The stereoscopic spectral imager combines the space technology and the spectrum technology, which can obtain the three-dimensional information and the spectral information of the target at the same time. A compact stereoscopic spectral imaging system is proposed in this paper. The stereoscopic spectral imaging system works at the wavelength range from 450 to 1000nm. The optical system consists of three telescopes and a spectrometer. The stereoscopic spectral imaging system uses the compact design of the shared spectrometer and detector, which effectively saves the volume weight and the cost of the system, and realizes the requirement of lightweight miniaturization. One of the three telescopes is perpendicular to the earth, the other two observe forward and rear along the direction of the flight. The side angle is 27 degree. The Offner-Chrisp imaging spectrometer based on curved surface prism is used in the system. Curved prism is a special optical element, which can effectively reduce the size of the system, reduce the spectral curvature and improve the performance of the system. The MTF values of all wavelengths at 46lp/mm are greater than 0.6 and the results demonstrated the good performance of the optical design. The stereoscopic spectral imaging system can achieve high-resolution imaging under the condition of wide spectral segment, has the high energy utilization efficiency and can obtain the spectral information in real time.
Wide field of view (FOV) can provide the high efficiency of remote sensing. In this paper, the optical fiber array is used to connect the telescope and the spectrometer, which makes the configuration of the imaging spectrometer flexible and compact with large FOV. In the proposed system, the optical fiber array is coupled with slit, and relay the image of the slit into the several spectrometers with short field or several parallel fields in a single spectrometer. The optical fiber array can avoid the problems of linear array of imaging fiber bundles without slit, such as manufacture difficulty of the single row fiber bundles, breakage of fiber and the difficulty of alignment the fiber with the pixels of detector. The optical design of the telescope based on TMA and the imaging spectrometer based on Fery prism are detailed in this paper. Moreover, the pushbroom scan experiment demonstrates the feasibility of the optical fiber array in the imaging spectrometer.
A novel shortwave infrared imaging spectrometer based on free-form has been presented .The method was proposed for the requirement of lightweight and wide swath for aerospace loads .The theory of aberration was analyzed based on offner structure. Simulations have been performed by software to confirm the methods. The imaging spectrometer was designed with spectrum (950-2500nm), focal length of 70mm, and field view of 20 degrees. The pixel size is 15 microns. The performance shows the spectral resolution is better than 11nm, the spectral keystone is less than 1nm, the MTF< 0.5@33lp/mm .
High resolution and large relative aperture have been urgent demands for the development of spectrometer. A design method of freeform was presented based on offner structure, The design of large relative aperture was realized by multi variables of freeform surface, the energy of system was doubled. The simulation was carried out by the methods. Spectrum of the system is 400~1000nm, the relative aperture is 1/2.4, the length of the slit is 20mm, and the number of spectral is 213. Based on the aberration theory, the system was optimized and the processing feasibility was analyzed. The analysis results show that the optical MTF of each wavelength is more than 0.7@42lp/mm, and the structure was compact. The system has the feasibility of processing and meets the needs of remote sensing.
The prototype of compact light-weighted hyperspectral imager based on the compact Offnerspectrometer is introduced. Two curved prisms are designed to disperse the incident light in the optical system with the benefits of low smile, keystone and lateral distortion. It has 148 spectral bands covering spectral range from 420 to 1000nm, the ground sampling distance is 50m@700km, and the swath width is 100km. But the weight is only 12.8kg, the outer dimensions are 362mm (X)* 343mm (Z)*139 mm (Y). As prisms are used for imaging spectrometer, the spectral sampling distance varies with wavelength. The width of the spectral response function varies from 1nm to 12nm. The mean bandwidth is less than 5nm. The sensor has achieved high performance levels in terms of signal to noise ratio(SNR), spectral calibration and image quality. It can be used for environmental and disaster monitoring.
