CN102271225B - Method for improving sensitivity of infrared push-scanning imaging system - Google Patents
Method for improving sensitivity of infrared push-scanning imaging system Download PDFInfo
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- CN102271225B CN102271225B CN 201110098321 CN201110098321A CN102271225B CN 102271225 B CN102271225 B CN 102271225B CN 201110098321 CN201110098321 CN 201110098321 CN 201110098321 A CN201110098321 A CN 201110098321A CN 102271225 B CN102271225 B CN 102271225B
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Abstract
The invention discloses a method for improving sensitivity of an infrared push-scanning imaging system, which is a novel imaging method based on the digital time delay integration. In the method, an infrared two-dimensional array probe is used for imaging in a linear-array push-scanning manner; one dimension of the two dimensions is used as a serial scanning dimension while the other dimension of the two dimensions is used as a push scanning dimension. A pixel voltage value which serially scans a same scenery during a push scanning process is read out by a read-out circuit inside the probe; the pixel voltage value is digitally accumulated and normalized inside an FPGA (Field Programmable Gate Array) after being amplified and quantized in an information obtaining circuit; the normalized image is transmitted to a storage medium. In an M-order infrared system of the digital time delay and integration, if noise inside the probe or noise of the information obtaining circuit is main noise, a signal to noise ratio of the system is proportional to M1/2; and if background photon noise is the main noise, the signal to noise ratio of the system is superior to M1/2.
Description
Technical field
This invention relates to a kind of infrared imagery technique, specifically refers to for high sensitivity infrared imaging method under the push-scanning image mode.It is applied to obtaining of high sensitivity infrared image.
Background technology
The raising of infrared imaging system detectivity be one important and be long-term developing direction, the sensitivity that improves detection system is for increasing detection range, detecting small-signal very important meaning is arranged.The sensitivity of infrared system is not only relevant with the optics bore of system imaging pattern, optical system, and and the detector detectivity, the noise of the time of integration and electronic system has relation.Wherein, the sensitivity of infrared system and the time of integration are directly related.The time of integration of extension system, except the technology such as key components such as development detector, new imaging pattern also is one of important measure, thereby purpose of the present invention is intended to by expansion raising time of integration infrared remote sensing imaging system detectivity.
In general, in visible light push-scanning image system, the detector image-forming that adopts time delay integration (TDI) function is a kind of maturation and mode commonly used.Mostly external TDI technology is that charge storage and the electric charge principle of transfer based on the CCD device postpones integration in detector inside, and its core is to expand the several times that reach the pixel residence time time of integration to arrive decades of times.Yet for infrared system, because therefore the restriction of domestic focus planardetector technical merit development, particularly the detector immature development of the TDI mode of operation of long alignment directly adopt the detector of TDI mode of operation also unrealistic.In addition, different with visible-light detector, the saturated time of integration of visible-light detector is longer, usually can reach millisecond rank even longer time, and the charge capacity of Infrared Detectors itself is less, generation is saturated easily, and the saturated time of integration is very short, usually arrives between the hundreds of microsecond in tens microseconds.The pixel residence time that space remote sensing is long can not be realized long integration, causes thus the sensitivity of system to be difficult to improve.Therefore, if will utilize relatively long residence time, realize infrared high sensitivity imaging detection, the mode of operation that needs development and the less infrared focal plane device of charge capacity to adapt realizes the expansion of the time of integration.
Summary of the invention
The purpose of this invention is to provide a kind of new infrared system imaging pattern, improve the detectivity of infrared system, can effectively solve in the infrared remote sensing imaging system the short time of integration of Infrared Detectors and relatively reside permanently the contradiction of staying between the time, expand the time of integration, thereby reach the purpose of raising system detectivity.
The present invention is that its key step is as follows for the formation method that improves sensitivity of infrared push-scanning imaging system:
(1) utilize and postpone Integral Technology digit time, infrared two-dimensional array detector is pushed away the mode of sweeping as alignment, wherein one dimension is swept dimension for string, and another dimension is swept dimension for pushing away;
(2) the window pattern of reading by detector make its output M capable * N row simulated image data, wherein, M refer to go here and there sweep the dimension pixel number, from the path that signal is propagated, noise source comprises the inner intrinsic noise of photon noise, detector and the acquisition of information circuit noise of incident in the infrared push-scanning image system, postpone in the infrared system of Integral Technology in the digit time of adopting the M rank, when detector internal noise or acquisition of information circuit noise are main noise, the signal to noise ratio of system and M
1/2Be directly proportional, when the background photon noise was main noise, system signal noise ratio was better than M
1/2, the M value can be adjusted according to the system sensitivity demand flexibly according to above-mentioned rule;
(3) aanalogvoltage of detector being read is input in the acquisition of information circuit and amplifies, quantizes;
(4) in system's push-scanning image process, each row pixel digital signal of the inswept same scenery of string of correspondence added up and average carry out normalization;
(5) normalized image transmitting is in storage medium.
