Television operating distance equivalent test conversion method based on target plates with different contrast ratios

Abstract

The invention relates to the technical field of airborne photoelectric detection and countermeasure, in particular to a television operating distance equivalent test conversion method based on different contrast target plates, which comprises the following steps: acquiring a first spatial frequency corresponding to an operating distance and an assessment condition and a system transfer function under a contrast condition; acquiring a second spatial frequency based on the existing test condition and a system transfer function under a contrast condition; adjusting the second spatial frequency to enable the theoretical calculation value of the system transfer function in the actual test to be equal to the first spatial frequency and the system transfer function under the contrast condition, so as to obtain the second spatial frequency corresponding to the equivalent test; and determining the MRC value after secondary conversion according to the contrast ratio of the second spatial frequency and the existing target plate. According to the invention, secondary conversion can be carried out on the MRC index, and the equivalent test of the operating distance index of any television sensor can be realized by relying on limited target plate resources.

Description

Technical Field

[0001] The invention relates to the technical field of airborne photoelectric detection and countermeasure, and in particular to a television action range equivalent test conversion method based on target plates with different contrast ratios. Background Art

[0002] The effective range of airborne TV sensors is generally tested on the ground using the method of testing the minimum resolvable contrast (MRC). MRC includes two aspects: spatial resolution and contrast. The TV sensor is used to measure the spatial resolution of targets with different contrast resolutions (see Figure 1 ) is used for imaging observation. Resolution targets are generally made by making multiple groups of resolution targets on a single contrast target plate. The magnification between adjacent groups of resolution targets is generally 1.122 times, that is, the magnification of the resolution targets of 6 groups is twice as much. A single test device is generally designed with several target plates of different resolutions. Due to the limitation of the number of target plates, the resolution target of the test device has the characteristics of a limited number of discrete values ​​for contrast and spatial resolution.

[0003] Due to the diversity of target types (target size, target-background contrast, etc.), the diversity of range requirements for different models, the diversity of atmospheric visibility, the diversity of aircraft flight altitudes and other factors, there are infinite combinations of spatial resolution and contrast for MRC testing. However, the contrast and resolution of the target plate equipped with the test equipment are only a few discrete values, which are difficult to directly match with the spatial resolution and contrast corresponding to the MRC test. If the corresponding target plate is customized according to each model, the scientific research cost will be significantly increased. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for converting the equivalent test of television range based on target plates with different contrast ratios. Combining the characteristics that a single contrast target plate contains multiple groups of resolution targets and the spatial resolution of adjacent groups of resolution targets is not much different (about 12.2%), the equations under the assessment conditions and test conditions are constructed based on the television sensor system transmission function to realize the secondary conversion of the MRC index. Relying on limited target plate resources, the equivalent test of the range index of any television sensor can be realized.

[0005] The present invention can realize equivalent assessment of different types of targets at different ranges based on a target plate with a small amount of contrast and resolution. Whether the human eye can distinguish the target is related to the system transmission function obtained by comprehensively considering multiple factors such as the contrast between the target and the background, the atmospheric transmission characteristics, the optical system transmission function, the detector transmission function, and the circuit transmission function.

[0006] The first object of the present invention is to provide a method for calculating the equivalent test of television range based on target plates with different contrast ratios, comprising: Based on the target size, working distance and the number of line pairs required by the resolution level, obtain the first spatial frequency corresponding to the MRC under the test conditions; According to the atmospheric transmittance of the TV working band on the path between the carrier and the target, and combined with the contrast between the target and the background, the equivalent contrast between the target and the background transmitted to the surface of the optical incident window of the TV sensor is obtained; According to the first spatial frequency and the equivalent contrast, based on the system transfer function calculation formula of the television sensor, the system transfer function under the first spatial frequency condition is obtained; According to the contrast of the existing target plate used in the actual test and the second spatial frequency randomly selected under the condition of the contrast of the existing target plate, the system transfer function in the actual test is obtained based on the calculation formula of the system transfer function of the television sensor; By adjusting the second spatial frequency, when the system transfer function in the actual test is equal to the system transfer function under the first spatial frequency condition, the corresponding second spatial frequency is obtained; The MRC value after secondary conversion is determined according to the second spatial frequency and the contrast of the existing target plate.

