An active noise reduction system, control method and application of an infrared camera

Abstract

The present invention belongs to the technical field of infrared camera imaging, and discloses an infrared camera active noise reduction system, a control method and an application thereof. The system is provided with a data acquisition device, a fixed pattern noise suppression device, an active sampling control device, and a training and decision-making device. The data acquisition device is respectively connected to the fixed pattern noise suppression device and the active sampling control device through connection lines. The fixed pattern noise suppression device is connected to the active sampling control device through a connection line. The data acquisition device is provided with an AD converter, a uniform radiation source, a servo mechanism, an optical unit and a detector. The training and decision-making device is provided with a single spectral band noise statistic, a data accumulation processor, a noise weighting statistic, and a threshold judge. The present invention has low comprehensive noise. At the same time, since the sampling points of each channel or spectral band can be adjusted, the instantaneous ground bounce disturbance caused by simultaneous sampling between channels / spectral bands is also suppressed, and it has the characteristics of strong real-time performance and small data operation volume.

Description

Technical Field

[0001] The present invention belongs to the technical field of infrared camera imaging, and particularly relates to an active noise reduction system, a control method and an application of an infrared camera. Background Art

[0002] Currently, detecting weak targets by using an infrared camera is a hot topic in the current remote sensing imaging field. The commonly used detection scheme at present is that the infrared camera is installed on an aircraft (such as a satellite, an airplane, etc.) for ground observation, or the infrared camera detects from the ground to the sky, and various targets including airplanes, meteors, and space stations are searched by high-resolution imaging.

[0003] With the development of remote sensing imaging technology, the requirement for the sensitivity of imaging is getting higher and higher, which means that the signal-to-noise ratio needs to be further improved. When the radiation intensity of the target signal is determined and the size of the signal that can be detected by the camera is basically determined, the signal-to-noise ratio can only be improved by further reducing the noise.

[0004] For an infrared camera, in addition to the core index of the signal-to-noise ratio in the traditional sense of remote sensing, the influence of background clutter cannot be ignored. Especially in the medium and long wave spectral bands, there is still an uneven background level, that is, fixed pattern noise, in the infrared detection system when there is no incident light, which directly affects the imaging effect. Therefore, in this field, people have analyzed various methods to reduce the influence of noise and clutter and thus improve the signal-to-clutter ratio, and often reduce the noise of the system by methods such as increasing the peak detectivity D* of the infrared detector, reducing the temperature of the optical system to reduce the background, and low-noise and high-stability electronics coupling. However, these methods either require major modifications to the system; or require high index requirements for components at the beginning of the design, with a high cost; or perform high-speed synchronous sampling in a multi-channel and multi-spectral band system while ignoring the influence of ground bounce, resulting in large differences in imaging noise among different channels or spectral bands. After the system is designed, only the system performance can be passively accepted, and during the use of the infrared camera, performance parameters need to be adjusted for different scenarios, which cannot meet the requirement of quick use.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows: the existing noise reduction methods for infrared cameras require major modifications to the system, have high index requirements for components, with a high cost, have large differences in imaging noise among different channels or spectral bands, and during the use of the infrared camera, performance parameters need to be adjusted for different scenarios, which cannot meet the requirement of quick use.

[0006] The difficulty in solving the above problems and defects is as follows: for different infrared systems, the noise distributions are different. Therefore, to improve the signal-to-noise ratio, traditional methods can only analyze and process individual specimens one by one, including methods such as increasing the peak detectivity D* of the infrared detector, reducing the temperature of the optical system to lower the background, and coupling with low-noise and high-stability electronics to reduce the noise of the system. However, these methods require major modifications to the system, consume a large amount of resources, and are difficult to adapt to the applications of most infrared systems for a single application environment.

[0007] The significance of solving the above problems and defects is as follows: for the characteristics of infrared systems, especially infrared systems applied in the detection field, the active noise reduction technology has a certain generality, can quickly complete the suppression of the noise of the infrared system, is conducive to highlighting the target of the infrared detection system, and solves the influence of the background noise of the infrared system on the detection performance of the system. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides an active noise reduction system for an infrared camera.

[0009] The present invention is implemented as follows. An active noise reduction system for an infrared camera is provided with:

[0010] a data acquisition device, a fixed pattern noise suppression device, and an active sampling control device;

[0011] The data acquisition device is respectively connected to the fixed pattern noise suppression device and the active sampling control device through connection lines, and the fixed pattern noise suppression device is connected to the active sampling control device through a connection line.

