Structural survey methods and infrared cameras

Abstract

To provide an investigation method of a structure that can suppress erroneous detection caused by reflecting the heat reflection in the surrounding environment on a photographed image of a surface of a subject, and an infrared camera.SOLUTION: A method of investigating a structure includes: an image acquisition process of acquiring a photographed image in which reflected infrared light is removed by photographing the structure using an infrared camera equipped with a polarizer that removes the reflected infrared light that becomes linearly polarized light; a detection process of detecting a temperature difference on a surface of the structure from the photographed image; and a determination process of determining a damaged state of the structure according to the temperature difference on the surface of the structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting a structure and an infrared camera. [Background technology]

[0002] Conventionally, infrared thermography has been used to inspect concrete structures for lifting and peeling, and to inspect building tiles for peeling.

[0003] However, when detecting the surface temperature of a concrete structure using infrared thermography, the heat reflected from the surrounding environment may be reflected on the concrete surface. This can lead to the temperature of the heat reflected from areas that are not abnormal being detected, resulting in a false positive detection of damage. Furthermore, even if there is a damaged area, the reflected temperature of the surrounding heat can mask the temperature difference between the normal and abnormal areas, potentially causing the damaged area to be overlooked.

[0004] Patent Document 1 below discloses an imaging device that includes two infrared cut filters, filter-like glass, an optical element that can arbitrarily change the polarization direction of light relative to the optical path of the lens, and an imaging element. In this imaging device, the optical element is located between one of the infrared cut filters and the imaging element, and is rotated by a rotation means to arbitrarily change the polarization direction of light relative to the optical path of the lens. This makes it possible to remove strong reflected light during the daytime and recognize the subject. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-67865 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned Patent Document 1 does not state that the imaging device is an infrared camera. Furthermore, Patent Document 1 does not state any technology for inspecting floating or peeling of concrete structures or peeling of tiles on buildings.

[0007] In consideration of the above, the present invention aims to provide a structure inspection method and an infrared camera that can suppress false detections caused by heat reflection from the surrounding environment appearing in the captured image of the subject's surface. [Means for solving the problem]

[0008] The method for inspecting a structure according to the first aspect includes an image acquisition process for acquiring an image from which the reflected infrared light has been removed by photographing the structure using an infrared camera equipped with a polarizer that removes reflected infrared light that becomes linearly polarized, a detection process for detecting a temperature difference on the surface of the structure from the photographed image, and a determination process for determining the state of damage to the structure based on the temperature difference on the surface of the structure.

[0009] In the above-mentioned method for inspecting a structure, the polarizer may be a polarizing filter, and in the image acquisition process, the polarizing filter may be rotated relative to the structure to acquire a captured image from which the reflected infrared light has been removed.

[0010] In the above-mentioned method for inspecting a structure, the polarizing filter may be rotated relative to the structure, and image processing may be performed to obtain a captured image from which the reflected infrared light has been removed based on image information obtained by photographing the structure at at least three different rotation angles.

[0011] In the above-mentioned structure inspection method, the polarizers are arranged in four different directions on the surface side of the infrared detector inside the infrared camera, and in the image acquisition process, image processing may be performed to acquire a captured image from which the reflected infrared light has been removed, based on image information from the polarizers arranged in the four directions.

[0012] In the structure inspection method, the image processing may be processing to generate an image with a minimum brightness value at the same pixel based on brightness information of the polarizers arranged in the four directions.

[0013] In the above-described structure inspection method, the determining step may determine, as the state of damage to the structure, at least one of whether or not there is internal damage to the structure and whether or not an exterior part of the structure has peeled off.

[0014] The infrared camera according to the second aspect comprises an infrared camera body, an infrared detector provided inside the infrared camera body to detect infrared rays emitted from a subject, a polarizer arrangement provided on the surface side of the infrared detector and having polarizers arranged in four different directions to remove reflected infrared light that becomes linearly polarized, and an image processing unit that performs image processing to obtain a captured image from which the reflected infrared light has been removed, based on image information from the polarizers in the four directions in the polarizer arrangement.

[0015] In the infrared camera, the image processing unit may perform processing to generate an image with a minimum brightness value at the same pixel based on brightness information of the polarizers in four directions. [Effects of the Invention]