[0007] Preferably, the first spatial frequency corresponding to the MRC under the test condition is calculated as follows:

[0008] In the formula, represents the first spatial frequency; Indicates the target size; Indicates the action distance; Indicates the number of line pairs required for the resolution level.

[0009] Preferably, the target-background equivalent contrast ratio transmitted to the optical incident window surface of the television sensor is calculated as follows:

[0010] In the formula, It indicates the equivalent contrast between the target and the background transmitted to the optical incident window surface of the TV sensor; Indicates the contrast between target and background; Indicates the atmospheric transmittance of the television working band on the path between the carrier and the target.

[0011] Preferably, the system transfer function under the first spatial frequency condition is calculated as follows:

[0012] In the formula, Indicates the frequency System transmission under conditions; Represents the optical transfer function. According to the spatial resolution Determine the optical transfer function value; Indicates the detector transmission letter; represents the circuit transfer function, which is related to the circuit noise and is approximately a constant for a given TV sensor.

[0013] Preferably, the detector transmission function is calculated as follows:

[0014] Where: Indicates the focal length of the TV sensor optical system; Represents the detector pixel size.

[0015] First, the system transfer function during the actual test is calculated as follows:

[0016] In the formula, It represents the second spatial frequency randomly selected under the existing target contrast condition; Indicates that there is target plate contrast; , , They respectively represent the optical transmission function, the detector transmission function and the system transmission function corresponding to the second spatial frequency.

[0017] The second object of the present invention is to provide a television range equivalent test conversion system based on target plates with different contrast ratios, comprising: The assessment data module is used to obtain the first spatial frequency corresponding to the MRC under the assessment conditions based on the target size, the effective distance and the number of line pairs required for the resolution level; obtain the target and background equivalent contrast transmitted to the optical incident window surface of the TV sensor according to the atmospheric transmittance of the TV working band on the path between the carrier and the target, and in combination with the target and background contrast; obtain the system transmission function under the first spatial frequency condition based on the calculation formula of the TV sensor system transmission function according to the first spatial frequency and the equivalent contrast; The actual test module is used to obtain the system transfer function during the actual test based on the contrast of the existing target plate used during the actual test and the second spatial frequency randomly selected under the condition of the contrast of the existing target plate and the calculation formula of the system transfer function of the television sensor; The conversion module is used to adjust the second spatial frequency so that the system transfer function during actual testing is equal to the system transfer function under the first spatial frequency condition, and obtain the corresponding second spatial frequency when they are equal; determine the MRC value after secondary conversion according to the second spatial frequency and the contrast of the existing target plate.

[0018] The third object of the present invention is to provide an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program implements the steps of the above method when executed by the processor.

[0019] A fourth object of the present invention is to provide a storage medium having a computer program stored thereon, which is used to execute the steps of the above method when the computer program is executed.

[0020] The present invention has at least the following beneficial effects: The invention provides a television action range equivalent test conversion method based on target plates with different contrast ratios. The invention is based on the equality of system transfer functions, constructs equations under assessment conditions and actual test conditions, calculates the spatial resolution that should be distinguished under the target plate contrast conditions used in the actual test, and observes whether the distinguishable spatial resolution is greater than or equal to the calculated value during the actual test, so as to perform MRC secondary conversion and action range equivalent test.

[0021] The present invention constructs an equation based on the equality of system transfer functions, and relies on the system transfer function value corresponding to MRC under the test conditions to calculate the spatial resolution that should be able to be distinguished under the target plate contrast conditions during the actual test, thereby realizing the secondary conversion of the MRC index and the equivalent test of any working distance of the television sensor under the condition of a small number of target plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The target style for TV resolution.

[0023] Figure 2 It is the simulation curve of optical transfer function of TV sensor and the corresponding optical transfer function values ​​at different spatial frequencies. DETAILED DESCRIPTION

[0024] In order to illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description in conjunction with embodiments.

