An adaptive underwater polarization detection device based on full stokes vector

Abstract

The application relates to the technical field of underwater target detection, in particular to a self-adaptive underwater polarization detection device based on a full Stokes vector. The device comprises a sealed cabin, two illumination modules outside the sealed cabin, a sensing module penetrating through the sealed cabin, a lens on one side in the sealed cabin, a light splitting module on one side of the lens, a B channel polarization camera for a first light ray of the light splitting module, a G channel polarization camera for a second light ray of the light splitting module, a R channel polarization camera for a third light ray of the light splitting module, and a processing module connected with the B channel polarization camera, the G channel polarization camera and the R channel polarization camera in the sealed cabin. The application can restore target objects in low-turbidity water bodies and high-turbidity water bodies, and the wavelength multi-channel information can be added to simultaneously restore color information of the target objects, so that the dimension of the target information is improved.

Description

Technical Field

[0001] This invention relates to the field of underwater target detection technology, specifically an adaptive underwater polarization detection device based on the full Stokes vector. Background Technology

[0002] Underwater target detection technology is an important foundation and prerequisite for marine environmental perception and resource development. As one of the core technologies of underwater robots, its detection results can provide important guidance for the operation of underwater robots and other related equipment.

[0003] However, underwater imaging environments are complex and variable, affected by water absorption and scattering. Especially in turbid waters with strong scattering, underwater imaging suffers from a severe "veil effect," where detailed information is submerged in background scattered light. Features commonly used in traditional imaging methods, such as color and brightness, are severely attenuated, leading to a significant reduction in underwater image clarity and system visibility, severely impacting the system's ability to identify underwater targets. Furthermore, due to the wavelength selectivity of light absorption in water, underwater imaging is often accompanied by problems such as color distortion.

[0004] Compared to traditional photoelectric imaging technology, polarization imaging technology, as a novel optical reconnaissance method, encompasses light intensity imaging. Besides providing measurements of light intensity, it also provides information such as the degree of polarization, polarization angle, and polarization ellipsoid after reflection, refraction, or scattering by the target. Therefore, polarization imaging technology can detect targets by fusing intensity and polarization information, thus obtaining more comprehensive target information.

[0005] However, in the process of realizing this invention, the inventors discovered the following problems with the prior art:

[0006] Firstly, existing polarization imaging methods for obtaining the full Stokes vector require at least four polarization modulation measurements to acquire the four parameters of the Stokes vector. This can be achieved through time-division or focal plane splitting methods. Traditional time-division measurement typically uses a combination of a quarter-wave plate and a linear polarizer, demodulating the polarization state of the incident light by changing the azimuth angle of the wave plate. However, commercial single-channel focal plane splitting linear polarizers cannot obtain the full Stokes vector in a single measurement, requiring a rotating wave plate to achieve full Stokes vector measurement. Neither of these methods is suitable for detecting dynamic targets. Therefore, a method capable of snapshot-style measurement of the full Stokes vector is needed.

[0007] Secondly, existing polarization imaging methods are all single-wavelength channel measurements or use interpolation to recover the color information of the target scene, which causes serious color distortion. Therefore, a polarization measurement method capable of multi-wavelength channels is needed to recover the true underwater colors. Summary of the Invention

[0008] This invention provides an adaptive underwater polarization detection device based on the full Stokes vector that can recover target objects in both low-turbidity and high-turbidity water bodies. The addition of multi-channel wavelength information can simultaneously recover the target's color information, thereby enhancing the dimensionality of target information.

[0009] The technical solution adopted in this invention is as follows: an adaptive underwater polarization detection device based on the full Stokes vector, characterized in that: it includes a sealed chamber, two illumination modules are provided on the outside of the sealed chamber, a sensing module is provided through the sealed chamber, a lens is provided on one side of the sealed chamber, a beam splitting module is provided on one side of the lens, the first beam of the beam splitting module is compared with a B-channel polarization camera, the second beam of the beam splitting module is compared with a G-channel polarization camera by passing through a waveplate that makes the wavelengths of the G and B channels 90 degrees out of phase, and the third beam of the beam splitting module is compared with an R-channel polarization camera by passing through a waveplate that makes the wavelengths of the R and B channels 90 degrees out of phase, and a processing module connected to the B-channel polarization camera, the G-channel polarization camera, and the R-channel polarization camera is provided inside the sealed chamber, the processing module is connected to a power supply module, and the B-channel polarization camera, the G-channel polarization camera, the R-channel polarization camera, the waveplate that makes the wavelengths of the G and B channels 90 degrees out of phase, and the waveplate that makes the wavelengths of the R and B channels 90 degrees out of phase are combined to form a polarization imaging module;

