Side-scan sonar image slope distance correction method

Abstract

The invention discloses a side-scan sonar image slope distance correction method. The method comprises the following steps: firstly, reading a side-scan sonar image with transverse geometric distortion; secondly, the position of a side-scan sonar image seabed line is detected, an anti-interference seabed point detection factor xi is designed, and the position of a seabed point of a single-frame echo sequence is determined; then eliminating a water column area of the side-scan sonar image, including obtaining an actual horizontal distance order of the side-scan sonar image and adjusting an original pixel slant distance order of the side-scan sonar image; and finally, outputting the side-scan sonar image after slope distance correction. According to the side-scan sonar image slope distance correction method, the transverse compression distortion of the image can be relieved, the original features of the side-scan sonar image can be recovered, the water column region of the side-scan sonar image can be removed, the connection smoothness of the two side-scan sonar images can be improved, and the detection precision of the side-scan sonar image can be improved.

Description

Technical Field

[0001] The present invention relates to a side-scan sonar image processing technology and a side-scan sonar image restoration and correction technology, and in particular to a side-scan sonar image slant range correction method. Background Art

[0002] Side scan sonar is an important underwater acoustic imaging technology used to obtain underwater target information. It is widely used in seabed detection, marine engineering and other tasks. The AUV equipped with side scan sonar is at a certain height from the seabed. The side scan sonar transmits signals obliquely downward along a fixed opening angle and receives reflected signals in the oblique direction. Due to the limitations of the working mechanism of the above side scan sonar itself, there is a difference between the obtained slant distance and the horizontal distance reflecting the actual seabed information. In addition, it takes a certain amount of time for the side scan sonar to receive the seabed reflection signal, which will cause no corresponding signal data during the window period, forming a water column area and lateral geometric distortion. Studying the slant distance correction method of side scan sonar images is an important part of achieving accurate detection of seabed targets. The commonly used slant distance correction method mainly uses the relationship between slant distance, seabed height and horizontal distance for slant distance correction. Because it is impossible to obtain a more accurate horizontal distance, the pixel spacing after slant distance correction increases, so that there is still a residual shadow at the middle connection of the corrected image. How to obtain a more accurate seabed point position in slant distance correction also has a certain impact on the result of slant distance correction. Commonly used methods for obtaining the position of seabed points include threshold method and edge extraction method. These methods are difficult to accurately extract the position of seabed points in side-scan sonar images in complex environments, resulting in large slant range correction errors.

[0003] Therefore, research on the slant range correction method for side-scan sonar images will help to remove the water column area of ​​side-scan sonar images in complex seabed environments and restore the information characteristics of side-scan sonar images, thereby improving the restoration accuracy of side-scan sonar images and ultimately achieving the goal of forming high-quality and high-precision side-scan sonar images. Summary of the invention

[0004] The purpose of the present invention is to provide a side scan sonar image slant range correction method to improve the side scan sonar image quality, thereby improving the subsequent image interpretation or automatic classification accuracy.

[0005] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0006] A side scan sonar image slant range correction method comprises the following steps:

[0007] S1, reads the side scan sonar image with lateral geometric distortion;

[0008] S2, detect the seabed line position of the side scan sonar image, design the anti-interference seabed point detection factor ξ and determine the seabed point position of the single frame echo sequence, where:

[0009] The design process of the anti-interference seabed point detection factor ξ is as follows:

[0010] 1) Set the position interval [m,n] from the track line to the two ends of the side scan sonar image;

[0011] 2) Design the seabed point detection factor ξ corresponding to the current detection position interval [m, n]. The specific formula is as follows:

[0012]

[0013] Where: Respectively represent the peak value and trough value in the position interval [m,n]; σ is the standard deviation of the radiation value of a single frame sequence in the position interval [m,n]; q is the pixel distance between the midpoint of the current position interval [m,n] and the track line;

[0014] The design formula for the seabed point position of a single-frame echo sequence is as follows:

[0015]

[0016] Where: are the peak and trough positions corresponding to the maximum seabed point detection factor ξ' respectively;

[0017] S3, eliminating the water column area of ​​the side scan sonar image, including obtaining the actual horizontal range position of the side scan sonar image and adjusting the original pixel slant range position of the side scan sonar image;

[0018] S4, outputs the side scan sonar image after slant range correction.

