Short-wave infrared band calibration method for polarization remote sensor based on background radiation correction

Abstract

The application discloses a polarization remote sensor short-wave infrared band polarization calibration method based on background radiation correction, and the method comprises the following steps: constructing a polarization response measurement model and a background radiance model, and measuring a Stokes vector of target radiation; adopting a wave band method to determine a background radiation polarization response mathematical model caused by an internal system of a remote sensor; acquiring a background radiation measurement matrix by using a light source and a polarization polarization system; determining a correlation coefficient between external background radiation and internal background radiation to establish a background radiation polarization response mathematical model caused by internal background radiation; according to an actual operation state of the polarization remote sensor, an improved inversion model of a polarization degree based on background radiation correction is established; and a comparison measurement normalized deviation method is adopted to verify the correction effect of the background radiation polarization response. The application can effectively solve the problems of background radiation caused polarization remote sensor short-wave infrared band background noise increase and dynamic range drift, and improve the polarization measurement precision.

Description

Technical Field

[0001] This invention relates to the field of remote sensor calibration data processing technology, and in particular to a polarization calibration method for shortwave infrared band polarization of polarization remote sensors based on background radiation correction. Background Technology

[0002] In the field of optical radiation polarization calibration, with the expansion of the application bands of polarization remote sensors and the increasing requirements for calibration accuracy, spaceborne and airborne polarization remote sensors covering the short-wave infrared band (1000-2500nm) need to consider the detection of both bright and dark targets and must meet the calibration requirements across the entire dynamic range. Based on application needs such as high-precision atmospheric aerosol parameter inversion, the polarization degree measurement uncertainty of polarization remote sensors should be better than 0.5%. Under conditions where apparent reflectance is below 5%, background radiation is a key factor affecting the polarization calibration accuracy of short-wave infrared band polarization remote sensors. Studies show that under these conditions, background radiation contributes as much as 20% to 40% to the polarization calibration uncertainty in the short-wave infrared band, having the greatest impact. Therefore, it is essential to solve the problem of the influence of background radiation on the short-wave infrared band polarization remote sensors under conditions where apparent reflectance is below 5%, and to improve the polarization measurement accuracy in the short-wave infrared band.

[0003] According to matrix optics theory and radiometry theory, the polarization characteristic parameters of a polarization remote sensor are related to the Stokes parameters (I, Q, U) of the target radiated beam as follows: , Where P is the degree of polarization, β is the polarization azimuth angle, and I, Q, and U represent the radiation intensity, horizontal / vertical polarization, and +45° / -45° polarization, respectively, with Q and U both expressed through I. Based on the measurement principle of polarization remote sensors, the radiation intensity I can be expressed as the product of the target signal spectral radiance L and the surface area A of the light source; that is, the polarization characteristic parameters P and β can both be expressed by the correlation function of the spectral radiance L. Since background radiation directly increases the background noise and dynamic range drift of the short-wave infrared band of the polarization remote sensor, it consequently affects the background radiation radiance L of the polarization remote sensor. bkg This will directly affect the spectral radiance L of the target signal, and therefore affect the measurement accuracy of the polarization characteristic parameters P and β of the polarization remote sensor.

[0004] Current polarization measurements are all conducted for calibration tasks of specific polarization remote sensors, lacking precise correction methods for background radiation and related research on quantitative analysis of background radiation polarization response. Therefore, in polarization calibration applications of polarization remote sensors, the influence of polarization response characteristics caused by background radiation on the polarization calibration results is often ignored. However, with the increasing demand for quantitative applications of polarization remote sensing data, it is urgent to address the impact of background radiation on the polarization calibration accuracy of shortwave infrared band polarization remote sensors under conditions where the apparent reflectivity is less than 5%.

