Imaging spectrometer can provide both scene image information and spectral information, thus providing in-depth analysis of the composition and characteristics of the scene target. It is an important equipment for observation, analysis and detection. Imaging spectrometers are now emerging as an important market growth point in the field of optoelectronic imaging. This paper presents a compact and lightweight snapshot broadband computational spectral imager, which provides a new approach to VIS-NIR spectral imaging and target identification techniques. Based on the Coded Aperture Snapshot Spectral Imager (CASSI), an imaging method with a shared primary mirror and a dual optical path is proposed. One optical path mainly consists of a coding mask, a relay lens, an Amici prism and a visible near-infrared enhancement detector. Its spatial and spectral resolution is determined by the coding mask and dispersive elements. The optical system finally obtains a blended two-dimensional image on the detector. Another optical path uses a visible NIR-enhanced detector to provide high-resolution spatial information. The high-resolution spectral image information is obtained by a compression-aware reconstruction algorithm. Optical simulations and experimental results show that the system offers significant performance improvements over existing systems, allowing the construction of compact and sensitive spectral imaging systems. We obtained 24 spectral images in the band range 0.44-0.8μm. The new spectral imager introduced in this paper has the advantages of real-time detection, long-range monitoring and high sensitivity. It is especially suitable for Unmanned Aerial Vehicle (UAV) and NanoSat. It can be widely used in the fields of environmental remote sensing, agricultural census, forest survey, vegetation assessment and management, mineral exploration, etc.
In this paper, the band structures of curved InGaAs/InP Quantum Well (QW) are investigated using the 8-band k·p method. The theoretical model adopts both the Luttinger-Kohn Hamiltonian considering spin-orbit interaction and 2- degenerated band, and the Pikus-Bir Hamiltonian for strained semiconductor. The Schrödinger equation is solved by Finite-Difference Method (FDM). It is found that band edges are inclined caused by the linearly distributed strain along z- direction of the curved QW, and the tilt direction is opposite under tension and compression. Within the material fracture limit, this strain field which is similar to the application of external electric field, can induce a variation in the band gap.
Aiming at the problems existing in the optical system of laser communication terminal, in order to improve the isolation level of the communication terminal, the off-axis four-mirror afocal system with ultra-long exit pupil distance used in the coude optical path laser communication terminal is studied. In this paper, the method of four-mirror afocal system design based on primary aberration is explored. The structural parameters are calculated according to primary aberration coefficient. The procedure for calculating initial structural parameters is programmed. Then a four-mirror afocal system is designed with an entrance pupil diameter of 100mm, a field of view of 500μrad, the operating wave band of 1.55μm, and compression ratio of 15 times. The distance of exit pupil is greater than 500mm. After assembly and adjustment, the wavefront error root mean square (RMS) value of the four-mirror afocal system is 0.0172λ(λ=1.55μm). The four-mirror afocal system in this paper can have good imaging quality, reduce the backreflection and scattering of the sensitive mirrors, and solve the contradiction between the ultra-long exit pupil distance and the ultra-large compression ratio. It has application prospect in the field of space laser communication and space gravitational wave detection.
Spectral imaging technology can obtain a three-dimensional data cube of the target, which has the advantage of "unification of maps". Analyzing the "fingerprint" spectral information of space targets is a powerful method for space target identification. In response to the needs of space target material identification and key part identification, this paper proposes a new method of computational spectral imaging with high Light utilization for space target detection. A high-resolution spatial spectral image is obtained through the combination of panchromatic channel and calculated spectral channel. Introduce the calibration technology of the system, including the target's spectrum calibration and the system's coding calibration technology. The multi-spectral image of the satellite model taken by the new spectral imaging system is used to expand the sample, and the training set data is used for training, and the entire data set is tested. The average recognition rate of the five categories of satellite main body, windsurfing board, pot body, antenna and space background is 74.86%. If only the identification of the target and the background is considered, and the non-critical part of the satellite antenna is not considered, the probability of correct recognition as a target is 98.92%, and the probability of correct recognition as a background is 99.11%.
