KR101812584B1 - Imaging optical system FOR EARTH OBSERVATION - Google Patents

Abstract

An imaging optical system for earth observation according to the present invention comprises at least three mirrors along an optical path from an incident part to a light receiving part. Here, the imaging optical system for earth observation includes a first mirror composed of a reflector with an elliptic surface, which transfers light emitted to the incident part to the inside of the optical system; a second mirror which reflects light emitted from the first mirror and is composed of a reflector with a hyperbolic surface; and a third mirror which reflects light emitted from the second mirror and emits it to the light receiving part, and is composed of a reflector with an elliptic surface. It is possible to obtain High SNR.

Description

Description of the Related Art [0002] Imaging optical system FOR EARTH OBSERVATION [0003]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system for observing the earth, and more specifically, to an imaging optical system mounted on a satellite and applicable to an imaging apparatus for observing the earth.

Earth Observation Satellites are satellites that are equipped with various sensor systems aimed at satellites and are launched into specific orbits to acquire and analyze various information such as weather, climate, ocean, and forests of the earth. Earth observation satellites have the advantage of acquiring more information by observing distant information on the earth 's surface from a distance over the earth.

Here, the imaging optical system mounted on Earth observation satellites is a super-precision optical system of large diameter requiring a large manufacturing cost and a considerable design time, and it is required to have excellent performance for obtaining a high resolution image.

In the satellite technology field, technology transfer between countries is limited and there is a strong tendency to minimize the disclosure of technology in order to prevent the risk of technology leakage. Due to such a practical problem, there are few published prior arts on the design technology of the satellite optical system, and there is a limit in the design of the imaging optical system for earth observation that can exhibit excellent performance.

Korean Patent No. 10-1599204

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide an imaging optical system for observing the earth, which has a wide viewing angle,

Other objects of the present invention will become apparent from the following description of preferred embodiments.

According to one aspect of the present invention, an imaging optical system for earth observation includes at least three mirrors along an optical path from an incident portion to a light receiving portion. Here, the optical system for earth observation includes a first mirror made of an ellipsoidal mirror, which makes the light incident on the incidence portion enter into the optical system; A second mirror that reflects light incident from the first mirror and is made up of a mirror of a hyperboloid; And a third mirror that reflects light incident from the second mirror and emits the light to the light receiving unit, the third mirror being an elliptic mirror.

In one embodiment, the imaging optical system for observing the earth can be designed so that an intermediate focal plane is formed on the optical path.

In one embodiment, the imaging optical system for observing the earth can be designed such that the first mirror and the second mirror have an intermediate focal plane on the optical path between the second mirror and the third mirror.

In one embodiment, the field-observing optical system for the earth observation may have a field stop at the position of the intermediate focal plane.

In one embodiment, the imaging optical system for earth observation has a straight line distance from the light receiving unit to the reflecting surface center point of the first mirror along the optical axis direction to D1, a distance from the light receiving unit to the reflecting surface center point of the second mirror D2 / D3 < 0.95 and a first condition of 0.94 < D1 / D3 < 0.95 where D3 is a straight line distance from the light receiving unit to the reflecting surface center point of the third mirror, 0.223 < / RTI &gt;

The first and second mirrors and the third mirror are disposed in the opposite directions with respect to the optical axis, and the first mirror and the third mirror are disposed in the opposite directions from the optical axis along the vertical direction of the optical axis, A straight line distance from the optical axis to the reflecting surface center point is L1, a straight line distance from the optical axis to the reflecting surface center point of the second mirror is L2, The third condition of 0.123 < L2 / L1 < 0.137 and the fourth condition of 0.401 < L3 / L1 < 0.414 can be designed when the straight line distance to the center point is L3.

In one embodiment, the first through third mirrors may be configured to incline by 0.5 degrees toward the incident portion with respect to the optical axis.

The imaging optical system for observing the earth according to the present invention has a wide viewing angle and shields the light with a high SNR and can have excellent performance.

1 is a reference view for explaining an optical system for observation of the earth according to the present invention.
2 to 4 are reference views for explaining an optical system for observation of the earth according to an embodiment of the present invention.
5 to 6 are reference views for explaining the performance of an imaging optical system for observation of the earth according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a reference view for explaining an optical system for observation of the earth according to the present invention.

The imaging optical system 100 for observing the earth according to the present invention is for capturing an image of the earth mounted on a satellite and can have a wide viewing angle and a high SNR when designed according to a preferred embodiment of the present invention to be described below, It can be more suitably used for observation.

1, an optical system 100 for observing the earth is an optical system including at least three mirrors along an optical path formed until an incident light 11 incident on an incident portion is emitted to a light receiving portion 40 .

Here, the earth observation imaging optical system 100 includes a first mirror 10 for making the light 11 incident on the incidence portion enter into the optical system, a second mirror 10 for reflecting the light incident from the first mirror 10, And a third mirror 30 that reflects the light incident from the second mirror 20 and outputs the reflected light to the light receiving unit 40.

In one embodiment, the first mirror 10 may be a reflector of an elliptical surface, the second mirror 20 may be a reflector of a hyperboloid, and the third mirror 30 may be an elliptic reflector.

