the second threshold values.

Preferably, the method further comprises:

s3-1, obtaining a beam footprint of the detection target to obtain a pre-judgment time width of the detection target, and obtaining the second threshold according to the pre-judgment time width.

Preferably, the method for calculating the prejudgment time width comprises the following steps:

wherein θ is the incident angle of the sonar beam, t is the round trip time of the sonar beam, and Θ is the-3 dB beam width of the sonar beam.

Preferably, the acquiring the beam footprint of the detection target includes: and acquiring beam footprints corresponding to the detection target in two continuous echo time intervals.

Preferably, in step S1, the receiving a signal to be detected including a noise signal and a target echo signal of a target to be detected includes:

and receiving the noise signal and a target echo signal of the target to be detected, and forming and detecting a receiving beam to obtain the signal to be detected.

Preferably, in step S2, the pre-detecting the signal to be detected by VI-CFAR includes:

acquiring a variability index VI in a detection sliding window, and judging whether the target to be detected is in a uniform environment or not according to the variability index VI;

when the environment is uniform, pre-detecting the signal to be detected through CA-CFAR;

and when the environment is non-uniform, pre-detecting the signal to be detected through CCA-CFAR.

Preferably, said obtaining the variability index VI within the detection sliding window comprises:

respectively obtaining the variability indexes VI of the front edge sliding window and the rear edge sliding window of the detection sliding window;

the method further comprises the following steps:

respectively comparing the variability index VI with a third set threshold value to confirm whether the front edge sliding window and the back edge sliding window are uniform sliding windows;

when any one of the front edge sliding window and the back edge sliding window is a uniform sliding window, pre-detecting the signal to be detected through the CA-CFAR based on the uniform sliding window;

when the front edge sliding window and the back edge sliding window are both uniform sliding windows, pre-detecting the signal to be detected through the CCA-CFAR based on the whole sliding window;

and when the front edge sliding window and the back edge sliding window are both non-uniform sliding windows, pre-detecting the signal to be detected through the CCA-CFAR based on the whole sliding window.

Preferably, in the step S4, the bottom detection method includes any one of WMT, a split sub-array method, and a multi-sub-array method.

The invention also constructs a multi-beam sonar sounding device based on constant false alarm detection, which comprises:

the sonar emission unit is used for emitting multi-beam sounding sonar beams;

the sonar receiving unit is used for receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected;

a signal processing unit for processing the signal to be detected according to the method of any one of the above.

The implementation of the constant false alarm detection-based multi-beam sonar sounding method and the system has the following beneficial effects: the detection effectiveness and stability are improved, and the multi-target accurate detection can be realized.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a flowchart of a procedure of an embodiment of the multi-beam sonar sounding method based on constant false alarm rate detection according to the present invention;

FIG. 2 is a schematic diagram of echo time intervals;

FIG. 3 is a schematic diagram of echo time intervals for a water target and a seafloor;

fig. 4 is a flowchart of the procedure of another embodiment of the multi-beam sonar sounding method based on constant false alarm rate detection according to the present invention;

FIG. 5 is a schematic diagram of beam-based footprint illumination;

FIG. 6 is a graph comparing the results of the present invention and the prior art test;

FIG. 7 is a graph showing the results of the detection according to the present invention;

fig. 8 is a logic block diagram of an embodiment of the multi-beam sonar sounding system based on constant false alarm detection according to the present invention.

Detailed Description

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in fig. 1, in an embodiment of the multi-beam sonar depth sounding method based on constant false alarm detection according to the present invention, the method includes the following steps:

s1, emitting a multi-beam sounding sonar beam, and receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected; specifically, when the underwater topography is detected, a multi-beam sounding sonar wave beam is emitted through an emission array, the sonar wave beam is received by a receiving array after being refracted by sea water and reflected by seabed or an intermediate in water, the received signal is used as a signal to be detected after being formed by the wave beam and detected, and the signal to be detected contains a target echo signal reflected by a target to be detected and also contains a noise signal generated due to environmental influence.

S2, pre-detecting a signal to be detected through VI-CFAR to obtain an echo time interval with the amplitude larger than a first threshold value in the signal to be detected; specifically, in the VI-CFAR pre-detection process, the echo time interval with the amplitude larger than the first threshold value in the signal to be detected is extracted according to the threshold value of the VI-CFAR, namely the first threshold value, so that a plurality of discrete echo time intervals related to the target to be detected are obtained. As shown in fig. 2, two time intervals (t 1, t 2) and (t 3, t 4) are obtained.

