JP2001296180A - Spectral image acquiring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spectral image acquiring apparatus with superior wavelength characteristics without requiring a drive means. SOLUTION: This spectral image acquiring apparatus is provided with a condensing optical system 3 for forming the middle image of a subject 1, a variable aperture 4 as a visual field limitation means that is placed near the focal point of the condensation optical system 3, a collimating optical system 7 for converting transmission light through the variable aperture 4 to parallel light, a dispersion element 8 for allowing a parallel light from the collimate optical system to have an angle difference for each wavelength, an image forming optical system 9 for obtaining the image of the subject by forming the image of light through the dispersion element, and an image pickup element 10 for converting the light intensity distribution of the subject image into an electrical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectral image acquisition apparatus used for remote sensing using the wavelength characteristic of an object.

[0002]

2. Description of the Related Art A spectral image is an image obtained by picking up images in different wavelength bands. For example, an object has a unique wavelength characteristic, such as a green leaf and a brown soil. Spectral images are effective for identifying what an object to be imaged belongs to and for examining the state of the object, and are widely used in the field of remote sensing.

There are various methods for obtaining a spectral image. For example, FIG. 9 is a configuration diagram showing an embodiment of a conventional spectral image acquiring apparatus disclosed in Japanese Patent Application Laid-Open No. 61-99485 and Japanese Patent Application Laid-Open No. 4-150593. In FIG. 9, reference numeral 1 denotes a subject which is an image-captured image; 24, an imaging optical system for forming an image of the subject 1 to be captured; Denotes an image sensor arranged two-dimensionally, and converts a light intensity distribution of a subject image formed by the imaging optical system 24 into an electric signal. Numeral 11 is a signal processing means for converting the electric signal into a video signal. Reference numerals 21a, 21b, and 21c denote interference filters that transmit different wavelength bands, respectively, and are fixed to the filter holding member 22. 23 is a driving means for rotating the filter holding member.

Next, the operation will be described. Incident light rays of all wavelength bands emitted from the subject 1 enter the spectral image acquisition device. First, the interference filter 21a is placed in the optical path. Of the incident light, only the light in the wavelength band passing through the interference filter 21a forms an image by the imaging optical system 24, and
, An image in the first wavelength band can be obtained. Next, the filter holding member 22 is rotated by the driving unit 23, and the interference filter 21a is replaced with the interference filter 21b. Thus, an image in the second wavelength band is obtained in the same manner. By performing this operation for all the interference filters, a spectral image can be obtained.

FIG. 10 shows, for example, Japanese Patent Application Laid-Open No. 7-126.
FIG. 25 is a configuration diagram showing a conventional spectral image acquisition device according to another embodiment disclosed in Japanese Patent Publication No. 48-48. The spectral image acquiring method by this spectral image acquiring device is known as Fourier spectroscopy, and is a kind of spectral image acquiring method using a Michelson two-beam interferometer. In FIG. 10, as a new code, 26 is a beam splitter, and 27 and 28 are plane mirrors. Reference numeral 29 denotes a driving unit for moving the plane mirror 28.

Next, the operation will be described. The incident light from the subject 1 is split into two light beams (light path 3
0 and 31). After the light on the optical path 30 is reflected by the beam splitter 26, the light is reflected by the plane mirror 27 and reaches the beam splitter 26 again. On the other hand, the light on the optical path 31 passes through the beam splitter 26, is reflected by the plane mirror 28, and reaches the beam splitter 26 again. At this time, the light on the optical path 30 and the light on the optical path 31 interfere with each other, and the information is detected by the image sensor 10 through the imaging optical system 24. By moving the plane mirror 28 using the driving means 29, the optical path difference between the optical path 30 and the optical path 31 can be changed, so that a well-known interferogram can be obtained.

[0007] Since the image pickup device 10 is composed of two-dimensionally arranged detection elements, an interferogram corresponding to each position of the subject 1 can be obtained for each detection element. Based on the theory of Fourier spectroscopy, it is possible to convert the interferogram into a wavelength characteristic of light intensity by performing a Fourier transform. By subjecting the signal processing unit 11 to Fourier transform of the interferogram corresponding to each location of the subject 1, a spectral image can be obtained.