Aiming at the problem that improper selection of detector spectrum has a serious impact on detection efficiency in point target detection. This paper analyzes the main factors affecting point target detection and proposes a point target detection spectrum selection method based on constant false alarms. This method takes detection probability as an evaluation index, comprehensively considers the target and background radiation characteristics, atmospheric radiation transmission, background clutter and sensor noise level. It can calculate the optimal detection spectrum for different target and background information. Taking the typical target detection as an example, the spectrum range where the detection probability meets the requirements under several conditions is calculated, and its feasibility is verified. Through the method in this paper, the point target detection spectrum that meets the requirements of false alarm rate and detection probability can be obtained
It is widely used to correct the atmospheric and surface emissivity by using the split window algorithm to eliminate the atmospheric influence through the combination of the measured values of two adjacent channels (10.3-12.5 m) In the thermal infrared remote sensing inversion of surface temperature. With the increasing demand for split-window spectral data, the development of space optical remote sensors with these two spectral bands has gradually increased in recent years. High-resolution 5 full-spectrum spectral imager is a typical example. Its spatial resolution of thermal infrared split-window spectral band reaches 40m, which is an international advanced level. A large number of studies have shown that the thermal infrared splitting window is very sensitive to the focal plane temperature. With the change of the focal plane temperature, the imager output digital signal varies greatly. For example, when the focal plane temperature changes 0.1K, the 10.3-11.4m spectral band changes 0.02V (equivalent to 13.6DN), 11.5-12.5m spectral band changes 0.006V (equivalent to 4.08DN), so the temperature of FPA must be corrected or controlled strictly.
With the development of high-resolution imaging infrared remote satellites, high resolution imaging and wide swath width are required. Now one effective way to get a wide imaging swath is to increase the length of infrared chip linear array. Restricted by the number of sensor elements on each chip, field butting of the multiple chips is often adopted to obtain a wide of the field of view (FOV). However, since each infrared chip is actually an array in physical structure, and there is also an outer cover for each chip, it is really impossible to place the multiple infrared chips directly as a straight line on the focal plane, and three non-collinear arranging style is adopted instead. Due to the control stability of the drift angle, a non-collinear arrangement of the three chips on the focal plane, the undulation of the ground elevation and so on, the sub-image separately captured by each infrared chip cannot directly from as an integrated image scene. In this paper, the image mode of the three non-collinear Infrared chips is proposed. What is more, some key factors that affect the imaging quality of the three non-collinear infrared chips are discussed in detail, including the control of the drift angle, the placement of the three infrared chips on the focal plane, the terrain undulation and so on. The scales of the effect caused by those factors are calculated in the paper. In order to test and verify the methods given in the paper, flight mission of sun synchronism circle orbit is taken as an example for simulation. Some practical conclusions are arrived at. When the drift angle is out of control, it can bring the effect of the drift angle on the overlapping degree about pixel number, and relative distortion variation tendency was given based on altitude difference.
Infrared camera, which works on cryogenic or normal temperature, has thermal radiation inside. It is called interior radiation. In the space optical remote sensor, interior radiation will produce a lot of bad effects. Firstly, it can depress image contrast. What is more, dynamic range and integral time will be decreased. Lastly, interior radiation is one of the main factors that affect the measurement accuracy. So, restraining interior radiation is one of the key technologies to enhance the quality of infrared thermal imaging technology. In this paper, the typical technology of restraining interior radiation is summarized. At the end of the paper, blue prints for restraining interior radiation are proposed.
Thermal radiation is an inherent property of all objects. Generally, it is believed that the body, which temperature is above absolute zero, can keep generating infrared radiation. Infrared remote sensing, using of satellite-borne or airborne sensors, collects infrared information to identify the surface feature and inversion of surface parameters, temperature, etc. In order to get more accurately feature information, quantitative measurement is required. Infrared radiometric calibration is one of the key technologies of quantitative infrared remote sensing.
Most high-resolution thermal imaging systems are cooling. For the infrared optical system which is having a cooled detector, there are some special phenomenons. Since the temperature of the detector’s photosensitive surface is generally low, which is very different from system temperature, it is a very strong cold radiation source. Narcissus refers to the case that the cooled detector can “see” its own reflecting image, which may affect the image quality of infrared system seriously. But for radiometric calibration of satellite-borne infrared camera, it can sometimes take advantage of the narcissus instead of cold cryogenic radiometric calibration. In this paper, the use of narcissus to carry out radiometric calibration is summarized, and simulation results show the feasibility.
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