S3, sequentially obtaining time intervals of continuous echo time intervals, and combining the echo time intervals when the time intervals are smaller than a second threshold value so as to finally obtain a complete echo time interval of the detection target; specifically, the time intervals of adjacent echo time intervals are compared, and when the time intervals of the two echo time intervals are smaller and meet certain requirements, namely meet a second threshold, the two echo time intervals can be considered to come from the same target to be detected, and the two echo time intervals can be combined. And carrying out continuous comparison, and combining the echo time intervals meeting the requirements, so that a complete echo interval of the target to be detected can be obtained. If the time interval between adjacent echo time intervals is equal to or exceeds the second threshold, the two echo time intervals are not from the same target to be measured, and the two echo time intervals are processed respectively. In the embodiment shown in fig. 2, the difference between the threshold and t3-t2 is compared, and when the difference satisfies the threshold requirement, (t 1, t 2) and (t 3, t 4) may be combined to obtain a complete echo time interval (t 1, t 4). With more echo time intervals, successive combining can be performed.

And S4, acquiring the accurate position of the detection target through a bottom detection method. Specifically, after a complete echo time interval of the target to be detected is obtained, an arrival angle DOA and arrival time TOA of a sonar wave beam reaching the target to be detected are accurately estimated on the obtained complete echo time interval of the target to be detected by using a bottom detection algorithm, and an accurate position of the target to be detected is obtained by combining a known sound velocity.

Further, the detection target includes a plurality of detection targets, and the second threshold includes a plurality of second thresholds respectively corresponding to the plurality of detection targets; in step S3, merging the echo time intervals to obtain a complete echo time interval of the detection target includes: and respectively obtaining complete echo time intervals corresponding to the detection targets according to the second threshold values. Specifically, as shown in fig. 3, the conventional submarine detection includes submarine topography detection and detection of a water target in the middle of seawater, where pre-detection results of the water target and the submarine are obtained, and discrete pre-detection results meeting requirements are combined into a continuous time interval, so that respective complete echo time intervals of the water target and the submarine can be obtained. A in the figure corresponds to a water body target, and B in the figure corresponds to a sea bottom, so that accurate calculation of the water body target and the sea bottom can be realized respectively without mutual interference.

Preferably, as shown in fig. 4, the multi-beam sonar depth sounding method based on constant false alarm detection further includes:

s3-1, obtaining a beam footprint of the detection target to obtain a pre-judgment time width of the detection target, and obtaining a second threshold according to the pre-judgment time width. Specifically, the second threshold may be calculated by obtaining a prejudged time width of the detection target through a beam footprint of the detection target, and obtaining the second threshold according to the prejudged time width. The predicted time width represents the broadening of the acoustic echo of the water body target or the sea bottom (the target echo will widen because the irradiation of the target by the acoustic beam is a surface, not a point). When the interval of the discrete time intervals is within the range, the discrete echoes are from the same target.

Further, the calculation method of the prejudgment time width comprises the following steps:

wherein, theta is the incident angle of the sonar wave beam, t is the round trip time of the sonar wave beam, and theta is the-3 dB wave beam width of the sonar wave beam. Specifically, due to the existence of a certain beam width Θ of the beams, the arrival time of the target echo at different positions of each beam footprint is different, and as shown in fig. 5, the return time of the echo at the point a in the beam footprint is shortest and the return time of the echo at the point B in the beam footprint is longest, so that the target echo signal in each beam has a certain spread in time. Assuming that the beam footprint is horizontal to the target and seafloor illumination in the body of water, the broadening widths of the echoes of the body of water target and seafloor in time can be approximated by the above formula.

Further, the obtaining of the beam footprint of the detection target includes: and acquiring beam footprints corresponding to the detection target in two continuous echo time intervals. Specifically, the beam footprint is to be associated with two time intervals to be combined, and may also be understood as to start to acquire the beam footprint by taking the starting time of the two time intervals to be combined, for example, in fig. 2, to compare the echo time intervals (t 1, t 2) and (t 3, t 4) to determine whether to combine, the starting time t1 is taken to calculate according to the above-mentioned method for calculating the prejudged time width, and a second threshold corresponding to the time is acquired, and when the echo time interval changes, the time in calculating the prejudged time width also changes, so that dynamic threshold setting is realized.