[0019] As a specific implementation, in step S2, the process of detecting the position of the seabed line of the side scan sonar image is as follows:

[0020] Step A: for a frame echo sequence, define {I1,I2,…I z ,…,I b} is a set of intensity values, I z is the intensity value on the track line;

[0021] Step B, using the single frame sequence intensity value I z As the starting point, with the position interval [m,n] as the unit, detect towards both ends of the side scan sonar image to obtain the detection factor values ​​of all seabed points;

[0022] Step C, find the peak position corresponding to the maximum seabed point detection factor ξ' Trough position And define is the location of the seabed point;

[0023] Step D, sequentially detecting the seabed point positions of all frame echo sequences of the side-scan sonar image, can complete the seabed line position detection of the side-scan sonar image.

[0024] As a specific implementation, in step S3, the process of adjusting the original pixel slant range position of the side scan sonar image is as follows:

[0025] Suppose a pixel point in the jth frame is (x j ,y j ), the pixel position after slant distance correction (x j ',y j ') is represented as:

[0026]

[0027] y j ′=y j =j

[0028] Where: B represents the pixel width of the side scan sonar image; ± corresponds to the position calculation formulas for the starboard and port sides respectively.

[0029] As a specific implementation, in step S3, the actual horizontal distance position of the side scan sonar image is obtained, that is, the horizontal distance w corresponding to all seawater layers passed by the side scan sound beam is calculated, and the specific calculation formula is as follows:

[0030]

[0031] Where: z is the number of seawater layers; λ i is the ratio of the current seawater layer height to the total depth; P i is the Snell constant of the current seawater layer.

[0032] As a specific implementation method, the Snell constant P of the current seawater layer i The calculation is as follows:

[0033] 1) Use the following formula to calculate the acoustic beam incident angle α1 corresponding to the horizontal pixel point,

[0034]

[0035] 2) Calculate the Snell constant P of the current seawater layer using the following formula: i :

[0036]

[0037] Where: V i 、V i+1 are the corresponding sound velocities of the i-th and i+1-th seawater layers respectively.

[0038] As a specific implementation, in step S3, the process of eliminating the water column area of ​​the side scan sonar image is as follows:

[0039] Step I: Calculate the horizontal pixel distance w between the sound beam and the seabed corresponding to the single-frame echo sequence of the side-scan sonar image;

[0040] Step II, adjusting the slant range position of the jth frame of the side scan sonar image, and adjusting the original slant range position pixel value to the horizontal range position;

[0041] Step III: After all slant range pixel values ​​of the jth frame are adjusted, the slant range pixel values ​​of other frames are adjusted in sequence, thereby completing the slant range correction of the side scan sonar image.

[0042] Compared with the prior art, the present invention is beneficial in that:

[0043] (1) The present invention designs an anti-interference seabed point detection factor ξ and uses the peak and trough difference of single-frame radiation Characterize the characteristics of radiation values ​​near the seabed points, use the radiation standard deviation σ in the detection interval [m,n] to highlight the degree of radiation dispersion near the seabed points, and use the distance q between the midpoint of the position interval [m,n] and the track line to reduce the interference of the radiation outside the image on the detection factor, improve the adaptability of seabed line detection under interference such as blur in the water column area, and improve the accuracy of seabed line detection in side scan sonar images;

[0044] (2) The present invention determines the seabed point position of a single-frame echo sequence and finds the peak position corresponding to the maximum seabed point detection factor ξ' Trough position and confirm The position of the seabed point radiated by the current frame can be confirmed more accurately, and the accuracy of the slant range correction benchmark of the side scan sonar image can be improved;

[0045] (3) The invention obtains the actual horizontal distance position of the side-scan sonar image and converts the horizontal pixel distance of the single-frame radiation seabed point into As the total seawater layer depth, the horizontal distance w corresponding to the side-scan sonar sound beam is calculated based on the refraction relationship of the sound beam in different seawater layers, which reduces the horizontal distance error caused by the commonly used triangulation method, improves the accuracy of the obtained horizontal distance position, and improves the adjustment accuracy of the side-scan sonar pixel slant range position;

[0046] (4) The present invention adjusts the original pixel slant range position of the side scan sonar image by adjusting the positional relationship between the actual horizontal range position of the side scan sonar image and the image width B, thereby completing the slant range correction of the side scan sonar image, removing the water column area of ​​the side scan sonar image, alleviating the lateral compression distortion of the image, restoring the original features of the side scan sonar image, and improving the smoothness of the connection between the two side images of the side scan sonar, thereby improving the detection accuracy of the side scan sonar image. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 It is a general flow chart of a side scan sonar image slant range correction method of the present invention;

