JPH0682303A - Radiometer with calibrating apparatus - Google Patents

Abstract

PURPOSE:To provide sensitivity characteristics, namely sensitivity deviation, of a plurality of photodetectors, by moving in the direction of the optical axis in an optical system, a light-receptor in which the photodetectors are juxtaposed. CONSTITUTION:An optical system 11 converges reflected rays of an observation object by a plane mirror 12 into a light-receptor 13, and a plurality of photodetectors within the receptor 13 output voltages proportioned to the intensity of light. On this, the receptor 13 is driven by a photodetector driver 55 and moved between the position 13b of the focal point of the system 11 and the position 13a shifted in the direction of the optical axis. In an observation mode, the receptor 13 is located in the position 13b of the system 11, and a focused image of the observation object is formed. In a calibration mode, on the other hand, the receptor 13 is shifted from the position 13b to the position 13a. An optical image inputted to the receptor 13 is fuzzy and extends over the whole surface in the case where the observation object for example is the sea, etc., small in irregularity of reflection characteristics, and the incident rays of photodetectors become almost uniform. Consequently, the parameters other than photodetector sensitivity in a specific equation of output computation of a radiometer can be used in common to each photodetector, and output data, namely sensitivity deviation data, corresponding to the sensitivity of each picture element of the light- receptor 13 are obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiometer, and more particularly to a radiometer with a calibration device for observing a radiation wave or a reflected wave of infrared rays or visible rays from an object to be observed, along with a calibration device.

[0002]

2. Description of the Related Art Radiometers installed on aircraft or satellites are JM Mesonouve and M Denguillar.
(14th CONGRESS OF THE INTERNATIONA by JM Maisonnuve and M. Dinguirard)
L SOCIETY FOR PHOTOGRAM METERY) SPOT IN Flight Calibration (SPOT IN
-FLIGHT CALIBATION), JP Midan (JPMid
an) to the 34th International Conference on Spaceflight (34th CONGRE
SS OF THE INTERNATIONAL ASTRONAUTICAL FEDERATION19
83) The SPOTE High Resolution Video Instrument Ann Overview of Design and Performance (T
HE SPOT-HRV [High Resolution Video] INSTRUMENT: A
N OVERVIEWOF DESIGN AND PERFORMANCE) etc. The contents are summarized below.

In FIG. 5, infrared rays or visible rays emitted from an observation object existing in a direction indicated by an arrow A are focused by a rotatable flat mirror 12 (state shown by a solid line) to form an optical system 11. The infrared ray or visible ray is focused by the optical system 11 and then enters the light receiver 13 arranged at the focal position of the optical system 11. Then, the light receiver 13 converts the intensity of the incident light into an electric signal and supplies the electric signal to the electric system 17 for signal processing.

On the other hand, the transmission characteristics of the optical system 11 which mainly focuses the incident light rays, the reflection characteristics of the plane mirror 12, and the light receiving element 1
Sensitivity fluctuation characteristics of 3 (including sensitivity deviation in case of multiple elements)
In addition, the plane mirror 12 can be rotated in order to calibrate the electrical system characteristics and the like. That is, when the plane mirror 12 is rotated in the direction toward the calibration lamp 14 and the lens 15 and fixed at the position of the plane mirror 12A as shown by the broken line in the drawing, the light from the observation target is in the same path. Visible rays or infrared rays from the lamp 14 as a reference light source are incident. Further, by monitoring the light amount of the reference lamp by the optical sensor 16 placed near the lamp,
Calibrate the radiometer.

FIG. 6 is an explanatory view showing an example of a conventional technique using sunlight as the reference light source. In this case, the sunlight prism 21 is rotated so that visible light or infrared rays from the sun are incident on the same path as the light from the observation target as a standard light source.

Further, FIG. 7 is an explanatory diagram showing an example of a conventional radiometer when the reflected light of an object on the ground is used as the reference light source. The radiometer acquires the image of the observation target while moving in the direction indicated by arrow C. Light receiving array 3 among observation objects
The reflected light of infrared rays or visible rays emitted from the area located on the scanning line 38, which is the projection of 3, is reflected by the plane mirror 12 toward the optical system 11, and is arranged at the focal position of the optical system 11 by the optical system 11. The light is collected by a light receiver 13 that houses a light receiving array in which a plurality of light receiving elements are arranged. Therefore, the scanning line 32 is divided according to the number of divisions into the light receiving elements, and the data corresponding to the divided areas is received by the light receiver 1.
It is obtained from the divided light receiving elements of the three light receiving arrays.