[0016] According to the technology of the present disclosure, it is possible to suppress erroneous detection caused by heat reflection from the surrounding environment appearing in a captured image of the surface of a subject. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a configuration diagram showing an example of an infrared camera applied to a structure inspection method according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing the main configuration of an electrical system of the infrared camera. [Figure 3] FIG. 2 is a block diagram showing the configuration of an electrical system of a user terminal applied to the structure inspection method of the first embodiment. [Figure 4]FIG. 1 is an explanatory diagram illustrating the effect of a polarizing filter used in an infrared camera. [Figure 5] FIG. 1 is a schematic diagram illustrating a polarizing filter used in an infrared camera. [Figure 6] (A) is a diagram showing the state where the rotation angle of the polarizing filter is 0°, (B) is a diagram showing the state where the rotation angle of the polarizing filter is 45°, (C) is a diagram showing the state where the rotation angle of the polarizing filter is 90°, and (D) is a diagram showing the state where the rotation angle of the polarizing filter is 135°. [Figure 7] FIG. 1 is a diagram showing a first example of imaging a concrete specimen using an infrared camera with a heat source reflection angle of 45°. [Figure 8] 10A and 10B show images of the first example of shooting corresponding to the rotation angle of the polarizing filter, where (A) is an image when the rotation angle of the polarizing filter is 0°, (B) is an image when the rotation angle of the polarizing filter is 45°, (C) is an image when the rotation angle of the polarizing filter is 90°, and (D) is an image when the rotation angle of the polarizing filter is 135°. [Figure 9] (A) is a diagram showing a corrected image of the first photographed example, (B) is a diagram showing a reference image of the first photographed example when there is no heat source, (C) is a diagram showing the degree of linear polarization of the first photographed example, (D) is a diagram showing the polarization angle of the first photographed example, and (E) is a diagram showing the amplitude of the sine wave of the first photographed example. [Figure 10] FIG. 10 is a diagram showing a second example of imaging a concrete specimen using an infrared camera with a heat source reflection angle of 45°. [Figure 11] 10A and 10B show images of the second example of shooting corresponding to the rotation angle of the polarizing filter, where (A) is an image when the rotation angle of the polarizing filter is 0°, (B) is an image when the rotation angle of the polarizing filter is 45°, (C) is an image when the rotation angle of the polarizing filter is 90°, and (D) is an image when the rotation angle of the polarizing filter is 135°. [Figure 12](A) is a diagram showing a corrected image of the second photographic example, (B) is a diagram showing a reference image of the second photographic example when there is no heat source, (C) is a diagram showing the degree of linear polarization of the second photographic example, (D) is a diagram showing the polarization angle of the second photographic example, and (E) is a diagram showing the amplitude of the sine wave of the second photographic example. [Figure 13] 10 is a graph showing the relationship between the rotation angle of the polarizing filter and the estimated heat reflection temperature. [Figure 14] 10 is a graph showing the relationship between the reflection angle and the estimated heat reflection temperature when the rotation angle of the polarizing filter is 90°. [Figure 15] 10 is a flowchart showing the flow of a structure survey process that is handled by a user terminal. [Figure 16] FIG. 10 is a configuration diagram showing an example of an infrared camera applied to a structure inspection method according to a second embodiment. [Figure 17] FIG. 11 is a configuration diagram showing an example of an infrared camera applied to a structure inspection method according to a third embodiment. [Figure 18] FIG. 11 is a configuration diagram showing an enlarged view of a part of an infrared camera applied to a structure inspection method according to a third embodiment. [Figure 19] FIG. 10 is a configuration diagram showing a polarizer arrangement and an infrared detector used in an infrared camera applied to a structure inspection method according to a third embodiment. [Figure 20] 10 is a flowchart showing the flow of a structure inspection process that is handled by an infrared camera. [Figure 21] FIG. 11 is a configuration diagram showing an example of an infrared camera applied to a structure inspection method according to a fourth embodiment. [Figure 22] FIG. 13 is a configuration diagram showing an example of an infrared camera applied to a structure inspection method according to a fifth embodiment. [Figure 23] 10A is a diagram showing the positional relationship for photographing a structure using an infrared camera applied to a structure inspection method of the fifth embodiment, and FIG. 10B is a diagram showing the photographed locations of the structure. [Figure 24](A) to (C) are figures showing images of a structure taken at regular intervals by rotating the polarizing filter of an infrared camera, and (D) is a figure showing a photographed image from which reflected infrared light has been removed. [Figure 25] (A) is a diagram showing the positional relationship when photographing a structure using an infrared camera of a comparative example, (B) is a diagram showing an image of the structure photographed during the day, and (C) is a diagram showing an image of the structure photographed at night. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings, in which elements less relevant to the present invention are omitted.

[0019] [First embodiment] The structure inspection method of the first embodiment will be described with reference to Figures 1 to 15. Figure 1 shows an example of an infrared camera that is applied to the structure inspection method of the first embodiment.

[0020] (Overall configuration of infrared camera) As shown in Fig. 1, the infrared camera 10 includes an infrared camera body 12 that constitutes a housing, and an entrance 14 provided at one end of the infrared camera body 12. The infrared camera 10 also includes a lens group 16 provided inside the infrared camera body 12 on the entrance 14 side, and an infrared detection unit 18 arranged behind the lens group 16 inside the infrared camera body 12. The lens group 16 is composed of multiple lenses. The infrared camera 10 also includes a polarizing filter 20 arranged inside the lens group 16, and a rotation control unit 22 that rotates the polarizing filter 20. The lens group 16 is an example of a lens, and the infrared detection unit 18 is an example of an infrared detector.

[0021] The infrared camera 10 also includes, between the lens group 16 and the infrared detection unit 18, an aperture (not shown), an aperture member 24, a shutter (not shown), and the like.

[0022] The infrared camera 10 captures energy in the infrared wavelength range emitted from a structure, which is an example of a subject. In the structure inspection method of this embodiment, the surface temperature of the structure is detected from the intensity of energy in the infrared wavelength range in the image captured by the infrared camera 10. Infrared light is a type of light, and is classified as having a wavelength range longer than visible light that humans can see (for example, wavelengths of 360 to 830 nm). The wavelength range detected by the infrared camera 10 is, for example, a short wavelength of 3 to 5 μm and a long wavelength of 8 to 14 μm.

[0023] Infrared rays emitted from a structure pass through the lens group 16, polarizing filter 20, and diaphragm member 24 of the infrared camera 10 and are imaged on the infrared detection unit 18. That is, the infrared detection unit 18 detects the infrared rays that have passed through the polarizing filter 20. The infrared detection unit 18 is, for example, configured with a light receiving element.

[0024] The polarizing filter 20 is an example of a polarizer, and has the function of removing reflected infrared light that becomes linearly polarized. The polarizing filter 20 is, for example, a circular or rectangular plate-like member, and is rotatably supported by a frame (not shown) provided inside the infrared camera body 12. The polarizing filter 20 is rotatable along the circumferential direction of the infrared camera body 12. The specific configuration of the polarizing filter 20 will be described later.

[0025] The rotation control unit 22 has the function of rotating the polarizing filter 20 in the circumferential direction of the infrared camera body 12. As an example, the rotation control unit 22 has a gear on the outer periphery of a circular member, and this gear meshes with a gear provided on the outer periphery of the polarizing filter 20. As a result, when the user manually rotates the rotation control unit 22, the polarizing filter 20 rotates in the circumferential direction.

[0026] (Main components of the infrared camera's electrical system) Fig. 2 is a block diagram showing an outline of the hardware configuration of the infrared camera 10. As shown in Fig. 2, the infrared camera 10 has an imaging section 30 equipped with an infrared detection section 18, an image processing section 31, a control section 32, an imaging operation section 33, an imaging drive section 34, a rotation operation section 22, a display section 35, a recording section 36, and a communication section 37.

[0027] In the infrared camera 10, data of the captured image detected by the infrared detection unit 18 is input to the image processing unit 31. The image processing unit 31 reads an image processing program stored in storage (not shown) and executes image processing.

[0028] Although not shown, the control unit 32 includes a CPU (Central Processing Unit: processor), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The control unit 32 controls each part of the infrared camera 10.

[0029] The imaging operation unit 33 includes operation units for imaging, such as the diaphragm member 24 and a shutter (not shown). An operation signal operated by the imaging operation unit 33 is input to the control unit 32. The control unit 32 controls the imaging drive unit 34 in response to the operation signal from the imaging operation unit 33. In this way, the infrared camera 10 performs an imaging operation.

[0030] As described above, the rotation operation unit 22 rotates the polarizing filter 20. Rotation information for rotating the polarizing filter 20 by the rotation operation unit 22 is input to the control unit 32. The rotation information includes, for example, the rotation angle of the polarizing filter 20.

