CALIBRATION MECHANISM FOR THERMAL IMAGING SYSTEMS

Abstract

A method and an imaging system for providing an infrared image of an object comprises an optical element configured to capture infrared radiation from the object, an infrared sensing module, a processing unit, and a shutter assembly. The infrared sensing module comprises a plurality of infrared detectors, each configured to receive the infrared radiation from the object after passage through the optical element and generate a measurement signal from the received infrared radiation. The processing unit is coupled to the infrared sensing module and configured to convert the measurement signals into temperature data associated with the object for providing the infrared image. The shutter assembly is disposed between the infrared sensing module and the optical element, and is configured to selectively pass the infrared radiation from the object through to the infrared sensing module. The shutter assembly comprises a temperature controller configured to adjust a temperature of the shutter assembly.

Claims

1. An imaging system for providing an infrared image of an object, the system comprising: an optical element configured to capture infrared radiation from the object; an infrared sensing module comprising a plurality of infrared detectors, each infrared detector configured to receive the infrared radiation from the object after passage through the optical element and generate a measurement signal from the received infrared radiation; a processing unit coupled to the infrared sensing module and configured to convert the measurement signals into temperature data associated with the object for providing the infrared image; and a shutter assembly disposed between the infrared sensing module and the optical element and configured to selectively pass the infrared radiation from the object through to the infrared sensing module, the shutter assembly comprising a temperature controller configured to adjust a temperature of the shutter assembly.

2. The system of claim 1, wherein the shutter assembly further comprises a temperature sensor configured to measure the temperature of the shutter assembly.

3. The system of claim 1, wherein the shutter assembly further comprises a shutter blade and a heating element coupled to the shutter blade, and wherein the temperature of the shutter assembly is adjusted by adjusting a temperature of the shutter blade using the heating element.

4. The system of claim 3, wherein the temperature controller is configured to adjust the temperature of the shutter blade when the shutter blade is at an open position, wherein the open position is a position for passing the infrared radiation from the object through to the infrared sensing module.

5. The system of claim 3, wherein the temperature sensor is configured to measure the temperature of the shutter assembly when the shutter blade is at a closed position, wherein the closed position is a position for blocking the infrared radiation from the object.

6. The system of claim 5, wherein the processing unit is configured to obtain reference temperature data from the measurement signals when the shutter blade is at the closed position and has the measured temperature achieved by heating and to use the obtained reference temperature data and the measured temperature for calibration.

7. The system of claim 5, wherein the processing unit is further configured to provide first reference temperature data from the measurement signals at a first temperature of the shutter assembly when the shutter blade is at said closed position, and to provide second reference temperature data from the measurement signals at a second temperature of the shutter assembly when the shutter blade is at said closed position.

8. The system of claim 7, wherein the temperature controller is configured to adjust the temperature of the shutter blade when the shutter blade is at an open position, wherein the open position is a position for passing the infrared radiation from the object through to the infrared sensing module, wherein between the provision of the first reference temperature data and the second reference temperature data, the shutter blade is at said open position and the temperature of the shutter blade is adjusted for bringing the temperature of the shutter blade to the second temperature.

9. The system of claim 7, wherein the first reference temperature data and the second reference temperature data are provided consecutively, substantially within a period of time that is required for bringing the temperature of the shutter blade to said second temperature.

10. The system of claim 7, wherein the processing unit is further configured to determine a characteristic parameter related to the generation of the measurement signal for each infrared detector of the plurality of infrared detectors based on a comparison between the first reference temperature data and the second reference temperature data.

11. The system of claim 10, wherein the characteristic parameter of a given infrared detector comprises a sensitivity and/or an offset of the given infrared detector.

12. The system of claim 11, wherein the sensitivity of the given infrared detector is determined further based on the first and second temperatures of the shutter assembly.

13. The system of claim 3, wherein the shutter blade comprises a surface of uniform and high emissivity.

14. The system of claim 3, wherein the temperature of the shutter blade is uniform across the shutter blade.

15. The system of claim 1, wherein the infrared image comprises an array of pixels and each infrared detector of the plurality of infrared detectors corresponds to a single pixel of the array.

16. The system of claim 1, wherein the temperature controller comprises a Proportional-Integral-Derivative (PID) temperature controller.

