Satellite-borne laser radar and optical remote sensing camera transmit-receive integrated optical system

Abstract

The invention relates to a satellite-borne laser radar and optical remote sensing camera transmit-receive integrated optical system, and relates to the technical field of space remote sensing. The optical system comprises a primary reflector, a secondary reflector, a first optical path folding reflector, a doublet lens group and a dichroscope, focuses of the primary reflector and the secondary reflector coincide; the system further comprises a laser radar transmitting unit, a laser signal receiving system and an optical imaging system. According to the satellite-borne laser radar and optical remote sensing camera transmitting and receiving integrated optical system, the off-axis two-reflection afocal telescope is adopted as a common-aperture optical antenna, so that the far-field light spot position of a laser beam is accurately aligned with the center of a receiving view field, and the transmitting and receiving axis matching error is fundamentally eliminated. Therefore, an optical axis monitoring camera, a laser footprint camera and a deviation angle adjusting mechanism do not need to be additionally arranged for transmitting and receiving matching, the system structure is simplified, and the system integration degree is improved.

Description

Technical Field

[0001] The present invention relates to the field of aerospace remote sensing technology, and particularly to an integrated optical system for transmitting and receiving a spaceborne lidar and an optical remote sensing camera. Background Art

[0002] Traditional optical remote sensing cameras perform excellently in providing surface two-dimensional multispectral image information, but there are problems such as relying on sunlight, limited detection time, and limited ability to obtain ground object elevation information; spaceborne lidars can accurately detect the three-dimensional structure of space targets, but it is difficult to obtain fine spectral information of ground objects. By combining a spaceborne lidar with an optical remote sensing camera, the structure, three-dimensional information, and spectral characteristics of the target object can be obtained simultaneously. This multi-modal information fusion provides a solid foundation for in-depth analysis and accurate interpretation of data, and helps to improve the effectiveness and comparability of remote sensing imaging data.

[0003] Currently, the above technology has been successfully applied to the land ecosystem carbon monitoring satellite "Gou Mang Hao". The multi-beam lidar carried on the satellite combines laser and camera for the first time in the world. While obtaining the ground vegetation height information by using the lidar, high-resolution ground multispectral images can also be obtained. This payload emits a directional laser beam to the ground through the lidar emission system, and uses an optical axis monitoring camera to monitor the emission optical axis of the laser to ensure that the far-field spot of the laser is within the field of view of the receiving system. The receiving system simultaneously receives the reflected laser signal and the ground object optical signal.

[0004] As the first truly active-passive remote sensing integrated system, the "Gou Mang Hao" land ecosystem carbon monitoring satellite has played a significant role in large-scale investigation of forest resources and carbon sink monitoring in China. However, its main disadvantage is that the lidar emission system and the receiving system adopt a split design, and the laser signal transmission and reception matching are realized through a laser footprint camera, an optical axis monitoring camera, and an offset angle adjustment mechanism. This split design method increases the system complexity and brings greater pressure to the volume and mass on the satellite. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art and make the best use of the limited space of the satellite platform, the present invention provides an integrated optical system for transmitting and receiving a spaceborne lidar and an optical remote sensing camera.

[0006] In order to solve the above technical problems, the technical solution of the present invention is specifically as follows:

[0007] An integrated optical system for transmitting and receiving a spaceborne lidar and an optical remote sensing camera, comprising: a primary mirror, a secondary mirror, a first optical path folding mirror, a doublet lens group, and a dichroic mirror, which are sequentially arranged in the optical path direction; the foci of the primary mirror and the secondary mirror coincide;

[0008] The optical system further includes: a lidar transmitting unit, a laser signal receiving system, and an optical imaging system; where:

[0009] The lidar transmitting unit includes: a laser.

[0010] The laser signal receiving system includes, successively arranged in the optical path direction: a third lens, a field stop, a second optical path folding mirror, a fourth lens, a narrowband filter, a fifth lens, and a photodetector device.

[0011] The optical imaging system includes, successively arranged in the optical path direction: a third optical path folding mirror and an image sensor; the image sensor is used to receive visible light ground object information and generate a two-dimensional image of the target.

[0012] The laser beam emitted by the laser passes through the secondary mirror and the primary mirror in sequence, expands the beam waist radius, reduces the divergence angle, and is directed towards the ground.