A non-contact heart rate detection method based on the dual-wavelength technique is proposed and demonstrated experimentally. The heart rate is obtained based on the PhotoPlethysmoGraphy (PPG). Each detection module uses the reflection detection probe which is composed of the LED and the photodiode. It is a well-known fact that the differences in the circuits of two detection modules result in different responses of two modules for motion artifacts. It will cause a time delay between the two signals. This poses a great challenge to compensate the motion artifacts during measurements. In order to solve this problem, we have firstly used the time registration and translated the signals to ensure that the two signals are consistent in time domain. Then the adaptive filter is used to compensate the motion artifacts. Moreover, the data obtained by using this non-contact detection system is compared with those of the conventional finger blood volume pulse (BVP) sensor by simultaneously measuring the heart rate of the subject. During the experiment, the left hand remains stationary and is detected by a conventional finger BVP sensor. Meanwhile, the moving palm of right hand is detected by the proposed system. The data obtained from the proposed non-contact system are consistent and comparable with that of the BVP sensor. This method can effectively suppress the interference caused by the two circuit differences and successfully compensate the motion artifacts. This technology can be used in medical and daily heart rate measurement.
The Offner-Chrisp spectrometer is the preferred optical configuration in many spectroscopic imaging applications because it has several advantages over other similar instruments. Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces, and offer many advantages in imaging application. An Offner-Chrisp imaging spectrometer with freeform surfaces is designed in this paper. The imaging spectrometer works at the wavelength range from 200 to 1500nm. The freeform surfaces are used to reduce the residual aberration over the large wavelength range and achieve a large flat field simultaneously. Different types of freeform surfaces are considered to evaluate their potential, e.g. anamorphic aspherical surface, X-Y polynomial surface and Zernike polynomial surface. Benefits from the freeform surfaces, the residual aberrations are well corrected, especially in the UV region and a flat field over the wide wavelength range is also obtained. The image quality is near diffraction limits. The smile and keystone are also well controlled <0.1μm.
The primary mirror is an important optical component of space camera. Its performance related to the optical image quality, and the weight directly affects the whole camera weight. The traditional design of primary mirror relies on much experience, lacking of precise theory, and many design parameters obtained by empirical formulas, thus the performance of the result is unstable. For this study, a primary mirror made of SiC with the diameter of 700mm was conceptual designed to get the optimized structure. Then sensitivity analysis was carried out to determine the optimum thickness of the back muscles. Finally, the optimum primary mirror fully satisfied the required was completed, with outstanding mechanical performance and light weight. A comparison between the optimum primary and traditional primary was performed and the results showed that the optimum primary has higher lightweight ratio increased by 5%, higher modal frequency increased by 81Hz.The maximum deformation under gravity reduced by 48nm, PV of the mirror surface reduced by 8.1nm and RMS reduced by 3.1nm. All the results indicated that the optimization method in the paper is reasonable and effective, which gives a reference to the primary mirror design in the future.
In order to reduce the volume and quality of the imaging system , and to improve spectral resolution and achieve large dispersion width with large field of view .A novel modified imaging system is presented. In this system, the second Fery prism combined reflection with twice dispersion, the beam passes through the prism twice to be dispersed. Therefore, the system realizes compact miniature compared with conventional one. The system overcomes the disadvantages of making convex grating and serious spectral overlapping effectively. This paper presents the results of design, the results show that the structure corrects spectral bending and spectral smiles, which satisfies the requirements of airborne imaging spectrometer.
Spectral curvature (smile effect) is universally existed in dispersive imaging spectrometer. Since most image processing systems considered all spatial pixels having the same wavelength, spectral curvature destroys the response consistence of the radiation energy in spatial dimension, it is necessary to correct the spectral curvature based on the spectral calibration data of the imaging spectrometer. Interpolation is widely used in resampling the measured spectra at the non-offset wavelength, but it is not versatile because the accuracy is different due to the spectral resolution changed. In the paper, we introduce the inverse distance weighted(IDW) method in spectrum resampling. First, calculate the Euclidean distance between the non-offset wavelength and the points near to it, the points number can be two, three, four or five, as many as you define. Then use the Euclidean distance to calculate the weight value of these points. Finally calculate the radiation of non-offset wavelength using the weight value and its corresponding radiation. The results turned out to be effective with the practical data acquired by the instrument, and it has the characteristics of versatility, simplicity, and fast.
The images obtained by large aperture static imaging spectrometer (LASIS) are two dimensional images which contain interference information. The acquisition of different places’ interferogram needs to pushbroom the whole field of view. Because of the instability of the pushbroom platform, the original LASIS image registration is required, and the interferogram after registration is no longer consistent with equal interval interference. The spectral information will be severely distorted while a fast Fourier transform (FFT) is used for the direct extraction of the interferogram. In view of the above problems, this paper introduces a method based on phase correlation, and proposes an adaptive fast interpolation algorithm. Experimental results show that the proposed method can recover the spectral information well when the registration accuracy is sufficient.