[0025] The present invention combines the characteristics that a single contrast target plate contains multiple groups of resolution targets and the spatial resolution of adjacent groups of resolution targets is not much different (about 12.2%), and proposes a TV action range equivalent test conversion method based on different contrast target plates. The method can perform secondary conversion on the MRC index and realize equivalent test of the action range index of any TV sensor by relying on limited target plate resources.

[0026] In order to achieve the above object, the present invention provides a TV range equivalent test conversion method based on target plates with different contrast ratios, comprising: S1. Based on the target size, working distance and the number of line pairs required by the resolution level, obtain the first spatial frequency corresponding to the MRC under the test conditions; The first spatial frequency corresponding to MRC under the test conditions is calculated as follows:

[0027] In the formula, represents the first spatial frequency; Indicates the target size; Indicates the action distance; Indicates the number of line pairs required for the resolution level.

[0028] S2, according to the atmospheric transmittance of the television working band on the path between the carrier and the target, and in combination with the contrast between the target and the background, obtaining the equivalent contrast between the target and the background transmitted to the surface of the optical incident window of the television sensor; The equivalent contrast ratio between the target and the background transmitted to the optical incident window surface of the TV sensor is calculated as follows:

[0029] In the formula, It indicates the equivalent contrast between the target and the background transmitted to the optical incident window surface of the TV sensor; Indicates the contrast between target and background; Indicates the atmospheric transmittance of the television working band on the path between the carrier and the target.

[0030] S3, according to the first spatial frequency and the equivalent contrast, based on the system transfer function calculation formula of the television sensor, obtaining the system transfer function under the first spatial frequency condition; The system transfer function under the first spatial frequency condition is calculated as follows:

[0031] In the formula, Indicates the frequency System transmission under conditions; Represents the optical transfer function. According to the spatial resolution Determine the optical transfer function value; Indicates the detector transmission letter; represents the circuit transfer function, which is related to the circuit noise and is approximately a constant for a given TV sensor.

[0032] The detector transfer function is calculated as follows:

[0033] Where: Indicates the focal length of the TV sensor optical system; Represents the detector pixel size.

[0034] S4, according to the contrast of the existing target plate used in the actual test, and the second spatial frequency randomly selected under the condition of the existing target plate contrast, based on the TV sensor system transfer function calculation formula, the system transfer function in the actual test is obtained; The system transfer function during the actual test is calculated as follows:

[0035] In the formula, It represents the second spatial frequency randomly selected under the existing target contrast condition; Indicates that there is target plate contrast; , , They respectively represent the optical transmission function, the detector transmission function and the system transmission function corresponding to the second spatial frequency.

[0036] S5, adjusting the second spatial frequency so that the system transfer function during the actual test is equal to the system transfer function under the first spatial frequency condition, and obtaining the second spatial frequency corresponding to the equal conditions; The MRC value after secondary conversion is determined according to the second spatial frequency and the contrast of the existing target plate.

[0037] In order to illustrate a television range equivalent test conversion method based on target plates with different contrast ratios provided by the present invention, it is described in conjunction with the accompanying drawings.

[0038] It should be noted that whether the human eye can distinguish the target is related to the system transmission function obtained by comprehensively considering multiple factors such as the contrast between the target and the background, atmospheric transmission characteristics, optical system transmission function, detector transmission function, circuit transmission function, etc. Based on the equality of the system transmission function, the equations under the assessment conditions and the actual test conditions are constructed to calculate the spatial resolution that should be distinguished under the target plate contrast conditions used in the actual test, and observe whether the distinguishable spatial resolution is greater than or equal to the calculated value during the actual test, so as to perform MRC secondary conversion and effective range equivalence test.