In this case, as the ground-based reference light source, for example, a target having a uniform luminance distribution is set within the observation visual field range 34 having a width of 60 to 100 km, and the target 3 is measured by the radiometer.
Make 9 observations. Further, the radiometer is calibrated by measuring the brightness of the target 39 from the ground or a low altitude sky with a calibrated measuring instrument and correcting the scattering and absorption by the atmosphere. Then, the light receiving array 33 converts the light intensity into an electric signal and supplies it to the electric system for signal processing.

[0008]

In the radiometer according to the above-mentioned conventional technique (for example, a conventional system using a lamp as a reference light source), the reference optical system including the calibration lens has restrictions such as size and weight. Also, the calibration light for calibration can be incident only on a part of the range of the optical system lens. Therefore, even if the reflection or transmission characteristics of a part of the plane mirror or the optical system lens is changed, it cannot be detected as a change in radiometer sensitivity.

Further, in the conventional method using the sun as the reference light source, for the same reason as the method using the lamp as the reference light source, the light for calibration can be incident only on a partial range of the plane mirror and the optical system lens. Therefore, it may not be possible to detect a change in the characteristics of a part of the plane mirror or the optical system lens. Also, the apparent angle of the sun is small (visual diameter is 0.
Therefore, in the case of a radiometer having a wide field of view using a linear array sensor or the like as a light receiving element, there is a drawback in that it is not possible to obtain sensitivity variation, that is, sensitivity deviation, for each element of all the light receiving elements.

Next, in a system in which an object on the ground is used as a reference light source, the incident light from the reference light source is incident on the entire range of the plane mirror and the optical system lens. Even if the reflection or transmission characteristics change,
It can be detected as a change in radiometer sensitivity. However, natural observation targets have a limited number and size of areas with uniform brightness, and the frequency of calibration is limited. In addition, since there is a limit to the size of the target placed on the ground, there is a drawback in that it is not possible to obtain sensitivity variations of all light receiving elements of a radiometer with a wide field of view, that is, sensitivity deviations.

Therefore, it is an object of the present invention to detect a change in the reflection or transmission characteristics of a part of a plane mirror or an optical system lens as a change in the sensitivity of the radiometer, and even in a radiometer with a wide field of view, all of the light receiving elements can be detected. An object of the present invention is to provide a radiometer with a calibration device capable of acquiring sensitivity fluctuations, that is, sensitivity deviations.

[0012]

The first invention of the present invention is as follows:
At least a radiometer mounted on an aircraft or a satellite flight vehicle for observing reflected light or radiant light of visible light or infrared light from a land area or sea area, and optical means for converging upon receiving the incident visible light or infrared light A light receiving means on which the light converged by the optical means is incident, and a first means for moving the light receiving means in the optical axis direction of the optical means,
Calibration signal generating means for generating a calibration symbol corresponding to a reference value for calibration while the focus of the optical means is deviated from the light receiving surface of the light receiving means.

A second invention of the present invention is a radiometer which is mounted on at least a flying body of an aircraft or an artificial satellite and observes visible light or infrared reflected light or radiant light from a land area or a sea area. Alternatively, optical means for receiving and converging infrared light, light receiving means for receiving the light converged by the optical means, and second means for changing the optical distance from the optical means to the light receiving means And a calibration signal generating means for generating a calibration signal corresponding to a reference value for calibration while the focus of the optical means is deviated from the light receiving surface of the light receiving means.

[0014]

First, the outline of the present invention will be described.

The present invention is a radiometer mounted on a flying body such as an aircraft or an artificial satellite, for observing radiated / reflected light of visible light or infrared light from land or sea.
Optical means for entering and converging visible light or infrared rays, a light receiving element for receiving the light converged thereby, means for varying the optical distance between the light receiving element and the above-mentioned optical means, It has means for generating the calibration data reference input level in a state where the focus of the optical means is deviated from the light receiving surface of the light receiving element.

More preferably, as a method of varying the optical distance between the light receiving element and the optical means, the wedge-shaped and glass or electrostrictive element inserted in the optical path is connected as an actuator to the light receiving element to position the light receiving element. The present invention provides a radiometer with a calibration device that employs a method of moving a laser beam in the optical axis direction.

Thus, according to the present invention, when the reference input level data for calibration is generated, the light receiving element is moved in the optical axis direction of the optical means, or the optical element to the light receiving element is moved. The target distance is changed, and an arbitrary area on the ground is observed while the focus of the optical means is deviated from the light receiving surface of the light receiving element. At the same time, the radiometer is calibrated by measuring the brightness of the above-mentioned region and correcting the scattering and absorption by the atmosphere.

