JP2009281863A - Non-cooled infrared imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a reliable non-cooled infrared imaging system capable of reducing an influence by a secular change of the characteristics of each detector, the transmittance characteristics of an optical system, and the like without requiring any components having a mechanical structure. <P>SOLUTION: By the standstill or rotation of a plane mirror 13, the traveling speed of an image on an image sensor 12 can be made fully shorter than the thermal time constant of the detector and an image flow is generated, thus equivalently creating a state where infrared rays having uniform intensity enter from an offset correction data acquisition region through an atmospheric window, and acquiring offset correction data without using any shutters or defocusing means. Also, sensitivity correction data are acquired from data acquired in two different sensitivity correction data acquisition regions during operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an uncooled infrared imaging system in which a thermal infrared detector such as a bolometer or SOI (Silicon on Insulator) diode is mounted on, for example, an artificial satellite and an infrared image of the ground is acquired from the sky. .

  In general, an uncooled infrared imaging system using a thermal infrared detector uses, for example, a two-dimensional thermal infrared detector (see, for example, Non-Patent Document 1). In this non-patent document 1, it appears in an image by performing correction (offset correction) for variations in output offset level between detectors and correction (sensitivity correction) for variations in sensitivity to incident infrared rays between detectors. Fixed pattern noise is reduced.

  Conventional non-cooling infrared imaging systems related to acquisition of correction data used for offset correction and sensitivity correction include the following (for example, see Patent Documents 1 to 3). In Patent Document 1, a shutter is provided at a position where a reference infrared ray having a substantially uniform intensity can be incident on each detector. Then, before the start of imaging at the start or during imaging, the shutter is temporarily closed and a reference infrared ray having a substantially uniform intensity is incident on each of the detectors, and correction data corresponding to variations in the output offset level of each detector. Acquiring. Further, the shutter is opened again, and the obtained correction data is subtracted for each output of the detector and output, thereby performing offset correction.

  Further, in Patent Document 2, a mechanical defocusing means for changing the optical distance between the optical system and the light receiving element is provided, and the calibration light in a state where the focusing position of the optical system is shifted from the light receiving surface of the light receiving element. The offset correction data is acquired.

  Further, in Patent Document 3, imaging is performed for a reference black body at two different temperatures, correction data relating to sensitivity variations of each pixel is calculated from the data, and written in a memory in the uncooled infrared imaging system at the manufacturing stage. . Then, sensitivity is corrected by multiplying and outputting for each output of each infrared detector during imaging.

T. Ishikawa, M. Ueno, Y. Nakai, K. Endo, Y. Ohta, J. Nakanishi, Y. Kosasayama, H. Yagi, T. sone and M. Kimata, “Performannce of 320 × 240 uncooled IRFPA with SOI Diode Detectors”, Proc. SPIE vol. 4130, July 2000, pp. 152-159. Japanese Patent No. 3261617 JP-A-6-82303 JP 2005-236550 A

However, the prior art has the following problems.
When an uncooled infrared imaging system is mounted on an artificial satellite, high reliability is required. For this reason, it is desirable to reduce the number of parts having a mechanical structure such as a shutter and a defocusing means in order to reduce the failure rate.

  In addition, due to stress received during operation, such as radiation exposure, the characteristics of each detector and the transmittance characteristics of the optical system change over time, and the correction effect due to the sensitivity correction data acquired at the manufacturing stage is reduced, and fixed pattern noise is reduced. There is a concern that will increase. However, in order to update the sensitivity correction data in orbit during operation, there is a problem that a reference black body must be mounted.

  The present invention has been made to solve the above-described problems, and does not require a component having a mechanical structure, and can reduce the effects of secular changes such as the characteristics of each detector and the transmittance characteristics of the optical system. An object is to obtain a highly reliable uncooled infrared imaging system.