[0005] Based on the current background radiation suppression level of shortwave infrared detection systems, the background radiation polarization response characteristics of polarization remote sensors are not only related to the degree of polarization, polarization azimuth angle, and spectral radiance of the target, but also directly related to parameters such as the emissivity of the system's own materials, temperature, and transmission path. There is no theoretical model or experimental research to support its laws. Traditional calibration methods for the visible and near-infrared bands do not consider the influence of background radiation factors and cannot be explained and corrected using existing polarization radiation matrix models. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies. This invention provides a polarization calibration method for short-wave infrared band polarization of polarization remote sensors based on background radiation correction. It can accurately measure the polarization response of background radiation in the short-wave infrared band of polarization remote sensors and correct the background radiation polarization response. It is applicable to the measurement and correction of background radiation of polarization remote sensors covering the short-wave infrared band, and reduces the impact of background radiation on the polarization calibration accuracy of polarization remote sensors when the apparent reflectivity of the short-wave infrared band is less than 5%.

[0007] This invention is achieved through the following technical solution:

[0008] A polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction includes the following steps:

[0009] Step (1), Stokes (I) of the target radiation beam in the λ band of the polarization remote sensor. λ Q λ U λ ) and polarization degree P λ and polarization azimuth angle β λ The relationship is:

[0010] (1)

[0011] Among them, I λ Q represents the spectral intensity at the entrance pupil of the polarization remote sensor. λ For horizontal / vertical polarization, U λ +45 ° / -45 ° Directional polarization.

[0012] Based on matrix optics theory and radiative transfer theory, the spectral intensity I at the entrance pupil of the polarization remote sensor is... λ Using spectral radiance L λ The Stokes matrix of the target is expressed as the product of the surface area A of the light source and the target surface area. λ Q λ U λ ] T A new Stokes matrix is ​​formed using spectral radiance, polarization degree, and polarization azimuth angle:

[0013] (2)

[0014] Step (2): Based on the radiative transfer theory, establish a quantitative relationship between the polarization response and the target polarization degree, polarization azimuth angle, and spectral radiance;

[0015] Step (3): Based on infrared radiation theory and blackbody radiation theory, the background radiance model caused by spontaneous emission of polarization remote sensor is derived as a function of blackbody spectral radiance with emissivity ε at the same operating temperature and the optical efficiency of its optical elements.

[0016] Step (4) utilizes the polarization response of the three polarization channels and their measurement matrix. This enables the measurement of the Stokes vector;

[0017] Step (5): Using the band sub-method, the background radiation spectrum range is divided into multiple bands. By using the mean value theorem of integrals, the mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is determined.

[0018] Step (6): Using the light source and polarization system, various polarization states are output sequentially to obtain the background radiation measurement matrix;

[0019] Step (7): By using the correlation coefficient between external background radiation and internal background radiation, establish a mathematical model of the background radiation polarization response caused by the internal background radiation in the shortwave infrared band of the polarization remote sensor.

[0020] Step (8): Based on the actual operating state of the polarization remote sensor and the positional rotation relationship between the polarizer and the filter, establish an improved inversion model based on the polarization degree after background radiation correction.

[0021] Step (9) uses the comparison measurement normalized deviation method to verify the correction effect of background radiation polarization response.

[0022] Furthermore, in step (2), the polarization remote sensor responds to S k Its system absolute spectral responsivity r(λ) k ) and spectral radiance at the entrance pupil The relationship between them is:

[0023] (3)

[0024] In the formula, [λ min , λ max [This refers to the operating spectral band of the polarization remote sensor.] The transmittance of the analyzer in each polarization channel. For the transmittance of other optical elements, A(α) k +kπ / 3) is the rotation matrix, α k +kπ / 3 represents the angle between the transmission axis direction of the analyzer in each polarization channel (channel number k=0,1,2) and the x-axis of the reference coordinate system. For the extinction ratio of the analyzer in each polarization channel, DC k (k=0,1,2) represents the background values ​​measured by the detectors of each polarization channel.

[0025] Furthermore, in step (3), it is assumed that the surface area A of the receiving light source in each polarization channel is... k Similarly, for the optical elements and structural components of a remote sensor detection system, when the change in the polarization degree of the observed target is small, they are all P. λ Meanwhile, the extinction ratio of the analyzer ( When the value is very high (>10000), then:

[0026] (4)

[0027] in,

[0028]

[0029] In the formula, (k=0,1,2) represents the background radiation polarization response of the polarization remote sensor. (k=0,1,2) represents the spectral radiance generated by the background radiation, ρ represents the reflectivity, ε represents the emissivity, τ represents the optical efficiency of the optical element, η represents the structural coefficient, and T represents the temperature.

