A linear array pushbroom imaging spectrometer system based on fiber optics

Abstract

The application relates to a linear array push-broom imaging spectrum system based on an optical fiber device, which comprises a spectrometer, an objective lens and an optical switch. The application fully utilizes the field of view of the objective lens itself, couples the second optical fiber of the linear array to the focal plane of the objective lens, and fills the one-dimensional field of view of the objective lens. The second optical fiber is connected with the optical switch, the on-off of the corresponding sub-optical fiber of different fields of view is rapidly controlled through the optical switch, the flight movement of the carrier platform is matched, different fields of view of the same high-speed spectrometer can be rapidly time-shared and detected, and the push-broom imaging detection effect similar to the imaging spectrum detection effect is realized. Compared with the conventional linear array swing-scan imaging spectrum system, the optical fiber array and the optical switch device are adopted to replace the swing-scan mechanism, the swing-scan mechanical movement part is not needed, the volume and weight of the imaging spectrum system are greatly reduced, and the influence on the flight stability of the carrier platform is extremely small.

Description

Technical Field

[0001] This invention relates to the field of spectral imaging instruments, and more specifically, to a linear array pushbroom imaging spectral system based on fiber optic devices. Background Technology

[0002] Spectral measurement and analysis technology is already a fundamental technology in the study of the composition and structure of matter. Spectral imaging technology, which combines imaging functions, can simultaneously acquire spatial and spectral information of a target and has become an important research direction in the field of optical remote sensing technology. It has been widely and deeply applied and studied in many fields such as resource exploration, agricultural and forestry remote sensing, water remote sensing, disaster monitoring, and deep space exploration.

[0003] Spectral imaging instruments can be classified into two types based on their imaging principles: swing-broom and push-broom. Swing-broom imaging spectrometers acquire the field of view in the flight direction by observing the aircraft's flight along its orbit, and obtain the field of view perpendicular to the flight track through mechanical scanning imaging. They use linear or area array detectors to receive spectral data for each band. Push-broom imaging spectrometers, on the other hand, acquire the field of view in the flight direction only by observing the aircraft's flight along its orbit, and use large area array detectors to acquire spectral information in the direction of crossing the track.

[0004] Figure 1 The diagram illustrates the structural principle of a typical pushbroom imaging spectrometer. Generally, under the same specifications, the main advantages of pushbroom imaging spectrometers are high imaging detection efficiency, the absence of sweeping motion, relatively simple structure, and small size. Furthermore, the ability to simultaneously acquire pixels along the track reduces the difficulty of image stitching. However, the field of view of a pushbroom imaging spectrometer is limited by the size of the array detector, and large array detectors are very expensive, making it difficult to achieve a large field of view. Additionally, instrument calibration of pushbroom imaging spectrometers is relatively difficult, and spectral bending also exists. In contrast, sweeping imaging spectrometer systems have a relatively complex structure, lower detection efficiency, and more complex sweeping motion control and image stitching processing; however, they offer advantages such as a large field of view and low cost, making them highly promising for application in UAV-borne imaging spectroscopic remote sensing.

[0005] Depending on the detector used, swing-broom imaging spectroscopic systems can be further divided into linear swing-broom systems (see reference). Figure 2 Two types: ) and area array sweeping (see reference) Figure 3 The mechanical scanning and spectroscopic detection sections of an area-array swing-broom imaging spectrometer are similar to those of a linear-array swing-broom spectrometer, such as... Figure 3 The diagram shows the principle of an area array oscillating imaging spectrometer. Compared with linear array oscillating imaging, the area array oscillating imaging mechanism has a lower scanning speed, which reduces the difficulty of designing, assembling, and controlling the oscillating mechanism, and the integration time is longer.

[0006] Currently, linear array push-broom imaging spectral systems have advantages such as low device cost and large field of view due to their detection principle, but they also have drawbacks such as the need for a push-broom mechanism, system complexity, low detection efficiency, and complex image processing. On the other hand, area array push-broom systems have advantages such as relatively simple structure, high scanning efficiency, and high resolution, but area array photodetectors, especially high-performance area array photodetectors in special bands such as ultraviolet and infrared, are expensive, resulting in the high cost of area array push-broom spectral imaging systems.

[0007] Therefore, the existing technology still has shortcomings and needs further improvement. Summary of the Invention

[0008] This invention provides a linear array pushbroom imaging spectral system based on fiber optic devices. To address the above problems, this invention uses fiber optic arrays and optical switching devices to replace the pushbroom mechanism, eliminating the need for mechanical moving parts, significantly reducing the size and weight of the imaging spectral system, and having minimal impact on the flight stability of the carrier platform.

[0009] This will at least address the technical problem of untimely handling of equipment malfunctions.

