The center, combined with the needs of China's medium- and long-term scientific and technological development, will pay close attention to the international development of this disciplines. Giving the priority to “ the science and technology of optoelectronic perception in complex environment”, we will focus on studying basic theories, key technologies and their applications in targeted photoelectric characteristics in complex environment, photoelectric detection technology and photoelectric information and image processing.
1. Targeted Photoelectric Characteristics in Complex Environment
In the research of this field, the cooperation will be continued by the project director, Professor Guo Lixin, academic backbones of our school) and overseas academic masters. The emphasis is laid on the following issues in three aspects.
1.1 Research on the propagation characteristics of electromagnetic wave and light wave in complex environment
(1) Propagation characteristics of radio wave in the complex atmospheric environment of the troposphere
Propagation mechanism and rules of microwave and millimeter wave in various environments, such as rain, snow, fog, sand, smoke, atmospheric turbulence, are investigated, and the attenuation prediction models of different transmission effects, i.e., attenuation, depolarization resolution, and environmental equivalent RCS, are established. What’s more, the propagation characteristics and anti-fading technology of tropospheric satellite communication are analyzed. The electromagnetic wave transmission model of ground - space path is also built.
(2) Research on the propagation characteristics of electric waves in the ionosphere
More efforts are made to explore the mechanism of electromagnetic wave scattering communication and the influence of space plasma layer on radar pulse beam broadening, scintillation and signal coherence. A simple and effective model of ionospheric heterogeneous body wave propagation is established. Moreover, we carry out the research on the ionospheric microwave signal tracking and migration and statistical modeling and prediction technology of electric wave environmental effects in the ionosphere. Studies on meteor trail scattering and polar physical radio wave propagation are conducted at the same time. We are also dedicated to studying the techniques of oblique return propagation of short-wave ionosphere and automatic interpretation of ionograms of return scattering, the efforts of short-wave scattering from ground to sea, and the influence of ionospheric disturbances and anomalies.
(3) Coupling of the earth, sea and atmosphere as well as propagation of electromagnetic waves
The effects of low-altitude atmosphere on the transmission characteristics of ground-sea signals are studied, because the low-altitude electromagnetic environment will cause the refraction, flicker, attenuation, cross-polarization, dispersion, delay and other wave environmental effects of information link signals. We seek to figure out the influence mechanism of the meteorological environment on the atmosphere duct as well as the reliable prediction of the atmosphere duct environment and anomalous propagation of the atmosphere, aiming to broaden the range of some information systems, like microwave radar, communication and detection. Developing deterministic propagation forecasting methods based on geographical features is another focus of us. We explore the theoretical methods and implementation approaches of anti-clutter, propagation fading and other propagation effects. Multi-path propagation characteristics of Terain and Sea in space system are under the research.
(4) Light propagation and application technology in Ground-to-Air Environment
The transmission characteristics of light beam in various complex environments are studied, especially the scintillation, drift and beam spreading of the ground-space oblique path propagation. Besides, laser echo characteristics of targets in turbulent atmosphere are in our list as well. We look to investigate the modeling and numerical calculation of the optical transmission characteristics of sunlight and background (including clouds) in atmosphere system on earth, which are used for modeling and simulation of targets and environmental optical characteristics. The laser’ transmission and backward scattering characteristics of different aerosols (fog, smoke) at a low visibility and their applications in the guidance and fuze are discussed in the research. What’s more, the effects of the transmission and distortion of laser pulses in complex atmosphere, ultraviolet atmospheric absorption and scattering as well as their influence in optical wireless communication are under study.
1.2 Electromagnetic Scattering Characteristics of Targets and Environment
(1) Electromagnetic scattering characteristics of complex targets
The electromagnetic scattering and inverse scattering characteristics of complex targets are studied. By using the time-domain and various high and low frequency methods, we try to figure out the scattering characteristics and transient responses of complex targets. Applying time-domain, frequency-domain and high-order equivalent edge-current methods, researches are carried out about the electromagnetic scattering characteristics of complex targets. Guided by engineering empirical model and vector radiation transport theory, we analyze the characteristics of electromagnetic scattering and time-domain of formation targets as well as chaff/foil jamming clouds with high density and large quantity.
(2) Electromagnetic scattering and radiation characteristics in complex background
We explore the multiband electromagnetic scattering, radiation modeling and clutter properties as well as parameter estimation in sea, ground objects and vegetation. The models of electromagnetic scattering and radiation characteristics of multi-frequency vegetation and different sea conditions have been build and ground - sea clutter characteristics have been analyzed. Combined with the space-borne synthetic aperture radar (SAR), we work to push for the numerical simulation of the typical targets and background electromagnetic scattering, radiation characteristic compound modeling, electromagnetic imaging as well as separation technology.