In one embodiment, the imaging optical system 100 for earth observation may be designed to form an intermediate focal plane on the optical path. Here, the intermediate focal plane 50 may be formed on the optical path between the second mirror 20 and the third mirror 30.

The position of the intermediate focal plane 50 is dependent on the design and position of each mirror and the intermediate focal plane 50 is formed between the second mirror 20 and the third mirror 30, The design and arrangement of the first mirror 10 and the second mirror 20 should be properly performed. Specific design and layout information for this will be described later.

In one embodiment, the field of view optical system 100 for earth observation may have a field stop at the position of the intermediate focal plane 50.

That is, according to an embodiment of the present invention, an intermediate focal plane 50 is formed on the optical path between the second mirror 20 and the third mirror 30, The provision of the diaphragm makes it possible to shield stray light incident outside the field of view and thus exhibit a high SNR.

The configurations of the imaging optical system 100 for observing the earth according to the present invention and the embodiments thereof have been described. Hereinafter, with reference to FIGS. 2 to 4, a description will be given of a specific embodiment of the present invention, which provides better performance, with specific design and layout information.

2 to 4 are reference views for explaining an optical system for observation of the earth according to an embodiment of the present invention.

Referring to Fig. 2, the imaging optical system for earth observation 200 may be designed to satisfy the following first and second conditions.

(First condition)

0.94 < D1 / D3 < 0.95

(Second condition)

0.218 < D2 / D3 < 0.223

Here, D1 to D3 are as follows.

D1: a straight line distance from the light receiving unit 400 to the center of the reflecting surface of the first mirror 10 along the on-axis direction

D2: a straight line distance from the light receiving section 40 to the center of the reflecting surface of the second mirror 20 along the optical axis direction

D3: a straight line distance from the light receiving portion 40 to the reflecting surface center point of the third mirror 30 along the optical axis direction

That is, according to an embodiment of the present invention, the first mirror 10, the second mirror 20, and the third mirror 30 are spaced apart from each other by a predetermined distance along the optical axis direction, 2 &lt; / RTI &gt; condition.

Referring to FIG. 3, the imaging optical system for earth observation 300 may be designed to satisfy the following third condition and fourth condition.

(Third condition)

0.123 < L2 / L1 < 0.137

(Fourth condition)

0.401 < L3 / L1 < 0.414

Here, L1 to L3 are as follows.

L1 is a straight line distance from the optical axis along the vertical direction of the on-axis to the center of the reflecting surface of the first mirror 10 (i.e., the stocking distance of the first mirror)

L2 is a straight line distance from the optical axis along the vertical direction of the optical axis to the center of the reflecting surface of the second mirror 20 (i.e., the storage distance of the second mirror)

L3: a straight line distance from the optical axis along the vertical direction of the optical axis to the center of the reflecting surface of the third mirror 30 (i.e., the storage distance of the third mirror)

Here, the first and second mirrors 10 and 20 and the third mirror 30 may be disposed in opposite directions with respect to the optical axis.

That is, according to an embodiment of the present invention, the first mirror 10, the second mirror 20, and the third mirror 30 are spaced apart from each other by a predetermined distance along the vertical direction of the optical axis, And the fourth condition.

Referring to FIG. 4, the first through third mirrors 10, 20, and 30 may be inclined by 0.5 degrees toward the incident side with respect to the optical axis. 4, the optical system frame composed of the first through third mirrors 10, 20, and 30 may be configured such that the reference axis 61 is inclined by -0.5 degrees from the optical axis (on-axis) have.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 2 to 4. Hereinafter, specific design information that satisfies the first to fourth conditions described above and can exhibit the best effects of the present invention I want to explain.

# Comment Radius of Curvature (mm) Thickness
(mm) Glass Semi-Diameter
(mm) Offset
Conic 4th order
 aspheric 6th order aspheric 0 Object Infinity Infinity - Infinity - - - - One Stop Infinity 600 - 100 - - - - 2 M1 -1006.565 -449.862 MIRROR 323.804 -220 -0.805 8.39E-12 1.86E-19 3 M2 -305.843 469.752 MIRROR 43.869 -28.3 -11.812 1.90E-09 -8.79E-14 4 M3 -471.429 -601.398 MIRROR 155.077 89.7 -0.188 -1.17E-11 -9.67E-18 5 Image Infinity - - 21.774 - - - - Design Program: ZEMAX
Telescope type: Three Mirror Anastigmat (TMA)
Pupil size: 200 mm
Effective focal length (EFL): 1200 mm
Ground Sampling Distance (GSD) @ GEO: 200 m @Nadir

According to the best embodiment of the present invention shown in Table 1, when the radius of curvature of the first mirror 10 is -1,006.565, the axial length L1 is 220 and the conic coefficient is -0.805, The curvature radius of the second mirror 30 is -471.429, the stocking distance L3 is 89.7 (mm), the curvature radius of the second mirror 20 is -305.843, the stocking distance L2 is 28.3 and the conic coefficient is -11.812. , And a conic coefficient of -0.188.