[0049] Figure 2 is a side-scan sonar lateral geometric distortion image collected in the embodiment;

[0050] Figure 3 This is a single frame echo sequence curve under complex environmental interference;

[0051] Figure 4 It is a schematic diagram of the working mechanism of the side-scan sonar in the present invention;

[0052] Figure 5 This is a schematic diagram of the refraction of the sound beam in the seawater layer;

[0053] Figure 6 This is the comparison diagram of slant range correction of side scan sonar image I. Figure 6 a represents the side scan sonar image I, Figure 6 b represents the side scan sonar image I triangulation slant range correction method, Figure 6 c represents the side scan sonar image Ⅰ the slant range correction method of the present invention;

[0054] Figure 7 Side scan sonar image II slant range correction comparison chart, Figure 7 a represents the side scan sonar image II, Figure 7 b represents the side scan sonar image II triangulation slant range correction method, Figure 7 c represents the side scan sonar image II the slant range correction method of the present invention;

[0055] Figure 8 Side scan sonar image III slant range correction comparison chart, Figure 8 a represents the side scan sonar image III, Figure 8 b represents the side scan sonar image III triangulation slant range correction method, Figure 8 c represents the side scan sonar image III the slant range correction method of the present invention;

[0056] Fig. 9 Side scan sonar image IV slant range correction comparison chart, Fig. 9 a represents the side scan sonar image Ⅳ, Fig. 9 b represents the side scan sonar image IV triangulation slant range correction method, Fig. 9c represents the side scan sonar image Ⅳ the slant range correction method of the present invention. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention:

[0058] like Figure 1 As shown, the present invention provides a side scan sonar image slant range correction method, the method comprising the following steps: firstly reading a side scan sonar image with lateral geometric distortion; secondly detecting the seabed line position of the side scan sonar image; then eliminating the water column area of ​​the side scan sonar image; and finally outputting the side scan sonar image after slant range correction.

[0059] Specifically, in step S1, a side-scan sonar image with lateral geometric distortion is read.

[0060] Step S2, detecting the position of the seabed line in the side scan sonar image.

[0061] It includes designing an anti-interference seabed point detection factor ξ and determining the seabed point position of a single-frame echo sequence.

[0062] The port and starboard image areas of the side scan sonar and the black water column area will form a Figure 2 The boundary shown is the seabed line. The slant range correction of the side scan sonar image is based on the seabed line, so it is necessary to extract the seabed line of the side scan sonar image. However, due to the interference of the complex marine environment, the water column area is usually not clear. The commonly used threshold method and image edge detection algorithm are no longer suitable for accurate extraction of the seabed line.

[0063] Figure 3 This is a single frame echo sequence curve under complex environmental interference. It can be seen from the figure that there are peaks and troughs in the intensity value near the seabed point. Even under environmental interference, this feature is obviously different from the fluctuation characteristics of the intensity value in other areas. From the data analysis, the peaks and troughs are not necessarily adjacent, but they will appear within a certain range. For a frame echo sequence, define {I1,I2,…I z ,…,I b} is a set of intensity values, and I z is the intensity value on the track line.

[0064] Here, the design process of the anti-interference seabed point detection factor ξ is as follows:

[0065] 1) Set the position interval [m,n] from the track line to the two ends of the side scan sonar image;

[0066] 2) The design formula of the seabed point detection factor ξ corresponding to the current detection position interval [m,n] is as follows:

[0067]

[0068] Where: They represent the peak value and trough value in the position interval [m,n] respectively; σ is the standard deviation of the intensity value of a single frame sequence in the position interval [m,n]; q is the pixel distance between the midpoint of the current interval and the track line.

[0069] Determine the position of the seabed point of a single-frame echo sequence, specifically using the following steps:

[0070] a) Obtaining the seabed point detection factors corresponding to all position intervals in a single frame sequence;

[0071] b) Find the peak position corresponding to the maximum seabed point detection factor ξ' Trough position

[0072] c) Determine the following positions as the seafloor point positions of the single frame sequence:

[0073]

[0074] Where: They are the peak and trough positions corresponding to the maximum seabed point detection factor ξ' respectively.

[0075] The determination of the position of the sea bottom line of the side scan sonar image is detected, including the following steps:

[0076] Step A: for a frame echo sequence, define {I1,I2,…I z ,…,I b} is a set of intensity values, and I z is the intensity value on the track line.

