CN118794536A - An airborne push-broom hyperspectral polarization integrated imaging system and its installation and adjustment method - Google Patents

Abstract

An airborne push broom hyperspectral polarization integrated imaging system and an adjusting method thereof belong to the technical field of optical imaging, and the optical system comprises: the device comprises an objective lens group, a slit, a collimating lens group, a prism, a grating, an imaging lens group and a polarization detector; the prism grating type spectrum structure is adopted, the polarization detector is matched, the stable forward motion of the airborne platform is utilized, the target information of the whole space can be obtained, the slit images with the same wavelength are spliced in sequence according to time sequence by utilizing a simple image reconstruction method, and the polarization information corresponding to different wavelengths of the target can be obtained. Combining intensity, spectrum and polarization information, wherein the intensity information reflects detection distance, target shape, target size, etc.; the spectrum information can reflect the material and the characteristic of the target; the polarization information can reflect the roughness of the target and the contrast with background information, and the three imaging methods are combined to be applied, so that the image contrast can be improved by 1 time, the working distance is improved, and the target detection probability is improved.

Description

An airborne push-broom hyperspectral polarization integrated imaging system and its installation and adjustment method

Technical Field

The present invention relates to the field of spectral polarization imaging, and in particular to an airborne push-broom hyperspectral polarization integrated imaging system and an assembly and adjustment method thereof.

Background Art

Spectral imaging technology is a technology that obtains the two-dimensional geometric shape and one-dimensional spectral information of the target. It can simultaneously obtain the spatial intensity and spectral information of the target, and has the advantage of combining the image and spectrum into one. Spectral information is extremely sensitive to the type and material of the target, and can effectively distinguish and identify the target. However, spectral imaging is easily affected by clouds, fog, complex lighting, etc., and the signal-to-noise ratio of spectral imaging decreases, resulting in reduced recognition accuracy and increased false alarm rate. As an emerging detection method, polarization is more sensitive to features such as atmospheric particles and object textures, and can significantly improve target detection capabilities and imaging contrast in complex environments.

Spectral polarization imaging technology is a new imaging technology that organically combines spectral imaging technology and polarization imaging technology, and simultaneously obtains and efficiently utilizes the spatial, spectral and polarization information of the target. Spectral polarization imaging technology expands the dimension of information perception of the target, not only plays the role of fine spectral identification, but also retains the advantage of polarization highlighting the target. It is expected to break the perception limitations of single-dimensional imaging in complex environments and is the future development direction of information perception. This technology can be widely used in many fields such as marine environment monitoring, earth remote sensing survey, medical material inspection, military reconnaissance and search and rescue.

However, current spectral polarization systems mostly use tunable filters, interference-type or snapshot-type imaging methods, which require a certain amount of sampling time, and have complex optical paths, large volumes, high difficulty in image reconstruction, and cannot meet the requirements of spectral polarization integrated imaging in the airborne field. Therefore, the present invention proposes an airborne push-broom hyperspectral polarization integrated imaging system, which utilizes a combination of a prism-grating spectroscopic element and a polarization detector to achieve simultaneous acquisition of spectral and polarization information in a single optical path, and has the characteristics of high spectral resolution, high spatial resolution, high temporal resolution, and rapid image reconstruction. In addition, the push-broom imaging method is also suitable for airborne platforms, and can provide the advantages of wide-area high-resolution observation, rapid response capability, and real-time data acquisition.

For any optical system, adjustment is inevitable, and the quality of adjustment directly determines the performance of the system. Therefore, accurate adjustment is an important link to ensure the successful development of the optical system. Even if the processing of the entire optical system and mechanical components meets the tolerance requirements, the system performance may be reduced due to the errors introduced during the adjustment process. However, the adjustment of spectral imaging systems currently studied at home and abroad is simply to use measuring instruments to roughly judge the direction of the outgoing light of the prism-grating spectrometer. There is no theoretical guidance, and it is impossible to achieve real-time prediction and accurate adjustment. Therefore, a new solution is urgently needed in the prior art to solve the above problems.