According to the best embodiment of the present invention shown in Table 1, the linear distance D1 from the light receiving portion 40 to the center of the reflection surface of the first mirror 10 along the optical axis direction is 559.4, The linear distance D2 from the light receiving section 40 to the reflecting surface center point of the second mirror 20 is 130.7 and the linear distance D3 from the light receiving section 40 to the reflecting surface center point of the third mirror 30 along the optical axis direction is 592 &lt; / RTI &gt;

In the preferred embodiment of the present invention, D1 / D3 satisfies the first condition, D1 / D3 satisfies the first condition, D2 / D3 equals 0.2208, and the second condition satisfies the first condition. L2 / L1 satisfies the third condition with 0.1286, and L3 / L1 satisfies the fourth condition with 0.4077.

According to the best embodiment of the present invention described above, the imaging optical system for earth observation is designed, and a field of view is formed at the position of the intermediate focal plane formed on the optical path between the second mirror 20 and the third mirror 30, When a diaphragm is constituted, it can have a wide viewing angle and a high SNR, and can be more suitably used for ocean observation.

Hereinafter, the performance of the imaging optical system for observing the earth according to the best mode of the present invention will be described with reference to Figs.

FIG. 5 is a Modulation Transfer Function (MTF) for evaluating the performance of an imaging optical system for earth observation designed according to the best mode of the present invention. This is an index indicating the image sharpness (final performance) of the optical system Can be interpreted.

Referring to FIG. 5, a photodetector having a pixel size of 6.8 mu m is used as a reference (based on a light detector of Chunlian Marine Satellite No. 2), and a diffraction limit at a nyquist frequency of 73.53 lp / mm is 0.784 , And the designed value shows 0.782 on the optical axis. Therefore, it can be seen that the design shows excellent performance in consideration of the fact that the design value does not substantially differ from the diffraction limit value.

FIG. 6 is a spot diagram for evaluating the performance of the imaging optical system for earth observation designed according to the best mode of the present invention, and shows the magnitude of focus for each field of view, And the like.

In Fig. 6, the black circle is an airy disk representing the physical limit, and it can be seen that the spot distribution of the designed optical system is located in the Airy disk. Here, the size of the Airy disc is 2.768 μm, and it can be seen that the designed optical system shows excellent performance considering that the RMS radius value of the spot distribution is within 1 μm at all viewing angles.

FIG. 7 is an RMS wavefront error for evaluating the performance of the imaging optical system for earth observation designed according to the best mode of the present invention. The RMS wavefront error is generated when the light receiving unit 40 is moved in the forward / Represents the wavefront error RMS value of the optical system, which can be interpreted as an index indicating the actual manufacturing performance of the optical system.

In FIG. 7, it can be seen that the black line at the top shows a very good performance considering the performance in the diffraction limit even if the designed optical system shifts by ± 10 μm in all viewing angles, which is the physical limit of the diffraction limit have.

The performance according to the best embodiment of the present invention shown in Table 1 has been described with reference to FIGS. 5 to 7, but it can exhibit sufficiently superior performance even in the range satisfying the first to fourth conditions described above, It should be construed that the invention is within the scope of the present invention.

It will be apparent to those skilled in the relevant art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. The appended claims are to be considered as falling within the scope of the following claims.

100, 200, 300, 400: imaging optical system for earth observation
10: First mirror
20: second mirror
30: Third mirror
40:
50: intermediate focal plane
60: Optical system frame

Claims (7)

An imaging optical system for earth observation, comprising at least three mirrors along an optical path from an incident portion to a light receiving portion,
The earth observation optical system
A first mirror made of an ellipsoidal reflector for making the light incident on the incident portion enter into the optical system;
A second mirror that reflects light incident from the first mirror and is made up of a mirror of a hyperboloid; And
A third mirror that reflects light incident from the second mirror and emits the light to the light receiving unit, the third mirror being a ellipsoidal mirror;
And,
The first mirror and the second mirror are designed to have an intermediate focal plane on the optical path between the second mirror and the third mirror,
A field stop is configured at the position of the intermediate focal plane,
A straight line distance from the light receiving unit to the reflection surface center point of the first mirror along the optical axis direction is D1, a straight line distance from the light receiving unit to the reflection surface center point of the second mirror is D2, And a straight line distance from the center of the third mirror to the center of the reflection surface is D3,
The first condition of 0.94 < D1 / D3 < 0.95 and the second condition of 0.218 < D2 / D3 <
The first and second mirrors and the third mirror are disposed in opposite directions with respect to the optical axis,
A straight distance from the optical axis to the center of the reflection surface of the first mirror is L1, a straight distance from the optical axis to the center of the reflection surface of the second mirror is L2 along the vertical direction of the optical axis, And a straight line distance from the optical axis along the vertical direction to the center of the reflecting surface of the third mirror is L3,
0.123 <L2 / L1 <0.137 and the fourth condition of 0.401 <L3 / L1 <0.414,
Wherein the first to third mirrors are inclined by 0.5 占 in the direction of the incident portion with respect to the optical axis. delete delete delete delete delete delete

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