[0031] The display unit 35 receives an image signal from the control unit 32 and displays the image captured by the imaging unit 30, the captured image that has been subjected to image processing by the image processing unit 31, etc. The recording unit 36 ​​receives an image signal from the control unit 32 and records the captured image that has been subjected to image processing by the image processing unit 31, etc.

[0032] The communication unit 37 is an interface for communicating with other devices such as the user terminal 50 (see FIG. 3). As an example, data of an image captured by the infrared camera 10 is transmitted to the user terminal 50 via the communication unit 37.

[0033] (User terminal electrical system configuration) FIG. 3 is a block diagram showing the configuration of the electrical system of the user terminal 50. As shown in FIG.

[0034] 3, the user terminal 50 includes a CPU (Central Processing Unit: processor) 51, a ROM (Read Only Memory) 52, a RAM (Random Access Memory) 53, a storage 54, an input unit 55, a display unit 56, and a communication unit 57. Each component is connected to each other via a bus 59 so as to be able to communicate with each other.

[0035] The CPU 51 is a central processing unit that executes various programs and controls each part. That is, the CPU 51 reads a program from the ROM 52 or the storage 54 and executes the program using the RAM 53 as a work area. The CPU 51 controls each of the above components and performs various arithmetic processing in accordance with the program recorded in the ROM 52 or the storage 54. In this embodiment, the ROM 52 or the storage 54 stores an investigation program for investigating a structure.

[0036] The ROM 52 stores various programs and various data. The RAM 53 serves as a working area and temporarily stores programs or data. The storage 54 is configured with an HDD (Hard Disk Drive) or SSD (Solid State Drive) and stores various programs including the operating system and various data.

[0037] The input unit 55 includes a pointing device such as a mouse and a keyboard, and is used to input various types of information.

[0038] The display unit 56 is, for example, a liquid crystal display, and displays various information. For example, the display unit 56 displays the captured image received from the infrared camera 10, the temperature of the captured structure, etc. Also, for example, the display unit 56 displays the results of determining the damage state of the structure using the structure inspection method of this embodiment.

[0039] The communication unit 57 is an interface for communicating with other devices such as the infrared camera 10. For example, standards such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark) are used for the communication unit 57. In this embodiment, captured image data from the infrared camera 10 is received by the user terminal 50 via the communication unit 57. Note that instead of wireless communication, the captured image data may be input from the infrared camera 10 to the user terminal 50 using a wired cable.

[0040] At the user terminal 50, an investigation of the damage state of the structure is carried out based on the images captured by the infrared camera 10.

[0041] (Issues with the infrared camera in the comparative example) Before describing the function of the polarizing filter 20 used in the infrared camera 10, the problems with the infrared camera 200 of the comparative example will be described.

[0042] 25(A) is a configuration diagram showing the positional relationship when photographing a structure 300 using an infrared camera 200 of the comparative example. The infrared camera 200 of the comparative example is not provided with a polarizing filter 20 like the infrared camera 10 of this embodiment. In the infrared camera 200 of the comparative example, infrared rays emitted from the structure 300 are detected as they are by the infrared detection unit of the infrared camera 200.

[0043] As shown in FIG. 25(A), structure 300 has overhang 302A that overhangs bridge 302. When illuminated by sunlight during the day, the pavement of road 310 below bridge 302 warms up, and infrared rays generated from the pavement of road 310 are reflected by overhang 302A of bridge 302, which is the subject of the image capture. When overhang 302A of bridge 302 is imaged with infrared camera 200 of the comparative example, as shown in FIG. 25(B), in the daytime image capture, infrared rays generated from the pavement of road 310 are reflected by overhang 302A of bridge 302, and region A1 of overhang 302A is detected as being higher in temperature than the actual temperature of structure 300.

[0044] As shown in Figure 25(C), when the same location was photographed at night using the infrared camera 200 of the comparative example, the temperature of the pavement of the road 310 had dropped and the reflection had disappeared, so area A2 of the protrusion 302A was detected at the original temperature of the structure 300.

[0045] As such, the effect of reflections (hereinafter sometimes referred to as "thermal reflections") that occur during infrared surveys of structure 300 is particularly pronounced during daytime surveys, and hinders infrared surveys of structure 300 during the day.

[0046] Furthermore, when photographing at night, the temperature of the night sky is much lower than the temperature of the upper wall of structure 300, and therefore, due to the influence of thermal reflection of the sky temperature, the upper wall of structure 300 may be detected as locally colder due to variations in the emissivity of the concrete surface.

[0047] (The function of the polarizing filter in an infrared camera) Next, the function of the polarizing filter 20 used in the infrared camera 10 of this embodiment will be described.

[0048] FIG. 4 is a schematic diagram illustrating the function of polarizing filter 20. Normally, natural light vibrates in all directions as a sine wave, but as shown in FIG. 4, when light is reflected by smooth mirror surface 320, polarized light is generated in which the vibration direction is aligned in one direction. In other words, reflected light W2 reflected by mirror surface 320 has a high degree of polarization (linearly polarized light). If only this reflected light W2 vibrating in one direction is removed by polarizing filter 20, the reflection from mirror surface 320 can be eliminated. Note that light W1 in FIG. 4 is light other than reflected light (transmitted light).

[0049] The concrete surface of the structure 300 (see FIG. 25(A)) is not smooth, so scattering occurs in the visible light wavelength range, making polarization difficult. However, due to the nature of light that is less likely to scatter as the wavelength becomes longer, reflection may occur even on the concrete surface of the structure 300 in the infrared wavelength range.

[0050] FIG. 5 is a schematic diagram showing the configuration of a polarizing filter 20. As shown in FIG. 5, the polarizing filter 20 includes a wire grid 20A in the form of fine vertical stripes arranged along a predetermined direction. The multiple wire grids 20A are arranged approximately parallel to one another. The polarizing filter 20 reflects infrared rays W3 that vibrate parallel to the direction of the wire grid 20A (the direction of the vertical stripes) (i.e., it reflects S waves). The polarizing filter 20 also transmits infrared rays W4 that vibrate in a direction perpendicular to the direction of the wire grid 20A (the direction of the vertical stripes) (i.e., it transmits P waves). For example, the polarizing filter 20 has an infrared transmittance of 84.83 to 90.43% in the wavelength range of 3 to 5 μm, and an extinction ratio (maximum transmittance / minimum transmittance) of 298.70 to 706.48. 4 and 5 show a rectangular polarizing filter 20, but in this embodiment, a circular polarizing filter 20 is used since it is disposed inside the infrared camera 10.