[0030] Furthermore, in step (4), the polarization remote sensor is a channel-type polarization remote sensor composed of three polarization channels to realize the measurement of the Stokes vector, as shown in equation (5):

[0031] (5)

[0032] In the formula, (k=0,1,2) is the measurement matrix.

[0033] Furthermore, in step (5), a band-segmentation method is used to divide the background radiation spectrum into multiple bands. The mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is shown in equation (6):

[0034] (6)

[0035] In the formula, This represents the background radiation response of the polarization remote sensor. The background radiation response measurement matrix, The background radiation response of the j-th band is... The degree of polarization generated by the background radiation in the j-th band. The polarization azimuth angle generated by the background radiation in the j-th band.

[0036] Further, in step (6), various polarization states are sequentially output using the light source and polarization system to obtain the background radiation measurement matrix; the Stokes vector S0=[I] is measured when the polarization degree P of the reference light source remains unchanged, the initial polarization azimuth angle is β, and the polarization azimuth angle is changed to β+θ. θ Q θ U θ ] T The pattern of change is shown in equation (7):

[0037] (7)

[0038] The measurement matrix is ​​obtained by solving the background radiation polarization response of the channel under test using a polarization remote sensor, as shown in equation (8):

[0039] (8)

[0040] In the formula, To ensure that the polarization degree P of the reference light source remains constant, the polarization azimuth angle is... The polarization remote sensor response at that time; The polarization azimuth angle is Background of remote sensors at that time; The polarization azimuth angle is The light intensity of the polarization remote sensor at that time.

[0041] Furthermore, in step (7), a mathematical model of the background radiation polarization response caused by the internal background radiation in the shortwave infrared band of the polarization remote sensor is established using the correlation coefficient between the external background radiation and the internal background radiation:

[0042] (9)

[0043] In the formula, The correlation coefficient is obtained through simulation using ray simulation software and the coating emissivity function of the system structure.

[0044] Given an incident light polarization degree of 1 and a constant light intensity, determine the correlation coefficient between the correlation coefficient and the polarization azimuth angle. The mathematical model of the background radiation polarization response caused by the background radiation inside the polarization remote sensor is shown in equation (10):

[0045] (10)

[0046] Furthermore, in step (8), during the actual operation of the polarization remote sensor, there is no relative rotation between the polarizer and the filter; that is, the intensity of the incident light on the filter remains constant, the degree of polarization is 1, and the polarization azimuth angle is fixed. It is a constant, and the improved inversion model based on the polarization degree after background radiation correction is shown in equation (11):

[0047] (11)

[0048] in, Background radiation measurement matrix The inverse matrix.

[0049] Furthermore, in step (9), the normalized deviation method of comparative measurement is used to verify the correction effect of the background radiation polarization response, including:

[0050] Adjusting the light source and polarization system, the system outputs partially polarized light states with known reference standard polarization parameters, and also adds partially polarized light states with background radiation polarization parameters. The polarization degree measurement is then compared with the corrected background radiation polarization response. With polarization reference value The deviation between the two was analyzed to assess the effectiveness of the background radiation polarization response correction; simultaneously, the normalized deviation E was compared with the measured deviation. n The effectiveness of the background radiation polarization response correction method is verified by the values.

[0051] Polarization reference value The measurements were obtained from a spectral polarization analyzer; the measured values ​​were compared and verified by measuring the polarization remote sensor using a polarization polarization system. Compare the measured values ​​using equation (12). and polarization reference value Deviation between:

[0052] (12)

[0053] In the formula, It is the polarization degree measurement value of the polarization remote sensor. This is a polarization reference value, obtained through actual measurement using a spectral polarization analyzer. It is a polarization degree measurement value, obtained through actual measurement using a polarization polarization system.

[0054] According to the general comparison standard for acceptance of measurement uncertainty, the normalized deviation E of the comparison measurement is adopted. n Experimental measurements of polarization remote sensors The consistency with the polarization reference value is evaluated as shown in Equation (13):

[0055] (13)

[0056] In the formula, u(P) is the measurement uncertainty of the spectral polarization analyzer. V ) represents the combined measurement uncertainty of the polarization remote sensor.