Wherein to postpone Integral Technology digit time be that relatively traditional simulated time postpones the integration Detection Techniques to step (1), when simulated time lagged product detector-dividing carries out time delay integration, the electric charge of same scenery formation that serial is inswept is to add up in detector inside, then after reading via reading circuit, in the acquisition of information circuit, amplify, digital quantization, and utilizing planar array detector to realize postponing in the integration imaging process digit time, the pixel magnitude of voltage of inswept same scenery of going here and there is read by the reading circuit of detector inside, in the acquisition of information circuit, amplify, it is digital cumulative to quantize laggard row, postpone integration and simulated time digit time and postpone to carry out after cumulative operation that basic different of integration are the former quantizes in the acquisition of information circuit, and the latter's is cumulative in the inner realization of detector.
Each row pixel digital signal of the inswept same scenery of string that step (4) is corresponding adds up and the normalization operation adopts FPGA to realize.
Advantage of the present invention is:
(1) can imaging in low target width of cloth brightness situation.Numeral TDI can realize the prolongation of the time of integration, thus imaging under the weak condition of incident ray energy.It is very helpful that this surveys weak target for space remote sensing.
(2) do not need the custom-made detector, can require the needed TDI exponent number of change according to actual design, thereby adapt to different detectivity requirements, the flexibility of application improves greatly.
(3) when infrared system when space environment is observed, sometimes can have the high-energy effect in the space, thereby cause that ion and particle are to the supersaturation radiation of detector.Numeral TDI can stop the radiation that is caused by ion and particle under the high-energy environment.In traditional simulation M level TDI system, be the summation of M pixel integration the time of integration, as long as there is a pixel to be subject to ionizing radiation, all pixel datas of these row are with destroyed so.This problem can solve with digital TDI.Solution is that the pixel to the pixel of framing and former frame compares, if the luminous intensity of the light strength ratio former frame of a pixel is much larger, this pixel will be left in the basket in averaging process so.Therefore, use digital TDI system, can remove the interference that the high-energy effect produces by the pixel of successive frame relatively.
Description of drawings
Fig. 1 is infrared imaging system hardware configuration schematic diagram of the present invention.
Fig. 2 is FPGA numeral TDI algorithm flow chart of the present invention.
Fig. 3 is 1 exponent number word TDI push-scanning image design sketch of the present invention.
Fig. 4 is 4 exponent number word TDI push-scanning image design sketchs of the present invention.
Fig. 5 is each pixel signal to noise ratio figure of 1 exponent number word TDI of the present invention.
Fig. 6 is each pixel signal to noise ratio figure of 4 exponent number word TDI of the present invention.
Embodiment
Below in conjunction with drawings and Examples, describe the present invention.
The inventive method is to realize at infrared imaging system hardware platform as shown in Figure 1.Infrared image converges on the focal plane that is imaged on detector through optical system, at first produce required bias voltage and the digital drive signals of detector by drive circuit, the A/D that is transferred to control circuit after the analog picture signal process filtering of output, the amplification quantizes, carry out lagged product divisional processing digit time via FPGA again, utilize at last the turntable push-scanning image and store infrared alignment image.
Wherein, the optical system effective aperture is 37.5mm, and focal length is 75m, and the F number is 2, instantaneous field of view 0.4mrad, 7.3 ° of total visual fields.
Planar array detector is by 320 row, and 256 row pixels consist of, the big or small 30 μ m of photosensitive unit * 30 μ m, response wave length 7.7～9.3 μ m, the highest output speed 6.6MHz of pixel.The detector playback mode can adopt stationary window pattern (320 * 256,320 * 240,256 * 256) or window scheme output, and the minimum window pattern is 64 row * 1 row.This example is used window scheme, and line direction is swept direction as string, the output that all exposes of column direction pixel.