  An uncooled infrared imaging system according to the present invention is mounted on a flying object, and in response to a received command, a desired image by radiant infrared is imaged by an imaging element including an infrared detector of a plurality of pixels via a plane mirror, A built-in imaging unit that generates digital data corresponding to the image of the image, and a command that is installed on the ground, transmits a command to the mounted imaging unit, and receives the digital data generated by the mounted imaging unit in response to the command. An uncooled infrared imaging system including a data processing unit that acquires data corresponding to an image, where the data processing unit wants to acquire offset correction data corresponding to the output offset level variation of the infrared detector, When the offset data command is transmitted to the mounted imaging unit and the mounted imaging unit receives the offset data command, the imaging element The moving time for one pixel of the infrared detector in the image is sufficiently shorter than the thermal time constant of the infrared detector, and an image flow occurs, and infrared light of uniform intensity enters from the offset correction data acquisition region through the atmospheric window. The plane mirror is stationary or rotated so as to create a state equivalent to the current state, and digital data to be offset correction data is generated, and the data processing unit converts the digital data generated by the mounted imaging unit in response to the offset data command. The offset correction data is updated by reception.

  According to the uncooled infrared imaging system of the present invention, a component having a mechanical structure is required by providing a configuration capable of acquiring offset correction data during operation without using a shutter or defocusing means. Instead, it is possible to obtain a highly reliable uncooled infrared imaging system that can reduce the influence of secular changes such as the characteristics of each detector and the transmittance characteristics of the optical system.

  Hereinafter, preferred embodiments of an uncooled infrared imaging system of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram of an uncooled infrared imaging system according to Embodiment 1 of the present invention. The uncooled infrared imaging system according to the first embodiment includes a mounted imaging unit 100 and a data processing unit 300.

  The mounted image pickup unit 100 in FIG. 1 is connected to the infrared optical system 11, the image pickup device 12 positioned on the imaging plane of the infrared optical system 11, the plane mirror 13 installed in the opening of the infrared optical system 11, and the image pickup device 12. Bias circuit 14, driver circuit 15 connected to the image sensor 12, signal processing circuit 16 connected to the image sensor 12, plane mirror control circuit 19 having a function of rotating the plane mirror 13 around the rotation axis 20, and transmission / reception A circuit 21 is provided. The signal processing circuit 16 includes an amplification circuit 17 and an A / D conversion circuit 18.

  On the other hand, the data processing unit 300 includes a transmission / reception circuit 31, a frame integration circuit 32, an offset correction memory 33 connected to the frame integration circuit 32, a sensitivity correction memory 34, and an offset correction circuit connected to the transmission / reception circuit 31 and the offset correction memory 33. 35, a sensitivity correction circuit 36 connected to the offset correction circuit 35 and the sensitivity correction memory 34, and a command generation circuit 37 are provided.

  Here, in the sensitivity correction memory 34, when the built-in imaging unit 100 is manufactured, the reference black body of two different temperatures is imaged and obtained by calculating from the output voltage of each detector with respect to the set black body temperature difference. Sensitivity correction data for each detector is written.

  FIG. 2 is a structural schematic diagram of each detector constituting the image sensor 12 according to Embodiment 1 of the present invention. 2 includes a light receiving portion 71 having a heat capacity Ct, a thermal conductance 72 having a conductance Gt, and a substrate 73. The thermal conductance 72 is connected between the light receiving portion 71 and the substrate 73. .

  For example, Non-Patent Document 2 (Paul W. Kruse, David D. Skatrud, SEMICONDUCTORS AND SEMIMETALS VOLUME47, “Uncooled Infrared Imaging Arrays and Systems”) and Patent Document 4 (Japanese Patent Laid-Open No. Hei 10-1990). As described in Japanese Patent No. 307061), the rising temperature of the mK order generated in the light receiving portion 71 due to absorption of incident infrared rays is converted into an electrical signal by a resistor, a diode or the like provided in the light receiving portion 71. This is based on the output principle.

  For this reason, the smaller the Gt, the higher the temperature rise of the light receiving unit 71 due to absorption of incident infrared rays, and the sensitivity is improved. On the other hand, each detector has a thermal time constant of τ = Ct / Gt with respect to a change in the intensity of incident infrared rays. Therefore, the smaller Gt, the larger the thermal time constant and the slower the response. For this reason, Gt is designed to be as small as possible in order to ensure sensitivity, while Ct is also designed to be as small as possible by making full use of fine processing technology in order to ensure responsiveness. However, at present, according to Non-Patent Document 2 and Patent Document 4, the value of the thermal time constant τ is about 10 to 20 msec.

  FIG. 3 is a diagram showing an operation mode of the uncooled infrared imaging system according to Embodiment 1 of the present invention. The on-board imaging unit 100 performs imaging from the satellite orbit and transmits image data and detector output data for creating offset correction data to the data processing unit 300 installed on the ground 400. The data processing unit 300 performs offset correction and sensitivity correction on the image data, and outputs an image with reduced fixed pattern noise.