[0057] The advantages of this invention are:

[0058] By constructing a mathematical model between background radiation and polarization response, and using a large dynamic range adjustable polarization state calibration technique to obtain the measurement matrix of background radiation, and verifying the background radiation polarization response correction results using the comparison measurement normalized deviation method, the problem of increased background noise and dynamic range drift in the shortwave infrared band of polarization remote sensors caused by background radiation can be effectively solved under the condition of apparent reflectivity below 5%. This reduces the polarization effect caused by background radiation and improves the accuracy of polarization measurement. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the experimental scheme for analyzing the polarization response characteristics of short-wave infrared background radiation of a polarization remote sensor using partially polarized light, according to the present invention.

[0060] Figure 2 This is a flowchart of the shortwave infrared band calibration method for polarization remote sensors based on background radiation correction according to the present invention.

[0061] Figure 3 This is a graph showing the measurement results of the shortwave infrared background radiation polarization response of the polarization remote sensor of the present invention. Detailed Implementation

[0062] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0063] This invention proposes a short-wave infrared polarization calibration method for polarization remote sensors based on background radiation correction. Based on radiative transfer theory, a quantitative relationship is established between the polarization response and the target polarization degree, polarization azimuth angle, and spectral radiance. A background radiance model caused by spontaneous emission from the polarization remote sensor is derived based on infrared radiation theory and blackbody radiation theory. The method utilizes the polarization responses of the three polarization channels and their measurement matrices. This study achieves the measurement of the Stokes vector. A band-segmentation method is used to divide the background radiation spectrum into multiple bands. The mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is determined using the integral mean value theorem. Various polarization states are sequentially output using the light source and polarization induction system to obtain the background radiation measurement matrix. The mathematical model of the background radiation polarization response caused by the internal background radiation in the short-wave infrared band of the polarization remote sensor is established by determining the correlation coefficient between the external and internal background radiation. Based on the actual operating state of the polarization remote sensor and the positional rotation relationship between the polarizer and the filter, an improved inversion model based on the polarization degree after background radiation correction is established. By modifying the background radiation polarization response model, the polarization parameters of the channel under test are inverted. A polarization parameter measurement comparison experiment is designed to verify the accuracy.

[0064] like Figure 1 As shown, the calibration device for a short-wave infrared polarization calibration method for polarization remote sensors based on background radiation correction according to the present invention includes a light source 1, a spectroradiometer 2, a polarization polarization system 3, a short-wave infrared polarization remote sensor 4, and a spectroradiometer 5. The light source 1 uses a wide-band light source such as a tungsten bromide lamp, a halogen tungsten lamp, or a white laser, whose spectral range covers the short-wave infrared band. By utilizing the spectral distribution characteristics of the integrating sphere, a verification band interval for the calibration results is selected to verify the calibration results under different dynamic ranges of the remote sensor. The spectroradiometer 2 is a light source radiance monitoring unit, whose spectral range covers the short-wave infrared band, used to monitor the radiance value of the light source. The polarization polarization system 3 can achieve adjustable linear polarization degree, and its spectral range covers the short-wave infrared band, used to obtain the background radiation measurement matrix. The polarization remote sensor 4 under test, whose spectral range covers the short-wave infrared band, is used to conduct background radiation measurement experiments. The spectroradiometer 5, whose spectral range covers the short-wave infrared band, is used to obtain a polarization degree reference value.

[0065] like Figure 2 As shown, the polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction according to the present invention specifically includes the following steps:

[0066] Step 1, the Stokes coefficient of the target radiation beam in the λ band of the polarization remote sensor is (I λ Q λ U λ ) and polarization degree P λ and polarization azimuth angle β λ The relationship is:

[0067] (1)

[0068] Among them, I λ Q represents the spectral intensity at the entrance pupil of the polarization remote sensor. λFor horizontal / vertical polarization, U λ +45 ° / -45 ° Directional polarization.