[0010] According to an embodiment of the present invention, a linear array pushbroom imaging spectral system based on fiber optic devices is provided, comprising the following steps:

[0011] A spectrometer is used to scan and detect the field of view;

[0012] Objective lens, connected to the spectrometer, is used to directly scan the field of view;

[0013] The optical switch is connected to the spectrometer at one end via a first optical fiber and to the objective lens at the other end via a second optical fiber of a linear array.

[0014] The second fiber is composed of several sub-fibers arranged in an array or in parallel, and the second fiber is coupled to the focal plane of the objective lens. Each sub-fiber is used to correspond to a field of view. The length direction of the second fiber optic instrument is parallel to the objective lens, so that the linear array push-broom imaging spectral system can acquire the field of view of the flight direction of the flight equipment and realize the acquisition of spectral information in the direction of track crossing.

[0015] The optical switch switches the field of view via a second optical fiber to enable time-division scanning of multiple fields of view in the spectrometer, thereby improving the scanning efficiency of the imaging spectrometer system.

[0016] Preferably, adjacent sub-fibers are arranged in a one-dimensional seamless connection.

[0017] Preferably, the second optical fiber is arranged in a double-row staggered configuration.

[0018] Preferably, the field of view angles corresponding to the sub-fibers are relatively fixed.

[0019] Preferably, the linear array pushbroom imaging spectral system further includes:

[0020] The detector, connected to the spectrometer, is used to acquire spectral data from each band of the receiving spectrometer.

[0021] Preferably, the detector is a linear array detector.

[0022] Preferably, the optical switch is any one of the following: mechanical, microelectromechanical, thermo-optic, electro-optic, magneto-optic, and acousto-optic switches.

[0023] Preferably, there are several optical switches, and each optical switch corresponds to a sub-optical fiber.

[0024] Preferably, the objective lens is a cemented doublet or a three-part achromatic objective lens.

[0025] The pushbroom-based linear array imaging spectroscopic system in this invention fully utilizes the field of view of the telescope objective itself. The second fiber of the linear array is coupled to the focal plane of the objective, filling its one-dimensional field of view. The second fiber is connected to an optical switch, which rapidly controls the on / off state of the corresponding sub-fibers for different fields of view. Combined with the flight motion of the carrier platform, rapid time-division detection based on different fields of view of the same high-speed spectrometer can be achieved, realizing imaging spectroscopic detection effects similar to pushbroom imaging detection. Compared to conventional linear array pushbroom imaging spectroscopic systems, this invention uses an optical fiber array and optical switch devices to replace the pushbroom mechanism, eliminating the need for mechanical moving parts, significantly reducing the size and weight of the imaging spectroscopic system, and having minimal impact on the flight stability of the carrier platform. Attached Figure Description

[0026] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0027] Figure 1 This is a schematic diagram of the structure of a typical pushbroom hyperspectral imager in the prior art;

[0028] Figure 2 This describes the principle of the linear array oscillating structure of a typical oscillating hyperspectral imager in the prior art.

[0029] Figure 3 This describes the principle of the area array sweeping structure of a typical swing-sweep hyperspectral imager in the prior art.

[0030] Figure 4 This is a schematic diagram of the linear array pushbroom imaging spectral system based on fiber optic devices according to the present invention.

[0031] Figure 5 This is a schematic diagram illustrating the improvement in ground pixels covered by a single push-broom scan and the detection efficiency of the present invention.

[0032] Figure description: 1-Spectrometer, 2-Optical switch, 3-Objective lens, 4-First optical fiber, 5-Second optical fiber, 6-Detector. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] See Figure 4 and Figure 5 According to an embodiment of the present invention, a linear array pushbroom imaging spectral system based on fiber optic devices is provided for field-of-view scanning of flight equipment, comprising:

[0036] Spectrometer 1 is used to detect spectral signals in each field of view;

[0037] Objective lens 3, connected to spectrometer 1, is used to collect light energy from the target scene and couple it into the second optical fiber to scan the field of view;

[0038] Optical switch 2, one end of which is connected to spectrometer 1 via first optical fiber 4, and the other end of which is connected to objective lens 3 via second optical fiber 5 of linear array;

[0039] The second optical fiber 5 is composed of several sub-optical fibers arranged in an array or in parallel, and the second optical fiber 5 is coupled to the focal plane of the objective lens 3. Each sub-optical fiber is used to correspond to a field of view. The length direction of the second optical fiber 5 is parallel to the objective lens 3, so that the linear array push-broom imaging spectral system can acquire the field of view of the flight direction of the flight equipment and realize the acquisition of spectral information in the direction of track crossing.

[0040] The optical switch 2 switches the field of view through the second optical fiber 5 to realize time-division scanning of multiple fields of view of the spectrometer 1 and improve the scanning efficiency of the spectrometer 1.