[0013] The dichroic mirror is used to separate the laser signal from the visible light band, deflect and reflect the laser signal onto the third lens, and the visible light passes through the dichroic mirror and the third optical path folding mirror and converges onto the image sensor.

[0014] The ground laser signal is reflected and received by the laser signal receiving system, and it passes through the primary mirror, the secondary mirror, the first optical path folding mirror, the doublet lens group, the dichroic mirror, the third lens, the field stop, the second optical path folding mirror, the fourth lens, the narrowband filter, and the fifth lens in sequence and is received by the photodetector device.

[0015] In the above technical solution, the reflecting surface of the primary mirror is a free-form surface characterized by an XY polynomial with a parabolic surface as the base. The aperture of the reflecting surface is a rectangle of 260 mm × 360 mm, and the radius of curvature is -720 mm.

[0016] In the above technical solution, the reflecting mirror of the secondary mirror is a free-form surface characterized by an XY polynomial with a parabolic surface as the base. The aperture of the reflecting surface is a rectangle of 32 mm × 44 mm, and the radius of curvature is -72 mm.

[0017] In the above technical solution, the laser is a semiconductor-pumped Nd:YAG pulsed laser that emits a laser beam with a wavelength of 1064 nm, the pulse energy is 1.5 mJ, the pulse width is 2 ns, the repetition frequency is 10 kHz, the spot size is 2 mm, and the divergence angle is 0.68 mrad.

[0018] In the above technical solution, the doublet lens group includes, successively arranged in the optical path direction: a first lens and a second lens.

[0019] The central thickness of the first lens is 6 mm, and the central thickness of the second lens is 3 mm.

[0020] In the above technical solution, the dichroic mirror is an optical glass with a dichroic film deposited on its surface.

[0021] In the above technical solution, the image sensor is a CMOS and is arranged on the imaging side of the optical imaging system.

[0022] In the above technical solution, the visible light band is 400 - 750 nm.

[0023] In the above technical solution, the laser ground footprint is located at the center of the receiving field of view of the laser signal receiving system.

[0024] The present invention has the following beneficial effects:

[0025] The integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention designs the optical remote sensing camera, the lidar transmitting system and the receiving system with a common aperture, avoiding the transceiver matching problem caused by the separate design of the laser transmitting system and the receiving system. At the same time, the system integrates the active and passive detection capabilities of the spaceborne lidar and the optical remote sensing camera, ensuring the spatio-temporal consistency of multi-source remote sensing images.

[0026] The integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention uses an off-axis two-mirror afocal telescope as the common aperture optical antenna, accurately aligning the far-field spot position of the laser beam with the center of the receiving field of view, fundamentally eliminating the transceiver axis matching error. Therefore, there is no need to additionally configure an optical axis monitoring camera, a laser footprint camera, and an offset angle adjustment mechanism for transceiver matching, simplifying the system structure and improving the system integration.

[0027] The integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention uses the primary mirror and the secondary mirror commonly for the three channels of optical remote sensing, laser emission, and laser reception, greatly improving the system integration, reducing the volume, weight, and cost of the equipment, adapting to the spaceborne remote sensing imaging environment, avoiding the problem of satellite platform installation volume limitation, and extending the operation time of the remote sensing satellite.

[0028] The integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention uses multiple optical path folding mirrors to achieve an optimal balance between system volume and performance. Its overall envelope size is 490 mm (length) × 260 mm (width) × 420 mm (height), and the mass ≤ 15 kg. At a satellite orbit altitude of 500 km, the system can achieve a ground pixel resolution of 1 m for optical remote sensing (MTF@Nyquist > 0.2) and a range resolution of 0.3 m for the lidar. Description of the Drawings

[0029] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] Figure 1 It is a schematic structural diagram of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0031] Figure 2 It is a schematic structural diagram of the lidar emission unit of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0032] Figure 3 It is a schematic structural diagram of the laser signal receiving system of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0033] Figure 4 It is a schematic structural diagram of the optical imaging system of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0034] Figure 5 It is a schematic structural diagram of the doublet lens group of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0035] Figure 6 It is the spot dispersion diagram of the lidar emission unit of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0036] Figure 7 It is the spot dispersion diagram of the laser signal receiving system of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0037] Figure 8 It is the spot dispersion diagram of the optical imaging system of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention

[0038] Figure 9 It is the MTF diagram of the optical imaging system of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention.