FIG. 11 is a block diagram showing a conventional spectral image acquiring apparatus according to still another embodiment disclosed in Japanese Patent Application Laid-Open No. H11-101692. In FIG. 11, reference numerals 2 and 3 denote new filters for blocking light of unnecessary wavelengths, a condenser optical system 3 for forming an intermediate image of the subject 1, and a slit 34 disposed on the image plane of the condenser optical system 3. Reference numeral 7 denotes a collimating optical system for converting light from the slit into parallel light, reference numeral 8 denotes a dispersive element such as a diffraction grating or a prism, and reference numeral 9 denotes an imaging optical system for reconnecting the dispersed light. A driving unit 33 moves the subject. further,
40 is a driving unit 33, an image sensor 10, a signal processing unit 1.
1 is a control means for mainly controlling timing.

Next, the operation will be described. The incident light from the subject 1 is blocked by the filter 2 from light in an unnecessary wavelength band, and only the light having the wavelength to be measured forms an image near the slit 34 by the focusing optical system 3. However, the portion that can pass through the opening of the slit 34 corresponds to a part of the subject 1. The light passing through the slit 34 is collimated by the collimating optical system 7 and is incident on the dispersion element 8. Even if the angle of incidence is the same, the angle of emergence from the dispersion element 8 differs depending on the wavelength. For example, in the case of a diffraction grating, the degree is determined by the diffraction order and the grating width, and in the case of a prism, it is determined by the wavelength dependence of the refractive index and the apex angle.

[0010] Even if the light is emitted from the same position of the subject, the light enters the imaging optical system 9 at different angles depending on the dispersive element, so that images are formed at different places on the image sensor 10.
In this manner, a spectral image of the band-like portion of the subject 1 corresponding to the slit 34 can be obtained. Further, the driving means 3
By slightly moving the subject according to 3, it is possible to change the position of the band-shaped portion for obtaining the spectral image. As described above, the imaging device 10 is operated while the subject is moved by the driving unit 33 under the control of the control unit 40, and a series of band-shaped spectral images is processed by the signal processing unit 11. Can be obtained.

FIG. 12 is a diagram for explaining the operation of the signal processing means 11. The wavelength to be imaged is λ1, λ2,.
λe, and the position of the subject is P1, P2,..., Pe. First, it is assumed that a strip-shaped spectral image at the position P1 of the subject is obtained, and the positions P2, P3,.
Is obtained. By decomposing these series of band-shaped spectral images, the position P
By rearranging in the order of 1, P2, ..., Pe,
A spectral image of the subject having the wavelength λ1 can be obtained. In exactly the same way, spectral images of the subject regarding the wavelengths λ2,..., Λe can be obtained, so that spectral image data as shown in FIG. 13 can be obtained.

When acquiring a natural scene or a spectral image of a large building, the subject 1 cannot be moved by the driving means 33, but a reflecting mirror 35 is provided as shown in FIG. The light is bent once, and then is incident on the condensing optical system.
You can move the position you are looking through 4.

[0013]

Since the conventional spectral image acquiring apparatus is configured as described above, there is a problem that a driving means is required in any case. For this reason, the size of the device is increased and the reliability is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a spectral image acquiring apparatus having excellent wavelength characteristics without requiring any driving means.

[0015]

According to the present invention, there is provided a spectral image acquiring apparatus, comprising: a condensing optical system for forming an intermediate image of a subject;
Field-of-view limiting means placed near the focal point of the light collection optical system,
A collimating optical system that converts the transmitted light through the visual field limiting unit into parallel light, a dispersing element that causes the parallel light from the collimating optical system to have an angle difference for each wavelength, and forms an image of light that has passed through the dispersing element. An imaging optical system that obtains a subject image by using the imaging device, and an image sensor that converts a light intensity distribution of the subject image into an electric signal.

[0016] The present invention is further characterized by further comprising control means for controlling a view restriction area of the view restriction means.

Further, the visual field limiting means comprises a variable aperture.