[0041] The push-broom imaging spectral system based on fiber optic devices in this embodiment of the invention fully utilizes the field of view of the telescope objective lens 3 itself. The second fiber 5 of the linear array is coupled to the focal plane of the objective lens 3, filling the one-dimensional field of view of the objective lens 3. The second fiber 5 is connected to an optical switch 2, which rapidly controls the on / off state of the corresponding sub-fibers for different fields of view. Combined with the flight motion of the carrier platform, rapid time-division detection based on different fields of view of the same high-speed spectrometer 1 can be achieved, realizing imaging spectral detection effects similar to push-broom imaging detection. Compared with conventional linear array push-broom imaging spectral systems, this invention uses a fiber optic array and optical switch 2 to replace the push-broom mechanism, eliminating the need for mechanical moving parts, significantly reducing the size and weight of the imaging spectral system, and having minimal impact on the flight stability of the carrier platform. See also Figure 5 This is a demonstration of the pixel coverage effect of the corresponding bottom surface in multi-line push-scan.

[0042] In one embodiment, reference Figure 4 The adjacent sub-fibers are connected in a one-dimensional, seamless manner. Specifically, Figure 4 The dashed box in the middle illustrates the principle of the linear array push-broom imaging spectral system based on fiber optic devices according to this invention. The fiber array is arranged in a one-dimensional seamless configuration. Due to the presence of an outer cladding layer on the fibers, this "one-dimensional seamless" arrangement is achieved through staggered splicing. The linear fiber array is coupled to the focal plane of the telescope objective 3. By rapidly controlling the on / off switching between each fiber and the spectrometer 1 via an optical switch 2, the one-dimensional field of view corresponding to the linear fiber array can be quickly traversed, completing a single-line target push-broom imaging process. As the airborne platform (flying equipment) moves forward, a large-scale linear array push-broom imaging spectral detection can be achieved.

[0043] To illustrate the beneficial effects of the present invention, the following comparison of the detection efficiency of the present invention and the traditional oscillating sweep spectral imaging system is conducted at the same spatial resolution and spectral resolution level, in order to demonstrate the improvement in imaging spectral detection efficiency of the present invention.

[0044] The designed UAV platform has a flight altitude of 100m, a ground resolution of 1m, a maximum turntable swing speed of 90° / s, and a 40% overlap rate in both scanning directions. The oscillating sweep spectral imaging system measures the spectral range of 1-2.5μm, with a spectral resolution of 12.5nm and an F-number of 4. The spectrometer 1 used has a slit size of 0.05×0.25mm, an optical system efficiency of 0.48, and an average quantum efficiency of 0.85 for the long linear array InGaAs photodetector 6. Under clear conditions, with a ground albedo of 0.3 and an exposure time of 5ms, the analysis imaging spectral system achieves a signal-to-noise ratio of approximately 91 at a wavelength of 2.4μm, which meets the requirements. At this time, the corresponding UAV flight speed is approximately 0.36m / s.

[0045] Under the same UAV platform, the same spectrometer 1 and spatial resolution, when using the solution of this invention, a total of 59 optical fibers are required to cover a 30° spatial field of view (with a 10% field of view overlap rate between optical fibers). At this time, the single frame exposure time is 5ms, the switching time of optical switch 2 is 2ms, and a single line of field of view scanning requires (5+2)*59=413ms. During the scanning time of one line, the UAV flies forward 1*0.6=0.6m (40% field of view overlap rate), so the flight speed is 0.6 / 0.413=1.45m / s.

[0046] Obviously, compared with conventional solutions, the scanning efficiency of the present invention is more than 4 times that of conventional solutions at the same spatial / spectral resolution level, and it does not require mechanical rotation of the scanning device, thus reducing the size and weight of the linear array oscillating imaging spectral system.

[0047] In one embodiment, reference Figure 4 The linear array pushbroom imaging spectral system also includes:

[0048] Detector 6 is connected to spectrometer 1 and is used to acquire spectral data of each band of the receiving spectrometer 1.

[0049] Specifically, compared with a short-wavelength infrared pushbroom imaging spectroscopy system of the same resolution, this invention reduces costs by several times or even more than ten times because it uses a linear InGaAs photodetector 6 instead of a planar detector 6. Therefore, it has a significant cost advantage over planar pushbroom imaging spectroscopy systems. The photodetector 6 in this application can be a linear detector 6.

[0050] In one embodiment, reference Figure 4 The second optical fiber 5 is arranged in a double-row staggered configuration. In other embodiments, in addition to the double-row staggered configuration described above, the arrangement of the optical fiber array can also be changed to other forms, as long as the optical fibers can fill the one-dimensional field of view "seamlessly".

[0051] In one embodiment, reference Figure 4Compared with conventional linear array oscillating imaging spectral systems, the relative positions of each fiber in the linear array fiber array of this invention are fixed, that is, the field of view corresponding to each fiber is relatively fixed during push-broom sampling; compared with traditional linear array oscillating imaging spectral systems, the field of view error during different field of view measurements is greatly reduced, thus reducing the difficulty of image stitching processing and improving the geometric stitching accuracy of images.