[0069] Based on matrix optics theory and radiative transfer theory, the spectral intensity I at the entrance pupil of the polarization remote sensor is... λ Spectral radiance L can be used λ The product of the surface area A of the light source and the target's Stokes matrix [I] is thus expressed as... λ Q λ U λ ] T A new Stokes matrix can be formed using spectral radiance, degree of polarization, and polarization azimuth angle:

[0070] (2)

[0071] In the formula, I λ L represents the spectral intensity at the entrance pupil of the polarization remote sensor. λ Let A be the target spectral radiance, and A be the surface area of ​​the light source.

[0072] Step 2: Based on the theory of radiative transfer, a quantitative relationship can be established between the polarization response and the target polarization degree, polarization azimuth angle, and spectral radiance.

[0073] Because the surface area A of the receiving light source in each polarization channel of a traditional channel-type polarization remote sensor is... k When they are the same, the polarization remote sensor response S can be established. k Its system absolute spectral responsivity r(λ) k ) and spectral radiance at the entrance pupil The relationship between them is:

[0074] (3)

[0075] In the formula, [λ min , λ max [This refers to the operating spectral band of the polarization remote sensor.] The transmittance of the analyzer in each polarization channel. For the transmittance of other optical elements, A(α) k +kπ / 3) is the rotation matrix, α k +kπ / 3 represents the angle between the transmission axis direction of the analyzer in each polarization channel (channel number k=0,1,2) and the x-axis of the reference coordinate system. For the extinction ratio of the analyzer in each polarization channel, DC k (k=0,1,2) represents the background values ​​measured by the detectors of each polarization channel.

[0076] Step 3: Based on infrared radiation theory and blackbody radiation theory, derive the background radiance model caused by spontaneous emission of the polarization remote sensor as a function of the blackbody spectral radiance with emissivity ε at the same operating temperature and the optical efficiency of its optical elements.

[0077] Assume that the surface area of ​​the light source received by each polarization channel is A. k Similarly, for the optical elements and structural components of a remote sensor detection system, when the change in the polarization degree of the observed target is small, they are all P. λ Meanwhile, the extinction ratio of the analyzer ( When the value is very high (>10000), then:

[0078] (4)

[0079] in,

[0080]

[0081] In the formula, (k=0,1,2) represents the background radiation polarization response of the polarization remote sensor. (k=0,1,2) represents the spectral radiance generated by the background radiation, ρ represents the reflectivity, ε represents the emissivity, τ represents the optical efficiency of the optical element, η represents the structural coefficient, and T represents the temperature.

[0082] Step 4: The polarization remote sensor is a channel-type polarization remote sensor composed of three polarization channels. Traditional channel-type polarization remote sensors utilize the polarization response of the three polarization channels and their measurement matrix. The measurement of the Stokes vector is achieved, as shown in equation (5):

[0083] (5)

[0084] In the formula, (k=0,1,2) is the measurement matrix.

[0085] Step 5: Using a band-segmentation method, the background radiation spectrum is divided into multiple bands. By applying the mean value theorem for integrals, the mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is obtained as shown in equation (6):

[0086] (6)

[0087] In the formula, This represents the background radiation response of the polarization remote sensor. The background radiation response measurement matrix, The background radiation response of the j-th band is... The degree of polarization generated by the background radiation in the j-th band. The polarization azimuth angle generated by the background radiation in the j-th band.

[0088] Step 6: To accurately establish the mathematical model of the background radiation polarization response, it is necessary to obtain the background radiation measurement matrix through forward modeling. Various polarization states are output sequentially using the light source and polarization induction system to measure the background radiation measurement matrix. The measurement principle of the background radiation measurement matrix is ​​as follows: When the polarization degree P of the reference light source remains constant, and the initial polarization azimuth angle is β, when its polarization azimuth angle is changed to β+θ, its Stokes vector S0=[I θ Q θ U θ ] T The pattern of change is shown in equation (7):

[0089] (7)

[0090] The measurement matrix is ​​obtained by solving the background radiation polarization response of the channel under test using a polarization remote sensor, as shown in equation (8):

[0091] (8)

[0092] In the formula, To ensure that the polarization degree P of the reference light source remains constant, the polarization azimuth angle is... The polarization remote sensor response at that time; The polarization azimuth angle is Background of remote sensors at that time; The polarization azimuth angle is The light intensity of the polarization remote sensor at that time.

