A system and method suitable for asteroid hyperspectral polarization characteristic flyby detection

Abstract

This invention discloses a system and method for flyby detection of asteroid hyperspectral polarization characteristics, belonging to the field of optical detection technology. The system comprises an orthogonal mirror module, a polarization spectral modulation module, a front imaging lens, a microlens array, a collimating lens, a spectral dispersive element, a focusing lens, an image detector, and a data processing unit. The detection system uses the orthogonal mirror module to enable a satellite platform to track and stare at the asteroid during high-speed flyby. It also introduces a microlens array to replace the slit in a traditional imaging spectrometer, and, combined with the polarization spectral modulation module, simultaneously acquires a two-dimensional image, hyperspectral, and polarization information of the target asteroid in a single measurement. This invention achieves multi-angle hyperspectral polarization snapshot imaging detection of asteroids during high-speed flyby.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, specifically relating to a system and method for flyby detection of the hyperspectral polarization characteristics of asteroids. Background Technology

[0002] As "living fossils" of the early formation and evolution of the solar system, asteroids not only retain their original chemical composition and physical information, but also contain significant resources such as minerals and water ice. Research shows that asteroids are rich in rare resources such as iron, nickel, platinum group metals, and water ice, possessing extremely high application value and becoming important targets for deep space exploration and resource discovery. Simultaneously, asteroids contain initial information about the formation and evolution of the universe; by probing their characteristics, it is hoped that our understanding of the origin of the solar system and astrophysical processes can be advanced. Therefore, exploring the surface characteristics, resource types, and distribution of asteroids is an essential and indispensable part of future research on the origin of celestial bodies and the utilization of asteroid resources. Common asteroid exploration methods include flyby missions, orbital orbits, and rendezvous missions. Among these, flyby missions, through the selection of target asteroids and reasonable orbital design, can achieve the successive exploration of multiple target asteroids with a single launch, making it a highly efficient exploration method and very suitable for deep space missions such as asteroid resource surveys.

[0003] Deep space resource exploration requires acquiring as comprehensive multi-source information about unknown celestial bodies as possible under limited conditions. Therefore, multi-dimensional information fusion detection is an inevitable choice for resource exploration. Hyperspectral polarization imaging can simultaneously acquire images, spectra, and polarization information of targets, greatly expanding the dimensions of optical detection and enabling a more comprehensive acquisition of the physicochemical properties and resource distribution characteristics of asteroid surfaces. Typically, visible and short-wave infrared spectral measurements can cover the characteristic identification bands of most mineral resources contained in asteroids (including silicates, hydrates, water ice, iron-nickel metals, etc.). Combined with polarization detection of the target surface's structure and scattering characteristics, it can not only acquire physical characteristics such as grain size distribution, roughness, and microstructure, but also improve the differentiation of homogeneous materials. This allows for more reliable mineral phase identification, hydrate detection, and differentiation of metal enrichment areas and rough / fine-grained coating states, which is crucial for assessing the exploitability of asteroid resources and determining engineering design parameters.