[0051] FIG. 6 shows the state in which the polarizing filter 20 arranged inside the infrared camera 10 (see FIG. 1) has been rotated. In FIG. 6(A), the rotation angle of the polarizing filter 20 is 0°, and this position of the polarizing filter 20 is the reference position. The direction of arrow B, which follows the direction of the wire grid 20A of the polarizing filter 20, is the direction of reflection and vibration of light reflected by the polarizing filter 20. In FIG. 6(B), the rotation angle of the polarizing filter 20 relative to the reference position is 45°. In FIG. 6(C), the rotation angle of the polarizing filter 20 relative to the reference position is 90°. In FIG. 6(D), the rotation angle of the polarizing filter 20 relative to the reference position is 135°.

[0052] In the structure inspection method of this embodiment, an infrared camera 10 equipped with a polarizing filter 20 that removes reflected infrared light that becomes linearly polarized light is used to photograph the structure, thereby obtaining a photographed image from which the reflected infrared light has been removed (image acquisition step). More specifically, the rotation operation unit 22 of the infrared camera 10 is operated to rotate the polarizing filter 20 relative to the structure, thereby obtaining a photographed image from which the reflected infrared light that becomes linearly polarized light has been removed.

[0053] (Verification of images captured by infrared camera 10) Next, we will explain the results of verifying images captured by the infrared camera 10. In this experiment, the reflection angle of the heat source 340 (see FIG. 7) was changed in 10° increments from 15 to 65°, and the structure was photographed by the infrared camera 10, and the captured images were verified.

[0054] FIG. 7 shows a first example of imaging in which the reflection angle of the heat source 340 is set to 45° and the heat source 340 is positioned so that specularly reflected heat is captured at the center of a concrete specimen 330, an example of a structure. A halogen lamp is used as the heat source 340. As an example, the imaging distance of the infrared camera 10 is set to 8 m, and a lens with a focal length of 50 mm is used. In the example of imaging shown in FIG. 7, the infrared light is polarized parallel to the reflecting surface of the concrete specimen 330, so the reflected infrared light is thought to vibrate in the vertical direction of the image.

[0055] 9(B) shows a reference image (teacher image) of the infrared camera 10 in the first photographing example when there is no heat source 340. As shown in FIG. 9(B), photographing is performed in a state where there is almost no temperature difference on the surface of the concrete specimen 330.

[0056] 8(A) to 8(D) show images taken by the infrared camera 10 when the rotation angle of the polarizing filter 20 is changed to 0°, 45°, 90°, and 135° in the first imaging example. As shown in FIG. 8(A), when the rotation angle of the polarizing filter 20 is 0°, the direction of the wire grid 20A is perpendicular to the vibration direction of the reflected light, resulting in a large temperature difference on the reflecting surface of the concrete specimen 330. As shown in FIG. 8(C), when the rotation angle of the polarizing filter 20 is 90°, the temperature difference on the reflecting surface of the concrete specimen 330 is minimized, and the reflected infrared light is removed.

[0057] Fig. 9(A) shows a corrected image obtained by the infrared camera 10 in the first photographing example. As shown in Fig. 9(A), the image processing unit 31 of the infrared camera 10 performs image processing to correct the image to that obtained when the rotation angle of the polarizing filter 20 is 90°. Fig. 9(C) is a diagram showing the degree of linear polarization (DoLP), Fig. 9(D) is a diagram showing the angle of polarization (AoP), and Fig. 9(E) is a diagram showing the amplitude a of the sine wave. The contents of Fig. 9 will be explained later.

[0058] FIG. 10 shows a second example of photography in which the reflection angle of the heat source 340 was set to 65° and the heat source was positioned so that specularly reflected heat was reflected at the center of the concrete specimen 330.

[0059] 12(B) shows a reference image (teacher image) of the infrared camera 10 in the second photographing example when there is no heat source 340. As shown in FIG. 12(B), photographing is performed in a state where there is almost no temperature difference on the surface of the concrete specimen 330.

[0060] 11(A) to 11(D) show images taken by the infrared camera 10 when the rotation angle of the polarizing filter 20 is changed to 0°, 45°, 90°, and 135° in the second photographing example. As shown in Fig. 11(C), when the rotation angle of the polarizing filter 20 is 90°, the temperature difference on the reflecting surface of the concrete specimen 330 is the smallest, and reflected infrared light is removed.

[0061] Fig. 12(A) shows a corrected image obtained by the infrared camera 10 in the second photographing example. As shown in Fig. 12(A), the image processing unit 31 of the infrared camera 10 performs image processing to correct the image to that obtained when the rotation angle of the polarizing filter 20 is 90°. Fig. 12(C) is a diagram showing an image of the degree of linear polarization (DoLP), Fig. 12(D) is a diagram showing the angle of polarization (AoP), and Fig. 12(E) is a diagram showing the amplitude a of the sine wave.

[0062] Looking at the degree of linear polarization (DoLP), as the reflection angle increases, the reflected component (linearly polarized light) increases (see Figures 9(C) and 12(C), etc.). Looking at the angle of polarization (AoP), as the reflection angle is small, the polarization angles are not uniform, but as the reflection angle increases, the range over which the polarization angles are uniform increases (see Figures 9(D) and 12(D), etc.). The amplitude a of the sine wave indicates the amount of polarization (reflection) that can be removed by polarization. In other words, the magnitude of the amplitude indicates the reflection intensity (here, reflected temperature) that can be removed by polarization. When the reflection angle is small, the reflected temperature itself is small, but the temperature that can be removed is also small, and as the reflection angle increases, the reflected temperature that can be removed increases (see Figures 9(E) and 12(E)).

[0063] FIG. 13 is a graph showing the relationship between the rotation angle of the polarizing filter 20 and the estimated reflected heat temperature. In this experiment, to make the heat reflection easier to understand, a heat source 340 was placed at the center of the concrete specimen 330 so that a heat reflection of 2.5°C would occur. According to the applicant's knowledge, the temperature of the reflected heat occurring on the concrete surface of a bridge is approximately 0.2°C. Therefore, the temperature of the reflected heat occurring on the bridge was estimated by subtracting the concrete specimen 330 without the heat source 340 from the thermal image of the heat reflected by the heat source 340, and then correcting the heat reflection (heat reflection × (0.2°C / 2.5°C)). This estimated temperature is the estimated reflected heat temperature.