[0039] The specific process is: 1) Based on target size (Unit: meter, m), operating distance (in kilometers, km) and the number of line pairs required for the resolution level , calculate the spatial frequency corresponding to MRC under the test conditions (unit: cycles per milliradian, c / mrad), as shown in formula (1): (1) 2) Based on atmospheric environmental conditions such as atmospheric visibility, relative humidity, geographical location, season, as well as the aircraft's flight altitude and target altitude, the atmospheric transmittance calculation software is used to calculate the atmospheric transmittance of the television working band on the path between the aircraft and the target. , and combined with the target and background contrast , the equivalent contrast ratio between the target and the background transmitted to the optical incident window surface of the TV sensor is calculated , as shown in formula (2): (2) The MRC assessment value directly corresponding to the action distance index is obtained from formulas (1) and (2): Indicates that for a contrast ratio of The target plate, the spatial resolution that the TV sensor can distinguish should be no less than The target plate corresponding to the MRC contrast and resolution may not be available in the existing test equipment, and further MRC secondary conversion is required; 3) Based on the TV sensor system transfer function calculation formula, the system transfer function corresponding to MRC is calculated, as shown in formula (3): (3) Where: —The frequency is System transmission under conditions; —Optical transfer function, based on the spatial resolution on the optical transfer function simulation curve Determine the optical transfer function value, such as Figure 2 As shown; —Detector transfer function, calculated according to formula (4); —Circuit transfer function, which is related to the circuit noise and is approximately constant for a given TV sensor.

[0040] (4) Where: —focal length of the optical system of the television sensor, in meters; —Detector pixel size, in mm.

[0041] 4) Based on the contrast of the existing target plate , and construct the equation with the system transfer function, as shown in formula (5): (5) Under the existing target contrast condition, a spatial resolution value is randomly selected. , and calculate the optical transfer function corresponding to the spatial resolution 、Detector transmission and system communication Generally, when the target contrast is measured Greater than the equivalent contrast transmitted to the sensor surface under the test conditions When the spatial resolution value is selected Should be greater than the corresponding spatial resolution under the test conditions , otherwise it should be less than; 5) If and If not equal, reselect The values ​​are calculated until they are equal, and the MRC value after the second conversion is determined to be , that is, the contrast of the TV sensor is The target plate imaging, the resolvable spatial resolution should be no less than .generally The calculated value is greater than Should increase value, otherwise decrease the value.

[0042] The present invention provides a television range equivalent test conversion system based on target plates with different contrast ratios, comprising: The assessment data module is used to obtain the first spatial frequency corresponding to the MRC under the assessment conditions based on the target size, the effective distance and the number of line pairs required for the resolution level; obtain the target and background equivalent contrast transmitted to the optical incident window surface of the TV sensor according to the atmospheric transmittance of the TV working band on the path between the carrier and the target, and in combination with the target and background contrast; obtain the system transmission function under the first spatial frequency condition based on the calculation formula of the TV sensor system transmission function according to the first spatial frequency and the equivalent contrast; The actual test module is used to obtain the system transfer function during the actual test based on the contrast of the existing target plate used during the actual test and the second spatial frequency randomly selected under the condition of the contrast of the existing target plate and the calculation formula of the system transfer function of the television sensor; The conversion module is used to adjust the second spatial frequency so that the system transfer function during actual testing is equal to the system transfer function under the first spatial frequency condition, and obtain the corresponding second spatial frequency when they are equal; determine the MRC value after secondary conversion according to the second spatial frequency and the contrast of the existing target plate.

[0043] The present invention provides an electronic device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the steps of the above method are implemented when the computer program is executed by the processor.

[0044] The present invention provides a storage medium on which a computer program is stored. When the computer program is run, it is used to execute the steps of the above method.

[0045] In summary, the present invention provides a method for converting the equivalent test of the TV range based on target plates with different contrasts. The range of airborne TV sensors is generally tested on the ground by the method of testing the minimum resolvable contrast (MRC), which includes two aspects: spatial resolution and contrast. Due to the influence of various factors such as the diversity of target types, the diversity of range index requirements of different models, the diversity of atmospheric visibility, and the diversity of aircraft flight altitudes, there are infinite combinations of spatial resolution and contrast corresponding to the MRC test, while the contrast and resolution of the target plates equipped with the test equipment are only a few discrete values, which are difficult to directly match with the spatial resolution and contrast corresponding to the MRC test.