[0010] In underwater target detection, Stokes vectors of different wavelengths contain a large number of scattering components. Within a certain wavelength range, the Stokes vector values ​​do not differ much. Multi-wavelength channel polarization imaging can make full use of the different phase delays provided by waveplates in different bands, so that the entire Stokes vector can be analyzed in a single sampling. In a single sampling, each superpixel has a total of 3*4, which is 12 sets of light intensity.

[0011] A fixed waveplate (compensator) is placed in front of a polarization camera of the corresponding wavelength. Based on the different phase delays of the waveplate in different wavelength bands, the light intensity of two wavelength channels is selected. The W matrix for a single sampling is:

[0012] The relationship between the probe light intensity and the Stokes vector is as follows: , and Let S = , where S is the phase delay of the waveplate at different wavelengths, and θ is the fixed azimuth angle of the waveplate. Compared to the single-channel W matrix, the multi-channel W matrix provides more polarization information and has a more stable inverse matrix form S = . ;

[0013] By optimizing the condition number of the W matrix and And the azimuth angle; the smaller the condition number, the stronger the noise resistance of the calculated Stokes vector. This can be achieved through a global optimization algorithm. and When the phase delay difference is 90°, the condition number of the W matrix reaches a minimum of 2 at any azimuth angle.

[0014] Sapphire was chosen as the waveplate, a birefringent crystal that satisfies the required phase retardation. The calculation formula is: .

[0015] in, For wavelength, The thickness of the waveplate, This is the difference in refractive index between the e-ray and the o-ray at that wavelength, i.e., the birefringence value.

[0016] As a further aspect of the present invention: the sensing module can measure the current turbidity of the water body. Under low turbidity water conditions, the system automatically uses the B-channel polarization camera and the G-channel polarization camera to operate. Under high turbidity water conditions, the sensing module sends a command signal to control the R-channel polarization camera to operate. That is, all polarization cameras operate simultaneously to improve the accuracy of Stokes vector calculation and imaging quality.

[0017] As a further aspect of the present invention: the beam splitting module uses a prism to split the light, generating three wavelength channels: R, G, and B. Each channel is received by a separate polarization detector. Compared to a single color polarization detector receiving light from all wavelength channels, this method can improve the overall energy utilization rate by three times. The R channel has a wavelength of around 700nm and is connected to an R-channel polarization camera; the G channel has a wavelength of around 546nm and is connected to a G-channel polarization camera; and the B channel has a wavelength of around 435nm and is connected to a B-channel polarization camera.

[0018] As a further aspect of the present invention: the polarization imaging module consists of one lens, two waveplates, and three polarization cameras. The lens focal length is adjustable, and all polarization cameras are linear polarization cameras. No waveplate is placed in front of the B-channel polarization camera; a waveplate is placed in front of the G-channel polarization camera to create a 90-degree phase delay between the G and B channels, resulting in a 90-degree phase difference between the wavelengths of the G and B channels; a waveplate is placed in front of the R-channel polarization camera to create a 90-degree phase delay between the R and B channels, resulting in a 90-degree phase difference between the wavelengths of the R and B channels. All waveplates are fixed and require no driving mechanism, thereby enabling dynamic and rapid imaging.

[0019] As a further aspect of the present invention: the processing module performs matrix operations on the polarization images obtained by each polarization imaging camera to obtain the full Stokes vector of the target, and performs polarization descattering operations to recover a clear underwater image. At the same time, it fuses the polarization data of different wavelength channels to restore the clear color of the underwater target object.

[0020] As a further aspect of the present invention: the power supply module is disposed inside the sealed chamber and is used to provide operating voltage for the illumination module, polarization imaging module and processing module.