  Next, the operation of the uncooled infrared imaging system in the first embodiment will be described. The mounted imaging unit 100 forms an image of the radiant infrared rays from the observation region for acquiring the offset correction data on the imaging element 12 via the plane mirror 13 and the infrared optical system 11 in the orbit. Further, a bias power supply and a drive clock are supplied from the bias circuit 14 and the driver circuit 15 to the image sensor 12.

  Next, the command generation circuit 37 in the data processing unit 300 transmits an offset correction data acquisition command to the mounted imaging unit 100 via the transmission / reception circuit 31. Then, the plane mirror control circuit 19 stops or rotates the plane mirror 13 so that the time Δt during which the image moves the distance of one pixel on the image sensor 12 is sufficiently shorter than the thermal time constant τ of the detector.

  As an example, the altitude h of the mounted imaging unit 100 is 500 km, the ground speed v is 7 km / sec, the focal length of the infrared optical system 11 is 10 m, and the pixel pitch of each detector is 25 μm. In this case, when the plane mirror 13 is stationary, the time Δt for which the image moves a distance of one pixel on the image sensor 12 is about 0.18 msec. Since this Δt is sufficiently short as compared with the thermal time constant of 10 to 20 msec of the detector, the response of the detector cannot catch up and image flow occurs. As a result, the infrared light having a uniform intensity is equivalent to being incident from the observation region through the atmospheric window.

  Next, the output of the image sensor 12 is amplified by the amplifier circuit 17 in the signal processing circuit 16 and converted into digital data by the A / D conversion circuit 18. Thereafter, it is transmitted to the data processing unit 300 via the transmission / reception circuit 21 as detector output data for creating offset correction data. In the data processing unit 300, the detector output data after the plane mirror 13 is stationary and the detector output is in a temporally stable state after a time more than several times the thermal time constant τ has elapsed since the image flow occurred. Is integrated by the frame integration circuit 32 for each detector output. Then, after improving the S / N, the frame integration circuit 32 writes the offset correction data in the offset correction memory 33 as offset correction data.

  Next, the command generation circuit 37 transmits an imaging start command to the mounted imaging unit 100 via the transmission / reception circuit 31. This time, on the image sensor 12, the plane mirror is set at an angular velocity at which the image is stationary or the image movement time Δt is sufficiently longer than the thermal time constant Δt of the detector so that no image flow occurs. 13 is rotated about the rotation axis 20 to image the observation region.

  Here, in imaging by satellite mounting, in order to increase the spatial resolution, the altitude h is set low and the focal length of the infrared optical system 11 is set long. However, the higher the spatial resolution, the faster the moving speed of the image on the image sensor 12. For this reason, in observation using a thermal infrared detector, the presence of the plane mirror 13 and its rotation are indispensable for obtaining sufficient spatial resolution.

  Next, the mounted image capturing unit 100 converts the output of the image sensor 12 into digital data by the signal processing circuit 16 and then transmits the digital data to the data processing unit 300 as image data. In response to this, the offset correction circuit 35 in the data processing unit 300 subtracts the offset correction data written in the offset correction memory 33 for each detector output, and performs offset correction.

  Then, the sensitivity correction circuit 36 performs sensitivity correction using sensitivity correction data written in advance in the sensitivity correction memory 34 at the time of manufacturing the mounted imaging unit 100. Further, the sensitivity correction circuit 36 outputs the data after reducing the fixed pattern noise by sensitivity correction as image data of the uncooled infrared imaging system.

  Note that the observation area for acquiring the offset correction data is preferably a place having a temperature distribution as uniform as possible, such as a sea area. FIG. 4 is a diagram showing an example of an observation region and a visual field range for acquiring offset correction data according to Embodiment 1 of the present invention. As an example, the height h of the mounted image pickup unit is 500 km, the ground speed v is 7 km / sec, the focal length of the infrared optical system is 10 m, the pixel pitch of each detector is 25 μm in both the X direction and the Y direction, and the pixels of the image sensor 12 The number is 480 (X direction) × 640 (Y direction), the readout frame rate is 30 Hz, and the number of frame integrations is 32.