[0004] During its flyby of the asteroid, the probe experienced a long-distance approach, a closest-point flyby, and then a period of moving away from the asteroid, with the observed phase angle (the angle between the Sun, the asteroid, and the probe) gradually changing from high to low and then to medium-high. To obtain the asteroid's surface physicochemical properties as accurately and comprehensively as possible, the probe is typically required to measure the target's spectral polarization information at various observation phase angles, thereby constructing polarization-phase curves for different spectral bands. The characteristic parameters of these polarization-phase curves are then used to invert the asteroid's surface properties. Therefore, the probe needs to continuously track and observe the asteroid during its high-speed flyby, and take snapshot-like images from different observation angles. However, during high-speed flight, satellite platforms cannot accurately point at asteroids in a short time through attitude adjustments, which requires the detection system to have scanning and tracking capabilities. In addition, existing slit imaging spectrometers can only acquire one-dimensional image information in a single exposure, and require successive fine sweeping of each part of the target to obtain a complete two-dimensional image spectrum, which is difficult to achieve during high-speed flyby observations by the probe. As for the acquisition of polarization information, traditional time-division and amplitude-division polarization detection methods are usually used, which have disadvantages such as poor real-time performance, low measurement accuracy for dynamic targets, high requirements for inter-channel calibration accuracy, and large size. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a system and method suitable for flyby detection of asteroid hyperspectral polarization characteristics. The system comprises an orthogonal mirror module, a polarization spectral modulation module, a front imaging lens, a microlens array, a collimating lens, a spectral dispersive element, a focusing lens, an image detector, and a data processing unit. The orthogonal mirror module enables the satellite platform to track and observe the asteroid during high-speed flyby. The microlens array replaces the slit in traditional imaging spectrometers. Combined with the polarization spectral modulation module, a single measurement simultaneously acquires a two-dimensional image, hyperspectral, and polarization information of the target asteroid, enabling multi-angle hyperspectral polarization snapshot imaging detection of the asteroid during high-speed flyby. This invention allows for continuous tracking and observation of asteroids during flyby detection, achieving multi-phase angle measurements, and simultaneously acquiring multiple dimensions of detection information, including a two-dimensional image, hyperspectral, and polarization information, in a single exposure.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A system for flyby detection of asteroid hyperspectral polarization characteristics includes an orthogonal mirror module, a polarization spectral modulation module, a front imaging lens, a microlens array, a collimating lens, a spectral dispersive element, a focusing lens, an image detector, and a data processing unit. The orthogonal mirror module receives reflected light from the asteroid and transmits it to the polarization spectral modulation module. The polarization spectral modulation module modulates the polarization information of the received light onto the spectral dimension to form a modulated beam and transmits it to the front imaging lens. The front imaging lens acquires two-dimensional image information of the target and transmits it to the microlens array. The microlens array, located at the focal point of the front imaging lens, segments the received image into unit images and transmits them to the collimating lens. The collimating lens collimates the unit images and transmits them to the spectral dispersive element. The spectral dispersive element disperses the collimated unit images and transmits them to the focusing lens. The focusing lens converges the dispersed beam and transmits it to the image detector. The image detector images and records the converged beam and transmits it to the data processing unit. The data processing unit performs polarization spectral demodulation and image reconstruction on the received image.

[0008] This invention also provides a method for flyby detection of asteroid hyperspectral polarization characteristics, employing the aforementioned system for flyby detection of asteroid hyperspectral polarization characteristics, comprising: an orthogonal reflector module continuously tracking and pointing at the asteroid during high-speed flyby of a satellite platform, receiving the asteroid's reflected light and transmitting it to a polarization spectrum modulation module; the polarization spectrum modulation module modulates the polarization information of the received light onto the spectral dimension, forming a modulated beam and transmitting it to a front imaging lens; the front imaging lens acquires a two-dimensional image of the asteroid and transmits it to a microlens array; the microlens array segments the target image into unit images with different fields of view and transmits them to a collimating lens; the collimating lens collimates the unit images and transmits them to a spectral dispersion element; the spectral dispersion element disperses the unit images into a spectrum and transmits it to a focusing lens; the focusing lens focuses the dispersive spectrum of the unit images and transmits it to an image detector; the image detector receives the beam and records the data, transmitting it to a data processing unit; the data processing unit performs polarization spectrum demodulation and image reconstruction on the received image, restoring the asteroid's two-dimensional image, hyperspectral information, and polarization information.

[0009] Beneficial effects:

[0010] This invention uses an orthogonal reflector module to set an appropriate scanning rate to counteract the effects of satellite platform motion, allowing the detection system to continuously point its observation direction at the asteroid. This enables continuous multi-angle observation of the asteroid, thereby obtaining a more complete polarization-phase curve. Simultaneously, the detection system introduces a microlens array to replace the slit in a traditional imaging spectrometer. Combined with a polarization spectral modulation module, it can simultaneously acquire two-dimensional image information of the target and corresponding hyperspectral and polarization information in a single measurement. Combining the advantages of these two technologies, this invention can perform hyperspectral polarization snapshot imaging of asteroids from multiple angles during high-speed satellite flybys. It boasts advantages such as high integration, rich detection information, and high robustness, which is of great significance for the study of asteroid surface characteristics and the exploration of resource types and distribution. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the optical structure of a system for flyby detection of hyperspectral polarization characteristics of asteroids according to the present invention.