[0039] The reference numerals in the figure are represented as:

[0040] 1 - primary mirror; 2 - secondary mirror; 3 - laser; 4 - first optical path folding mirror; 5 - doublet lens group; 5.1 - first lens; 5.2 - second lens; 6 - dichroic mirror;

[0041] 7 - third optical path folding mirror; 8 - image sensor; 9 - third lens; 10 - field stop; 11 - second optical path folding mirror; 12 - fourth lens; 13 - narrowband filter; 14 - fifth lens; 15 - photodetector.

[0042] The first surface of the doublet lens group; the second surface of the doublet lens group; the third surface of the doublet lens group. Detailed implementation manners

[0043] The inventive concept of the present invention is as follows:

[0044] In order to make the best use of the limited space of the satellite platform, for the integrated transmitting and receiving optical system of the spaceborne lidar and the optical remote sensing camera of the present invention, since its laser footprint is always located at the center of the receiving field of view, there is no need to adjust the offset angle mechanism to match the transmission and reception of the laser signal.

[0045] The integrated transmitting and receiving optical system of the spaceborne lidar and the optical remote sensing camera of the present invention adopts the method of sharing the primary and secondary mirrors, and conducts integrated design of the lidar transmitting system, the laser signal receiving system and the optical remote sensing camera, solving the problems of high complexity, high resource occupation and low application efficiency brought by the separate design of the spaceborne lidar transmitting and receiving system and the optical remote sensing camera system in the existing remote sensing technology. The primary mirror and the secondary mirror are used as the laser beam expander lens of the lidar transmitting system to compress the divergence angle of the laser beam emitted by the laser; at the same time, they are used as the receiving antennas of the laser signal receiving system and the optical remote sensing camera to realize the synchronous detection of the spectral information of the ground object and the three-dimensional structure of the target.

[0046] The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system of the present invention mainly includes: a laser radar transmitting unit, a laser signal receiving system, and an optical imaging system. Among them: the laser radar transmitting unit includes: a laser beam expansion system composed of a primary reflector and a secondary reflector, and a laser. The laser beam emitted by the laser is reflected by the secondary reflector and the primary reflector in turn, and the beam waist radius is expanded to 10 times the original, and the divergence angle is reduced to 1 / 10 of the original, and then emitted to the ground; the laser signal receiving system receives the reflected laser signal, and passes through the primary reflector, the secondary reflector, the first optical path folding reflector, the first lens, the second lens, the dichroic mirror, the third lens, the field of view aperture, the second optical path folding reflector, the fourth lens, the narrowband filter, and the fifth lens in turn, and finally converted into an electrical signal output by a photoelectric detection device. The working wavelength of the laser signal receiving system is 1064nm, the focal length is 1600mm, the working F number is 6.4, and the receiving field of view is 0 .1mrad, the Airy disk radius is 7.78μm, and the RMS radius of the image-side diffuse spot is less than 7μm; the spectral information of the ground objects received by the optical imaging system passes through the primary reflector, the secondary reflector, the first optical path folding reflector, the first lens, the second lens, the dichroic mirror, the third optical path folding reflector in sequence, and is finally received by the image sensor. The working wavelength of the optical imaging system is 400-750nm, the focal length is 3500mm, the working F number is 14, the full field of view is 0.294°, when the orbit altitude is 500km, the corresponding width is 2.6km, the ground pixel resolution is 1m, the Airy disk radius is 10μm, the RMS radius of the image-side diffuse spot is less than 4μm, and the modulation transfer function of each field of view is greater than 0.2 at the Nyquist frequency (72lp / mm).

[0047] The three-dimensional size of the satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system of the present invention is approximately 490mm×260mm×420mm, and both the on-axis field of view and the off-axis field of view achieve diffraction-limited image quality, realizing the compact design of the integrated laser radar transmitting system, laser radar receiving system and optical imaging system.

[0048] The present invention is described in detail below with reference to the accompanying drawings.

[0049] like Figures 1-5 As shown, the satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system of the present invention includes: a laser radar transmitting unit, a laser signal receiving system and an optical imaging system.