  In this case, as shown in FIG. 4, the visual field range is 600 m (X direction) × 800 m (Y direction), and the moving distance of the visual field center during 32 frame integrations is 7.5 km in the X direction. As a result, the observation area for acquiring the offset correction data is 8.1 km × 0.8 km, which is a range where a uniform temperature distribution can be sufficiently expected in the sea area or the like.

  As described above, according to the first embodiment, a state where infrared light having a uniform intensity is incident from the offset correction data acquisition region through the atmospheric window by using the image flow caused by the stationary or rotating plane mirror. It has a configuration that can be created equivalently. As a result, offset correction data can be acquired during operation without using a shutter or defocusing means, the influence of secular changes such as the characteristics of each detector and the transmittance characteristics of the optical system can be reduced, and the number of parts can be reduced. An uncooled infrared imaging system with few and high reliability can be obtained.

Embodiment 2. FIG.
In the first embodiment, the case where the sensitivity correction is performed using the sensitivity correction data written in advance in the sensitivity correction memory 34 when the mounted imaging unit 100 is manufactured has been described. On the other hand, in the second embodiment, a case will be described in which sensitivity correction data is also updated during operation to perform sensitivity correction.

  FIG. 5 is a block diagram of an uncooled infrared imaging system according to Embodiment 2 of the present invention. The uncooled infrared imaging system according to the first embodiment includes a mounted imaging unit 100 and a data processing unit 500. The mounted imaging unit 100 in FIG. 5 is the same as the mounted imaging unit 100 in FIG. 1 in the first embodiment.

  On the other hand, the data processing unit 500 in FIG. 5 has a first memory 51, a second memory 52, and a second memory 52 connected to the frame integration circuit 32, as compared with the on-board imaging unit 300 in FIG. A sensitivity correction data calculation circuit 53 is further provided. The sensitivity correction data calculation circuit 53 is connected to the sensitivity correction memory 34, and the sensitivity correction data can be updated during operation to perform sensitivity correction.

  Moreover, FIG. 6 is a figure which shows the operation | use form of the uncooled infrared imaging system in Embodiment 2 of this invention. The on-board image pickup unit 100 picks up an image from the orbit of the satellite and sets the image data, detector output data for creating offset correction data, and detector output data for creating sensitivity correction data on the ground 400. Sent to 500. The data processing unit 500 performs offset correction and sensitivity correction on the image data, and outputs an image with reduced fixed pattern noise.

  Next, the operation of the uncooled infrared imaging system in the second embodiment will be described. The offset correction method is the same as that in the first embodiment, and here, the sensitivity correction method will be described.

  In the sensitivity correction according to the second embodiment, first, a first sensitivity correction data acquisition command is transmitted from the command generation circuit 37 to the mounted imaging unit 100. Then, by an operation equivalent to the offset correction data acquisition described in the first embodiment, the time Δt during which the image moves the distance of one pixel on the image sensor 12 is sufficiently shorter than the thermal time constant τ of the detector. The plane mirror 13 is stationary or rotated so as to be equivalent to a state in which image flow occurs and infrared light having a uniform intensity is incident from the first region through the atmospheric window.

  In this state, the frame integration circuit 32 outputs the first sensitivity correction data creation detector output data corresponding to the observation of the first region to the first memory by the same operation as in the first embodiment. 51.

  Next, a second sensitivity correction data acquisition command is transmitted from the command generation circuit 37 to the mounted imaging unit 100. Then, similarly to the data in the first area, the frame integration circuit 32 records the detector output data for creating the second sensitivity correction data corresponding to the observation in the second area in the second memory 52. .

  Next, the sensitivity correction data calculation circuit 53 calculates the difference between the detector output voltages in the two areas for each detector and records it as the latest sensitivity correction data in the sensitivity correction memory 34.

  Thereafter, imaging is started, and the sensitivity correction circuit 36 performs offset correction by the same operation as in the first embodiment, and performs sensitivity correction using the sensitivity correction data recorded in the sensitivity correction memory 34. Further, the sensitivity correction circuit 36 outputs the data after reducing the fixed pattern noise by sensitivity correction as image data of the uncooled infrared imaging system.

  In addition, if the detector characteristics and optical system transmittance characteristics change over time due to stress received during operation, such as radiation exposure in space, the correction effect of the sensitivity correction data once acquired will be reduced. It is conceivable that the fixed pattern noise after the correction is increased. Therefore, in such a case, the above-described sensitivity correction data is reacquired, and sensitivity correction data is created and updated. As a result, it is possible to perform sensitivity correction using the updated sensitivity correction data during operation.