17. The system of claim 1, further comprising an infrared filter configured to select a wavelength of the infrared radiation to be passed to the infrared sensing module.

18. A shutter assembly for use in an infrared imaging system, the shutter assembly comprising: a shutter blade configured to move between an open position and a closed position to selectively pass infrared radiation from an object captured by an optical element through to an infrared sensing module of the infrared imaging system; and a temperature controller coupled to the shutter blade and configured to adjust a temperature of the shutter blade.

19. The shutter assembly of claim 18, further comprising a temperature sensor configured to measure the temperature of the shutter blade when the shutter blade is at the closed position, wherein the closed position is a position at which the shutter blade blocks the infrared radiation from the object.

20. The shutter assembly of claim 18, further comprising a heating element coupled to the shutter blade, wherein the temperature of the shutter blade is adjustable using the heating element.

21. The shutter assembly of claim 20, wherein the heating element comprises a metal plate attached to a periphery of the shutter blade to adjust the temperature of the shutter blade when the shutter blade is at the open position, wherein the open position is a position at which the shutter blade allows passage of the infrared radiation from the object through to the infrared sensing module.

22. The shutter assembly of claim 21, wherein the shutter blade is configured to be at said closed position for providing first reference temperature data corresponding to a first temperature of the shutter blade and for providing second reference temperature data corresponding to a second temperature of the shutter blade higher than the first temperature of the shutter blade, and wherein, between the provision of the first reference temperature data and second reference temperature data, the shutter blade is at said open position for adjusting the temperature of the shutter blade to reach the second temperature of the shutter blade.

23. The shutter assembly of claim 22, configured to output measurements of the first and second temperatures of the shutter blade, for determining a characteristic parameter including a sensitivity and/or an offset of a given infrared detector within the infrared sensing module.

24. The shutter assembly of claim 18, wherein the shutter blade comprises a surface of uniform and high emissivity.

25. The shutter assembly of claim 18, wherein the temperature of the shutter blade is uniform across the shutter blade.

26. The shutter assembly of claim 18, wherein the temperature controller comprises a Proportional-Integral-Derivative (PID) temperature controller.

27. A method for providing an infrared image of an object using an imaging system having a shutter assembly, the shutter assembly selectively passing infrared radiation from the object captured by an optical element through to an infrared sensing module of the imaging system, the infrared sensing module comprising a plurality of infrared detectors to generate, based on the received infrared radiation, a plurality of measurement signals to be converted into temperature data associated with the object for providing the infrared image, the method comprising: measuring a first temperature of the shutter assembly; providing, when the shutter assembly is in a closed state for blocking the infrared radiation from the object, first reference temperature data from the measurement signals corresponding to the measured first temperature of the shutter assembly; adjusting a temperature of the shutter assembly; measuring a second temperature of the shutter assembly; providing, when the shutter assembly is in said closed state, second reference temperature data from the measurement signals corresponding to the measured second temperature of the shutter assembly; and determining a characteristic parameter related to the generation of the measurement signals for each infrared detector of the plurality of infrared detectors based on the first reference temperature data and the second reference temperature data.

28. The method of claim 27, wherein the temperature of the shutter assembly is adjusted when the shutter assembly is in an open state, wherein the open state allows passage of the infrared radiation from the object through to the infrared sensing module.

29. The method of claim 27, wherein adjusting a temperature of the shutter assembly further comprises adjusting a temperature of a shutter blade of the shutter assembly using a heating element.

30. The method of claim 29, wherein the temperature of the shutter assembly is adjusted when the shutter assembly is in an open state, wherein the open state allows passage of the infrared radiation from the object through to the infrared sensing module, wherein the shutter assembly is in said open state between the provision of the first reference temperature data and the second reference temperature data, and the temperature of the shutter blade is adjusted for reaching the second temperature of the shutter assembly.

31. The method of claim 29, wherein the first reference temperature data and the second reference temperature data are provided consecutively, substantially within a period of time that is required for bringing the temperature of the shutter blade to said second temperature.

32. The method of claim 27, wherein the characteristic parameter of a given infrared detector comprises a sensitivity and/or an offset of the given infrared detector.

33. The method of claim 32, wherein the sensitivity for the given infrared detector is determined further based on the measured first and second temperatures of the shutter assembly.