[0012] The attached figures are labeled as follows: orthogonal mirror module 1; first mirror 1-1; second mirror 1-2; polarization spectrum modulation module 2; achromatic 1 / 4 waveplate 2-1; multi-level waveplate 2-2; polarizer 2-3; front imaging lens 3; microlens array 4; collimating lens 5; spectral dispersive element 6; focusing lens 7; image detector 8; and data processing unit 9. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0014] like Figure 1 As shown, a system for flyby detection of hyperspectral polarization characteristics of asteroids according to the present invention includes an orthogonal mirror module 1, a polarization spectrum modulation module 2, a front imaging lens 3, a microlens array 4, a collimating lens 5, a spectral dispersive element 6, a focusing lens 7, an image detector 8, and a data processing unit 9.

[0015] The orthogonal mirror module 1 is located at the front of the optical system, receiving the reflected light from the asteroid and transmitting it to the polarization spectrum modulation module 2. The orthogonal mirror module 1 includes a first mirror 1-1 and a second mirror 1-2. To counteract the polarization effect of the mirrors, the surfaces of the first mirror 1-1 and the second mirror 1-2 must be orthogonal. Therefore, the first mirror 1-1 needs to be configured as follows: Figure 1The rotating shaft is rotated 90°. When the external light beam is incident, it forms a 45° angle with the normal of the first reflecting mirror 1-1. After reflection, it reaches the second reflecting mirror 1-2, where the incident light also forms a 45° angle with its normal. The first reflecting mirror 1-1 and the second reflecting mirror 1-2 are connected to their respective rotating shafts, and a motor drives the scanning mirror to rotate. By setting an appropriate scanning rate to counteract the influence of platform motion, the observation direction of the detection system can be continuously pointed at the asteroid. This not only ensures a stable exposure time for the detection system but also allows for continuous multi-angle observation of the asteroid during flight, thereby obtaining a more complete polarization-phase curve. The first reflecting mirror 1-1 and the second reflecting mirror 1-2 remain orthogonal during the scanning process. The polarization change introduced by the first reflecting mirror 1-1 to the incident light is canceled out by the second reflecting mirror 1-2, providing good polarization compensation. Furthermore, the subsequent optics of the scanning mirror do not require rotation, giving the system good mechanical stability.

[0016] The polarization spectral modulation module 2 comprises an achromatic quarter-wave plate 2-1, a multi-level wave plate 2-2, and a polarizer 2-3 arranged sequentially. The fast axis of the achromatic quarter-wave plate 2-1 and the fast axis of the multi-level wave plate 2-2 form a 45° angle, and the optical transmission axis of the polarizer 2-3 is parallel to the fast axis of the quarter-wave plate. The polarization spectral modulation module 2 modulates the polarization information of the asteroid's reflected light onto the spectral dimension, forming a modulated beam, which is then sent to the front imaging lens 3.

[0017] The front imaging lens 3 acquires two-dimensional image information of the distant target asteroid and sends it to the microlens array 4.

[0018] The microlens array 4 is located at the focal point of the front imaging lens 3. The microlens array 4 receives the target image and performs field-of-view segmentation. Each microlens unit forms a microaperture behind it, which replaces the slit of a traditional imaging spectrometer as the entrance aperture. The microlens array 4 segments the target image into several unit images and sends them to the collimating lens 5. By rotating the microlens array 4, the dispersive spectrum is rotated on the image detector 8, ensuring that the spectrum of a particular microlens unit falls within the gaps in the spectra of its surrounding microlens units. This prevents the dispersive spectra of each microlens unit from overlapping on the detector image plane. The rotation angle of the microlens array 4 is related to parameters such as the number of microlens units, the spectral resolution of the detection system, the number of detector pixels, and the pixel size.