(3) Electromagnetic scattering characteristics of complex background and targets
Combined with high frequency approximation method, numerical algorithm and hybrid algorithm, we launch the researches on the target complex electromagnetic scattering and radiation characteristics of various ground, vegetation, jungle and sea from frequency domain and time domain. For example, we study various small and medium moving targets above the sea surface under different sea conditions, as well as target scattering characteristics in the actual ocean, composite scattering as well as detection and recognition of targets in complex background of wide band and ultra wide band. Complex terrain environment and target SAR image characteristics as well as SAR image identification, interpretation and target recognition technology are under discussion. We take into account the influence of some weather conditions-atmospheric turbulence, sandstorm, rainfall, cloud, fog, snow, etc.- on the electromagnetic scattering characteristics of the target, thus improving the ability for the platform to detect targets.
1.3 Researches on optical characteristics of complex Targets and Environment
(1) New mechanism of laser scattering characteristics
The analytical theory of beam scattering of anisotropic particles and the applications of biological and environmental detection, antenna and electromagnetic near-field scattering are developed. We also implement the measurement and theoretical modeling of BRDF as well as its ultraviolet spectrum. We continue to work on the hyperspectral analysis and laser SAR and target laser Doppler imaging technology. The high order matrix characteristics and speckle effect of turbulent medium and rough surface scattering are studied. Moreover, we investigate composite light scattering characteristics of the rough surface and embedded (or upper) particles. Light scattering of random cluster particles and their applications in smoke and dust detection are under way. Single photon transmission effect in the atmosphere and Preparation and physical properties of nanostructured materials are also important parts in our research.
(2) Light scattering and radiation characteristics of targets and environment
We give priority to the scattering characteristics of visible light, near infrared and laser of space dynamic targets. Beyond that, we focus on the target laser (or spectral) bidirectional reflection distribution function measurement and modeling technology, laser and spectral scattering characteristics in various surfaces. Doppler imaging of target laser range and micro-motion feature detection as well as the ultraviolet spectral scattering characteristics of space targets are also studied.
(3) Modeling and simulation of optical characteristics of complex target and environment
As for infrared physical characteristics of targets and background in multiple dimensions (space, time, spectral etc.), we study the scenario generation technique with a large scale and high fidelity, the multi-spectrum scenario generation technique, the infrared scene-driven engine technology, etc., Among which the research of 3D terrain automatic generation technology, texture mapping technology and rapid building of large-scale scene are included. In addition, we work to collect real texture collection and measure its inversion technology to acquire more realistic texture. In a bid to realize the large scale and high fidelity scene generation, we are also dedicated to dynamic replacement technology of the scene. Besides, texture data management technology and band deduction technology are discussed, so as to realize multi-spectral scene generation.
2.Photoelectric Detection Technology
In the research of this field, many academic backbones of our school (i.e., Professor Wei Zhiyi, Professor Han Xiang’e, Professor Zhou Huixin, Professor Shao Xiaopeng, Professor Wang Shiyu, Professor Liu Jifang ) and overseas academic masters (Bormin Huang, Yang Zhang, Haomin Zhou) are involved in this cooperation. The basic issues are discussed from three aspects.
2.1 Infrared Imaging Detection Technology
(1) Large array infrared detector with high sensitivity
In the pursuit of a higher level of infrared detection technology, in the future, we will focus on the research on dual-mode main passive IRFPA detector with long waves, double and multi colors. We explore IRFPA detector with pixel-level light splitting in situ integration and pixel-level polarization selection at the target radiation incident direction and create a new technology or mechanism to make IRFPA detector more sensitive. Meanwhile, the researches on the modeling, design and process of quantum dot infrared detector and superlattice infrared detector are conducted.
(2) Wide-field infrared imaging technology with super resolution
In view of the future wide-area infrared imaging detection needs, the wide-field super-resolution infrared imaging technology is studied from the perspectives of optical system design, new mode sampling, computational imaging, etc. We explore the applications of new devices, structures and technologies in the infrared imaging system designs as well.
(3) Polarized/multispectral infrared imaging detection technology
Driven by the increasing demands of the photoelectric information to be more refined and visualized, we step up efforts to multi-dimensional imaging and sensing technology based on the combination of “Imaging +spectral +polarization”, and explore its application of detecting typical target in complex scene. In doing so, we can meet the needs of target detection in complex background or environment, effectively inhibit complicated background clutter, and extract target features.
2.2 Multi/hyperspectral Imaging Detection Technology
(1) Construction of hyperspectral image inversion model and standard spectral database
Based on the optical characteristics of typical targets and considering the radiation transmission characteristics of the atmosphere, the satellite-borne imaging system effects are used for obtaining the spectral data of the benchmark targets consistent with the shooting conditions. According to the features of camouflaged target’ spectral curve in hyperspectral images, camouflaged target spectrum feature extraction model is set up. We will introduce physical characteristics carried by spectral curve to the hyperspectral image target detection model and establish a coupling link model based on target detection algorithm and physical properties of ground objects, so as to study the spectrum database of typical target in complex background.
(2) High Spectral Imaging Acquisition and Parallel Detection
As for the hyperspectral detection of moving targets in complex environment, researches on high spectral imaging video acquisition equipment are carried out. We make a parallel design of hyperspectral camouflaged target detection model. With the help of CUDA, we greatly improve the computational efficiency of detecting and recognizing hyperspectral camouflaged targets.