The principle of all types of spectrometers and structural features are studied , a new metrhod to design prism
spectrometer system with wide field of view is proposed ,which is based on the offner struture .This type of spectrometer
allows twice dispersion through the same prism.Compared with the traditional dispersive spectrometer system ,which
can be greater dispersion width and smaller volume.Compared with the gating spectrometer ,which overcomes low
diffracion efficiency,spectrum overlapping, ghosts, low SIR and other shortcomings. Finally, the design results were
analyzed, and the image quality was evaluated.The results from the design anslysis showed the spectrometer has a
smaller spectrum bending ,the MTF of the system at different wavelengths is close to the diffraction limit and the design
meets the requirements .
As a novel detection approach which simultaneously acquires two-dimensional visual picture and one-dimensional
spectral information, spectral imaging offers promising applications on biomedical imaging, conservation and
identification of artworks, surveillance of food safety, and so forth. A novel moderate-resolution spectral imaging system
consisting of merely two optical elements is illustrated in this paper. It can realize the function of a relay imaging system
as well as a 10nm spectral resolution spectroscopy. Compared to conventional prismatic imaging spectrometers, this
design is compact and concise with only two special curved prisms by utilizing two reflective surfaces. In contrast to
spectral imagers based on diffractive grating, the usage of compound-prism possesses characteristics of higher energy
utilization and wider free spectral range. The seidel aberration theory and dispersive principle of this special prism are
analyzed at first. According to the results, the optical system of this design is simulated, and the performance evaluation
including spot diagram, MTF and distortion, is presented. In the end, considering the difficulty and particularity of
manufacture and alignment, an available method for fabrication and measurement is proposed.
Coded aperture spectral imaging is a new system to captures multiframes images and reconstructs them into spectral
image cube based on compressive sensing theory (CS). However, using dynamic transformed coded aperture pattern can
cause two primary problems, firstly the whole exposure procedure needs to be staring on the same surface feature which
is depended on a high quality stable platform; secondly the coded aperture’s transformation might reduce the system’s
stability. To avoid these problems without a loss of information for precise reconstruction, in the paper we propose
dividing the single image panel into encoding spatial overlapped sub-districts. We design a pushbroom scan pattern to
ensure each sub-district have enough sampling measurements. In each sub-district, we infer its measurement matrix can
satisfy the sparsely requirements needed for accurate estimation and final reconstruction with CS sampling. Considering
with efficiency and accuracy, we design a orthogonal self-loop coding mask (lines irrelevant) to guarantee the coding are
irrelevant among distinct snapshot of the same scene. The simulation experiment reveals the design helping reconstruct
the scene spectral cube with high throughput and resolution.
In order to meet the needs of space borne and airborne hyperspectral imaging system for light weight, simplification and high spatial resolution, a novel design of Féry-prism hyperspectral imaging system based on Zemax multi-configuration method is presented. The novel structure is well arranged by analyzing optical monochromatic aberrations theoretically, and the optical structure of this design is concise. The fundamental of this design is Offner relay configuration, whereas the secondary mirror is replaced by Féry-prism with curved surfaces and a reflective front face. By reflection, the light beam passes through the Féry-prism twice, which promotes spectral resolution and enhances image quality at the same time. The result shows that the system can achieve light weight and simplification, compared to other hyperspectral imaging systems. Composed of merely two spherical mirrors and one achromatized Féry-prism to perform both dispersion and imaging functions, this structure is concise and compact. The average spectral resolution is 6.2nm; The MTFs for 0.45~1.00um spectral range are greater than 0.75, RMSs are less than 2.4um; The maximal smile is less than 10% pixel, while the keystones is less than 2.8% pixel; image quality approximates the diffraction limit. The design result shows that hyperspectral imaging system with one modified Féry-prism substituting the secondary mirror of Offner relay configuration is feasible from the perspective of both theory and practice, and possesses the merits of simple structure, convenient optical alignment, and good image quality, high resolution in space and spectra, adjustable dispersive nonlinearity. The system satisfies the requirements of airborne or space borne hyperspectral imaging system.