[0019] The collimating lens 5 collimates the unit images of the target image in different fields of view and sends them to the spectral dispersive element 6.

[0020] The spectral dispersive element 6 is a beam-splitting optical element such as a transmission grating or a beam-splitting prism. The spectral dispersive element 6 disperses the individual unit images and sends the dispersed monochromatic beam to the focusing lens 7.

[0021] The focusing lens 7 converges the light beam and sends it to the image detector 8.

[0022] Image detector 8 records the image of the converging beam and sends the data to data processing unit 9.

[0023] Data processing unit 9 performs polarization spectrum demodulation on the received image and reconstructs the polarization spectrum image to restore the two-dimensional image, hyperspectral and polarization information of the asteroid.

[0024] This invention also provides a method for flyby detection of asteroid hyperspectral polarization characteristics, comprising:

[0025] Each of the orthogonal reflector modules is connected to a corresponding rotating shaft. The orthogonal reflectors are driven to rotate by a motor. During the high-speed flyby of the satellite platform, the orthogonal reflectors continuously track and point towards the asteroid, receive the reflected light from the asteroid, and send it to the polarization spectrum modulation module.

[0026] The polarization spectral modulation module modulates the polarization information of the asteroid's reflected light onto the spectral dimension, forming a modulated beam that is sent to the front imaging lens.

[0027] The front imaging lens acquires images of the asteroid and sends them to the microlens array;

[0028] The microlens array is placed at the focal point of the front imaging lens, and the image of the asteroid target is cut into several unit images with different fields of view and then sent to the collimating lens;

[0029] The collimating lens collimates the unit images of different fields of view and sends them to the spectral dispersive element;

[0030] The spectral dispersive element disperses each unit image into a corresponding spectrum and sends it to the focusing lens;

[0031] The focusing lens focuses the dispersive spectrum of the unit image and sends it to the image detector;

[0032] The image detector receives the focused light beam and sends it to the data processing unit;

[0033] The data processing unit performs polarization spectral demodulation and polarization spectral image reconstruction on the images received by the image detector to restore the two-dimensional image, hyperspectral and polarization information of the asteroid.

[0034] Furthermore, the orthogonal reflector module includes a first reflector and a second reflector, the surfaces of which are set in an orthogonal state. The first reflector needs to be aligned as follows: Figure 1 The rotating shaft is rotated 90°, and the first and second reflecting mirrors remain orthogonal throughout the scanning process.

[0035] Furthermore, the polarization spectral modulation module includes an achromatic quarter-wave plate, a multi-level wave plate, and a polarizer. The fast axis of the achromatic quarter-wave plate and the fast axis of the multi-level wave plate form an angle of 45°, and the optical transmission axis of the polarizer is parallel to the fast axis of the quarter-wave plate.

[0036] In summary, this invention solves two major technical challenges in asteroid flyby detection: (1) it is difficult for the satellite platform to accurately point to the target asteroid during high-speed flyby, and (2) it is difficult for traditional polarization spectral imaging systems to simultaneously acquire two-dimensional images, hyperspectral and polarization information of the target asteroid in a single measurement. This invention can perform hyperspectral polarization snapshot imaging detection of the asteroid from multiple angles during the flyby, and has advantages such as high integration, rich detection information and high robustness. It is of great significance for the study of asteroid surface characteristics and the exploration of resource types and distribution.

Claims

1. A system suitable for flyby detection of asteroid hyperspectral polarization characteristics, characterized in that, It includes an orthogonal mirror module, a polarization spectral modulation module, a front imaging lens, a microlens array, a collimating lens, a spectral dispersive element, a focusing lens, an image detector, and a data processing unit; the orthogonal mirror module receives the light reflected by the asteroid and sends it to the polarization spectral modulation module; The polarization spectral modulation module modulates the polarization information of the received light onto the spectral dimension to form a modulated beam and sends it to the front imaging lens; A front imaging lens acquires two-dimensional image information of the target and sends it to a microlens array. The microlens array, located at the focal point of the front imaging lens, segments the received image into unit images and sends them to a collimating lens. The collimating lens collimates the unit images and sends them to a spectral dispersion element. The spectral dispersion element disperses the collimated unit images and sends them to a focusing lens. The focusing lens converges the dispersed beam and sends it to an image detector. The image detector records the converged beam and sends it to a data processing unit. The data processing unit performs polarization spectral demodulation and image reconstruction on the received image.