[0012] Further, the data acquisition device is provided with an AD converter, a uniform radiation source, a servo mechanism, an optical unit, and a detector. The uniform radiation source is located at one end of the incident optical path of the optical unit, the detector is located at one end of the outgoing optical path of the optical unit, the detector is connected to the AD converter through a connection line, and the servo mechanism is connected to the optical unit.

[0013] Further, the optical unit is provided with a reflector and an optical lens, and the optical lens is located at one end of the reflection pipeline of the reflector.

[0014] Further, the fixed pattern noise suppression device is provided with a DA converter and a subtractor.

[0015] Further, the active sampling control device is provided with a timing controller, a first data memory, and a second data memory, and the first data memory is connected to the second data memory through the timing controller.

[0016] Another object of the present invention is to provide a control method for implementing the active noise reduction system of an infrared camera. The control method includes: turning the emission mirror at the incident end of the camera to a uniform blackbody radiation source through a servo mechanism, heating and controlling the temperature of the radiation source through a uniform radiation source controller, converging and imaging the radiation source by an optical unit, using a detector for photoelectric conversion, and using a high-speed AD converter to convert the analog signal generated by the detector exposure into a digital signal; a fixed pattern noise suppression device is used to record the data obtained by the camera for the uniform radiation source at a low temperature point as the background, and subtract the background signal at the low temperature point of the radiation source from the camera signal at the high temperature point of the uniform radiation source, thereby completing the suppression of the fixed pattern noise; the timing controller in the active sampling control device controls the timing of the AD and DA and data transceiver, and the first data memory is used to store the background data, and then cache and output it to the DA, restore it to the analog front end, and perform a subtraction operation with the current signal. The first data memory is used to store the quantization data in various states for the processing module to analyze and calculate.

[0017] An active noise reduction method for an infrared camera specifically includes the following steps:

[0018] S1. Turn the reflection mirror at the incident end of the infrared camera to a uniform radiation source, set the subtractor in the fixed pattern noise suppression device to subtract 0, output the signal of the M-element detector, and record the readout frequency as f det , obtain the data at the first temperature point, i.e., the low temperature point, through the AD converter, and the sampling points and sampling frequency of the AD converter are preset default values;

[0019] S2. Write the data at the first temperature point into the first memory, and after multi-frame accumulation and averaging, use it as the background data and write it into the first memory;

[0020] S3. Heat up the uniform radiation source to the second temperature point, i.e., the high temperature point;

[0021] S4. Read out the background data in the first memory, send it to the DA converter in the fixed pattern noise suppression device to convert it into an analog signal, i.e., the background signal;

[0022] S5. Connect the background signal to the subtraction circuit of the fixed pattern noise suppression device, subtract the current signal output by the infrared detector from the background signal, and deduct the fixed pattern noise;

[0023] S6. Send the subtracted signal to the AD converter for analog-to-digital conversion, and the readout frequency of the pixel signal is f det , the sampling frequency is recorded as N*f det , set the time difference between the starting sampling point within one readout period of a detector pixel and the rising edge of the detector readout clock CLKrd as ts. For different spectral bands or channels, different ts can be set. N is the oversampling times within the pixel, and the converted data is written into the second memory;

[0024] S7. The training and decision-making device processes the data written into the second memory:

[0025] 1) The data accumulation processor accumulates and averages the data, and the number of accumulations is the same as the oversampling number N;

[0026] 2) For the data after accumulation and averaging, partition and parallel process it according to the transmitted channels or spectral bands, and statistically calculate the root mean square n element by element in the time series i , and the average value is the channel or spectral band noise:

[0027]

[0028] i is the channel number or spectral band number, Mi is the number of pixels in the channel or spectral band, and the number of statistical samples is not less than 50;

[0029] 3) Statistically calculate the comprehensive noise:

[0030]

[0031] L is the number of channels or spectral bands, and ai is the weight of each channel or spectral band;

[0032] S8. Determine whether the comprehensive noise has reached the threshold. If not, change the sampling point position, that is, adjust the time difference ts between the starting sampling point within the detector pixel readout period and the rising edge of the detector readout clock CLKrd, adjust the sampling number N, and continue from S6 for cyclic iteration until the requirements are met, and then keep the current parameters and start imaging detection.

[0033] Another object of the present invention is to provide a weak target imaging detection method, and the weak target imaging detection method uses the infrared camera active noise reduction system.

[0034] Another object of the present invention is to provide a remote sensing imaging method, and the remote sensing imaging method uses the infrared camera active noise reduction system.