[0021] The beneficial effects of this invention are:

[0022] This invention uses water turbidity information obtained by sensors to control a polarization camera, thereby achieving full Stokes vector acquisition. It is adaptable to target object recovery in both low and high turbidity waters. Simultaneously, the addition of multi-channel wavelength information allows for the recovery of target color information, enhancing the dimensionality of target information. This invention effectively adapts to different aquatic environments and solves the color distortion problem during underwater object recovery.

[0023] This invention proposes a method for snapshot-based measurement of the Stokes vector using a multi-channel polarization camera combined with a waveplate compensator. This method can measure and calculate the polarization distribution of a scene in a single sampling. The method has a simple structure and does not require complex optical path alignment and correction. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of an adaptive underwater polarization detection device based on the full Stokes vector according to the present invention. Detailed Implementation

[0025] The present invention will be further described below.

[0026] An adaptive underwater polarization detection device based on the full Stokes vector is characterized by: a sealed chamber 700, two illumination modules 300 on the outside of the sealed chamber 700, a sensing module 400 extending through the sealed chamber 700, a lens 100 on one side inside the sealed chamber 700, and a beam splitting module 200 on one side of the lens 100. The beam splitting module 200's first beam is compared to a B-channel polarization camera 001; the beam splitting module 200's second beam passes through a waveplate 012 that creates a 90-degree phase difference between the G and B channel wavelengths, compared to a G-channel polarization camera 002; and the beam splitting module 200's third beam... Light passes through a waveplate 013 that creates a 90-degree phase difference between the wavelengths of the R and B channels, and is compared with an R-channel polarization camera 003. A processing module 500 is provided inside the sealed chamber 700, which is connected to the B-channel polarization camera 001, the G-channel polarization camera 002, and the R-channel polarization camera 003. The processing module 500 is connected to a power supply module 600. The B-channel polarization camera 001, the G-channel polarization camera 002, the R-channel polarization camera 003, the waveplate 012 that creates a 90-degree phase difference between the wavelengths of the G and B channels, and the waveplate 013 that creates a 90-degree phase difference between the wavelengths of the R and B channels are combined to form a polarization imaging module.

[0027] The physical meanings of the four parameters of the Stokes vector are as follows: S0 represents the total intensity of the incident light; S1>0 represents that the vibration direction of the incident light is closer to the x-direction, S1<0 represents that the vibration direction of the incident light is closer to the y-direction, and S0=S1 represents that the incident light is linearly polarized light vibrating in the x-axis direction; S2>0 represents that the vibration direction of the incident light is closer to +45°, and S2<0 represents that the vibration direction of the incident light is closer to -45°; S3>0 represents that the incident light is closer to right-handed circularly polarized light, and S3<0 represents that the incident light is closer to left-handed circularly polarized light.

[0028] In low-turbidity water, linearly polarized light (the S1 and S2 terms of the Stokes vector) exhibits better polarization preservation than circularly polarized light (the S4 term of the Stokes vector), while in high-turbidity water, circularly polarized light exhibits better polarization preservation than linearly polarized light. For different wavelengths, blue light travels a longer distance than red light in low-turbidity water, while the opposite is true in high-turbidity water, where red light travels a longer distance than blue light. Therefore, this invention obtains the full Stokes vector of the target by using blue and green wavelength channels in low-turbidity water. In high-turbidity water, it obtains the full Stokes vector of the target by using three wavelength channels: red, green, and blue light, while simultaneously improving the color reproduction of the target. This scheme enables dynamic detection of the target's Stokes vector and simultaneously solves the problem of underwater color distortion.

[0029] The sensor module 400 can measure the current turbidity of the water body. In low turbidity water bodies, the system automatically uses the B-channel polarization camera 001 and the G-channel polarization camera 002 to work. In high turbidity water bodies, the sensor module 400 sends a command signal to control the R-channel polarization camera 003 to work. That is, all polarization cameras work simultaneously to improve the accuracy of Stokes vector calculation and imaging quality.

[0030] The beam splitter module 200 uses a prism to split the light, generating three wavelength channels: R, G, and B. Each channel is received by a separate polarization detector. Compared to a single color polarization detector receiving light from all wavelength channels, this method improves overall energy efficiency by three times. The R channel has a wavelength around 700nm and is connected to R-channel polarization camera 003; the G channel has a wavelength around 546nm and is connected to G-channel polarization camera 002; and the B channel has a wavelength around 435nm and is connected to B-channel polarization camera 001. The beam splitting method is not limited to this method; all beam splitting methods capable of generating three wavelength channels are within the scope of this invention.