By shifting the focus in this way, the light incident on the radiometer can be made uniform, even if the observation target has a luminance distribution, and a uniform reference obtained over a wide field of view can be obtained. It is possible to get light. Therefore, according to the present invention, it is possible to detect a change in the reflection characteristic of the plane mirror, a change in the transmission characteristic of the optical system lens, a sensitivity deviation of all the light receiving elements, a change in the electric system characteristic, etc. without being limited to the calibration frequency.

Next, an embodiment of the present invention will be specifically described with reference to FIGS.

FIG. 2 is an explanatory view showing the principle of the present invention.
In this, the plane mirror 12 is interposed on the optical axis of the optical system 11, reflects the light from the observation object 44 existing in the direction indicated by the arrow A in the figure, and reflects it to the light receiver 13 at the position 13a of the optical system. On the optical axis of. The optical system 11 is a plane mirror 1.
The light reflected by 2 is focused on the light receiver 13, and the light receiver 1
The light receiving element in 3 outputs a voltage proportional to the intensity of the condensed light. The light receiver 13 is, for example, a two-dimensional sensor in which light receiving elements are aligned and embedded.

The electric system 17 amplifies and outputs the output voltage of the light receiver 13. The light receiver 13 is an optical system 1 indicated by a broken line in the figure.
It is supported by a suitable supporting means so that it can reciprocate along the optical axis of the optical system 11 between the focal position 13a of 1 and the position 13b slightly deviated from the focal position. Therefore, the light receiver 13 is moved to the position 1 by the moving means.
Move between 3a and 13b.

FIG. 1 is an example of a block diagram showing a configuration of an embodiment of the present invention. The light receiver 13 is driven by a light receiving element driver 55 which is a part of the electric system 17. On the other hand, the output of the light receiver 13 is amplified by the amplifier 56, converted into a digital signal by the sampling circuit 58 and the AD conversion circuit 59, then formatted by the format circuit 60 into a transmission modulation signal, and output to the transmission section of the satellite 61. . Next, the operation of the radiometer configured as described above will be described.

In the normal observation mode, the light receiver 13
Is located at the focal position 13a of the optical system 11, and the focused image from the observation object is made incident on the photodetector 13 (however, the photodetector 13 is superposed on one of the photodetector positions 13a or 13b). However, positions 13a and 13b are not shown in FIG. 1). On the other hand, in the calibration mode, the light receiver 13 is moved in the optical axis direction of the optical system 11 to be positioned at the position 13b. Now, if the observation target is, for example, a desert or the sea where the variation of the reflection characteristics is relatively small, if the focus position of the optical system 11 does not match the light receiving surface of the light receiver 13, the light is input to the light receiver 13. Since the image of the light is blurred and covers the entire surface of the light receiver 13, the light input to the plurality of light receiving elements existing in the light receiver 13 becomes almost uniform.

A description will be given below with reference to mathematical formulas and drawings.

In FIG. 2, the pixel pitch of the light receiver 13 which can move between the positions 13a and 13b of the light receiver is a, the focal length of the optical system 11 composed of a compound lens is f, and the effective diameter is d. The distance from the principal point of the system 11 to the light receiver 13 is h,
The distance from the principal point of the optical system 11 to the focus position on the observation target 41a side is L.

Generally, the ground surface resolution D can be expressed as D = H · a / f, and can be written as L = [(1 / f)-(1 / h)] ⁻¹ as a characteristic of the optical system. Here, in normal observation, the distance H from the principal point of the optical system 11 to the observation target 41a is equal to the distance L in the above equation, and the distances L and H are greater than the focal length f and the distance h.
Is extremely large, so h = f.

Here, the light flux which forms an image at the position 13b of the photodetector obtained by shifting the distance f from the principal point of the optical system 11 to the position 13a of the photodetector by Δh is L = [(1 / f) from the above equation. -{1 / (f + Δh)}] ^-1 . In this case, the luminous flux Dd formed by the optical system 11 on the light receiving element 13b corresponds to the integrated light quantity of the light from the range of the diameter Dd of the ground surface 41b which can be expressed by Dd = d · (HL) / L. It will be done.

[0028] Thus, the influence of variation in luminance of the observation target region that is incident on the radiometer, by shifting the ^{focus, D 2 / (π · Dd} 2/4) ≒ 4a 2 (f + Δh) 2 / d
It can be increased by ² / π / (Δh) ² .