[0093] Step 7: Establishing the mathematical model of the background radiation polarization response caused by external background radiation, determined by the correlation coefficient between external and internal background radiation. If the spatial distribution of scattered light intensity is independent of the polarization state of the incident light, then the mathematical model of the background radiation polarization response caused by the internal background radiation in the short-wave infrared band of the polarization remote sensor can be established entirely by equation (9):

[0094] (9)

[0095] In the formula, The correlation coefficient is obtained through simulation using ray simulation software and the coating emissivity function of the system structure.

[0096] Based on the installation method of the polarization remote sensor, the polarizer is installed before the optical filter, therefore the polarization degree of the incident light is close to 1. Assuming the incident light polarization degree is 1 and its intensity remains constant, determine the relationship between the correlation coefficient and the polarization azimuth angle. The mathematical model for the background radiation polarization response caused by the background radiation inside the polarization remote sensor is shown in equation (10):

[0097] (10)

[0098] Step 8: During actual operation of the polarization remote sensor, there is no relative rotation between the polarizer and the filter. That is, the intensity of the incident light on the filter remains constant, the degree of polarization is 1, and the polarization azimuth angle is fixed. Therefore... It is a constant, and the improved inversion model based on the polarization degree after background radiation correction is shown in equation (11):

[0099] (11)

[0100] in Background radiation measurement matrix The inverse matrix.

[0101] Step 9: To verify the correction effect of the background radiation polarization response, it is necessary to use some means or method to measure and compare the measurement results with a specified reference standard. The measurement and comparison test process and method for the background radiation polarization response correction effect are designed as follows: Adjust the light source and polarization system to output the partially polarized light state with known reference standard polarization parameters and the partially polarized light state with increased background radiation polarization parameters, respectively. Compare the polarization degree measurement values ​​after background radiation polarization response correction. With polarization reference value The deviation between the two was analyzed to assess the effectiveness of the background radiation polarization response correction; simultaneously, the normalized deviation E was compared with the measured deviation. n The effectiveness of the background radiation polarization response correction method is verified.

[0102] Specifically, the polarization degree reference value The measurements were obtained from a spectral polarization analyzer; the measured values ​​were compared and verified by measuring the polarization remote sensor using a polarization polarization system. Compare the measured values ​​using equation (12). and polarization reference value Deviation between:

[0103] (12)

[0104] In the formula, It is the polarization degree measurement value of the polarization remote sensor. This is a polarization reference value, obtained through actual measurement using a spectral polarization analyzer. It is a polarization degree measurement value, obtained through actual measurement using a polarization polarization system.

[0105] Specifically, based on the general comparison standard for acceptance assessment of measurement uncertainty, the normalized deviation E of the comparison measurement is adopted. n Experimental measurements of polarization remote sensors The consistency with the polarization reference value is evaluated as shown in Equation (13):

[0106] (13)

[0107] In the formula, u(P) is the measurement uncertainty of the spectral polarization analyzer. V ) represents the combined measurement uncertainty of the polarization remote sensor.

[0108] In this invention, the spatial distribution of the background radiation intensity can be simulated and analyzed by optical software. The physical optical model of the short-wave infrared band of the polarization remote sensor is imported into the ray simulation software. The polarization light source parameters (degree of polarization, polarization azimuth angle and spectral radiance), the emissivity function of the coating of the mechanical structure, the materials of other optical components, and related optical parameters and optical path conditions are set through the software interface to perform ray tracing of the background radiation and analyze the simulated spatial distribution of the background radiation intensity.

[0109] In this invention, the spectral distribution characteristics of the integrating sphere are utilized to select a calibration result verification band range, thereby verifying the calibration results of the remote sensor under different dynamic ranges. The integrating sphere's spectral range can cover the entire solar reflection band, while simultaneously achieving a wide dynamic range, isochromatic color temperature, and near-linearly adjustable radiance simulation output with a blackbody spectral radiance of 200K to 500K. By changing the driving current of the integrating sphere's radiative unit, the working color temperature and radiance output dynamic range of the integrating sphere can be adjusted. Near-linear adjustment with a wide dynamic range and isochromatic color temperature can be achieved by adjusting the precision adjustable aperture.