34. The method of claim 29, the temperature of the shutter blade is uniform across the shutter blade.

35. The method of claim 27, wherein each infrared detector of the plurality of infrared detectors corresponds to a single pixel of the infrared image.

36. The method of claim 27, wherein the temperature controller comprises a Proportional-Integral-Derivative (PID) temperature controller.

37. The method of claim 27, further comprising selecting a wavelength of the infrared radiation to be passed to the infrared sensing module using an infrared filter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0051] Embodiments of the disclosure are described below in an exemplary manner with reference to the accompanying drawings, wherein:

[0052] FIG. 1 illustrates an example of an infrared (IR) imaging system for providing an infrared image of an object according to an embodiment of the disclosure;

[0053] FIG. 2 illustrates an example of a shutter assembly for use in the infrared imaging system according to an embodiment of the disclosure;

[0054] FIG. 3 illustrates a detailed view of the shutter assembly of FIG. 2 when the shutter assembly is at an open position (a) and when the shutter assembly is at a closed position (b) according to an embodiment of the disclosure; and

[0055] FIG. 4 illustrates processing steps for an example of a method for providing an infrared image of an object using the imaging system having the shutter assembly according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0056] FIG. 1 illustrates an infrared (IR) imaging system 100 for providing an infrared image of an object according to an embodiment of the disclosure. The infrared imaging system 100 may be, for example, an infrared camera for installation in small satellites for space applications, for example. Herein, the IR imaging system 100 includes an optical element 101 (such as an IR optical lens, for example) to capture infrared radiation from an object (not shown) external to the IR imaging system 100. The IR imaging system 100 also includes an infrared sensing module 103 (e.g., an IR sensor) having a plurality of infrared detectors (e.g., an IR detector array or microbolometer). As mentioned above, each of the infrared detectors is configured to receive the infrared radiation from the object after passage through the optical element 101 and then generate a measurement signal from the received infrared radiation. The respective measurement signal is generated based on or in accordance with the characteristic parameter(s) for each of the detectors, such as a gain/sensitivity (e.g., information on how a given change in IR radiation translates into a corresponding change in the measurement signal) and/or an offset value (e.g., information on a magnitude of the measurement signal in the absence of IR radiation).

[0057] The IR imaging system 100 also includes a processing unit 104, such as a processor, microcontroller, or any other suitable processing device for executing instructions (e.g., software instructions) and processing data (e.g., measurement data, temperature data, image data, etc.) stored in a memory or provided to the processing unit 104 in any other suitable form. The processing unit 104 is coupled to the infrared sensing module 103 to convert the measurement signals (i.e., measurement signals generated by the infrared detectors) into temperature data associated with the object for providing an infrared (IR) image. The processing unit 104 is configured to further convert the temperature data into the IR image of the object to visually show a temperature distribution of the object. Accordingly, the infrared image may comprise an array of pixels and each of the plurality of infrared detectors may correspond to a single pixel of the array.

[0058] The IR imaging system 100 further includes a shutter assembly 102 disposed between the optical element 101 and the infrared sensing module 103. The shutter assembly 102 is configured to selectively pass the infrared radiation from the object through to the infrared sensing module 103. For example, the shutter assembly 102 can be put into an open state to allow the infrared radiation from the object to pass through to the infrared sensing module 103, or the shutter assembly 102 can be put into a closed state to block the infrared radiation of the object from reaching the infrared sensing module 103. Also, the shutter assembly 102 may comprise a temperature controller (not shown) to adjust or control a temperature of the shutter assembly 102.

[0059] As mentioned above, the shutter assembly 102 itself may act as a radiation source having a temperature that is adjustable/controllable, when the shutter assembly 102 is in the closed state. In this case, the infrared sensing module 103 receives infrared radiation from the shutter assembly 102 (i.e., samples IR radiation from the (closed) shutter assembly 102) and each detector of the infrared sensing module 103 will then produce a corresponding measurement signal at a given/preset temperature of the shutter assembly 102 (i.e., a measurement signal corresponding to the given/preset temperature of the shutter assembly 102). The respective measurement signals corresponding to the given temperature of the shutter assembly 102 will then be converted into corresponding temperature data (and possibly also an IR image) representing a temperature profile of the shutter assembly 102 as measured by the infrared sensing module 103.