[0050] in:

[0051] The laser radar transmitting unit includes: a primary reflector 1, a secondary reflector 2, and a laser 3;

[0052] The laser signal receiving system includes: a primary mirror 1, a secondary mirror 2, a first optical path folding mirror 4, a doublet lens group 5, a dichroic mirror 6, a third lens 9, a field stop 10, a second optical path folding mirror 11, a fourth lens 12, a narrowband filter 13, a fifth lens 14, and a photoelectric detection device 15; the dichroic mirror 6 that transmits visible light and reflects laser is the beam splitting unit; the doublet lens group 5 includes, in the optical path direction in sequence: a first lens 5.1 and a second lens 5.2;

[0053] The optical imaging system includes: a primary mirror 1, a secondary mirror 2, a first optical path folding mirror 4, a doublet lens group 5, a dichroic mirror 6, a third optical path folding mirror 7, and an image sensor 8.

[0054] In the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention, the primary mirror 1, the secondary mirror 2, the first optical path folding mirror 4, the doublet lens group 5, and the dichroic mirror 6 are respectively shared by the lidar transmitting unit, the laser signal receiving system, and the optical imaging system.

[0055] As Figure 5 shown, the doublet lens group in the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention includes: a first surface 16 of the doublet lens group, a second surface 17 of the doublet lens group, and a third surface 18 of the doublet lens group.

[0056] As Figures 6-9 shown, the optical performance evaluation of the integrated transceiver optical system of the spaceborne lidar and optical remote sensing camera of the present invention includes: the spot dispersion diagram of the lidar transmitting unit, the spot dispersion diagram of the laser signal receiving system, the spot dispersion diagram of the optical imaging system, and the MTF diagram of the optical imaging system.

[0057] Among them:

[0058] The spot dispersion diagram of the lidar transmitting unit shows the RMS angular deviation of the outgoing beam and the diffraction limit of the angular error of the outgoing beam. Figure 6 The solid circle in the middle represents the diffraction limit of the angular error of the outgoing beam, and the blue spot represents the angular deviation of the actual outgoing beam. It can be seen that the angular deviation of the outgoing beam is much smaller than the diffraction limit, and the quality of the outgoing beam is excellent.

[0059] The spot dispersion diagram of the laser signal receiving system shows the size of the scattered light spot and the size of the Airy disk at the image plane of the laser signal receiving system. Figure 7 The solid circle in the middle represents the size of the Airy disk, and the blue spot represents the degree of dispersion of the actual spot. It can be seen that the radius of the Airy disk is 7.78 μm, and the RMS radius of the actual scattered light spot is less than 7 μm, and the imaging quality is excellent.

[0060] The spot diagram of the optical imaging system shows the size of the diffused spot and the Airy disk size at the image plane of the optical imaging system. Figure 8 The solid circle represents the size of the Airy disk, and the colored spot represents the degree of diffusion of the actual spot. It can be seen that the radius of the Airy disk is 10μm, and the RMS radius of the actual diffused spot is less than 4μm, indicating excellent imaging quality.

[0061] The MTF diagram of the optical imaging system shows the modulation transfer function curves of each field of view of the optical imaging system. Figure 9 It can be seen that the modulation transfer functions of each field of view of the optical imaging system exceed 0.2 at the Nyquist frequency (72 lp / mm), indicating excellent optical system performance.

[0062] Specifically:

[0063] The lidar transmitting unit includes: a primary mirror 1, a secondary mirror 2, and a laser 3; the reflecting surface of the primary mirror 1 is a free-form surface characterized by an XY polynomial based on a paraboloid. The aperture of the reflecting surface is a rectangle of 260mm×360mm, the radius of curvature is -720mm, the substrate material is aluminum-based silicon carbide, and the surface is coated with an anti-reflection film in the 400nm - 750nm band and at a wavelength of 1064nm; the reflecting surface of the secondary mirror 2 is a free-form surface characterized by an XY polynomial based on a paraboloid. The aperture of the reflecting surface is a rectangle of 32mm×44mm, the radius of curvature is -72mm, the substrate material is aluminum-based silicon carbide, and the surface is coated with an anti-reflection film in the 400nm - 750nm band and at a wavelength of 1064nm; the foci of the primary mirror 1 and the secondary mirror 2 coincide, and the two form an off-axis two-mirror afocal system, serving as the laser beam expander lens of the lidar transmitting unit; the laser 3 is a semiconductor-pumped Nd:YAG pulsed laser that can emit a laser beam with a wavelength of 1064nm, with a pulse energy of 1.5mJ, a pulse width of 2ns, a repetition frequency of 10kHz, a spot size of 2mm, and a divergence angle of 0.68mrad. The laser beam emitted by the laser 3 is reflected by the secondary mirror 2 and the primary mirror 1 in sequence, and the beam waist radius is expanded to 20mm, and the divergence angle is reduced to 0.068mrad and then shoots towards the ground. The spot diameter of the laser ground footprint of the satellite at an orbital altitude of 500km is 35m. Simulation shows that the angular deviation of the laser beam emitted by the lidar transmitting unit is much smaller than the diffraction limit, and the quality of the emitted laser beam is excellent.