What FPGA adopted is the Cyclone3 family chip of ALTERA company, and inside has 24,624 logical blocks approximately, 594Kbits, and 66 Multipliers, 4 PLL and 148 I/O pins are suitable for Video processing.
Turntable is the common one dimension turntable of orientation rotation, and the orientation rotation angle is 0～360 °, 0.1 °/s of rotating speed～2 °/s.
FPGA is inner to realize digital TDI algorithm flow chart as shown in Figure 2, at first carries out initialization, defines 3 bufferings and is used for realizing that digital TDI is cumulative, be i.e. Now_buf, Res_buf and Out_buf.Wherein, Now_buf is used for storing the current frame data that read, and Res_buf is used for storing the middle accumulation result of corresponding pixel, and Out_buf is final digital TDI accumulation result.It is M that detector numeral TDI exponent number is set, then drive detector and produce (M capable * 320 row) photofit picture metadata, when data arrive, read window data, the first row data deposit among the Now_buf, read simultaneously the data of Res_buf intermediate buffering, and get back among the Res_buf with depositing after the data of the corresponding same spatial location of remaining row add up, when finish M numeral cumulative after, the view data that reads after cumulative carries out storing in the storage medium after the normalization divided by M.Because incipient M-1 frame data do not carry out M time adding up, and are considered as invalid frame and are abandoned.
1 rank and 4 exponent number word TDI infrared imaging effect are as shown in Figure 3 and Figure 4.From imaging effect, 1 rank image exposure quantity not sufficient, image is fuzzyyer; 4 rank TDI image ratios, 1 rank TDI image quality is obviously improved, and clear picture is higher for the resolution capability of weak signal.
Fig. 5 and Fig. 6 have provided 1 rank and 4 each pixel signal to noise ratio figure of exponent number word TDI system.Because the LONG WAVE INFRARED system signal noise ratio is weighed with noise equivalent temperature difference, recording at last the average pixel noise equivalent temperature difference of 1 exponent number word TDI is 34mK, and the average pixel noise equivalent temperature difference of 4 exponent number word TDI is 17mK.Therefore can find out that digital TDI can the infrared detectivity that pushes away the system of sweeping of Effective Raise.
Claims (2)
1. a formation method that is used for improving sensitivity of infrared push-scanning imaging system is characterized in that comprising the steps:
1) utilize and postpone Integral Technology digit time, infrared two-dimensional array detector is pushed away the mode of sweeping as alignment, wherein one dimension is swept dimension for string, and another dimension is swept dimension for pushing away; Postponing Integral Technology described digit time is to utilize infrared two-dimensional array detector to realize postponing in the integration imaging process digit time, the pixel magnitude of voltage of inswept same scenery of going here and there is read by the reading circuit of infrared two-dimensional array detector inside, and it is digital cumulative to amplify, quantize laggard row in the acquisition of information circuit;
2) the window pattern of reading by infrared two-dimensional array detector make its output M capable * N row simulated image data, wherein, M refers to go here and there the number of sweeping the dimension pixel, the M value is chosen according to the foundation that the signal to noise ratio of system is directly proportional with M1/2;
3) aanalogvoltage of infrared two-dimensional array detector being read is input to and amplifies in the acquisition of information circuit and quantize;
4) in system's push-scanning image process, each row pixel digital signal of the inswept same scenery of string of correspondence added up and average carry out normalization;
5) normalized image transmitting is in storage medium.
2. a kind of formation method for improving sensitivity of infrared push-scanning imaging system according to claim 1 is characterized in that: step 4) described in each row pixel digital signal of the inswept same scenery of string of correspondence add up and normalization operation employing FPGA realizes.
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| CN104486562B (en) * | 2014-12-26 | 2017-11-24 | 昆明物理研究所 | Embedded infrared image superframe processing method based on the fixed time of integration |
| CN106101583B (en) * | 2016-07-29 | 2019-03-22 | 中国科学院长春光学精密机械与物理研究所 | Infrared imaging method based on numeric field TDI |
| CN114323279A (en) * | 2021-12-23 | 2022-04-12 | 中国科学院西安光学精密机械研究所 | Method for improving image signal-to-noise ratio of space-time joint modulation interference type spectrometer |
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| CN101809990A (en) * | 2007-08-10 | 2010-08-18 | 原子能委员会 | Method of correcting sensitivity and matrix image sensor for implementing this method |
| CN101472095A (en) * | 2007-12-26 | 2009-07-01 | 原相科技股份有限公司 | Cursor control method and device using the method |
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