[0060] As described above, the processing unit 104 is configured to obtain reference temperature data from the measurement signals when the shutter assembly 102 is in the closed state and has the measured temperature achieved through the adjustment by the temperature controller, and configured to use the obtained reference temperature data and the measured temperature for calibration. The reference temperature data associated with the shutter assembly 102 being at the closed position as obtained from the measurement signals generated by the IR sensor 103 can be further converted into a reference IR image to be compared to the measured actual temperature of the shutter assembly 102 (measured by a temperature sensor, not shown) to estimate the measurement errors of the IR sensor 103 for the calibration. Alternatively, the reference temperature data may be directly compared to the measured actual temperature of the shutter assembly 102 to estimate the measurement errors of the IR sensor 103 for the calibration.

[0061] The processing unit 104 is further configured to provide two or more sets of temperature data as reference for the calibration. For example, first reference temperature data from the measurement signals at a first temperature of the shutter assembly 102 may be provided when the shutter assembly 102 is in said closed state, and second reference temperature data from the measurement signals at a second temperature of the shutter assembly 102 may be provided when the shutter assembly is in said closed state. Between the provision of the first reference temperature data and the second reference temperature data, the shutter assembly may be in said open state and the temperature of the shutter assembly 102 may be adjusted for bringing the temperature of the shutter assembly 102 to the second temperature.

[0062] FIG. 2 illustrates a shutter assembly 200 for use in the infrared imaging system 100 according to an embodiment of the disclosure. The shutter assembly 200 corresponds to the shutter assembly 102 of the system 100 in FIG. 1. and includes a shutter blade 201 which can move between an open position and a closed position to selectively pass infrared radiation from an object captured by the optical element 101 through to the infrared sensing module 103 of the infrared imaging system 100. The shutter assembly 200 also includes a temperature controller (e.g., a PID controller, not shown) for adjusting a temperature of the shutter blade 201. The shutter assembly 200 further includes a heating element 202 (e.g., a flat heating element) coupled to the shutter blade 201, so that the temperature controller can adjust the temperature of the shutter blade using the heating element 202. The heating element may contain a variable resistance 203. Besides, the shutter assembly 200 can also have one or more temperature sensors (not shown) to measure the actual temperature of the shutter assembly 200 or the shutter blade 201.

[0063] As mentioned above, the heating element 202 can be connected to a power source (e.g., power supply) to convert electrical energy into heat (e.g., via a heating process) to heat up the shutter blade 201. The heating element 202 is also connected to the temperature controller for adjusting/raising the temperature of the shutter blade 201 through the heating process controlled by the temperature controller. It should be noted that the shutter blade 201 has a surface of uniform and high emissivity and can be regarded as a blackbody radiation source. In addition, the temperature of the shutter blade 201 may be uniform across the shutter blade 201.

[0064] FIG. 3 illustrates a detailed view of the shutter assembly 200 in FIG. 2 according to an embodiment of the disclosure. The shutter assembly 300 includes a shutter blade 301 that moves between an open position (a) and a closed position (b) to selectively pass infrared radiation from an external object. The shutter assembly 300 further includes a flat heating element 302 coupled to the shutter blade 301 for adjusting the temperature of the shutter blade 301. The flat heating element 302 can be made from a metal plate or a flat wire winding pattern attached to a periphery of the shutter blade 301. As shown in the example of FIG. 3, both the shutter blade 301 and the heating element 302 are circular plates having a common center (i.e., being concentric). However, any other shape of plates may also be feasible in the context of the present disclosure.

[0065] According to the configuration as shown in FIG. 3, the circular plate of the shutter blade 301 is placed within a concentric inner hole of the circular plate of the heating element 302, where the periphery of the shutter blade 301 is attached to the periphery of the inner hole of the heating element 302. The shutter blade 301 can move towards its periphery to be at the open position (as illustrated by FIG. 3(a)) at which the shutter blade 301 allows passage of the infrared radiation of the object through to the infrared sensing module 103, while the shutter blade 301 can move towards its center to be at the closed position (as illustrated by FIG. 3(b)) at which the shutter blade 301 blocks the infrared radiation of the object. Accordingly, the shutter blade 301 can be properly placed on a surface of the flat heating element 302 to have good physical contact with the heating element 302 for heat exchange and temperature adjustment when the shutter blade 301 is at the open position.