[0064] The dichroic mirror 6 that transmits visible light and reflects laser is a beam splitting unit. It is located on the common path of the laser signal receiving system and the optical imaging system. It is an optical glass with a dichroic film coated on its surface, used to separate the laser signal with a wavelength of 1064nm from the visible light band, reflect the laser signal by 90° to the third lens 9, and the visible light in the 400 - 750nm band passes through the dichroic mirror 6 and converges to the image sensor 8.

[0065] The receiving field of view of the laser signal receiving system is 0.1 mrad. The laser ground footprint is located at the center of the receiving field of view of the laser signal receiving system. After the ground laser signal is reflected, it is received by the laser signal receiving system. It successively passes through the primary mirror 1, secondary mirror 2, first optical path folding mirror 4, doublet lens group 5, dichroic mirror 6, third lens 9, field stop 10, second optical path folding mirror 11, fourth lens 12, narrowband filter 13 and fifth lens 14, and then is received by the photoelectric detection device 15. The primary mirror 1 and the secondary mirror 2 jointly form the optical receiving antenna of the laser signal receiving system; The first optical path folding mirror 4 is located 340 mm behind the secondary mirror 2 along the optical axis, with an aperture of 44 mm × 52 mm, and is coated with an anti-reflection film in the 400 nm - 750 nm band and at the 1064 nm wavelength. Its function is to deflect the optical path by 90° and reduce the system volume; The doublet lens group 5 includes a first lens 5.1 and a second lens 5.2. It is located 100 mm behind the first optical path folding mirror 4 along the optical axis, and its function is to converge the light. The material of the first lens 5.1 is calcium fluoride, and the material of the second lens 5.2 is the flint glass H-LAK7A produced by Chengdu Guangming. The two materials effectively correct the chromatic aberration of the optical system and improve the imaging quality. The first surface 16 of the doublet lens group 5 is the front surface of the first lens 5.1, with an even aspheric surface type, a curvature radius of -1979.706 mm, the second surface 17 is the rear surface of the first lens 5.1, with a spherical surface type, a curvature radius of -64.796 mm, the third surface 18 is the rear surface of the second lens 5.2, with an even aspheric surface type, a curvature radius of -98.223 mm; The central thickness of the first lens 5.1 is 6 mm, and the central thickness of the second lens 5.2 is 3 mm; The dichroic mirror 6 is located 200 mm behind the doublet lens group 5 along the optical axis; The third optical path folding mirror 7 is located 60 mm behind the dichroic mirror 6 along the optical axis, and is coated with an anti-reflection film in the 400 nm - 750 nm band. Its function is to deflect the optical path by 90° and reduce the system volume; The third lens 9 is located 20 mm behind the dichroic mirror 6 along the optical axis (at this time, the optical axis of the laser signal receiving system has been deflected by 90°). The material of the third lens 9 is fused silica glass (F_SILICA) with high transmittance in the near infrared. The front surface of the third lens 9 is spherical, with a curvature radius of 40.527 mm, the rear surface is spherical, with a curvature radius of 341.323 mm, and the central thickness is 4 mm; The field stop 10 is located 54.5 mm behind the third lens 9 along the optical axis (the position of the primary imaging plane of the laser signal receiving system). The diameter of its central hole is about 0.15 mm, which plays a role in restricting the off-axis field of view and filtering the stray light with a field angle greater than 0.1 mrad in the laser signal receiving channel; The second optical path folding mirror 11 is located 9. behind the field stop 10 along the optical axis.At a position of 2 mm, the surface is coated with an anti-reflection film with a wavelength of 1064 nm, which is used to deflect the optical path by 90° and reduce the volume of the system; the fourth lens 12 is located at a position 20 mm behind the second optical path folding mirror 11 along the optical axis, and its function is to converge the divergent light beam into a parallel light beam, facilitating the narrowband filter to achieve precise filtering; the material of the fourth lens 12 is fused silica glass (F_SILICA), the front surface of the fourth lens 12 is a spherical surface with a radius of curvature of 29.609 mm, the rear surface is an even aspherical surface with a radius of curvature of -23.477 mm, and the central thickness is 3 mm; the narrowband filter 13 is located at a position 2 mm behind the fourth lens 12 along the optical axis, allowing infrared signals with wavelengths in the range of 1064 ± 0.4 nm to pass through, reducing the background light noise generated by the sun, and improving the signal-to-noise ratio of lidar signal acquisition; the fifth lens 14 is located at a position 2 mm behind the narrowband filter 13 along the optical axis, and its function is to converge the parallel light to the photodetector device. The material of the fifth lens 14 is fused silica glass (F_SILICA), the front surface of the fifth lens 14 is an even aspherical surface with a radius of curvature of 36.964 mm, the rear surface radius of curvature is -21.775 mm, and the central thickness is 3 mm; the photodetector device 15 uses InGaAs-APD (indium gallium arsenide avalanche photodiode), which is set at a position 29.167 mm behind the fifth lens 14 along the optical axis (the imaging side of the laser signal receiving system) to receive the 1064 nm wavelength laser signal transmitted through the fifth lens 14 and generate the target three-dimensional information. InGaAs-APD uses InGaAs (indium gallium arsenide) as the absorption layer material and InP (indium phosphide) as the multiplication layer material, and its working band is 800 nm to 1750 nm, and it has a high quantum efficiency for lasers with a wavelength of 1064 nm. Through simulation, it shows that the Airy disk radius of the laser signal receiving system is 7.78 μm, and the RMS radius of the actual diffused light spot is less than 7 μm, and the imaging quality is excellent.