[0077] Step B, using a single frame sequence to radiate the value I z As the starting point, with the position interval [m,n] as the unit, detect from the track line to both ends of the side scan sonar image to obtain the detection factor values ​​of all seabed points;

[0078] Step C, find the peak position corresponding to the maximum seabed point detection factor ξ' Trough position and confirm is the seabed point position of the current frame;

[0079] Step D, sequentially detecting the seabed point positions of all frame echo sequences of the side-scan sonar image, can complete the seabed line detection of the side-scan sonar image.

[0080] Step S3, eliminating the water column area of ​​the side scan sonar image, including obtaining the actual horizontal range position of the side scan sonar image and adjusting the original pixel slant range position of the side scan sonar image.

[0081] The data collection order of the side scan sonar is determined by the distance of the signal return one-way, and this order reflects the horizontal pixel position of the image. Since the AUV equipped with the side scan sonar is at a certain height from the seabed, and the side scan sonar transducer has a fixed tilt angle, the horizontal pixel position of the image is the slant distance rather than the horizontal distance. Figure 4 As shown in the figure, taking pixel points A' and B' as an example, the closer they are to the AUV track line, the smaller the corresponding opening angle θ, the greater the change of slant range OA' (OA) and OB' (OB), and the more serious the image compression. Therefore, it is necessary to use the horizontal range positions O'A' and O'B' that reflect the actual situation of the seabed to represent the image. If the side scan sonar data is not corrected, it is easy to cause image distortion.

[0082] like Figure 5 As shown, when the sound velocity V in the i-th seawater layer is i > greater than the i+1th layer V i +1, the refraction angle of the sound beam is α i +1, otherwise α' i +1. Use the horizontal pixel distance of the sea bottom point As the total seawater depth.

[0083] The process of obtaining the actual horizontal range position of the side scan sonar image includes the following steps:

[0084] (A) The horizontal pixel distance of the seabed point As the total seawater layer depth;

[0085] (B) Calculate the horizontal distance w corresponding to the side scan acoustic beam passing through all seawater layers. The calculation formula is as follows:

[0086]

[0087] Where: z is the number of seawater layers; λ i is the ratio of the current seawater layer height to the total depth; P i is the Snell constant of the current seawater layer.

[0088] The process of adjusting the original pixel slant range position of the side scan sonar image is as follows:

[0089] Take the position of a pixel point (x j ,y j ) as an example, in this example, the adjustment of the original pixel slant range position of the side scan sonar image is based on the position of a certain pixel point (x j ,y j ) as an example, the pixel position after slant distance correction (x j ',yj ') can be expressed as:

[0090]

[0091] y j ′=y j =j

[0092] Where: B represents the pixel width of the side scan sonar image; ± corresponds to the position calculation formulas of the starboard and port sides respectively; α1 is the incident angle of the sound beam.

[0093] The method of eliminating the water column area of ​​the side scan sonar image specifically comprises the following steps:

[0094] Step I: Calculate the horizontal pixel distance w from the sound beam corresponding to the single-frame echo sequence of the side-scan sonar image to the seabed.

[0095] Step II: adjust the slant range position of the jth frame of the side scan sonar image, and adjust the original slant range position pixel value to the horizontal range position.

[0096] Step III: After the slant range position adjustment of all pixel values ​​of the jth frame is completed, the slant range position adjustment of the pixel values ​​of other frames is performed in sequence, thereby completing the slant range correction of the side scan sonar image.

[0097] Step S4, outputting the side-scan sonar image after slant range correction.

[0098] In order to verify the effectiveness of the side-scan sonar image slant correction method of the present invention, underwater wind turbine pile foundation side-scan sonar images and seabed terrain side-scan sonar images are selected for radiation correction verification, and the correction results are compared with the results of trigonometric slant range correction.

[0099] The lateral geometric distortion caused by the working mechanism of the side scan sonar, such as the water column area and the compression of the two-sided images, see Figure 6 a. Figure 7 a. Figure 8 a. Fig. 9 a Four side-scan sonar images collected. Figure 6 b. Figure 7 b. Figure 8 b. Fig. 9 b shows the trigonometric slope distance correction result. Since this method only uses the relationship between slope distance, seabed height and horizontal distance for slope distance correction, it is unable to obtain a more accurate horizontal distance, which results in an increase in the pixel spacing after slope distance correction, so that there are still residual shadows at the junction of the corrected image, and the pile foundation and terrain features separated by the water column area are not well connected. Figure 6 c. Figure 7 c. Figure 8 c. Fig. 9c is the result after correction by the slant range correction method of the present invention. As can be seen from the figure, the water column area of ​​the image is basically eliminated, the pile foundation and terrain features separated by the left and right sides are well connected and smoothly transitioned, and the lateral compression area of ​​the image is restored. This is mainly due to the anti-interference seabed point detection factor designed in the article, which obtains the position of the seabed point based on the discrete degree of interval amplitude and the distance from the track line, and obtains a more realistic horizontal distance based on the underwater refraction relationship of the sound beam, thereby realizing the effective slant range correction of the side scan sonar image.