[0035] Another object of the present invention is to provide an aircraft ground observation method, and the aircraft ground observation method uses the infrared camera active noise reduction system.

[0036] Another object of the present invention is to provide an infrared camera ground-to-air detection method, and the infrared camera ground-to-air detection method uses the infrared camera active noise reduction system.

[0037] Combining all the above technical solutions, the advantages and positive effects of the present invention are as follows: The integrated noise of the present invention is small. At the same time, since the sampling points of each channel or spectral band can be adjusted, the instantaneous ground bounce disturbance caused by simultaneous sampling between channels / spectral bands is also suppressed. It has the characteristics of strong real-time performance and small data operation volume. After application, it can effectively reduce the system noise of the infrared camera, solve the ground bounce disturbance caused by synchronous sampling between multiple spectral bands and multiple channels, and improve the system sensitivity. For the mid-wave infrared camera adopting this method, the measured value of the system noise index after dynamic training of sampling points is 0.35 mV (integration time 500 us), while the system noise value of the same type of mid-wave infrared camera without adopting this method is 0.65 mV (integration time 500 us), a reduction of about 46%, and relatively, the system signal-to-noise ratio is increased by about 85%. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 It is a schematic structural diagram of an active noise reduction system for an infrared camera provided by an embodiment of the present invention.

[0040] Figure 2 It is a schematic connection diagram of an active noise reduction system for an infrared camera provided by an embodiment of the present invention.

[0041] Among them, 1. Data acquisition device, 2. Uniform radiation source, 3. Reflecting mirror, 4. Optical unit, 5. AD converter, 6. Detector, 7. Servo mechanism, 8. Fixed pattern noise suppression device, 9. First data memory, 10. Timing controller, 11. Second data memory, 12. Main control sampling control device, 13. DA converter, 14. Subtractor, 15. Training and decision-making device, 16. Noise weighted statistical device, 17. Threshold judgment device, 18. Single spectral band noise statistical device, 19. Data accumulation processor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will further describe the present invention in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0043] In view of the problems existing in the prior art, the present invention provides an active noise reduction system for an infrared camera, which will be described in detail below with reference to the drawings.

[0044] The active noise reduction system for an infrared camera provided by an embodiment of the present invention includes a data acquisition device, a fixed pattern noise suppression device, and an active sampling control device;

[0045] The data acquisition device is respectively connected to the fixed pattern noise suppression device and the active sampling control device through connection lines, and the fixed pattern noise suppression device is connected to the active sampling control device through a connection line.

[0046] The data acquisition device is provided with an AD converter, a uniform radiation source, a servo mechanism, an optical unit, and a detector. The uniform radiation source is located at one end of the incident optical path of the optical unit, the detector is located at one end of the outgoing optical path of the optical unit, the detector is connected to the AD converter through a connection line, and the servo mechanism is connected to the optical unit.

[0047] The optical unit is provided with a mirror and an optical lens, and the optical lens is located at one end of the reflection pipeline of the mirror.

[0048] The fixed pattern noise suppression device is provided with a DA converter and a subtractor.

[0049] The active sampling control device is provided with a timing controller, a first data memory, and a second data memory. The first data memory is connected to the second data memory through the timing controller.

[0050] The training and decision-making device is provided with a single-spectrum noise statistic, a data accumulation processor, a noise weighting statistic, and a threshold judgment device. The data accumulation processor is connected to the single-spectrum noise statistic through a line, the single-spectrum noise statistic is connected to the noise weighting statistic through a line, and the noise weighting statistic is connected to the threshold judgment device through a line.

[0051] When the present invention is in use, the servo mechanism turns the emission mirror at the incident end of the camera towards the uniform radiation source. The uniform radiation source can be a standard surface source blackbody. The surface source blackbody is heated and temperature-controlled through a uniform radiation source controller. The optical unit converges and images the radiation source. The detector is used for photoelectric conversion, and the high-speed AD converter is used to convert the analog signal generated by the detector exposure into a digital signal. The fixed pattern noise suppression device is used to record the data obtained by the camera for the uniform radiation source at a low temperature point as the background, and subtract the background signal of the radiation source at the low temperature point from the camera signal at the high temperature point of the uniform radiation source, thus completing the suppression of the fixed pattern noise. The timing controller in the active sampling control device controls the timing of the AD and DA and the data transceiver. The first data memory is used to store the background data, and then buffer and output it to the DA, restore it to the analog front end, and perform a subtraction operation with the current signal. The first data memory is used to store the quantization data in various states for the training and decision-making device to analyze and calculate.