[0064] 13, when the reflection angle is small (rotation angle of 15°), changing the rotation angle of polarizing filter 20 does not change the estimated heat reflected temperature much, but the estimated heat reflected temperature is generally low, below 0.1°C. As the reflection angle increases, the heat reflection increases when the rotation angle of polarizing filter 20 is 0°, but when the rotation angle of polarizing filter 20 is 90°, the heat reflection can be eliminated by polarizing filter 20.

[0065] FIG. 14 is a graph showing the relationship between the reflection angle and the estimated heat reflection temperature when the rotation angle of the polarizing filter 20 is 90°. In the case of typical specular reflection, the reflection angle (i.e., Brewster's angle) at which the degree of polarization is maximized is approximately 60°, at which point the reflected afterglow is also minimized. As shown in FIG. 14, the estimated heat reflection temperature also decreases as the reflection angle (reflection angle) increases, reaching its minimum at a reflection angle of 65°, showing a similar trend. The results of these experiments show that when the reflection angle (reflection angle) is small, the heat reflection itself is small, and when the reflection angle is large, the polarizing filter 20 can eliminate the heat reflection.

[0066] In the infrared camera 10 of this embodiment, the rotation control unit 22 is used to rotate the polarizing filter 20 to remove heat reflection (i.e., reflected infrared light) from the surface of a structure. As an example, images obtained when the polarizing filter 20 is rotated at multiple rotation angles (e.g., 0°, 45°, 90°, and 135°) are compared, and an image from which reflected infrared light has been removed is acquired based on brightness information for a predetermined portion of the structure. For example, images obtained when the polarizing filter 20 is rotated at multiple rotation angles may be compared, and an image with a low brightness value for a predetermined portion of the structure may be selected. Alternatively, the image processing unit 31 may compare images obtained at multiple rotation angles of the polarizing filter 20 and select the image with the lowest brightness value for the predetermined portion of the structure as the corrected image (see FIGS. 9A and 12A). This allows the infrared camera 10 to capture an image from which reflected infrared light, which is linearly polarized, has been removed.

[0067] (Process flow for structure investigation method) 15 is a flowchart showing the flow of the structure inspection process handled by the user terminal 50. The CPU 51 reads out an inspection processing program from the ROM 52 or storage 54, loads it into the RAM 53, and executes it, thereby performing the inspection process.

[0068] 15, the CPU 51 acquires a captured image of a structure from which reflected infrared light has been removed (step S101). For example, in the infrared camera 10, the polarizing filter 20 is rotated using the rotation operation unit 22 to capture an image from which reflected infrared light has been removed. In the user terminal 50, the CPU 51 acquires the captured image from which reflected infrared light has been removed from the infrared camera 10 via the communication unit 57. Although not shown in the figure, for example, the CPU 51 may display the captured image on the display unit 56.

[0069] The CPU 11 detects the temperature difference on the surface of the structure from the captured image (step S102). For example, in a part where the surface of the exterior of the structure is made of the same material, the CPU 11 detects the temperature difference on that part.

[0070] The CPU 11 determines whether the detected temperature difference is equal to or greater than a threshold value (step S103). For example, if the interior of a structure is damaged or the exterior peels off, the air layer in the damaged or peeled part has poor thermal conductivity and becomes hotter than the surrounding area, so damage or peeling can be detected from the temperature difference. The threshold value is set according to the components of the surface of the structure.

[0071] If the temperature difference is equal to or greater than the threshold value (step S103: YES), the CPU 11 determines that there is damage to the surface of the structure (damage present) (step S104). As a result, the damage state of the structure is determined according to the detected temperature difference. The damage state of the structure may be determined, for example, by whether or not there is damage inside the structure, or whether or not the exterior part of the structure has peeled off. Although not shown in the drawings, for example, the CPU 51 may display the determination result on the display unit 56.

[0072] If the temperature difference is smaller than the threshold value (step S103: NO), the CPU 11 determines that there is no damage to the surface of the structure (no damage) (step S105). Although not shown in the figure, for example, the CPU 51 may display the determination result on the display unit 56. This ends the processing based on the investigation processing program.

[0073] (Summary of the functions and effects of this embodiment) In the structure inspection method of this embodiment, an infrared camera 10 equipped with a polarizing filter 20 that removes reflected, linearly polarized infrared light is used to photograph the structure, thereby obtaining a captured image from which reflected infrared light has been removed (image acquisition process). By removing reflected, linearly polarized infrared light using the polarizing filter 20, heat reflection from the surrounding environment or temperature reflection from the sky is prevented from appearing in the captured image of the structure's surface. Furthermore, in the structure inspection method, a temperature difference on the structure's surface is detected from the captured image (detection process), and the damage state of the structure is determined based on the temperature difference on the structure's surface (determination process).

[0074] Therefore, the method for inspecting a structure according to this embodiment can suppress erroneous detections caused by the reflection of heat from the surrounding environment or the temperature reflection from the sky appearing in the captured image of the surface of the object, thereby enabling more accurate inspection of the damage state of the structure.

[0075] Furthermore, in the structure inspection method of this embodiment, a rotatable polarizing filter 20 is provided inside the infrared camera 10, and reflected infrared light is removed by rotating the polarizing filter 20 relative to the structure using the rotation control unit 22. Therefore, in the structure inspection method of this embodiment, it is possible to prevent heat reflection from the surrounding environment or temperature reflection from the sky from appearing in the captured image of the structure's surface.

[0076] In the structure inspection method of this embodiment, the determination step determines at least one of the presence or absence of internal damage to the structure and the presence or absence of peeling of the exterior part of the structure as the damage state of the structure. Therefore, in the structure inspection method of this embodiment, it is possible to more accurately determine at least one of the presence or absence of internal damage to the structure and the presence or absence of peeling of the exterior part of the structure in accordance with the detected temperature difference on the surface of the structure.

[0077] Second Embodiment Next, a description will be given of a structure inspection method according to a second embodiment. Note that the same components as those in the first embodiment described above are given the same reference numerals and the description thereof will be omitted.

[0078] Figure 16 shows an example of an infrared camera that is applied to the structure inspection method of the second embodiment. As shown in Figure 16, the infrared camera 70 includes a polarizing filter 72 that is arranged on the rear end side of the lens group 16 that is arranged inside the infrared camera body 12. The polarizing filter 72 is an example of a polarizer. The polarizing filter 72 is fixed to the inner wall of the infrared camera body 12. The infrared camera 70 includes a support part 74 that supports the infrared camera body 12, and a rotation device 76 that rotates the support part 74.