Further, the variable aperture is made of a liquid crystal, and a light transmitting part for transmitting light is controlled by the control means.

Further, the variable aperture is characterized in that the movement of the light transmitting section is controlled by the control means.

Further, the variable aperture is characterized in that a plurality of light transmitting portions are provided by the control means.

Further, the visual field limiting means comprises a variable mirror.

Further, the variable mirror is characterized in that a plurality of minute mirrors whose angles can be controlled by the control means are two-dimensionally arranged.

Further, the variable mirror is controlled by the control means so that only the minute mirror in one or a plurality of band-shaped regions is tilted so that the reflected light proceeds in a predetermined direction.

Further, the dispersion element is formed of a diffraction grating.

Further, the diffraction grating is characterized by comprising an interference filter and reflecting mirrors arranged at different angles with respect to the interference filter.

Further, a plurality of the interference filters are provided, and are arranged at different angles from the reflecting mirror.

Further, the diffraction grating is formed of a wedge-shaped component provided with an interference filter on one side and a reflection film on the other side.

Further, the diffraction grating comprises a wedge-shaped part provided with an interference filter on one side and another interference filter on the other side, and a reflecting mirror arranged at an angle to the wedge-shaped part. It is assumed that.

Further, the dispersive element is characterized by being made of a prism.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram showing a spectral image acquiring apparatus according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a subject, 2 denotes a filter, 3 denotes a condensing optical system for forming an intermediate image of the subject 1, 4 denotes a variable aperture provided near the converging optical system 3 as a field limiting means, and 5 denotes This is control means for switching between the light-transmitting part and the light-blocking part of the variable aperture 4, that is, the control means for controlling the viewing restriction area. The switching control is performed by applying a known technique such as a liquid crystal to the variable aperture 4. It is possible. As shown, the variable aperture 4
When the control means 5 controls the light to pass through only the central portion of the slit, the slit works in the same way as a conventional slit.

Reference numeral 7 denotes a collimating optical system for converting the light transmitted through the variable aperture 4 into parallel light, 8 denotes a dispersing element for causing the parallel light from the collimating optical system 7 to have an angle difference for each wavelength, and 9 denotes a dispersing element. An imaging optical system that forms a subject image by forming light passing through 8, an image pickup device 10 that converts a light intensity distribution of the subject image into an electric signal, and 11 obtains a spectral image based on an output from the image pickup device 10. Signal processing means.

Next, the operation according to the first embodiment will be described. The incident light from the subject 1 is blocked by the filter 2 from light in an unnecessary wavelength band, and only the light of the wavelength to be measured forms an image near the variable aperture 4 by the condensing optical system 3. However, the portion that can pass through the light transmitting portion of the variable aperture 4 is a portion corresponding to a part of the subject 1. The light that has passed through the variable aperture 4 is collimated by a collimating optical system 7 and is incident on a dispersion element 8. Even if the angle of incidence is the same, the angle of emergence from the dispersion element 8 differs depending on the wavelength. Even if the light is emitted from the same position of the subject, the light enters the imaging optical system 9 at different angles due to the dispersive element 8, so that images are formed at different places on the image sensor 10. In this manner, a spectral image of the band-like portion of the subject 1 corresponding to the light transmitting portion of the variable aperture 4 can be obtained.

Next, by moving the light transmitting portion of the variable aperture 4 by the width by the control means 5,
It is possible to change the position of the band-shaped portion for obtaining the spectral image. According to the liquid crystal, the movement of the light transmitting portion can be controlled at a high speed as in the image acquisition rate of the image sensor. In this way, by sequentially moving the light transmitting portion of the variable aperture 4, it is possible to obtain a band-shaped spectral image of a different position of the subject from the imaging device 10. This output is output to the subject 1 in the same manner as the processing in the signal processing means 11.
By swapping the positions and wavelengths, a spectral image of the subject 1 can be obtained. Movement of the light transmitting portion of the variable aperture 4, output of a band-shaped spectral image by the image sensor 10,
The timing of the signal processing is controlled by the control means 5.