[0066] The optical imaging system includes, sequentially arranged from the object surface to the image surface: a primary mirror 1, a secondary mirror 2, a first optical path folding mirror 4, a doublet lens group 5, a dichroic mirror 6, a third optical path folding mirror 7, and an image sensor 8. The primary mirror 1 and the secondary mirror 2 together form the optical receiving antenna of the optical imaging system; the image sensor 8 uses CMOS (complementary metal oxide semiconductor image sensor), which is set on the imaging side of the optical imaging system and is used to receive visible light ground object information in the 400 - 750 nm band and generate a two-dimensional image of the target. The sensor size is 18.2 × 6.1 mm, and the pixel size is 7 μm. Through simulation, it shows that the Airy disk radius of the optical imaging system is 10 μm, and the RMS radius of the actual diffused light spot is less than 4 μm, and the imaging quality is excellent; the modulation transfer function of each field of view of the optical imaging system exceeds 0.2 at the Nyquist frequency (72 lp / mm), and the optical system performance is excellent.

[0067] In the above embodiments, in the present invention, the primary mirror 1 and the secondary mirror 2 in the transceiver integrated optical system of the spaceborne lidar and the optical remote sensing camera are designed as free-form surfaces to increase more optimization degrees of freedom. Aiming at the asymmetry characteristics of the system in the sagittal direction, a free-form surface characterized by the XY polynomial is used to correct the aberration. The surface height of the free-form surface is defined by superimposing the Taylor polynomial on the quadratic basis:

[0068]

[0069] where k is the conic coefficient; c is the reciprocal of the vertex curvature radius; N is the total number of polynomial coefficients in the series; A i is the coefficient of the i-th XY polynomial.

[0070] The XY polynomial free-form surface parameters of the primary mirror in the above embodiments are shown in Table 1 (the normalized radius is taken as 100):

[0071] Table 1 XY polynomial free-form surface parameters of the primary mirror in the above embodiments