Further, in step S1, receiving a signal to be detected including a noise signal and a target echo signal of a target to be detected includes: and forming and detecting the received noise signal and a target echo signal of the target to be detected through a receiving wave beam to obtain a signal to be detected. Specifically, the received noise signal and the target echo signal of the target to be detected are detected to obtain the required signal to be detected. The detection method here may be envelope detection or square rate detection.

Further, in step S2, the pre-detecting the signal to be detected by the VI-CFAR includes: acquiring a variability index VI in the detection sliding window, and judging whether the target to be detected is in a uniform environment or not according to the variability index VI; when the environment is uniform, pre-detecting the signal to be detected through CA-CFAR; and when the environment is non-uniform, pre-detecting the signal to be detected through CCA-CFAR. Specifically, the process of detecting the signal to be detected includes calculating a variability index VI in a detection sliding window:

wherein X is the data of the sliding window,

is the mean of the corresponding sliding window, and n is the length of the corresponding sliding window. Then by comparing VI with a set threshold K _VI Whether the sliding window is uniform or not is judged, and the judgment method comprises the following steps:

the VI-CFAR detector selects a different constant false alarm detector depending on whether the sliding window is uniform. For a uniform environment, the CA-CFAR detector has optimal detection performance; in this case, the VI-CFAR detector selects a sliding window as a unit for estimating the background noise, and the detection is performed by using the CA-CFAR detector. For the non-uniform case, the VI-CFAR detector selects CCA-CFAR at this time, improving the detection performance of the detector in the presence of unknown interference in the sliding window, while maintaining the detection performance of the detector in other cases.

Further, obtaining the variability index VI within the detection sliding window comprises: respectively obtaining variability indexes VI of a front edge sliding window and a rear edge sliding window of a detection sliding window; the method further comprises the following steps: respectively comparing the variability index VI with a third set threshold value to determine whether the front edge sliding window and the back edge sliding window are uniform sliding windows; when any one of the front edge sliding window and the back edge sliding window is a uniform sliding window, pre-detecting a signal to be detected through CA-CFAR based on the uniform sliding window; when the front edge sliding window and the back edge sliding window are both uniform sliding windows, pre-detecting a signal to be detected through CCA-CFAR based on the whole sliding window; and when the front edge sliding window and the back edge sliding window are non-uniform sliding windows, pre-detecting the signal to be detected through CCA-CFAR based on the whole sliding window. Specifically, when the variability index VI in the detection sliding window is calculated, the leading edge sliding window and the trailing edge sliding window of the detection sliding window may be calculated respectively, the leading edge sliding window and the trailing edge sliding window are judged respectively, and the CA-CFAR detector has an optimal detection performance in the case where both the leading edge sliding window and the trailing edge sliding window are uniform; the VI-CFAR detector selects the whole sliding window as a unit of background noise estimation, and the CA-CFAR detector is used for detection. For the case where one of the leading and trailing edge sliding windows is uniform and the other is non-uniform, the VI-CFAR detector selects the uniform sliding window as the unit of background noise estimation and uses the CA-CFAR detector for detection, which improves the performance of the detector in this case. For the case where there is target interference in both the leading and trailing edge sliding windows, the VI-CFAR detector uses CCA-CFAR.

Further, in step S4, the bottom detection method includes any one of WMT, a split sub-array method, and a multi-sub-array method. Specifically, based on the obtained echo time interval of the target to be detected, a conventional bottom detection algorithm such as WMT, a split sub-array method, a multi-sub-array method and the like is used to obtain an accurate arrival time estimate t and an accurate arrival angle estimate θ, and a known sound velocity c and a formula are combined:

and further determining the accurate positions of the target to be detected, such as a water body target and the seabed, and realizing the simultaneous detection of the water body target and the seabed terrain. And the traditional bottom detection algorithm can only keep one measurement result of the water body target and the seabed. The bottom detection method generally used herein is not limited to the above examples.

Referring to fig. 6, (a) is WMT as an example, and multi-beam sounding sonar measured data is detected. The conventional WMT bottom detection method only detects the seafloor topography. And (B) according to the constant false alarm detection-based multi-beam sonar depth sounding method, the detection result is obtained, the submarine topography B is detected, and meanwhile, the target position in the water body, namely the water body target B is also detected, so that the detection capability of the multi-beam depth sounding sonar is improved. The multi-beam sounding sonar water body imaging graph obtained according to the method can be referred to fig. 7.