[0031] The polarization imaging module consists of one lens, two waveplates, and three polarization cameras. The lens focal length is adjustable, and all polarization cameras are linear polarization cameras. Specifically, no waveplate is placed in front of the B-channel polarization camera 001; a waveplate 012, which creates a 90-degree phase delay between the G and B channels, resulting in a 90-degree phase difference between their wavelengths, is placed in front of the G-channel polarization camera 002; and a waveplate 013, which creates a 90-degree phase delay between the R and B channels, resulting in a 90-degree phase difference between their wavelengths, is placed in front of the R-channel polarization camera 003. All waveplates are fixed and require no driving mechanism, thus enabling dynamic and rapid imaging.

[0032] The processing module 500 performs matrix operations on the polarization images acquired by each polarization imaging camera to obtain the full Stokes vector of the target, and performs polarization descattering operations to recover a clear underwater image. Simultaneously, it fuses polarization data from different wavelength channels to restore the clear colors of the underwater target object.

[0033] The power module 600 is located inside the sealed chamber 700 and is used to provide operating voltage for the illumination module 300, the polarization imaging module, and the processing module 500.

[0034] In underwater target detection, Stokes vectors at different wavelengths contain a large number of scattering components, and their values ​​do not differ significantly within a certain wavelength range. Multi-wavelength channel polarization imaging can fully utilize the different phase delays provided by waveplates in different bands, enabling the analysis of the entire Stokes vector in a single sample. In a single sample, each superpixel has a total of 3*4 light intensities, totaling 12 sets. Theoretically, only two wavelength channels and 8 sets of light intensities are needed to calculate the complete Stokes vector. This invention proposes a snapshot-based method for measuring Stokes vectors using a multi-channel polarization camera combined with a waveplate compensator. This method can measure and calculate the polarization distribution of the scene in a single sample. The method has a simple structure and does not require complex optical path alignment and correction.

[0035] A fixed waveplate (also called a compensator) is placed in front of a polarization camera of the corresponding wavelength. Based on the different phase delays of the waveplate in different wavelength bands, the light intensities of two wavelength channels are selected. The W matrix for a single sampling is:

[0036] The relationship between the probe light intensity and the Stokes vector is as follows: , and Let S = , where S is the phase delay of the waveplate at different wavelengths, and θ is the fixed azimuth angle of the waveplate. Compared to the single-channel W matrix, the multi-channel W matrix provides more polarization information and has a more stable inverse matrix form S = . .

[0037] By optimizing the condition number of the W matrix and And the azimuth angle; the smaller the condition number, the stronger the noise resistance of the calculated Stokes vector. This can be obtained through a global optimization algorithm. and When the phase delay difference is 90°, the condition number of the W matrix reaches a minimum of 2 at any azimuth angle.

[0038] In specific applications, sapphire can be selected as the waveplate. This patent applies to all birefringent crystals that meet the corresponding phase retardation requirements. Phase retardation The calculation formula is: .