[0066] In the embodiment, the heating element 302 is connected to a power source (e.g., power supply or power regulator) 304 for converting electrical energy into heat (e.g., via a heating process) to heat up the shutter blade 301 when the shutter blade 301 is at the open position (a). At the end of the heating process, thermal equilibrium between the heating element 302 and the shutter blade 301 can be achieved, so that the temperature of the heating element 302 and the temperature of the shutter blade 301 become substantially the same. Preferably, the shutter blade 301 may be a uniform and thin plate so as to shorten the required time for reaching the thermal equilibrium. The shutter blade 301 may also have high emissivity to serve as a blackbody radiation source when being in the closed state.

[0067] Furthermore, a temperature controller 303 (e.g., PID controller) is connected to the power supply 304 for controlling a power input for the heating element 302 and for adjusting the temperature of the shutter blade 301. Additionally, one or more temperature sensors 305 may be coupled (e.g., connected) to the shutter blade 301 (or alternatively, disposed on the shutter blade) to measure the actual temperature of the shutter blade 301, in particular when the shutter blade 301 is at the closed position. Notably, the temperature sensor(s) 305 may be also coupled (e.g., connected) to the temperature controller 303 so that the temperature controller 303 can controls the temperature adjustment based on the temperature of the shutter assembly 301 as measured by the temperature sensor(s) 305.

[0068] FIG. 4 illustrates a method for providing an infrared image of an object using the imaging system 100 having the shutter assembly 200, 300, according to an embodiment of the disclosure. The method 400 includes measuring a first temperature of the shutter assembly (step 401) and providing, when the shutter assembly is in a closed state for blocking the infrared radiation from the object, first reference temperature data from the measurement signals corresponding to the measured first temperature of the shutter assembly (step 402).

[0069] The method 400 further includes adjusting/controlling a temperature of the shutter assembly (step 403). The method also includes measuring a second temperature of the shutter assembly (step 404) and providing, when the shutter assembly is in said closed state, second reference temperature data from the measurement signals corresponding to the measured second temperature of the shutter assembly (step 405). Moreover, the method includes determining a characteristic parameter related to the generation of the measurement signals for each of the plurality of infrared detectors based on the first reference temperature data and the second reference temperature data (step 406).

[0070] Configured as above, temperature measurements of the shutter assembly (acting as a radiation source when being in the closed state) can be easily performed to provide reference temperature data at different operating temperatures. It is appreciated that the results of the measurements (e.g., the temperature data of the shutter assembly) may be used as reference (e.g., reference temperature data) for calibrating the infrared sensing module (e.g., IR sensor). As noted above, since the shutter assembly may be placed directly in front of the infrared sensing detector without optics, the shutter assembly may be assumed to be a homogeneous temperature surface, rather than to accurately map a temperature curve of the shutter assembly with the detector.

[0071] For example, the resulting temperature profile of the shutter assembly measured or observed by the infrared sensing module (e.g., as reference temperature data) can be compared to the actual temperature of the shutter assembly (which may be obtained by for example a temperature sensor) to estimate the measurement errors of the infrared sensing module (which may occur for example due to changes of ambient temperature). The comparison may then be used to correct subsequent measurement results for objects external to the imaging system (e.g., objects placed in front of the optical element, such as the Earth surface).

[0072] Accordingly, prior to taking a temperature measurement of an external object, measurement errors caused by the infrared sensing module can be effectively and efficiently estimated/determined by providing a reference temperature profile or reference temperature data (which may then be further converted into an IR image as reference, i.e., a reference IR image) at one or more given (operating) temperatures of the shutter assembly (where the temperature is controllable/adjustable). Such measurement errors may be taken into account to ensure a subsequent temperature measurement of an external object to be conducted in a more accurate (and reliable) manner.

[0073] In other words, the proposed method and imaging system provides a simple and improved calibration mechanism that allows continuous temperature measurements of an object even with just simple temperature stabilization of the infrared sensing module. In particular, the proposed calibration mechanism may be used for calibrating the change of properties of a microbolometer detector which may happen due to launch of satellites, due to radiation over time or due to changes in pixel response after the detector has looked into the sun.

[0074] It should be further noted that the description and drawings merely illustrate the principles of the proposed device. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope. Furthermore, all examples and embodiments outlined in the present document are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed device. Furthermore, all statements herein providing principles, aspects, and embodiments of the present disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0075] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.