[0110] In this invention, by utilizing a light source and a polarization system, partially polarized light and natural light output can be achieved, enabling the measurement of the background radiation measurement matrix. The polarization system changes the degree of polarization of the emitted light by adjusting the angle between the normal direction of the polarization system and the incident light ray, and the polarization azimuth angle is adjusted by rotating the polarization system perpendicular to the incident light ray direction. Figure 3 As shown, the polarization degree can be continuously adjusted from 0 to 0.72 within the range of 350nm to 2500nm, and the polarization azimuth angle can be adjusted from 0 to 2π. Installing a high extinction ratio linear polarizer at the output of the polarization system can extend the polarization degree adjustment range to 0 to 1.

[0111] In this invention, in order to accurately establish a mathematical model of the background radiation polarization response, the background radiation measurement matrix is ​​obtained through forward modeling analysis. Various polarization states are output sequentially using a light source and a polarization induction system to measure the background radiation measurement matrix.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of the present invention.

Claims

1. A polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction, characterized in that, Includes the following steps: Step (1), Stokes (I) of the target radiation beam in the λ band of the polarization remote sensor. λ Q λ U λ ) and polarization degree P λ and polarization azimuth angle β λ The relationship is: (1) Among them, I λ Q represents the spectral intensity at the entrance pupil of the polarization remote sensor. λ For horizontal / vertical polarization, U λ +45 ° / -45 ° Directional polarization; Based on matrix optics theory and radiative transfer theory, the spectral intensity I at the entrance pupil of the polarization remote sensor is... λ Using spectral radiance L λ The Stokes matrix of the target is expressed as the product of the surface area A of the light source and the target surface area. λ Q λ U λ ] T A new Stokes matrix is ​​formed using spectral radiance, polarization degree, and polarization azimuth angle: (2) Step (2): Based on the radiative transfer theory, establish a quantitative relationship between the polarization response and the target polarization degree, polarization azimuth angle, and spectral radiance; Step (3): Based on infrared radiation theory and blackbody radiation theory, the background radiance model caused by spontaneous emission of polarization remote sensor is derived as a function of blackbody spectral radiance with emissivity ε at the same operating temperature and the optical efficiency of its optical elements. Step (4) utilizes the polarization response of the three polarization channels and their measurement matrix. This enables the measurement of the Stokes vector; Step (5): Using the band subdivision method, the background radiation spectrum range is divided into multiple bands. By using the mean value theorem for integrals, the mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is determined. The mathematical model of the background radiation polarization response caused by the internal system of the remote sensor is shown in Equation (6): (6) In the formula, This represents the background radiation response of the polarization remote sensor. The background radiation response measurement matrix, The background radiation response of the j-th band is... The degree of polarization generated by the background radiation in the j-th band. The polarization azimuth angle generated by the background radiation in the j-th band; Step (6): Using the light source and polarization system, various polarization states are output sequentially to obtain the background radiation measurement matrix; when the polarization degree P of the reference light source remains unchanged, the initial polarization azimuth angle is β, and the polarization azimuth angle is changed to β+θ, its Stokes vector S0=[I θ Q θ U θ ] T The pattern of change is shown in equation (7): (7) The measurement matrix is ​​obtained by solving the background radiation polarization response of the channel under test using a polarization remote sensor, as shown in equation (8): (8) In the formula, To ensure that the polarization degree P of the reference light source remains constant, the polarization azimuth angle is... The polarization remote sensor response at that time; The polarization azimuth angle is Background of remote sensors at that time; The polarization azimuth angle is The light intensity of the polarization remote sensor at that time ; Step (7): Using the correlation coefficient between external and internal background radiation, establish a mathematical model of the background radiation polarization response caused by the internal background radiation in the shortwave infrared band of the polarization remote sensor; using the correlation coefficient between external and internal background radiation, establish the mathematical model of the background radiation polarization response caused by the internal background radiation in the shortwave infrared band of the polarization remote sensor as follows: (9) In the formula, The correlation coefficient was obtained through simulation using ray simulation software and the coating emissivity function of the system structure. Given an incident light polarization degree of 1 and a constant light intensity, determine the correlation coefficient between the correlation coefficient and the polarization azimuth angle. The mathematical model of the background radiation polarization response caused by the background radiation inside the polarization remote sensor is shown in equation (10): (10) Step (8): Based on the actual operating state of the polarization remote sensor and the positional rotation relationship between the polarizer and the filter, establish an improved inversion model based on the polarization degree after background radiation correction. Step (9) uses the comparative measurement normalized deviation method to verify the correction effect of the background radiation polarization response; the comparative measurement normalized deviation method is used to verify the correction effect of the background radiation polarization response, including: Adjusting the light source and polarization system, the system outputs partially polarized light states with known reference standard polarization parameters, and also adds partially polarized light states with background radiation polarization parameters. The polarization degree measurement is then compared with the corrected background radiation polarization response. With polarization reference value The deviation between the two was analyzed to assess the effectiveness of the background radiation polarization response correction; simultaneously, the normalized deviation E was compared with the measured deviation. n The effectiveness of the background radiation polarization response correction method is verified by the values. Polarization reference value The measurements were obtained from a spectral polarization analyzer; the measured values ​​were compared and verified by measuring the polarization remote sensor using a polarization polarization system. Compare the measured values ​​using equation (12). and polarization reference value Deviation between: (12) In the formula, It is the polarization degree measurement value of the polarization remote sensor. This is a polarization reference value, obtained through actual measurement using a spectral polarization analyzer. It is a polarization degree measurement value, obtained through actual measurement using a polarization polarization system; According to the general comparison standard for acceptance of measurement uncertainty, the normalized deviation E of the comparison measurement is adopted. n Experimental measurements of polarization remote sensors The consistency with the polarization reference value is evaluated as shown in Equation (13): (13) In the formula, u(P) is the measurement uncertainty of the spectral polarization analyzer. V ) represents the combined measurement uncertainty of the polarization remote sensor.