[0079] The support part 74 is an L-shaped member extending from the infrared camera body 12. The support part 74 includes a plate-like part 74A that is joined to the lower part of the infrared camera body 12 and extends in a substantially horizontal direction, and an extension part 74B that is bent from the end of the plate-like part 74A and is arranged to face the end part 12A of the infrared camera body 12 on the opposite side from the lens group 16.

[0080] The rotation device 76 is attached to the extension portion 74B and is supported on an installation stand (not shown). The rotation device 76 rotates the support portion 74 having the extension portion 74B using a motor (not shown). The rotation device 76 is configured to rotate around a rotation axis along the optical axis of the infrared camera 70. By rotating the extension portion 74B, the rotation device 76 rotates the polarizing filter 72 fixed to the inner wall of the infrared camera body 12 in a counter-rotating manner relative to the structure. Other configurations of the infrared camera 70 are the same as those of the infrared camera 10 of the first embodiment.

[0081] The structure inspection method of this embodiment has the following actions and effects in addition to the actions and effects of the same configuration as the structure inspection method of the first embodiment.

[0082] In the structure inspection method of this embodiment, a polarizing filter 72 is fixed inside the infrared camera 10, and reflected infrared light is removed by rotating the polarizing filter 72 relative to the structure using a rotation device 76. Therefore, in the structure inspection method of this embodiment, it is possible to suppress false detections caused by heat reflection from the surrounding environment or temperature reflection from the sky appearing in the captured image of the structure's surface.

[0083] Third Embodiment Next, a structure inspection method according to a third embodiment will be described. Note that the same components as those in the first and second embodiments described above will be assigned the same reference numerals and descriptions thereof will be omitted.

[0084] 17 and 18 show an example of an infrared camera applied to the structure inspection method of the third embodiment. As shown in FIG. 17, the infrared camera 120 includes an infrared detection unit 122 disposed inside the infrared camera body 12. The infrared detection unit 122 is an example of an infrared detector. As shown in FIG. 18, the infrared camera 120 includes a polarizer arrangement 124 provided on the surface side (front side) of the infrared detection unit 122. The infrared camera 120 also includes a cold stop 126, an example of a cooled shielding diaphragm member, located opposite the polarizer arrangement 124. A cover glass 128 is provided in front of the cold stop 126. The infrared camera 120 also includes an image processing unit 130 that performs image processing of image data detected by the infrared detection unit 122, and a control unit 132 that controls each unit of the infrared camera 120 (including the image processing unit 130). The infrared detection unit 122 is configured, for example, with a cooled Insb sensor, and the wavelength range detected by the infrared detection unit 122 is 3 to 5 μm.

[0085] As shown in FIG. 19, the polarizer arrangement 124 includes polarizers 124A, 124B, 124C, and 124D that remove reflected, linearly polarized infrared light. The polarizers 124A, 124B, 124C, and 124D are arranged in four different directions. As an example, the polarizer 124A is arranged in the 0° direction (reference position), the polarizer 124B is arranged in the 45° direction relative to the reference position, the polarizer 124C is arranged in the 90° direction relative to the reference position, and the polarizer 124D is arranged in the 135° direction relative to the reference position. The polarizers 124A, 124B, 124C, and 124D are arranged in two vertical and two horizontal rows to form one set, and this set is repeatedly arranged vertically and horizontally. The repeated arrangement of one set of polarizers 124A, 124B, 124C, and 124D is called a Bayer array.

[0086] Polarizers 124A, 124B, 124C, and 124D in four different directions are arranged on each pixel of the infrared detection unit 122 on the surface side (front side) of the infrared detection unit 122. As shown in the figure, a microlens is arranged on the surface side (front side) of the polarizer array 124 for each of the polarizers 124A, 124B, 124C, and 124D.

[0087] When polarized light enters the polarizer arrangement 124, different amounts of light are transmitted through the four different polarizers 124A, 124B, 124C, and 124D.

[0088] The image processing unit 130 performs image processing to obtain a captured image from which reflected infrared light has been removed, based on image information from the four-directional polarizers 124A, 124B, 124C, and 124D in the polarizer array 124. For example, the image processing unit 130 performs processing to create an image with the minimum brightness value at the same pixel, based on the brightness information from the four-directional polarizers 124A, 124B, 124C, and 124D.

[0089] In the case of linearly polarized light, it approximates a sine wave. As a result, if polarization information in four directions can be obtained, the minimum and maximum values ​​of the vibration direction of the reflected light can be estimated even if the minimum and maximum angles of the vibration direction of the reflected light do not coincide with the four directions. Here, the light intensity Ipol is expressed by the following equation 1 (see equation 1).

[0090]

number

[0091] In Equation 1, Ipol is the magnitude of the signal (light intensity) output from each pixel, and θpol is the angle of the polarizers 124A, 124B, 124C, and 124D on the polarizer array 124 (i.e., the angle of the vibration direction transmitted through the polarizers). Additionally, Imax is the maximum amplitude, Imin is the minimum amplitude, and φ is the polarization direction of the incident light (i.e., the vibration direction of the polarized light).

[0092] In Equation 1, there are three unknown parameters: Imax, Imin, and φ. Therefore, if the intensities of light that have passed through at least three different polarizers are known, Equation 1 can be solved to determine the polarization state of the incident light (i.e., the degree of polarization and polarization direction). The degree of polarization is expressed by Equation 2 (see Equation 2). The degree of polarization is an index of how polarized the vibration direction of light is.

[0093]

number

[0094] From the above, the polarization state of the reflected light (i.e., the degree of polarization ρ and polarization direction φ) can be determined. Therefore, image processing can be performed based on the luminance information (i.e., brightness information) of the four-directional polarizers 124A, 124B, 124C, and 124D.

[0095] 20 is a flowchart showing the flow of the structure inspection process handled by the infrared camera 120. Although not shown, the control unit 132 of the infrared camera 120 has components such as a CPU, ROM, RAM, and storage. In the control unit 132, the CPU reads out an inspection processing program from the ROM or storage, expands it into RAM, and executes it, thereby performing the inspection process.

[0096] As shown in FIG. 20, the CPU of the control unit 132 acquires image information of the four-directional polarizers 124A, 124B, 124C, and 124D of the polarizer array 124 (step S151).

[0097] The CPU of the control unit 132 compares the luminance information at the same set of locations based on the image information of the four-directional polarizers 124A, 124B, 124C, and 124D (step S152). Here, the same set of locations refers to the same set of locations where four data units (sometimes pixel units) of the four-directional polarizers 124A, 124B, 124C, and 124D arranged in a Bayer array are grouped together.