Summary of the invention

In order to solve the problem that the existing spectral polarization systems mostly adopt tunable filters, interference type or snapshot type imaging methods, which require a certain sampling time, have complex optical paths, large volumes, high difficulty in image reconstruction, and cannot meet the spectral polarization integrated imaging technology in the airborne field, the present invention proposes an airborne push-scanning hyperspectral polarization imaging integrated system, which mainly includes an objective lens group, a slit, a collimating lens group, a prism, a grating, an imaging lens group and a polarization detector. Through the stable forward movement of the airborne platform, the target information of the entire space is obtained, and according to the staggered distribution of the pixels of different polarization orientations in the polarization detector, the polarization information corresponding to the space targets of different wavelengths is solved by an interpolation algorithm. At the same time, the problem of low efficiency and poor accuracy in the prism-grating adjustment process of the airborne push-scanning hyperspectral polarization integrated imaging system is also solved. The derived formula of the incident angle of the incident light when the prism-grating is tilted is used as a theoretical basis for adjustment, and the adjustment accuracy is high.

The object of the present invention is to provide an airborne push-scan hyperspectral polarization integrated imaging system, the optical system comprising: an objective lens group, a slit, a collimator lens group, a prism, a grating, an imaging lens group and a polarization detector;

The objective lens group focuses the light beam from the target light onto the slit;

The target light is parallel light at infinity that contains multi-spectral light information of the target and the background;

The collimating lens group is placed behind the slit and is used to collimate the outgoing light from the slit into a parallel light beam;

The prism and the grating are sequentially placed behind the collimator lens to disperse the target light within the visible light range;

The imaging lens group and the polarization detector sequentially focus and image the dispersed target light.

The imaging system uses a slit to limit the imaging range and realizes imaging through a push-scan motion.

The imaging system is suitable for an airborne platform.

A method for assembling and adjusting the airborne push-broom hyperspectral polarization integrated imaging system as described above comprises the following steps:

Step 1: Use monochromatic light of known wavelength to align the center of the scale frame set on the optical platform. At this time, the center of the scale frame is the spot of monochromatic light;

Step 2: Place the objective lens group and the collimator lens group in sequence, and adjust their positions to keep the light spot position at the center of the scale frame;

Step 3: placing a prism and a grating in sequence after the collimator lens group, and adjusting the prism and the grating so that the light spot remains at the center of the scale frame;

Step 4: placing an imaging lens group behind the prism and the grating, keeping the light spot position at the center of the scale frame, and placing a polarization detector at the rear focal plane of the imaging lens group;

Step 5: Use a collimator and add a small circular hole on the front side of the collimator, use a polarization detector for imaging, and adjust the position of the polarization detector until the smallest circular bright spot is found;

Step 6: Place a slit at the front focal plane of the collimating lens group, replace the white light source so that it completely covers the imaging system, and continuously adjust the direction of the slit so that the slit image is parallel to the longitudinal direction of the polarization detector. At this time, adjust the position of the polarization detector until the width of the slit image in the entire field of view is minimized.

The adjustment in the step is to adjust the prism and the grating through the dispersion equation and the deflection angle formula. The dispersion equation is:

in,

θ ₁ = α + δ

The deflection angle formula is

Among them, the incident angle of the dispersion module is θ ₁ , the refractive index of the prism is n, the prism vertex angle is α, the grating constant is d, the diffraction order is k, the wavelength of the monochromatic light is λ, the diffraction angle is φ, and the deflection angle of the prism grating spectrometer module is The prism tilt angle is δ (when tilted clockwise, δ>0; when tilted counterclockwise, δ<0), the grating tilt angle is γ (when tilted clockwise, γ<0; when tilted counterclockwise, γ>0), and the maximum counterclockwise tilt angle of the prism is α.

The beneficial effect of the present invention is that the present invention adopts a prism grating type spectral structure, cooperates with a polarization detector, and utilizes the stable forward motion of an airborne platform to obtain target information of the entire space, and utilizes a simple image reconstruction method to splice slit images of the same wavelength in chronological order, so as to obtain polarization information corresponding to different wavelengths of the target. Combining intensity, spectrum and polarization information is a beneficial supplement to traditional imaging detection. Among them, intensity information reflects the detection distance, target shape and target size, etc.; spectrum information can reflect the target material and characteristics; polarization information can reflect the target roughness and the contrast with the background information. By combining the three imaging methods, the image contrast can be increased by 1 times, thereby increasing the working distance and helping to improve the probability of target detection. As for the adjustment method, since the prism grating is tilted during the adjustment process, it is difficult to adjust it to be completely perpendicular to the horizontal plane and requires extremely precise instruments. Therefore, the derived prism grating exit angle formula is used in combination with the diffraction spot position to achieve efficient and high-accuracy adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of an airborne push-broom hyperspectral polarization integrated imaging system of the present invention.