  Note that the first region and the second region are preferably a combination having a uniform temperature distribution and a certain temperature difference, such as a high latitude sea area and a low latitude sea area.

  As described above, according to the second embodiment, a state in which infrared light having a uniform intensity is incident from the sensitivity correction data acquisition region through the atmospheric window by using the image flow due to the stationary or rotation of the plane mirror. It has a configuration that can be created equivalently. Furthermore, it has a configuration in which the sensitivity correction data can be updated during operation by calculating the difference between the detector output voltages in the two regions for each detector.

  As a result, in addition to the effects of the first embodiment, the reference blackbody is unnecessary and high in reliability, and the characteristics of each detector and the transmittance characteristics of the optical system are changed over time due to stress received during operation such as radiation exposure. Even if it occurs, the optimum sensitivity correction data can be reacquired. As a result, an uncooled infrared imaging system capable of always obtaining an image with reduced fixed pattern noise can be realized.

It is a block diagram of the uncooled infrared imaging system in Embodiment 1 of this invention. It is a structure schematic diagram of each detector which comprises the image sensor in Embodiment 1 of this invention. It is a figure which shows the operation | use form of the non-cooling infrared imaging system in Embodiment 1 of this invention. It is the figure which showed an example of the observation area | region and visual field range which acquire the offset correction data in Embodiment 1 of this invention. It is a block diagram of the uncooled infrared imaging system in Embodiment 2 of this invention. It is a figure which shows the operation | use form of the non-cooling infrared imaging system in Embodiment 2 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Infrared optical system, 12 Image pick-up element, 13 Plane mirror, 14 Bias circuit, 15 Driver circuit, 16 Signal processing circuit, 17 Amplifier circuit, 18 A / D conversion circuit, 19 Plane mirror control circuit, 20 Rotating shaft, 21 Transmission / reception circuit, 31 transmission / reception circuit, 32 frame integration circuit, 33 offset correction memory, 34 sensitivity correction memory, 35 offset correction circuit, 36 sensitivity correction circuit, 37 command generation circuit, 51 first memory, 52 second memory, 53 sensitivity correction data Calculation circuit, 100 on-board imaging unit, 300, 500 data processing unit.

Claims (2)

A desired image based on radiated infrared rays is picked up by an imaging device including an infrared detector of a plurality of pixels via a plane mirror in accordance with a received command, and digital data corresponding to the desired image is generated according to a received command. An on-board imaging unit;
Data that is installed on the ground, transmits the command to the mounted imaging unit, and acquires the data corresponding to the desired image by receiving the digital data generated by the mounted imaging unit in response to the command An uncooled infrared imaging system comprising a processing unit,
When the data processing unit wants to obtain offset correction data corresponding to the output offset level variation of the infrared detector, it transmits an offset data command to the mounted imaging unit,
When the mounted imaging unit receives the offset data command, the moving time for one pixel of the infrared detector of the image on the imaging device is sufficiently shorter than the thermal time constant of the infrared detector. The plane mirror is stationary or rotated so as to create an equivalent state where infrared light of uniform intensity is incident from the offset correction data acquisition region through the atmospheric window, and the digital data that becomes offset correction data is obtained. Generate
The non-cooling infrared imaging system, wherein the data processing unit updates the offset correction data by receiving the digital data generated by the mounted imaging unit in response to the offset data command. The uncooled infrared imaging system according to claim 1,
When the data processing unit wants to obtain sensitivity correction data corresponding to variations in sensitivity to incident infrared rays between the infrared detectors, it sends a sensitivity correction data command to the mounted imaging unit,
When the mounted imaging unit receives the sensitivity correction data command, the moving time for one pixel of the infrared detector of the image on the imaging device is sufficiently shorter than the thermal time constant of the infrared detector. Sensitivity correction data is obtained by moving the plane mirror stationary or rotating so that a flow is generated and a uniform intensity infrared ray is incident on the two sensitivity correction data areas from the observation area through the atmospheric window. To generate digital data
The non-cooling infrared imaging system, wherein the data processing unit updates sensitivity correction data by receiving the digital data generated by the mounted imaging unit in response to the sensitivity correction data command.

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