[0098] The CPU of the control unit 132 selects an image with the minimum brightness value in the same pair of locations based on the brightness information of the four-directional polarizers 124A, 124B, 124C, and 124D (step S153).

[0099] The CPU of the control unit 132 determines whether or not all the locations of the same set have been processed (step S154).

[0100] If all the locations of the same set have not been processed (step S154: NO), the CPU returns to the process of step S152.

[0101] When all the locations of the same set have been processed (step S154: NO), the CPU of the control unit 132 forms an entire image based on the selected minimum brightness image (step S155). That is, the minimum brightness image is selected for each pixel, thereby forming an entire image.

[0102] The CPU of the control unit 132 stores the formed overall image as a captured image (step S156). For example, the captured image is stored in a storage or the like. Although not shown in the drawings, for example, the CPU of the control unit 132 may display the captured image on a display unit. This ends the processing based on the investigation processing program.

[0103] The structure inspection method of this embodiment has the following actions and effects in addition to the actions and effects of the same configuration as the structure inspection method of the first embodiment.

[0104] In the structure inspection method of this embodiment, polarizers 124A, 124B, 124C, and 124D are arranged in four different directions on the surface side of the infrared detection unit 122 inside the infrared camera 120. In the image acquisition step, image processing is performed to acquire a captured image from which reflected infrared light has been removed, based on image information from the polarizers 124A, 124B, 124C, and 124D arranged in the four directions. This makes it possible to prevent heat reflection from the surrounding environment or temperature reflection from the sky from appearing in the captured image of the structure's surface. This makes it possible to prevent erroneous detection due to heat reflection from the surrounding environment or temperature reflection from the sky from appearing in the captured image of the structure's surface.

[0105] Furthermore, the structure inspection method of this embodiment performs image processing to create an image with the minimum brightness value at the same pixel based on the brightness information from polarizers 124A, 124B, 124C, and 124D arranged in four directions, thereby making it possible to efficiently obtain a captured image from which reflected infrared light has been removed.

[0106] The infrared camera 120 also includes an infrared detection unit 122 provided inside the infrared camera body 12, and a polarizer arrangement 124 provided on the surface side of the infrared detection unit 122. The polarizer arrangement 124 includes polarizers 124A, 124B, 124C, and 124D arranged in four different directions. The infrared camera 120 also includes an image processing unit 130 that performs image processing to obtain a captured image from which reflected infrared light has been removed, based on image information from the polarizers 124A, 124B, 124C, and 124D arranged in four different directions.

[0107] In the infrared camera 120, an infrared detection unit 122 provided inside the infrared camera body 12 detects infrared rays emitted from a subject (e.g., a structure). A polarizer arrangement 124, in which polarizers 124A, 124B, 124C, and 124D are arranged in four different directions, is provided on the front side of the infrared detection unit 122. As a result, infrared rays transmitted through the polarizer arrangement 124 are detected by the infrared detection unit 122. Furthermore, the image processing unit 130 performs image processing based on image information from the four polarizers 124A, 124B, 124C, and 124D in the polarizer arrangement 124 to obtain a captured image from which reflected infrared light has been removed. This makes it possible to prevent heat reflection from the surrounding environment or temperature reflection from the sky from appearing in the captured image of the surface of the subject (e.g., a structure). Therefore, when investigating a structure using the infrared camera 120, it is possible to prevent erroneous detection due to heat reflection from the surrounding environment or temperature reflection from the sky from appearing in the captured image of the surface of the structure.

[0108] In the infrared camera 120, the image processing unit 130 performs processing to create an image with the minimum brightness value at the same pixel based on the brightness information from the four-directional polarizers 124A, 124B, 124C, and 124D. This allows the infrared camera 120 to efficiently capture a captured image from which reflected infrared light has been removed.

[0109] [Fourth embodiment] Next, a structure inspection method according to a fourth embodiment will be described. Note that the same components as those in the first to third embodiments described above are given the same reference numerals and the description thereof will be omitted.

[0110] FIG. 21 shows a portion of an infrared camera 170 as an example of an infrared camera that can be used in the structure inspection method of the fourth embodiment. As shown in FIG. 21, the infrared camera 170 includes an infrared detection unit 172 disposed inside the infrared camera body 12. The infrared camera 170 includes a polarizer arrangement 124 provided on the surface side (front side) of the infrared detection unit 172. The infrared camera 170 also includes an aperture member 176 located opposite the polarizer arrangement 124. A cover glass 178 is provided in front of the aperture member 176. The infrared detection unit 172 is formed of, for example, an uncooled microbolometer, and the wavelength range detected by the infrared detection unit 172 is 8 to 14 μm. Other configurations of the infrared camera 170 are similar to those of the infrared camera 120 of the third embodiment.

[0111] The structure inspection method of this embodiment has the same configuration as the structure inspection method of the third embodiment, and can provide the same actions and effects.

[0112] The infrared camera 170 of this embodiment has the same configuration as the infrared camera 120 of the third embodiment, and can therefore achieve the same functions and effects.

[0113] Fifth Embodiment Next, a structure inspection method according to the fifth embodiment will be described. Note that the same components as those in the first to fourth embodiments described above will be assigned the same reference numerals and their description will be omitted.

[0114] 22, infrared camera 400 includes polarizing filter 20, a rotating unit 402 that rotates while supporting polarizing filter 20, a drive unit 404 that drives the rotating unit 402, and a control unit 412 that controls the drive unit 404. The control unit 412 drives the drive unit 404 in response to a signal from an operation unit (not shown), thereby rotating polarizing filter 20 supported by the rotating unit 402. Infrared camera 400 also includes an imaging control unit 408 that controls imaging by imaging unit 34 (see FIG. 2), and an image processing unit 410 that processes captured image data.

[0115] In this embodiment, the driving unit 404 rotates the polarizing filter 20 in the circumferential direction at a constant speed. The imaging control unit 408 captures an image of a structure 350 (see FIG. 23 ), which will be described later, at regular intervals. In this case, it is preferable to capture an image of the structure 350 while rotating the polarizing filter 20 through at least three different angles. For example, the structure 350 is captured every time the polarizing filter 20 rotates 30°, which is the regular interval.