[0052] The specific process is as follows:

[0053] S1. The mirror at the incident end of the infrared camera turns towards the built-in blackbody. Set the subtraction circuit in the fixed-pattern noise suppression device to subtract 0. The output signal of the 2048-element detector has a readout frequency of 1 MHz. Obtain the data of the first temperature point through an AD converter, with the temperature measurement accuracy controlled within ±0.1 K. The sampling points of the AD converter are set to be synchronized with the detector readout clock, and the sampling frequency is 16 MHz. The AD converter uses AD9240;

[0054] S2. The data of the first temperature point is written into the first memory. After 16-frame accumulation and averaging, it is used as background data and written into the first memory. The memory uses an SDRAM with a capacity of 128 Mbit;

[0055] S3. Heat the built-in blackbody to the second temperature point, i.e., the high-temperature point. The temperature difference between the second temperature point and the first temperature point is greater than 5 °C, and it cannot cause the output signal of the infrared system to saturate;

[0056] S4. Read out the background data in the first memory and send it to the DA converter in the fixed-pattern noise suppression device to convert it into an analog signal, i.e., the background signal. The DA converter selects AD9761;

[0057] S5. Connect the background signal to the subtraction circuit of the fixed-pattern noise suppression device. Subtract the current output signal of the infrared detector from the background signal to deduct the fixed-pattern noise. The subtractor selects AD8042;

[0058] S6. Send the subtracted signal to the AD converter for analog-to-digital conversion. The readout frequency of the pixel signal is 1 MHz, and the sampling frequency is 16 MHz. The time difference between the starting sampling point within one detector pixel readout cycle and the rising edge of the detector readout clock CLKrd is set to 0, and the oversampling times within the pixel is 16. The converted data is written into the second memory;

[0059] S7. The training and decision-making device is implemented by 4 parallel DSP TMS320C6416s to process the data written into the second memory:

[0060] 1) The data accumulation processor accumulates and averages the data. The number of accumulations is the same as the oversampling times, which is 16;

[0061] 2) For the data after accumulation and averaging, perform partitioned parallel processing according to the transmitted channels or spectral bands. Statistically calculate the root mean square ni element by element in the time series, and the average value is the channel or spectral band noise:

[0062]

[0063] i is the channel number or spectral band number, Mi is the number of pixels in the channel or spectral band, and the number of statistical samples is 100;

[0064] 3) Statistical comprehensive noise:

[0065]

[0066] L is the number of channels or spectral bands, and ai is the weight of each channel or spectral band;

[0067] S8. Determine whether the comprehensive noise has reached the threshold. The threshold can be set to 0.3 LSB. If it has not reached, change the sampling point position, that is, adjust the time difference ts between the starting sampling point within the readout period of the detector pixels of each channel or spectral band and the rising edge of the detector readout clock CLKrd. Adjust the number of sampling times to 32, and continue from S6 for iterative loop until the requirements are met, then keep the current parameters and start imaging detection.

[0068] For the mid-wave infrared camera adopting this method, the measured value of the system noise index after dynamic training of the sampling points is 0.35 mV (integration time 500 us), while for the same type of mid-wave infrared camera without adopting this method, the system noise value is 0.65 mV (integration time 500 us), which is reduced by about 46%, and relatively the system signal-to-noise ratio is increased by about 85%.

[0069] In the description of the present invention, unless otherwise specified, "a plurality of" means two or more; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0070] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention by those skilled in the art within the technical scope disclosed by the present invention shall be covered by the protection scope of the present invention.