FIG. 2 is a schematic diagram of a prism grating spectroscopic element of an airborne push-scan hyperspectral polarization integrated imaging system of the present invention.

FIG3 is a schematic diagram showing the principle of tilting the prism grating spectrometer element of an airborne push-scan hyperspectral polarization integrated imaging system according to the present invention.

FIG. 4 is a diagram showing the imaging principle of the polarization detector according to the present invention.

FIG. 5 is a schematic diagram of the scale frame of the present invention.

Reference numerals: 1 - objective lens group, 2 - slit, 3 - collimator lens group, 4 - prism, 5 - grating, 6 - imaging lens group, 7 - polarization detector.

DETAILED DESCRIPTION

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described with reference to the accompanying drawings. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In the description of the present invention, unless otherwise specified, the term "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this patent can be understood according to the specific circumstances.

An airborne push-scan hyperspectral polarization integrated imaging system, as shown in FIGS. 1 to 5 , comprises: an objective lens group 1, a slit 2, a collimator lens group 3, a prism 4, a grating 5, an imaging lens group 6 and a polarization detector 7;

The objective lens group 1 focuses the light beam from the target light onto the slit 2;

The target light is parallel light at infinity that contains multi-spectral light information of the target and the background;

The collimating lens group 3 is placed behind the slit 2 and is used to collimate the outgoing light from the slit 2 into a parallel light beam;

The prism 4 and the grating 5 are sequentially placed behind the collimator 3 to disperse the target light within the visible light range;

The imaging lens group 6 and the polarization detector 7 focus and image the dispersed target light in sequence.

The imaging system uses a slit to limit the imaging range and realizes imaging through a push-scan motion.

The imaging system is suitable for an airborne platform.

The present invention also provides a method for assembling and adjusting the airborne push-broom hyperspectral polarization integrated imaging system as described above, comprising the following steps:

Step 1: Use monochromatic light of known wavelength to align the center of the scale frame set on the optical platform. At this time, the center of the scale frame is the spot of monochromatic light;

Step 2: Place the objective lens group 1 and the collimator lens group 3 in sequence, and adjust their positions to keep the light spot position at the center of the scale frame;

Step 3: placing a prism 4 and a grating 5 in sequence after the collimating lens group 3, and adjusting the prism 4 and the grating 5 so that the light spot remains at the center of the scale frame;

Step 4: placing an imaging lens group 6 behind the prism 4 and the grating 5, keeping the light spot position at the center of the scale frame, and placing a polarization detector 7 at the rear focal plane of the imaging lens group 6;

Step 5: Use a collimator and add a small circular hole on the front side of the collimator, use a polarization detector 7 to perform imaging, and adjust the position of the polarization detector 7 until the smallest circular bright spot is found;

Step 6: Place the slit 2 at the front focal plane of the collimating lens group 3, replace the white light source so that it completely covers the imaging system, and continuously adjust the direction of the slit 2 so that the slit image is parallel to the longitudinal direction of the polarization detector 7. At this time, adjust the position of the polarization detector 7 until the width of the slit image in the entire field of view is minimized.

The adjustment in step 3 is to adjust the prism 4 and the grating 5 by using the dispersion equation and the deflection angle formula. The dispersion equation is:

in,

θ ₁ = α + δ

The deflection angle formula is

Among them, the incident angle of the dispersion module is θ ₁ , the refractive index of the prism is n, the prism vertex angle is α, the grating constant is d, the diffraction order is k, the wavelength of the monochromatic light is λ, and the diffraction angle is φ. As shown in Figures 2 and 3, the deflection angle of the prism grating spectrometer module is The prism tilt angle is δ (when tilted clockwise, δ>0; when tilted counterclockwise, δ<0), the grating tilt angle is γ (when tilted clockwise, γ<0; when tilted counterclockwise, γ>0), and the maximum counterclockwise tilt angle of the prism is α.