Embodiment 2 FIG. 2 shows a configuration of another embodiment of the visual field limiting means used in the spectral image acquisition device according to the second embodiment of the present invention. In the second embodiment, the light transmitting portions of the variable aperture 4 made of liquid crystal are provided at a plurality of places (two places in FIG. 2) under the control of the control means 5. By doing so, two spectral images of the band-like portion of the subject 1 can be obtained at the same time. Therefore, a spectral image of the subject 1 can be obtained earlier.

Embodiment 3 FIG. FIG. 3 shows the configuration of another embodiment of the visual field limiting means used in the spectral image acquisition device according to the third embodiment of the present invention. 1 and 2
The same parts as those in the first and second embodiments shown in FIG. As a new code, reference numeral 6 denotes a variable mirror as a view restriction means, as shown in FIG.
It is a component in which a plurality of micromirrors 6a whose angles can be controlled are two-dimensionally arranged, and can be manufactured by well-known semiconductor technology.

As shown in FIG. 4, by tilting a certain micro mirror 6a, it is possible to selectively change only a part of the incident light in different directions. Therefore, only the micromirrors 6a in the central band-shaped area of the variable mirror 6 are tilted so that the reflected light travels in a predetermined direction, and the light reflected in other areas is reflected in a direction other than the predetermined direction for imaging. If no contribution is made, this variable mirror 6 has exactly the same function as the variable aperture 4 described in the first and second embodiments. Therefore, a spectral image of the subject 1 can be obtained as described in the first and second embodiments. Of course, the area in which the micromirror 6a is tilted so that the reflected light travels in a predetermined direction is not limited to one band, and may be a plurality of band-like areas.

Embodiment 4 FIG. In the above description, the condensing optical system 3, the collimating optical system 7, and the imaging optical system 9 are illustrated and described as a single lens, but these may be an optical system including a plurality of lenses, An optical system may be used.

Further, the filter 2 for blocking the light of the unnecessary wavelength is not always necessary, and the light of the unnecessary wavelength is not detected due to the efficiency of the optical parts and the sensitivity of the image pickup device 10, or When the influence is extremely small, the filter 2 may be omitted. In addition, in the above description, the filter 2 is described as being placed on the object side of the condenser lens 3, but it is needless to say that the filter 2 is not limited to this position and may be placed anywhere in the optical path.

The field of view to be imaged can be adjusted by the focal length of the condensing optical system, the length of the strip of the variable aperture 4 and the variable mirror 6, and the like. Further, the wavelength range and the wavelength interval for imaging can be adjusted by the focal length of the collimating optical system 7 and the imaging optical system 9 and the like. Therefore, the condensing optical system 3,
By providing the collimating optical system 7 and the imaging optical system 9 with a zoom function, it is possible to arbitrarily change the field of view, the wavelength range, and the wavelength interval for imaging.

Further, in the above description, the dispersion element 8 is illustrated as a transmission type, but this is for the sake of convenience.
Of course, a reflective diffraction grating or a prism may be used.

In the above description, a diffraction grating, a prism, or the like has been described as an example of the dispersion element 8, but a configuration as shown in FIG. 5 may be used. In FIG. 5, reference numeral 8 denotes a dispersion element, which includes an interference filter 12a and a reflecting mirror 12b. The interference filter 12a transmits light in a predetermined wavelength band and reflects light in other wavelength bands. Reflector 1
2b is arranged at a different angle with respect to the interference filter 12a.

Now, assuming that the wavelength range reflected by the interference filter 12a is λ1 and the wavelength range transmitted is λ2, the light of λ1 reflected by the interference filter 12a and the light transmitted by the interference filter 12a and reflected by the reflecting mirror 12b to be reflected again. An angle difference is generated between the light of λ2 transmitted through the interference filter 12a. The lights of λ1 and λ2 having an angle difference enter the imaging optical system 9 and form images at different positions on the image sensor 10 with λ1 and λ2 even in the same subject part. Will have.

Also, as shown in FIG. 6, a plurality of interference filters (two in FIG. 6, 13a and 13b) are provided, and even if they are arranged at different angles from the reflecting mirror 13c, the same dispersion function can be obtained. .