For example, a = 10 μm, d = 100 mm,
When f = 500 mm, when Δh = 200 μm, the influence of luminance variation in the observation area is about 1/12, and when the moving distance is 600 μm, it is 1/100 or less.

In this case, the absolute value of the amount of light incident on the light receiver 13 is determined by the angle of the optical system 11 of the light receiver 13, and the moving distance is sufficiently smaller than the focal length of the optical system 11. Therefore, the change in the absolute value of the light amount due to the movement of the light receiver 13 can be set to a negligible value.

Generally, the output V of a radiometer is: V = K [(Lx · cos θ + Ha) · τ + Na] · Tm
・ It can be expressed as To ・ Rp ・ G. Here, Lx: radiance of the observed object, θ:
Solar zenith angle, Ha: Sky radiation, τ: Atmospheric transmittance, Na:
Optical path brightness, Tm: plane mirror reflectance, To: optical system transmittance,
Rp: light receiving element sensitivity, G: electric circuit gain, K: constant.

Therefore, because of the uniform light described above, all parameters except the above-mentioned sensitivity Rp of the light receiving element are common to all the light receiving elements, so that output data corresponding to the sensitivity of each pixel of the light receiving device 13 can be obtained. . That is, the data of the sensitivity deviation can be acquired.

In addition, the luminance measurement data of the object to be observed on the ground measured from a turret, an airplane, etc .: (L · cos θ
+ Ha), using the atmospheric model, sky radiation H
a, by correcting the atmospheric transmittance τ, Tm: plane mirror reflectance, To: optical system transmittance, Rp: light receiving element sensitivity,
G: Sensitivity characteristic data due to variations in electric circuit system gain can be measured.

Needless to say, the present invention is not limited to the above embodiment. Further, the state where the focus of the optical means is out of the light receiving surface of the light receiver is not limited to the movement of the light receiving element 13, and the optical distance from the optical system 11 to the light receiver 13 is changed by, for example, a wedge made of optical glass. It can also be created by

A specific description of the outline will be given with reference to FIGS. 3 and 4.

First, the change of the optical distance includes the change of the physical distance and the change of the length of the portion through which the transparent object is inserted into the optical path. Since the necessary change distance is considered to be around 0.2 to 1 mm, a mechanically stable moving method may be used, but it is necessary to improve the accuracy. Here, as a relatively simple method, as shown in FIG. 6, the photodetector 13 has electrodes on both sides of an electrostrictive material, and a DC voltage is applied to the electrodes to expand and contract the electrostrictive material. 54 is attached to the fixed plate, and the light receiver 13 for receiving the incident light 64 is attached directly or via the connecting rod 53. At this time, if the electrostrictive material is thinned and attached to both surfaces of the electrode, and a plurality of these are stacked and connected in parallel as the actuator 54, the operating voltage becomes low, which is preferable for use.

Next, there is a method in which the incident light 64 is passed through a transparent material to make the physical distance longer than the length in vacuum by an amount corresponding to the refractive index of the material. According to FIG. 4, transparent wedges 71A and 71B made of, for example, glass fixed to the fixed plate are slidably in contact with or close to each other, and one of the transparent wedges 71B has a screw 72 fixed to the fixed plate 74 and a screw. The other end of the screw 72 is connected to the micromotor 73, and the transparent wedge 71 that is rotatably joined to the screw head by the rotation of the micromotor 73.
B moves up and down, and the incident light 75 transmits the transparent wedge 71A.
The length of light passing through 71B varies, and the substantial optical path length of the incident light 75 can be varied.

[0038]

As described above, according to the present invention, a light receiver having a plurality of light receiving elements arranged side by side is moved in the optical axis direction of the optical system, or the optical distance from the optical system to the light receiver is changed by a transparent wedge or the like. Observing an arbitrary area on the ground in a changed state, at the same time, measuring the brightness of an arbitrary area on the ground from a high tower, an airplane, etc., and by correcting the scattering and absorption by the atmosphere, There is an effect that it is possible to calibrate with uniform reference light, that is, to detect the reflection characteristic of the plane mirror, the change of the transmission characteristic of the optical system lens, the sensitivity variation of all the light receiving elements, that is, the sensitivity deviation and the variation of the electrical system characteristic.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is an explanatory view showing a means for adjusting a distance between a light receiving element and an optical system.

FIG. 4 is an explanatory view showing a means for adjusting the distance between the light receiving element and the optical system.

FIG. 5 is an explanatory diagram showing an example of a conventional technique using a lamp as a reference light source.