[0052] In one embodiment, reference Figure 4 The optical switch 2 device can be selected in various forms. In terms of the implementation principle of the optical switch 2, this application allows for the use of any one of the following optical switches 2: mechanical, micro-electro-mechanical system (MEMS), or based on thermo-optic, electro-optic, magneto-optic, and acousto-optic principles.

[0053] In one embodiment, reference Figure 4 Optical switches 2 can be classified by their form, such as 1-to-1, 1-to-N, and M-to-N. Depending on the specific system parameters, these optical switches 2 can be used in various imaging spectral systems. This application uses a plurality of optical switches 2, with each optical switch 2 corresponding one-to-one with a sub-fiber. This application uses a second fiber 5 consisting of a seven-fiber array or arranged in parallel.

[0054] This application couples several sub-fibers to the focal plane of objective lens 3 to correspond to multiple fields of view. An optical switch 2 then switches between the sub-fibers, enabling rapid switching of the on / off state of each field of view's sub-fiber. Specifically, the implementation of objective lens 3 can be flexibly selected based on specific system design specifications. This application utilizes cemented doublet or triplet achromatic objectives to effectively guarantee paraxial field-of-view imaging quality.

[0055] This invention employs fiber optic array imaging and controls the on / off state of fibers corresponding to different fields of view via optical switch 2. Combined with a high-speed spectrometer 1, it enables time-division rapid linear array push-broom imaging spectral detection based on a single spectrometer 1. Compared with traditional linear array push-broom spectral imaging systems, the system of this application has the following main advantages:

[0056] 1. Compared with conventional linear array sweeping imaging spectral systems, it eliminates the need for sweeping mechanical moving parts, significantly reducing the size and weight of the imaging spectral system, and has minimal impact on the flight stability of the carrier platform.

[0057] 2. This invention uses an optical switch 2 to replace the oscillating mechanical structure to achieve detection of different fields of view. The detection efficiency depends on the integration time of the spectrometer 1 and the switching speed of the optical switch 2. Under the same conditions, the detection efficiency is much higher than that of the existing linear array oscillating imaging spectrometer system.

[0058] 3. Compared with conventional linear array oscillating scanning imaging spectral systems, the relative positions of each fiber in the linear array fiber array of the present invention are fixed, that is, the field of view of each fiber is relatively fixed during push-broom sampling; compared with traditional linear array oscillating scanning imaging spectral systems, the field of view error during different field of view measurements is greatly reduced, thus reducing the difficulty of image stitching processing and improving the geometric stitching accuracy of images.

[0059] 4. Compared with conventional area array pushbroom imaging spectral systems, the photodetector 6 of this invention can be a linear array detector 6, which has a significant low-cost advantage.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A linear array pushbroom imaging spectral system based on fiber optic devices, applied to field-of-view scanning of flight equipment, characterized in that, include: A spectrometer is used to detect the field of view; An objective lens, connected to the spectrometer, is used to scan the field of view; An optical switch, one end of which is connected to the spectrometer via a first optical fiber, and the other end of which is connected to the objective lens via a second optical fiber of a linear array; The second optical fiber is composed of several sub-optical fibers arranged in an array, and the second optical fiber is coupled to the focal plane of the objective lens. Each sub-optical fiber is used to correspond to a field of view. The length direction of the second optical fiber is parallel to the objective lens, so that the linear array pushbroom imaging spectral system can acquire the field of view of the flight direction of the flight equipment and realize the acquisition of spectral information in the direction of track crossing. The optical switch switches the field of view through the second optical fiber to achieve time-division scanning of multiple fields of view of the spectrometer, thereby improving the scanning efficiency of the imaging spectroscopy system.

2. The linear array push-broom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The adjacent sub-fibers are connected in a one-dimensional seamless manner.

3. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The second optical fiber is arranged in a double-row staggered pattern.

4. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The field of view between the sub-fibers is relatively fixed.

5. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The linear array pushbroom imaging spectral system also includes: The detector is connected to the spectrometer and is used to acquire and receive spectral data of each band of the spectrometer.

6. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 5, characterized in that, The detector is a linear array detector.

7. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The optical switch can be any one of the following: mechanical, microelectromechanical, thermo-optical, electro-optical, magneto-optical, or acousto-optic switches.

8. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The optical switches are configured in multiple units, and each optical switch corresponds to a sub-optical fiber.

9. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The second optical fiber is composed of an array of seven of the aforementioned sub-fibers.

10. The linear array pushbroom imaging spectroscopic system based on fiber optic devices according to claim 1, characterized in that, The objective lens is a cemented doublet or a three-part achromatic objective lens.

Images