[0046] The invention proposes a TV action distance equivalent test conversion method based on target plates with different contrast ratios, which can realize equivalent tests of any MRC and TV action distance based on a few existing resolution targets, thereby reducing the R&D and testing costs of TV sensors.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A TV range equivalent test conversion method based on target plates with different contrast ratios, characterized in that: include: Based on the target size, working distance and the number of line pairs required by the resolution level, obtain the first spatial frequency corresponding to the MRC under the test conditions; According to the atmospheric transmittance of the TV working band on the path between the carrier and the target, and combined with the contrast between the target and the background, the equivalent contrast between the target and the background transmitted to the surface of the optical incident window of the TV sensor is obtained; According to the first spatial frequency and the equivalent contrast, based on the system transfer function calculation formula of the television sensor, the system transfer function under the first spatial frequency condition is obtained; According to the contrast of the existing target plate used in the actual test and the second spatial frequency randomly selected under the condition of the existing target plate contrast, the system transfer function under the actual test conditions is obtained based on the calculation formula of the television sensor system transfer function; By adjusting the second spatial frequency, the system transfer function in the actual test is made equal to the system transfer function under the first spatial frequency condition, and the corresponding second spatial frequency is obtained when they are equal; The MRC value after secondary conversion is determined according to the second spatial frequency and the contrast of the existing target plate.

2. The TV range equivalent test conversion method based on target plates with different contrast ratios according to claim 1 is characterized in that: The first spatial frequency corresponding to MRC under the test conditions is calculated as follows: In the formula, represents the first spatial frequency; Indicates the target size; Indicates the action distance; Indicates the number of line pairs required for the resolution level.

3. The TV range equivalent test conversion method based on target plates with different contrast ratios according to claim 1 is characterized in that: The equivalent contrast ratio between the target and the background transmitted to the optical incident window surface of the TV sensor is calculated as follows: In the formula, It indicates the equivalent contrast between the target and the background transmitted to the optical incident window surface of the TV sensor; Indicates the contrast between target and background; Indicates the atmospheric transmittance of the television working band on the path between the carrier and the target.

4. The TV range equivalent test conversion method based on target plates with different contrast ratios according to claim 1 is characterized in that: The system transfer function under the first spatial frequency condition is calculated as follows: In the formula, Indicates the frequency System transmission under conditions; Represents the optical transfer function. According to the spatial resolution Determine the optical transfer function value; Indicates the detector transmission letter; represents the circuit transfer function, which is related to the circuit noise and is approximately a constant for a given TV sensor.

5. The TV range equivalent test conversion method based on target plates with different contrast ratios according to claim 4 is characterized in that: The detector transfer function is calculated as follows: Where: Indicates the focal length of the TV sensor optical system; Represents the detector pixel size.

6. The TV range equivalent test conversion method based on target plates with different contrast ratios according to claim 1 is characterized in that: The system transfer function during the actual test is calculated as follows: In the formula, It represents the second spatial frequency randomly selected under the existing target contrast condition; Indicates that there is target plate contrast; , , They respectively represent the optical transmission function, the detector transmission function and the system transmission function corresponding to the second spatial frequency.

7. A TV range equivalent test conversion system based on target plates with different contrast ratios, characterized in that: include: The assessment data module is used to obtain the first spatial frequency corresponding to the MRC under the assessment conditions based on the target size, the effective distance and the number of line pairs required for the resolution level; obtain the target and background equivalent contrast transmitted to the optical incident window surface of the TV sensor according to the atmospheric transmittance of the TV working band on the path between the carrier and the target, and in combination with the target and background contrast; obtain the system transmission function under the first spatial frequency condition based on the calculation formula of the TV sensor system transmission function according to the first spatial frequency and the equivalent contrast; The actual test module is used to obtain the system transfer function during the actual test based on the contrast of the existing target plate used during the actual test and the second spatial frequency randomly selected under the condition of the contrast of the existing target plate, based on the calculation formula of the system transfer function of the television sensor; The conversion module is used to adjust the second spatial frequency so that the system transfer function during actual testing is equal to the system transfer function under the first spatial frequency condition, and obtain the corresponding second spatial frequency when they are equal; determine the MRC value after secondary conversion according to the second spatial frequency and the contrast of the existing target plate.

8. An electronic device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the computer program implements the steps of the method according to any one of claims 1 to 6 when executed by the processor.

9. A storage medium, characterized in that: A computer program is stored thereon, and when the computer program is run, it is used to execute the steps of the method according to any one of claims 1 to 6.

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