The airborne push-broom hyperspectral polarization integrated imaging system of the present invention has the following advantages: in order to simultaneously obtain intensity, spectrum, and polarization information, a prism grating is used as a light splitting element, and a polarization detector is used as a polarization receiver. It has a simple structure, high spectral resolution, no need for complex image processing algorithms, high temporal resolution, and only a single optical path is required to achieve simultaneous acquisition of intensity, spectrum, and polarization information. The system also uses a push-broom imaging method, which is suitable for airborne platforms and can provide the advantages of wide-area high-resolution observation, rapid response capability, and real-time data acquisition.

The adjustment method of an airborne push-scan hyperspectral polarization integrated imaging system of the present invention has the following advantages: by utilizing the deflection angle formula of the prism grating when tilted in combination with the diffraction angle of the prism grating, simple, efficient and accurate adjustment of the prism grating spectroscopic element can be achieved during the adjustment process due to theoretical guidance.

The specific implementation modes described above are preferred implementation modes of the present invention, and are not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to the specific implementation modes. All equivalent changes made in accordance with the shape and structure of the present invention are within the protection scope of the present invention.

Claims (5)

1. An airborne push broom hyperspectral polarization integrated imaging system, comprising: the device comprises an objective lens group (1), a slit (2), a collimating lens group (3), a prism (4), a grating (5), an imaging lens group (6) and a polarization detector (7);

The objective lens group (1) focuses a beam from the target light to the slit (2);

the target light is parallel light which contains target and background multispectral light information in infinity;

The collimating lens group (3) is arranged behind the slit (2) and is used for collimating emergent light of the slit (2) into parallel light beams;

the prism (4) and the grating (5) are sequentially arranged behind the collimating mirror (3) and are used for dispersing the target light in the visible light range;

and the imaging lens group (6) and the polarization detector (7) focus and image the dispersed target light in sequence.

2. The on-board push broom hyperspectral polarization integrated imaging system of claim 1, wherein: the imaging system limits the imaging range by using the slit, and realizes imaging by a push-broom movement mode.

3. The on-board push broom hyperspectral polarization integrated imaging system of claim 1, wherein: the imaging system is suitable for an airborne platform.

4. A method of tuning an on-board push broom hyperspectral polarization integrated imaging system as claimed in any one of claims 1 to 3 comprising the steps of:

step 1: aligning the center of a scale frame arranged on an optical platform by utilizing monochromatic light with known wavelength, wherein the center of the scale frame is a spot of the monochromatic light;

Step 2: an objective lens group (1) and a collimating lens group (3) are sequentially arranged, and the positions of the objective lens group and the collimating lens group are adjusted to keep the light spot position at the center of the scale frame;

Step 3: a prism (4) and a grating (5) are sequentially arranged behind the collimating lens group (3), and the prism (4) and the grating (5) are regulated so that the light spots are kept at the center of the scale frame;

step 4: an imaging lens group (6) is arranged behind the prism (4) and the grating (5), the light spot position is kept at the center of the scale frame, and a polarization detector (7) is arranged at the back focal plane of the imaging lens group (6);

step 5: using a collimator, adding a small round hole in the front side of the collimator, imaging by using a polarization detector (7), and adjusting the position of the polarization detector (7) until the smallest round bright spot is found;

Step 6: and placing a slit (2) at the front focal plane of the collimating lens group (3), replacing a white light source to completely contain the imaging system, continuously adjusting the direction of the slit (2) to enable a slit image to be parallel to the longitudinal direction of the polarization detector (7), and adjusting the position of the polarization detector (7) until the width of the slit image of the whole view field is minimum.

5. The method for adjusting the airborne push broom hyperspectral polarization integrated imaging system according to claim 4, wherein the method is characterized by comprising the following steps: the adjustment in the step 3 is to adjust the prism (4) and the grating (5) through a dispersion equation and a deflection angle equation, wherein the dispersion equation is that

Wherein,

θ₁＝α+δ

The deflection angle formula is

Wherein the incidence angle of the dispersion module is theta ₁, the refractive index of the prism is n, the vertex angle of the prism is alpha, the grating constant is d, the diffraction order is k, the wavelength of monochromatic light is lambda, the diffraction angle is phi, and the deflection angle of the prism grating light-splitting module isThe prism tilt angle is delta, the grating tilt angle is gamma, and the counterclockwise tilt angle of the prism is alpha at maximum.