Claims

1. A control method for an active noise reduction system of an infrared camera, characterized in that, The control method includes: turning the emission mirror at the incident end of the camera towards the uniform radiation source through a servo mechanism, heating and controlling the temperature of the radiation source through a uniform radiation source controller, converging and imaging the radiation source by an optical unit, using a detector for photoelectric conversion, and using a high-speed AD converter to convert the analog signal generated by the detector exposure into a digital signal; the fixed pattern noise suppression device is used to record the data obtained by the camera for the uniform radiation source at a low temperature point as the background, and subtract the background signal at the low temperature point of the radiation source from the camera signal at the high temperature point of the uniform radiation source, thus completing the suppression of the fixed pattern noise; the timing controller in the active sampling control device controls the timing of the AD and DA and data transceiver, the first data memory is used to store the background data, and then caches and outputs it to the DA, restores it to the analog front end, and performs a subtraction operation with the current signal, and the first data memory is used to store the quantization data in various states for the processing module to analyze and calculate; In the first step, the reflecting mirror at the incident end of the infrared camera turns towards the uniform radiation source, sets the subtractor in the fixed pattern noise suppression device to subtract 0, the M-element detector outputs a signal, the readout frequency is denoted as fdet, and the data at the first temperature point, i.e., the low temperature point, is obtained through the AD converter. The sampling points and sampling frequency of the AD converter are preset default values; In the second step, the data at the first temperature point is written into the first memory, and after multi-frame accumulation and averaging, it is used as the background data and written into the first memory; In the third step, the uniform radiation source is heated to the second temperature point, i.e., the high temperature point; In the fourth step, the background data in the first memory is read out and sent to the DA converter in the fixed pattern noise suppression device to be converted into an analog signal, i.e., the background signal; In the fifth step, the background signal is connected to the subtraction circuit of the fixed pattern noise suppression device, and the current signal output by the infrared detector is subtracted from the background signal to subtract the fixed pattern noise; In the sixth step, the subtracted signal is sent to the AD converter for analog-to-digital conversion. The readout frequency of the pixel signal is fdet, the sampling frequency is denoted as N*fdet, and the time difference between the starting sampling point within one readout period of a detector pixel and the rising edge of the detector readout clock CLKrd is set as ts. For different spectral bands or channels, different ts are set. N is the oversampling times within the pixel, and the converted data is written into the second memory; In the seventh step, the training and decision device processes the data written into the second memory: 1) The data accumulation processor accumulates and averages the data, and the number of accumulations is the same as the oversampling times N; 2) For the data after accumulation and averaging, it is processed in parallel by partitioning according to the transmitted channels or spectral bands, and the root mean square ni is statistically calculated element by element in the time series, and the average value is the channel or spectral band noise: ； i is the channel number or spectral band number, M i is the number of channel or spectral band pixels, and the number of statistical samples is not less than 50; 3) Statistically calculate the comprehensive noise: ； L is the number of channels or spectral bands, a i is the weight of each channel or spectral band; In the eighth step, it is judged whether the comprehensive noise reaches the threshold. If not, the sampling point position is changed, that is, the time difference ts between the starting sampling point within the detector pixel readout period and the rising edge of the detector readout clock CLKrd is adjusted, the sampling times N are adjusted, and it continues from the sixth step, iterating in a loop until the requirements are met, and then the current parameters are maintained and imaging detection starts.

2. The control method of the active noise reduction system of the infrared camera according to claim 1, characterized in that The infrared camera active noise reduction system is provided with: Data acquisition device, fixed pattern noise suppression device, active sampling control device, training and decision-making device; The data acquisition device is respectively connected to the fixed pattern noise suppression device and the active sampling control device through connection lines. The fixed pattern noise suppression device is connected to the active sampling control device through a connection line. The active sampling control device is connected to the training and decision-making device through a connection line; The data acquisition device is provided with an AD converter, a uniform radiation source, a servo mechanism, an optical unit, and a detector. The uniform radiation source is located at one end of the incident optical path of the optical unit. The detector is located at one end of the outgoing optical path of the optical unit. The detector is connected to the AD converter through a connection line. The servo mechanism is connected to the optical unit; The optical unit is provided with a reflector and an optical lens. The optical lens is located at one end of the reflection pipeline of the reflector.

3. The control method of the active noise reduction system of the infrared camera according to claim 2, characterized in that, The fixed pattern noise suppression device is provided with a DA converter and a subtractor.

4. The control method of the active noise reduction system of the infrared camera according to claim 2, characterized in that, The active sampling control device is provided with a timing controller, a first data memory, and a second data memory. The first data memory is connected to the second data memory through the timing controller.

5. The control method of the active noise reduction system of an infrared camera according to claim 2, characterized in that, The training and decision-making device is provided with a single spectral band noise statistic, a data accumulation processor, a noise weighted statistic, and a threshold judge. The data accumulation processor is connected to the single spectral band noise statistic through a line. The single spectral band noise statistic is connected to the noise weighted statistic through a line. The noise weighted statistic is connected to the threshold judge through a line.

6. A method for imaging and detecting weak targets, characterized in that, The method for detecting weak target imaging uses the control method of the infrared camera active noise reduction system according to any one of claims 1 to 5.

7. A remote sensing imaging method, characterized in that, The remote sensing imaging method uses the control method of the infrared camera active noise reduction system according to any one of claims 1 to 5.

8. A method for an aircraft to observe the ground, characterized in that, The method for the aircraft to observe the ground uses the control method of the infrared camera active noise reduction system according to any one of claims 1 to 5.

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