[0039] in, For wavelength, The thickness of the waveplate, This is the difference in refractive index between the e-ray and the o-ray at that wavelength, i.e., the birefringence value.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An adaptive underwater polarization detection device based on the full Stokes vector, characterized in that: The system includes a sealed chamber (700), with two illumination modules (300) on the outside of the chamber (700). A sensing module (400) is installed through the chamber (700). A lens (100) is installed on one side of the chamber (700), and a beam splitter (200) is installed on one side of the lens (100). The first beam of the beam splitter (200) is compared with a B-channel polarization camera (001). The second beam of the beam splitter (200) is compared with a G-channel polarization camera (002) by passing through a waveplate (012) that makes the wavelengths of the G and B channels 90 degrees out of phase. The third beam of the beam splitter (200) is compared with a waveplate (012) that makes the wavelengths of the R and B channels 90 degrees out of phase. A waveplate (013) with a 90-degree phase difference is used to compare with an R-channel polarization camera (003). The sealed chamber (700) is equipped with a processing module (500) connected to a B-channel polarization camera (001), a G-channel polarization camera (002), and an R-channel polarization camera (003). The processing module (500) is connected to a power supply module (600). The B-channel polarization camera (001), the G-channel polarization camera (002), the R-channel polarization camera (003), the waveplate (012) with a 90-degree phase difference between the wavelengths of the G and B channels, and the waveplate (013) with a 90-degree phase difference between the wavelengths of the R and B channels are combined to form a polarization imaging module. In underwater target detection, Stokes vectors of different wavelengths contain a large number of scattering components. Within a certain wavelength range, the Stokes vector values ​​do not differ much. Multi-wavelength channel polarization imaging can make full use of the different phase delays provided by waveplates in different bands, so that all Stokes vectors can be analyzed in a single sampling. In a single sampling, each superpixel has a total of 3*4, which is 12 sets of light intensity. A fixed waveplate, also known as a compensator, is placed in front of a polarization camera of the corresponding wavelength. Based on the different phase delays of the waveplate in different wavelength bands, the light intensities of two wavelength channels are selected. The W matrix for a single sampling is: ; The relationship between the probe light intensity and the Stokes vector is as follows: , and Let S = π, θ, and θ be the phase delay of the waveplate at different wavelengths, respectively, and θ be the fixed azimuth angle of the waveplate. Compared with the single-channel W matrix, the multi-channel W matrix provides more polarization information and has a more stable inverse matrix form S = π / 2. ; By optimizing the condition number of the W matrix and And the azimuth angle; the smaller the condition number, the stronger the noise resistance of the calculated Stokes vector. This can be achieved through a global optimization algorithm. and When the phase delay difference is 90°, the condition number of the W matrix reaches a minimum of 2 at any azimuth angle. Sapphire was chosen as the waveplate, a birefringent crystal that satisfies the required phase retardation. The calculation formula is: ; in, wavelength, The thickness of the waveplate, This is the difference in refractive index between the e-ray and the o-ray at that wavelength, i.e., the birefringence value.

2. The adaptive underwater polarization detection device based on the full Stokes vector as described in claim 1, characterized in that: The sensing module (400) can measure the current turbidity of the water body. Under low turbidity water body conditions, the system automatically uses the B-channel polarization camera (001) and the G-channel polarization camera (002) to work. Under high turbidity water body conditions, the sensing module (400) sends a command signal to control the R-channel polarization camera (003) to work. That is, all polarization cameras work at the same time to improve the accuracy of the Stokes vector solution and the imaging quality.

3. The adaptive underwater polarization detection device based on the full Stokes vector as described in claim 2, characterized in that: The beam splitting module (200) uses a prism to split the light, generating three wavelength channels: R, G, and B. Each channel is received by a polarization detector. Compared to a single color polarization detector receiving light from all wavelength channels, this method can improve the overall energy utilization rate by three times. The R channel has a wavelength of around 700nm and is connected to the R channel polarization camera (003). The G channel has a wavelength of around 546nm and is connected to the G channel polarization camera (002). The B channel has a wavelength of around 435nm and is connected to the B channel polarization camera (001).

4. The adaptive underwater polarization detection device based on the full Stokes vector as described in claim 3, characterized in that: The polarization imaging module consists of one lens, two waveplates, and three polarization cameras. The lens focal length is adjustable, and all polarization cameras are linear polarization cameras. The B-channel polarization camera (001) does not have a waveplate in front of it; the G-channel polarization camera (002) has a waveplate (012) in front of it that creates a 90-degree phase delay between the G and B channels, resulting in a 90-degree phase difference between the wavelengths of the G and B channels; the R-channel polarization camera (003) has a waveplate (013) in front of it that creates a 90-degree phase delay between the R and B channels, resulting in a 90-degree phase difference between the wavelengths of the R and B channels. All waveplates are fixed and do not require a driving mechanism, thereby enabling dynamic and rapid imaging.

5. The adaptive underwater polarization detection device based on the full Stokes vector as described in claim 4, characterized in that: The processing module (500) performs matrix operations on the polarization images obtained by each polarization imaging camera to obtain the full Stokes vector of the target, and performs polarization descattering operations to recover a clear underwater image. At the same time, it fuses the polarization data of different wavelength channels to restore the clear color of the underwater target object.

6. The adaptive underwater polarization detection device based on the full Stokes vector as described in claim 5, characterized in that: The power module (600) is located inside the sealed chamber (700) and is used to provide operating voltage for the illumination module (300), polarization imaging module and processing module (500).

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