As shown in fig. 8, the multi-beam sonar depth sounding device based on constant false alarm detection according to the present invention includes:

the sonar emission unit is used for emitting multi-beam sounding sonar beams;

the sonar receiving unit is used for receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected;

a signal processing unit for processing the signal to be detected according to the method of any one of the above. Specifically, the mutual cooperation and working among the units of the multi-beam sonar depth sounding device based on constant false alarm detection refer to the above method, and are not described herein again.

It is to be understood that the foregoing examples, while indicating the preferred embodiments of the invention, are given by way of illustration and description, and are not to be construed as limiting the scope of the invention; it should be noted that, for those skilled in the art, the above technical features can be freely combined, and several changes and modifications can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention; therefore, all equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims (8)

1. A multi-beam sonar sounding method based on constant false alarm detection is characterized by comprising the following steps:

s1, emitting a multi-beam sounding sonar beam, and receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected;

s2, pre-detecting the signal to be detected through VI-CFAR to obtain an echo time interval with the amplitude larger than a first threshold value in the signal to be detected;

s3, sequentially obtaining time intervals of continuous echo time intervals, and combining the echo time intervals when the time intervals are smaller than a second threshold value so as to finally obtain a complete echo time interval of the target to be detected;

s4, acquiring the accurate position of the target to be detected through a bottom detection method;

the method further comprises the following steps:

s3-1, obtaining a beam footprint of the target to be detected to obtain a pre-judgment time width of the target to be detected, and obtaining the second threshold according to the pre-judgment time width;

the calculation method of the prejudgment time width comprises the following steps:

wherein θ is the incident angle of the sonar beam, t is the round trip time of the sonar beam, and Θ is the-3 dB beam width of the sonar beam.

2. The constant false alarm detection-based multi-beam sonar depth sounding method according to claim 1, wherein the target to be measured includes a plurality of targets to be measured, and the second threshold includes a plurality of second thresholds respectively corresponding to the plurality of targets to be measured;

in step S3, the merging the echo time intervals to obtain a complete echo time interval of the target to be measured includes:

and respectively obtaining complete echo time intervals corresponding to the multiple targets to be detected according to the multiple second threshold values.

3. The constant false alarm detection-based multi-beam sonar depth sounding method according to claim 1, wherein the obtaining of the beam footprint of the target to be measured includes: and acquiring beam footprints corresponding to the target to be detected in two continuous echo time intervals.

4. The multi-beam sonar depth sounding method based on constant false alarm detection according to claim 1, wherein in step S1, the receiving a signal to be detected including a noise signal and a target echo signal of a target to be detected includes:

and receiving the noise signal and a target echo signal of the target to be detected, and forming and detecting through a receiving beam to obtain the signal to be detected.

5. The constant false alarm detection-based multi-beam sonar depth sounding method according to claim 1, wherein in step S2, the pre-detecting the signal to be detected by VI-CFAR comprises:

acquiring a variability index VI in a detection sliding window, and judging whether the target to be detected is a uniform environment or not according to the variability index VI;

when the environment is uniform, pre-detecting the signal to be detected through CA-CFAR;

and when the environment is non-uniform, pre-detecting the signal to be detected through CCA-CFAR.

6. The constant false alarm detection-based multi-beam sonar sounding method according to claim 5, wherein the obtaining a variability index VI within a detection sliding window comprises:

respectively obtaining the variability indexes VI of the front edge sliding window and the rear edge sliding window of the detection sliding window;

the method further comprises the following steps:

respectively comparing the variability index VI with a third set threshold value to determine whether the leading edge sliding window and the trailing edge sliding window are uniform sliding windows;

when any one of the front edge sliding window and the back edge sliding window is a uniform sliding window, pre-detecting the signal to be detected through the CA-CFAR based on the uniform sliding window;

when the front edge sliding window and the back edge sliding window are both uniform sliding windows, pre-detecting the signal to be detected through the CCA-CFAR based on the whole sliding window;

and when the front edge sliding window and the back edge sliding window are both non-uniform sliding windows, pre-detecting the signal to be detected through the CCA-CFAR based on the whole sliding window.

7. The constant false alarm detection-based multi-beam sonar sounding method according to claim 1, wherein in step S4, the bottom detection method includes any one of WMT, a split sub-array method, and a multi-sub-array method.

8. The utility model provides a multi-beam sonar sounding device based on constant false alarm detects which characterized in that includes:

the sonar emission unit is used for emitting multi-beam sounding sonar beams;

the sonar receiving unit is used for receiving a signal to be detected comprising a noise signal and a target echo signal of a target to be detected;

signal processing unit for processing the signal to be detected according to the method of any of claims 1 to 7.

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