[0100] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A side scan sonar image slant range correction method, characterized in that: The following steps are involved: S1, reads the side scan sonar image with lateral geometric distortion; S2, detect the seabed line position of the side scan sonar image, design the anti-interference seabed point detection factor ξ and determine the seabed point position of the single frame echo sequence, where: The design process of the anti-interference seabed point detection factor ξ is as follows: 1) Set the position interval [m,n] from the track line to the two ends of the side scan sonar image; 2) Design the seabed point detection factor ξ corresponding to the current detection position interval [m, n]. The specific formula is as follows: Where: Respectively represent the peak value and trough value in the position interval [m,n]; σ is the standard deviation of the radiation value of a single frame sequence in the position interval [m,n]; q is the pixel distance between the midpoint of the current position interval [m,n] and the track line; The design formula for the seabed point position of a single-frame echo sequence is as follows: Where: are the peak and trough positions corresponding to the maximum seabed point detection factor ξ' respectively; S3, eliminating the water column area of ​​the side scan sonar image, including obtaining the actual horizontal range position of the side scan sonar image and adjusting the original pixel slant range position of the side scan sonar image; S4, outputs the side scan sonar image after slant range correction.

2. A side scan sonar image slant range correction method according to claim 1, characterized in that: In step S2, the process of detecting the seabed line position of the side scan sonar image is as follows: Step A: for a frame echo sequence, define {I1,I2,…I z ,…,I b } is a set of intensity values, I z is the intensity value on the track line; Step B, using the single frame sequence intensity value I z As the starting point, with the position interval [m,n] as the unit, detect towards both ends of the side scan sonar image to obtain the detection factor values ​​of all seabed points; Step C, find the peak position corresponding to the maximum seabed point detection factor ξ' Trough position And define is the seabed point location; Step D, sequentially detecting the seabed point positions of all frame echo sequences of the side-scan sonar image, can complete the seabed line position detection of the side-scan sonar image.

3. The side scan sonar image slant range correction method according to claim 1, characterized in that: In step S3, the process of adjusting the original pixel slant range position of the side scan sonar image is as follows: Suppose a pixel point in the jth frame is (x j ,y j ), the pixel position after slant distance correction (x j ',y j ') is represented as: y j ′=y j =j Where: B represents the pixel width of the side scan sonar image; ± corresponds to the position calculation formulas for the starboard and port sides respectively.

4. The side scan sonar image slant range correction method according to claim 1, characterized in that: In step S3, the actual horizontal distance rank of the side scan sonar image is obtained, that is, the horizontal distance w corresponding to all seawater layers passed by the side scan sound beam is calculated, and the specific calculation formula is as follows: Where: z is the number of seawater layers; λ i is the ratio of the current seawater layer height to the total depth; P i is the Snell constant of the current seawater layer.

5. A side scan sonar image slant range correction method according to claim 4, characterized in that: The Snell constant P of the current seawater layer i The calculation is as follows: 1) Use the following formula to calculate the acoustic beam incident angle α1 corresponding to the horizontal pixel point, 2) Calculate the Snell constant P of the current seawater layer using the following formula: i : Where: V i 、V i+1 are the corresponding sound velocities of the i-th and i+1-th seawater layers respectively.

6. A side scan sonar image slant range correction method according to claim 1, characterized in that: In step S3, the process of eliminating the water column area of ​​the side scan sonar image is as follows: Step I: Calculate the horizontal pixel distance w between the sound beam and the seabed corresponding to the single-frame echo sequence of the side-scan sonar image; Step II, adjusting the slant range position of the jth frame of the side scan sonar image, and adjusting the original slant range position pixel value to the horizontal range position; Step III: After all slant range pixel values ​​of the jth frame are adjusted, the slant range pixel values ​​of other frames are adjusted in sequence, thereby completing the slant range correction of the side scan sonar image.

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