[0116] The image processing unit 410 uses pattern matching to superimpose multiple captured images taken at regular intervals. Then, for the same pixel of the image data, the minimum and maximum values ​​of the vibration direction of the reflected light are calculated using the above-mentioned sine wave approximation (see Equations 1 and 2). This allows for the acquisition of a captured image from which reflected infrared light has been removed. The other configurations of the infrared camera 400 are the same as those of the infrared camera 10 of the first embodiment.

[0117] FIG. 23(A) is a diagram showing the state in which a structure 350 is photographed by an infrared camera 400, and FIG. 23(B) is a diagram showing a photographing location 360A of the structure 350 by the infrared camera 400. As shown in FIG. 23(A), an overhang 352A of a bridge 352 is photographed as the structure 350 by the infrared camera 400. When illuminated by sunlight in the daytime, infrared rays (i.e., pavement heat) shown by the arrows generated from the pavement of the road 310 are reflected by the overhang 352A of the bridge 352 being photographed. As shown in FIG. 23(B), the infrared camera 400 photographs a photographing location 360A of the overhang 352A of the structure 350.

[0118] 24(A) to 24(C) are images of a structure 350 captured with the polarizing filter 20 rotated 0°, 30°, and 60° from the reference position. As shown in FIGS. 24(A) to 24(C), these images contain reflected infrared light. From this image information (image data), the minimum and maximum values ​​of the vibration direction of the reflected light are calculated for the same pixel using the sine wave approximation described above. This makes it possible to obtain a captured image from which the reflected infrared light has been removed, as shown in FIG. 24(D).

[0119] The structure inspection method of this embodiment has the following actions and effects in addition to the actions and effects of the same configuration as the structure inspection method of the first embodiment.

[0120] In the structure inspection method of this embodiment, the polarizing filter 20 is rotated relative to the structure 350, and the structure 350 is photographed at at least three different rotation angles. Then, based on the image information obtained by photographing the structure 350, image processing is performed to obtain a photographed image from which reflected infrared light has been removed. In this embodiment, the minimum and maximum values ​​of the vibration direction of the reflected light are calculated to obtain a photographed image from which reflected infrared light has been removed. Therefore, the structure of the infrared camera 400 is simple, and photographed images from which reflected infrared light has been removed can be obtained efficiently. Furthermore, depending on the rotation speed of the polarizing filter 20 and the photographing interval, the above-mentioned sine wave approximation may not be necessary.

[0121] 〔supplementary explanation〕 In the first and second embodiments, the components of the infrared cameras 10, 70 can be changed.

[0122] In the third and fourth embodiments, the infrared cameras 120 and 170 equipped with the polarizer arrangement 124 in which the polarizers 124A, 124B, 124C, and 124D are arranged in four different directions are configured not to rotate, but the technology of the present disclosure is not limited to this configuration. For example, the infrared cameras 120 and 170 may be configured to rotate by a rotation device similar to that of the second embodiment.

[0123] In the third and fourth embodiments, polarizers 124A, 124B, 124C, and 124D are provided in four directions, but in the case of a high pixel count, it is possible to obtain data in nine directions, 3 × 3. In this case, accuracy can be ensured and processing speed is increased simply by finding the minimum and maximum values ​​in the vibration directions of the reflected light, without performing approximation processing.

[0124] In the first to fourth embodiments, the damage state of the structure is determined by the user terminal 50, but the present invention is not limited to this configuration. For example, a captured image may be displayed on the display unit of an infrared camera or a user terminal, and the user may determine the damage state of the structure based on the temperature difference on the surface of the structure.

[0125] In the fifth embodiment, the polarizing filter 20 is rotated at a constant speed to capture images of the structure at regular intervals, but the present invention is not limited to this configuration. For example, the infrared camera 70 of the second embodiment may be used, the infrared camera 70 may be rotated at a constant speed to capture images of the structure at regular intervals, and the same image processing as in the fifth embodiment may be performed.

[0126] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to such embodiments, and that various other embodiments are possible within the scope of the present invention. [Explanation of symbols]

[0127] 10. Infrared Camera 12 Infrared camera body 16 lens groups 18 Infrared detector 20 Polarizing filter (an example of a polarizer) 22 Rotation control unit 50 user terminals 70 Infrared Camera 72 Polarizing filter (an example of a polarizer) 76 Rotating Device 120 Infrared Camera 122 Infrared detection unit (an example of an infrared detector) 124 Polarizer arrangement 124A polarizer 124B Polarizer 124C polarizer 124D polarizer 130 Image processing section 170 Infrared Camera 172 Infrared detection unit (an example of an infrared detector) 350 Structures 400 Infrared Camera 402 Rotating part 404 Drive unit 410 Image Processing Unit

Claims

1. an image acquisition step of acquiring an image from which the reflected infrared light has been removed by photographing the structure using an infrared camera equipped with a polarizer that removes reflected infrared light that becomes linearly polarized; a detection step of detecting a temperature difference on the surface of the structure from the captured image; a determination step of determining a damage state of the structure according to a temperature difference on the surface of the structure; and the polarizer is a polarizing filter, In the image acquisition process, the polarizing filter is rotated relative to the structure, and based on image information obtained by photographing the structure at at least three different rotation angles, the minimum and maximum values ​​of the vibration direction of the reflected light are calculated for the same pixel of the image data using a sine wave approximation, and image processing is performed to obtain a photographed image from which the reflected infrared light has been removed.

2. 2. The method for inspecting a structure according to claim 1, wherein the image acquisition process compares the images obtained when the polarizing filter is rotated through a plurality of rotation angles, and selects an image with a low brightness value for a specified portion of the structure, thereby acquiring a captured image in which the reflected infrared light has been removed according to brightness information for the specified portion of the structure.

3. an image acquisition step of acquiring an image from which the reflected infrared light has been removed by photographing the structure using an infrared camera equipped with a polarizer that removes reflected infrared light that becomes linearly polarized; a detection step of detecting a temperature difference on the surface of the structure from the captured image; a determination step of determining a damage state of the structure according to a temperature difference on the surface of the structure; and the polarizers are arranged in four different directions on a surface side of an infrared detector inside the infrared camera, In the image acquisition step, image processing is performed to acquire a captured image from which the reflected infrared light has been removed, based on image information from the polarizers arranged in the four directions; The structure inspection method includes, as the image processing, processing to obtain an image with the minimum brightness value at the same pixel based on the brightness information of the polarizers arranged in the four directions.

4. A method for inspecting a structure described in any one of claims 1 to 3, wherein the determination step determines the damage state of the structure by determining at least one of the presence or absence of internal damage to the structure and the presence or absence of peeling of the exterior part of the structure.

Images