A wedge-shaped dispersion element 8 as shown in FIG. 7 may be used. An interference filter 14a having wavelength selectivity is formed on one surface of the dispersion element 8, and a reflection film 14b is formed on the other surface. At the interference filter 14a, a part of the light is reflected and the remaining light is transmitted. Since the spectral unit 8 has a wedge shape, the interference filter 14a
And the reflection film 14b are not parallel and are formed with an angle difference. Therefore, there is an angle difference between the light reflected by the interference filter 14a and the light transmitted through the interference filter 14a, reflected by the reflection film 14b, and transmitted again through the interference filter 14a. Therefore, it has a distribution function.

Further, a dispersion element 8 as shown in FIG. 8 may be used. It comprises an interference filter 15a having wavelength selectivity formed on one surface of a wedge-shaped substrate, an interference filter 15b formed on the other surface of the wedge-shaped substrate, and a reflecting mirror 15c. The reflecting mirror 15c is arranged such that the optical path reflected by the interference filter 15a or 15b and the optical path reflected by the reflecting mirror 15c have an angle difference.
In this case, the optical path can be divided into three optical paths: an optical path reflected by the interference filter 15a, an optical path reflected by the interference filter 15b, and an optical path reflected by the reflecting mirror 15c. Of course, the number of wedge-shaped interference filters may be increased to two or more, or a parallel plate interference filter may be added.

It is needless to say that the same effect can be obtained by combining a plurality of the dispersion elements 8 described above.

[0047]

As described above, according to the present invention, a light-collecting optical system for forming an intermediate image of a subject, a field-of-view limiting means placed near a focal point of the light-collecting optical system, and the field-of-view limiting means A collimating optical system that converts light transmitted through the collimating light into parallel light, a dispersive element that causes the parallel light from the collimating optical system to have an angle difference for each wavelength, and forms an image of a subject by forming light passing through the dispersive element. By providing the imaging optical system to be obtained and the imaging device for converting the light intensity distribution of the subject image into an electric signal, it is possible to obtain a spectral image acquisition device having excellent wavelength characteristics without requiring a driving unit. .

Further, by further providing a control means for controlling the view restriction area of the view restriction means, it is possible to control the spectral image of the subject.

Further, a variable aperture can be used as the visual field limiting means.

Further, the variable aperture is composed of liquid crystal, and the control means controls the light transmitting portion that transmits light, so that the spectral image can be easily controlled.

The position of the band-shaped spectral image can be moved by controlling the movement of the light transmitting portion of the variable aperture by the control means.

Further, by providing a plurality of light transmitting portions of the variable aperture by the control means, a plurality of band-shaped spectral images can be obtained at the same time, and a spectral image of the subject can be obtained quickly.

Further, a variable mirror can be used as the visual field limiting means.

Further, a plurality of minute mirrors whose angles can be controlled by the control means can be two-dimensionally arranged as the variable mirror.

Further, the variable mirror is controlled by the control means so that only the minute mirror in one or a plurality of band-shaped regions is tilted so that the reflected light travels in a predetermined direction, whereby one or a plurality of band-shaped spectral images are obtained. Can be obtained.

Further, the dispersion element can be constituted by using a diffraction grating.

In addition, since the diffraction grating includes an interference filter and a reflecting mirror arranged at a different angle with respect to the interference filter, the diffraction grating can have a dispersion function.

Further, by providing a plurality of the interference filters and arranging them at different angles from the reflection mirror, a dispersion function can be provided.

In addition, since the diffraction grating is formed of a wedge-shaped component provided with an interference filter on one side and a reflection film on the other side, a dispersion function can be provided.

Further, the diffraction grating is composed of a wedge-shaped component having an interference filter on one surface and another interference filter on the other surface, and a reflecting mirror arranged at an angle to the wedge-shaped component. Can have functions.

Further, when the dispersion element is constituted by a prism, it can have a dispersion function.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a spectral image acquiring apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram showing a spectral image acquiring apparatus according to Embodiment 2 of the present invention.

FIG. 3 is a configuration diagram showing a spectral image acquiring apparatus according to Embodiment 3 of the present invention.