2. The system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 1, characterized in that, The orthogonal reflector module includes a first reflector and a second reflector. The surfaces of the first reflector and the second reflector are set in an orthogonal state. The first reflector and the second reflector are respectively connected to a rotating shaft and driven to rotate by a motor. The first reflector and the second reflector always maintain an orthogonal state during the scanning process.

3. The system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 1, characterized in that, The polarization spectrum modulation module includes an achromatic quarter-wave plate, a multi-level wave plate, and a polarizer arranged sequentially along the optical path. The fast axis of the achromatic quarter-wave plate forms a 45° angle with the fast axis of the multi-level wave plate, and the optical transmission axis of the polarizer is parallel to the fast axis of the quarter-wave plate.

4. A system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 1, characterized in that, The microlens array is located at the focal point of the front imaging lens, receives the target image and forms a micro-aperture at its focal plane through the microlens unit, which serves as the incident aperture of the spectrometer.

5. A system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 2, characterized in that, The polarization change introduced by the first reflecting mirror on the incident light is canceled out by the second reflecting mirror, thus achieving polarization compensation.

6. A system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 4, characterized in that, The microlens array is rotated, and the rotation angle is related to the number of microlens arrays, the system spectral resolution, the number of detector pixels, and the pixel size. This is used to prevent the spectrum from overlapping on the detector image plane after dispersion.

7. A system for flyby detection of asteroid hyperspectral polarization characteristics according to claim 1, characterized in that, The spectral dispersive element is a transmission grating or a beam splitter.

8. A method for flyby detection of hyperspectral polarization characteristics of asteroids, employing the system for flyby detection of hyperspectral polarization characteristics of asteroids as described in any one of claims 1-7, characterized in that, include: The orthogonal reflector module continuously tracks and points at the asteroid during the high-speed flyby of the satellite platform, receives the light reflected by the asteroid and sends it to the polarization spectrum modulation module; The polarization spectral modulation module modulates the polarization information of the received light onto the spectral dimension, forming a modulated beam and sending it to the front imaging lens. The front imaging lens acquires a two-dimensional image of the asteroid and sends it to the microlens array. The microlens array segments the target image into unit images with different fields of view and sends them to the collimating lens. The collimating lens collimates the unit images and sends them to the spectral dispersion element. The spectral dispersion element disperses the unit images into a spectrum and sends it to the focusing lens. The focusing lens focuses the dispersive spectrum of the unit images and sends it to the image detector. The image detector receives the beam, records the data, and sends it to the data processing unit. The data processing unit performs polarization spectral demodulation and image reconstruction on the received image to restore the two-dimensional image, hyperspectral data, and polarization information of the asteroid.

9. A method for flyby detection of hyperspectral polarization characteristics of asteroids according to claim 8, characterized in that, The orthogonal reflector module includes a first reflector and a second reflector. The surfaces of the first reflector and the second reflector are set in an orthogonal state. The first reflector and the second reflector are respectively connected to a rotating shaft and driven to rotate by a motor. The first reflector and the second reflector always maintain an orthogonal state during the scanning process.

10. A method for flyby detection of hyperspectral polarization characteristics of asteroids according to claim 8, characterized in that, Polarization spectral modulation is achieved by sequentially arranging an achromatic quarter-wave plate, a multi-stage wave plate, and a polarizer along the optical path. The fast axis of the achromatic quarter-wave plate forms a 45° angle with the fast axis of the multi-stage wave plate, and the optical transmission axis of the polarizer is parallel to the fast axis of the quarter-wave plate.

Images