[0072] Item <![CDATA[Coefficient A i > Item <![CDATA[Coefficient A i > <![CDATA[X 1 Y 0 > -0.102 <![CDATA[X 3 Y 1 > 0 <![CDATA[X 0 Y 1 > 0.044 <![CDATA[X 2 Y 2 > -3.859E-005 <![CDATA[X 2 Y 0 > 0.027 <![CDATA[X 1 Y 3 > 0 <![CDATA[X 1 Y 1 > 0 <![CDATA[X 0 Y 4 > 0 <![CDATA[X 0 Y 2 > 0.017 <![CDATA[X 5 Y 0 > 0 <![CDATA[X 3 Y 0 > -1.115E-03 <![CDATA[X 4 Y 1 > -7.979E-007 <![CDATA[X 2 Y 1 > 1.539E-005 <![CDATA[X 3 Y 2 > 0 <![CDATA[X 1 Y 2 > -1.116E-003 <![CDATA[X 2 Y 3 > 4.416E-006 <![CDATA[X 0 Y 3 > -9.831E-005 <![CDATA[X 1 Y 4 > 0 <![CDATA[X 4 Y 0 > 0 <![CDATA[X 0 Y 5 > 0

[0073] The XY polynomial free-form surface parameters of the secondary mirror in the above embodiments are shown in Table 2 (the normalized radius is taken as 100):

[0074] Table 2 XY polynomial free-form surface parameters of the secondary mirror in the above embodiments

[0075] Item <![CDATA[Coefficient A i > Item <![CDATA[Coefficient A i > <![CDATA[X 1 Y 0 > -0.402 <![CDATA[X 3 Y 1 > 0 <![CDATA[X 0 Y 1 > 0.439 <![CDATA[X 2 Y 2 > 0 <![CDATA[X 2 Y 0 > 2.689 <![CDATA[X 1 Y 3 > 0 <![CDATA[X 1 Y 1 > 0 <![CDATA[X 0 Y 4 > 0 <![CDATA[X 0 Y 2 > 1.695 <![CDATA[X 5 Y 0 > 0 <![CDATA[X 3 Y 0 > 0 <![CDATA[X 4 Y 1 > 0 <![CDATA[X 2 Y 1 > 0.221 <![CDATA[X 3 Y 2 > 0 <![CDATA[X 1 Y 2 > 0 <![CDATA[X 2 Y 3 > 0 <![CDATA[X 0 Y 3 > 0.220 <![CDATA[X 1 Y 4 > 0 <![CDATA[X 4 Y 0 > -0.019 <![CDATA[X 0 Y 5 > 0

[0076] In the above embodiments, in the present invention, the first surface 16 of the doublet lens group, the third surface 18 of the doublet lens group, the rear surface of the fourth lens 12, and the front surface of the fifth lens 14 in the transceiver integrated optical system of the spaceborne lidar and the optical remote sensing camera are designed as even aspheres, so as to effectively correct spherical aberration and improve the imaging quality of the system. The surface height is described as follows:

[0077]

[0078] where k is the conic coefficient; c is the reciprocal of the vertex curvature radius; r is the radial coordinate in lens units, α 4 、α 6 、α 8 、α 10 are high-order aspheric coefficients.

[0079] The even aspheric parameter lists used in the above embodiments are shown in Table 3 below:

[0080] Table 3 Even aspheric parameters in the above embodiments

[0081]

[0082] Simulations show that the spaceborne lidar and the integrated transceiver optical system of the optical remote sensing camera of the present invention are practical and effective.

[0083] For the integrated transceiver optical system of the spaceborne lidar and the optical remote sensing camera of the present invention, a common aperture design is adopted for the optical remote sensing camera, the lidar transmitting system and the receiving system, avoiding the transceiver matching problem caused by the separate design of the laser transmitting system and the receiving system. At the same time, the system integrates the active and passive detection capabilities of the spaceborne lidar and the optical remote sensing camera, ensuring the spatio-temporal consistency of multi-source remote sensing images.

[0084] Existing spaceborne lidars generally adopt a structural scheme in which the transmitting optical system and the receiving optical system are separated. Transceiver matching is carried out through an optical axis monitoring camera, a laser footprint camera and an offset angle adjustment mechanism to ensure that the laser footprint is located at the center of the receiving field of view, thereby maximizing the reception efficiency of the target scattering signal. However, this design increases the complexity, volume and mass of the system, which is not conducive to the optimized integration of the spaceborne platform. The integrated transceiver optical system of the spaceborne lidar and the optical remote sensing camera of the present invention uses an off-axis two-mirror afocal telescope as the common aperture optical antenna, enabling the far-field spot position of the laser beam to be accurately aligned with the center of the receiving field of view, fundamentally eliminating the transceiver axis matching error. Therefore, there is no need to additionally configure an optical axis monitoring camera, a laser footprint camera and an offset angle adjustment mechanism for transceiver matching, simplifying the system structure and improving the system integration level.