2. The polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction according to claim 1, characterized in that, In step (2), the polarization remote sensor responds to S k Its system absolute spectral responsivity r(λ) k ) and spectral radiance at the entrance pupil The relationship between them is: (3) In the formula, [λ min , λ max [This refers to the operating spectral band of the polarization remote sensor.] The transmittance of the analyzer in each polarization channel. For the transmittance of other optical elements, A(α) k +kπ / 3) is the rotation matrix, α k +kπ / 3 represents the angle between the transmission axis of the analyzer and the x-axis of the reference coordinate system for each polarization channel. For the extinction ratio of the analyzer in each polarization channel, DC k Here are the background values ​​measured by the detectors of each polarization channel, where the channel number k = 0, 1, 2.

3. The polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction according to claim 2, characterized in that, In step (3), it is assumed that the surface area A of the receiving light source in each polarization channel is... k Similarly, for the optical elements and structural components of a remote sensor detection system, when the change in the polarization degree of the observed target is small, they are all P. λ Meanwhile, the extinction ratio of the analyzer If the value is greater than 10000, then: (4) in, In the formula, This refers to the background radiation polarization response of a polarization remote sensor. ρ is the spectral radiance generated by background radiation, ε is the reflectivity, τ is the optical efficiency of the optical element, η is the structural coefficient, T is the temperature, and k = 0, 1, 2.

4. The polarization calibration method for shortwave infrared band polarization of a polarization remote sensor based on background radiation correction according to claim 3, characterized in that, In step (4), the polarization remote sensor is a channel-type polarization remote sensor composed of three polarization channels, which realizes the measurement of the Stokes vector, as shown in equation (5): (5) In the formula, Let k be the measurement matrix, k=0,1,2.

5. The polarization calibration method for a shortwave infrared band polarization remote sensor based on background radiation correction according to claim 4, characterized in that, In step (8), during actual operation of the polarization remote sensor, there is no relative rotation between the polarizer and the filter; that is, the intensity of the incident light on the filter remains constant, the degree of polarization is 1, and the polarization azimuth angle is fixed. It is a constant, and the improved inversion model based on the polarization degree after background radiation correction is shown in Equation (11): (11) in, Background radiation measurement matrix The inverse matrix.

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