FIG. 4 is a configuration diagram of the variable mirror of FIG. 3;

FIG. 5 is a configuration diagram showing an example of a dispersion element 8 according to the present invention.

FIG. 6 is a configuration diagram showing another example of the dispersion element 8 according to the present invention.

FIG. 7 is a configuration diagram showing still another example of the dispersion element 8 according to the present invention.

FIG. 8 is a configuration diagram showing still another example of the dispersion element 8 according to the present invention.

FIG. 9 is a configuration diagram illustrating a spectral image acquisition device according to a conventional example.

FIG. 10 is a configuration diagram showing a spectral image acquisition device according to another conventional example.

FIG. 11 is a configuration diagram showing a spectral image acquiring apparatus according to another conventional example.

FIG. 12 is an explanatory diagram showing the operation of the signal processing means 11;

FIG. 13 is an explanatory diagram regarding acquisition of spectral image data.

FIG. 14 is a configuration diagram showing a spectral image acquisition apparatus according to still another conventional example.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 subject, 2 filters, 3 condensing optical system, 4 variable aperture, 5 control means, 6 variable mirror, 6 a minute mirror, 7 collimating optical system, 8 dispersive element, 9
Imaging optical system, 10 image sensor, 11 signal processing means, 1
2a, 14a, 15a, 15b interference filter, 12
b, 15c reflecting mirror, 14b reflecting film.

Claims (15)

[Claims] A focusing optical system that forms an intermediate image of a subject; a visual field restricting unit disposed near a focal point of the optical focusing system; and a light beam transmitted through the visual field limiting unit is converted into parallel light. A collimating optical system, a dispersive element that causes the parallel light from the collimating optical system to have an angle difference for each wavelength, an image forming optical system that forms an object image by forming an image of light passing through the dispersive element, An spectral image acquisition device, comprising: an image sensor that converts a light intensity distribution into an electric signal. 2. The spectral image acquiring apparatus according to claim 1, further comprising control means for controlling a visual field restriction area of said visual field restricting means. 3. The spectral image acquiring apparatus according to claim 1, wherein said visual field restricting means comprises a variable aperture. 4. The spectral image acquiring apparatus according to claim 3, wherein the variable aperture is made of a liquid crystal, and a light transmitting unit that transmits light is controlled by the control unit. . 5. The spectral image acquiring apparatus according to claim 4, wherein a movement of a light transmitting part of the variable aperture is controlled by the control unit. 6. The spectral image acquiring apparatus according to claim 4, wherein the variable aperture is provided with a plurality of light transmitting units by the control unit. 7. The spectral image acquiring apparatus according to claim 1, wherein the visual field restricting unit comprises a variable mirror. 8. The spectral image acquisition apparatus according to claim 7, wherein the variable mirror is configured by two-dimensionally arranging a plurality of minute mirrors whose angles can be controlled by the control unit. apparatus. 9. The spectral image acquiring apparatus according to claim 8, wherein the variable mirror is controlled by the control means such that only the minute mirror in one or a plurality of band-shaped regions is tilted so that reflected light travels in a predetermined direction. A spectral image acquisition apparatus. 10. The spectral image acquiring apparatus according to claim 1, wherein said dispersion element is a diffraction grating. 11. The spectral image acquisition apparatus according to claim 10, wherein the diffraction grating is constituted by an interference filter and a reflecting mirror arranged at a different angle with respect to the interference filter. Acquisition device. 12. The spectral image acquiring apparatus according to claim 11, wherein a plurality of the interference filters are provided, and the interference filters are arranged at different angles from the reflecting mirror. 13. The spectral image acquiring apparatus according to claim 10, wherein the diffraction grating is a wedge-shaped component having an interference filter on one side and a reflective film on the other side. 14. The spectral image acquiring apparatus according to claim 10, wherein the diffraction grating is provided with a wedge-shaped component provided with an interference filter on one surface and another interference filter on the other surface, and arranged at an angle with the wedge-shaped component. A spectroscopic image acquisition apparatus, comprising: 15. The spectral image acquisition device according to claim 1, wherein the dispersive element is a prism.