[0085] For the integrated transceiver optical system of the spaceborne lidar and the optical remote sensing camera of the present invention, the primary mirror and the secondary mirror are shared for the three channels of optical remote sensing, laser emission and laser reception, greatly improving the system integration level, reducing the volume, weight and cost of the equipment, adapting to the spaceborne remote sensing imaging environment, avoiding the problem of installation volume limitation on the satellite platform, and extending the operation time of the remote sensing satellite.

[0086] For the integrated transceiver optical system of the spaceborne lidar and the optical remote sensing camera of the present invention, multiple optical path folding mirrors are used to achieve an optimized balance between the system volume and performance. Its overall envelope size is 490 mm (length) × 260 mm (width) × 420 mm (height), and the mass ≤ 15 kg. At a satellite orbit altitude of 500 km, the system can achieve a ground pixel resolution of 1 m for optical remote sensing (MTF@Nyquist > 0.2) and a range resolution of 0.3 m for the lidar.

[0087] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system, characterized in that: The invention comprises: a main reflector (1), a secondary reflector (2), a first light path folding reflector (4), a doublet lens group (5), and a dichroic mirror (6) which are arranged in sequence in the direction of the light path; the focal points of the main reflector (1) and the secondary reflector (2) are overlapped; The optical system also includes: a laser radar transmitting unit, a laser signal receiving system and an optical imaging system; wherein: The laser radar transmitting unit comprises: a laser (3); The laser signal receiving system comprises: a third lens (9), a field aperture (10), a second optical path folding reflector (11), a fourth lens (12), a narrow band filter (13), a fifth lens (14) and a photoelectric detection device (15) which are arranged in sequence in the direction of the optical path; The optical imaging system comprises: a third optical path folding reflector (7) and an image sensor (8) which are arranged in sequence in the direction of the optical path; the image sensor (8) is used to receive visible light ground object information and generate a two-dimensional image of the target; The laser beam emitted by the laser (3) is reflected by the secondary reflector (2) and the primary reflector (1) in sequence, and then the beam waist radius is expanded, the divergence angle is reduced, and the laser beam is emitted toward the ground; The dichroic mirror (6) is used to separate the laser signal from the visible light band, so that the laser signal is folded and reflected onto the third lens (9), and the visible light is converged to the image sensor (8) through the dichroic mirror (6) and the third optical path folding reflector (7); After being reflected, the ground laser signal is received by the laser signal receiving system, and then passes through a primary reflector (1), a secondary reflector (2), a first optical path folding reflector (4), a double cemented lens group (5), a dichroic mirror (6), a third lens (9), a field stop (10), a second optical path folding reflector (11), a fourth lens (12), a narrowband filter (13) and a fifth lens (14) in sequence, and then is received by a photoelectric detection device (15).

2. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The reflective mirror surface of the main reflector (1) is a free-form surface characterized by an XY polynomial with a parabola as the base. The diameter of the reflective mirror surface is a rectangle of 260 mm×360 mm, and the radius of curvature is -720 mm.

3. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The reflective mirror surface of the secondary reflector (2) is a free-form surface characterized by an XY polynomial with a parabola as the base. The diameter of the reflective mirror surface is a rectangle of 32 mm×44 mm, and the radius of curvature is -72 mm.

4. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The laser (3) is a semiconductor-pumped Nd:YAG pulse laser that emits a 1064nm wavelength laser beam, with a pulse energy of 1.5mJ, a pulse width of 2ns, a repetition frequency of 10kHz, a spot size of 2mm, and a divergence angle of 0.68mrad.

5. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The double cemented lens group (5) comprises, in sequence in the direction of the optical path: a first lens (5.1) and a second lens (5.2); The center thickness of the first lens (5.1) is 6 mm, and the center thickness of the second lens (5.2) is 3 mm.

6. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The dichroic mirror (6) is an optical glass with a dichroic film coated on the surface.

7. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to claim 1, characterized in that: The image sensor (8) is a CMOS and is arranged on the imaging side of the optical imaging system.

8. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to any one of claims 1 to 7, characterized in that: The visible light band is 400-750nm.

9. The satellite-borne laser radar and optical remote sensing camera transceiver integrated optical system according to any one of claims 1 to 7, characterized in that: The laser ground footprint is located at the center of the receiving field of view of the laser signal receiving system.

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