FIG. 6 is an explanatory diagram showing an example of a conventional technique using sunlight as a reference light source.

FIG. 7 is an explanatory diagram showing the principle of a conventional technique using sunlight as a reference light source.

[Explanation of symbols]

 11 optical system 12 plane mirror 13 light receiver 17 electric system 61 satellite

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[Procedure amendment]

[Submission date] June 26, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

FIG. 2 is an explanatory view showing the principle of the present invention.
In this, the plane mirror 12 is interposed on the optical axis of the optical system 11, reflects the light from the observation object 44 existing in the direction indicated by the arrow A in the figure, and reflects it to the light receiver 13 at the position 13a of the optical system. On the optical axis of. The optical system 11 is a plane mirror 1.
The light reflected by 2 is focused on the light receiver 13, and the light receiver 1
The light receiving element in 3 outputs a voltage proportional to the intensity of the condensed light. The light receiver 13 is, for example, a two-dimensional sensor in which light receiving elements are aligned and embedded (see FIG. 7).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

The electric system 17 amplifies and outputs the output voltage of the light receiver 13. The light receiver 13 is an optical system 1 indicated by a broken line in the figure.
It is supported by a suitable supporting means so that it can reciprocate along the optical axis of the optical system 11 between the focal position 13b of 1 and the position 13a slightly deviated from this focal position. Therefore, the light receiver 13 is moved to the position 1 by the moving means.
Move between 3a and 13b.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

In the normal observation mode, the light receiver 13
Is located at the focal position 13b of the optical system 11, and a focused image from the observation object is made incident on the photodetector 13 (however, the photodetector 13 is superposed on one of the positions 13a or 13b of the photodetector). However, positions 13a and 13b are not shown in FIG. 1). On the other hand, in the calibration mode, the light receiver 13 is moved in the optical axis direction of the optical system 11 to be positioned at the position 13a. Now, if the observation target is, for example, a desert or the sea where the variation of the reflection characteristics is relatively small, if the focus position of the optical system 11 does not match the light receiving surface of the light receiver 13, the light is input to the light receiver 13. Since the image of the light is blurred and covers the entire surface of the light receiver 13, the light input to the plurality of light receiving elements existing in the light receiver 13 becomes almost uniform.

[Procedure amendment 4]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

Here, the light flux which forms an image at the position 13b of the light receiver, which is obtained by shifting the distance f from the principal point of the optical system 11 to the position 13b of the light receiving element by Δh, is L = [(1 / f) -{1 / (f + Δh)}] ^-1 . In this case, the light flux D _d formed by the optical system 11 on the light receiving element 13a is obtained by integrating the light from the range of the diameter D _d of the ground surface 41b which can be represented by D _d = d · (HL) / L. It corresponds to the amount of light.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028] Thus, the influence of variation in luminance of the observation target region that is incident on the radiometer, by shifting the ^{focus, D 2 / (π · D} d 2/4) ≒ [4a 2 (f + Δh) 2 /
d ² ] · [π / (Δh) ² ].

Claims (4)

[Claims] 1. A radiometer mounted on an aircraft or an air vehicle including an artificial satellite for observing reflected light or radiant light of visible light or infrared light from a land area or a sea area and converging upon receiving the visible light ray or infrared light. The optical means, the light receiving means on which the light converged by the optical means is incident, the first means for moving the light receiving means in the optical axis direction of the optical means, and the focus of the optical means. A radiometer with a calibration device, comprising: a calibration signal generating means for generating a calibration symbol corresponding to a reference value for calibration while being displaced from the light receiving surface of the light receiving means. 2. A radiometer, which is mounted on an aircraft or an air vehicle including an artificial satellite and observes reflected light or radiant light of visible light or infrared light from a land area or a sea area, upon receiving the visible light or infrared light. Optical means for converging, and light receiving means for receiving the light converged by the optical means,
Second means for changing the optical distance from the optical means to the light receiving means, and a calibration signal corresponding to a reference value for calibration in a state where the focus of the optical means is deviated from the light receiving surface of the light receiving means. A radiometer with a calibration device, comprising: 3. A first means comprising an electrostrictive actuator having one working surface fixed and a light receiving means fixed to the other working surface and moving in a direction perpendicular to the light receiving surface of the light receiving means. The radiometer with a calibration device according to claim 1, wherein 4. The second means, wherein the inclined surfaces of two sets of wedge-shaped transparent members are overlapped with each other so that the wedge-shaped transparent members on one side can move in parallel with the overlapped inclined surface. The radiometer with a calibration device according to claim 2, wherein