2.3 Laser radar Detection Technique
(1) New pulse laser technology
This research applies to high-efficiency and miniaturized new laser radiation sources for photoelectronic imaging and detection in complex environment. We carry out the research both in theory and practices from various aspects such as the distribution and measurement of crystal heat loss in DPL, analysis and calculation of steady-state and transient crystal thermal lens effect, analysis and measurement of crystal end face deformation, design of thermal insensitive cavity and crystal heat dissipation technology under high power pumping. More attention is paid to small-scale practical laser devices with high repetition rate, high peak power, high beam quality, high reliability and long service life.
(2) Ultra-fast laser technology
It is a new technology for all-solid-state LD-pumped ultrafast laser to generate and amplify. When conversing nonlinear ultra-fast laser frequency in the research, tunable ultrafast laser sources in the 3-5μm mid-infrared band are required both theoretically and experimentally. On the basis of high-stability ultra-fast lasers with all-fiber structure, we endeavor to meet strict requirements that makes vehicle and airborne photoelectric detection systems more stable. We try our best to research ultra-fast integrated microphotonics and ultra-fast laser micro-machining technology for realizing practical ultra-high-speed compact optical communication unit devices.
(3)Laser detection technology
Researches on laser target automatic recognition technology, synthetic aperture laser radar technology and laser wake detection technology are carried out. We study the cross section of target laser radar, characteristics of echo time domain, depolarization effect of rough target echo and the application of target vibration spectrum in automatic target recognition technology. The effect of laser echo decoherence on the detection of optical heterodyne is studied by actual target rough surface, and a statistical model of echo optical heterodyne signal is established. The effects of wake field on laser beam quality, spatial spectrum, pulse characteristics, and time spectrum are studied. A new method for ship wake detection based on laser spot drift, laser spatial spectral intensity, laser pulse characteristics and laser Doppler shift characteristics is proposed.
3.Photoelectric Information and Image Processing
In the research of this field, cooperation will be made by academic backbones of our school and overseas academic masters. They mainly focus on three basic issues: multi/hyperspectral image processing, infrared image processing, and new photoelectric information processing and systems. The specific details are as follows.
3.1 Multi /hyperspectral Image Processing
Studying endmember extraction, subpixel positioning, image classification and anomaly detection in multi/hyperspectral image processing not only has important theoretical value, but also improves the utilization of hard-won hyperspectral images. To extract more useful information from hyperspectral images makes image processing algorithms more efficient and upgrades its performance, supporting the subsequent processing of hyperspectral images. For multi/hyperspectral image processing, the following three aspects of collaborative research are mainly carried out.
(1)Endmember Extraction and Subpixel Positioning
Due to limited spatial resolution of spectral imager, a pixel corresponds to an area on the ground in actual imaging, and this area may be a mixture of various substances, thus analysis on pixels cannot be performed directly and it needs to be unmixed. This study, by hybrid nonlinear optics, will extract the lowest-mixed pixel from the hypothetical image as an end element, and obtain pure spectrum directly from high-mixed images as the end-member spectra, increasing abundance estimation and obtaining high-precision endmember extraction. In addition, because of the low spatial resolution of spectral image and the ubiquity of the mixed pixels, the detected target pixel is usually a mixture of the target component and the background component. Generally, accurate spatial position of the target has great value, so it is necessary to perform subpixel localization research on target detection of hyperspectral images. The research will make the best of spatial correlation for subpixel positioning.
(2)Image Classification
As an important means of obtaining information, classification is promised to classify all pixels in images automatically. According to different criteria, the classification of hyperspectral images can be divided into supervised classification, parametric and non-parametric classification, deterministic and non-deterministic classification and others. The research can determine the proportion of various ground objects in mixed pixels by decomposing them, and then identify the type of mixed pixels according to the proportion. That will reduce the possibility of misclassification and improve the accuracy of classification.
(3)Anomaly Detection
For the problem of abnormal detection of hyperspectral remote sensing images without prior information, the research introduces the theory and methods of multivariate statistical analysis, establishes an anomaly detection model, realizes an effective anomaly detection algorithm and establishes an evaluation method for testing results. Anomaly detection not only can be used as a pretreatment of target detection and recognition system, but also an auxiliary tool for other image sensors, and a final output as reconnaissance services.
3.2 Infrared Image Processing
Infrared image processing is a key part in infrared imaging applications. The Center launches a full-chain research on image acquisition, image pretreatment, image processing for specific tasks, and software and hardware systems of image processing.
(1)Image Pretreatment
This process is designed for the problems of infrared imaging non-uniformity and low contrast. The research gives priority to super-resolution image reconstruction technology, adaptive non-uniformity correction technology for infrared focal plane array (IFPA), photoelectric image enhancement technology and real-time implementation technology. In doing so, it will effectively improve imaging quality, equivalently promote imaging performance of the system, and provide an effective technical basis for subsequent system.
(2)Image Processing for Specific Tasks
For the application requirements of space object monitoring and tracking, high-resolution earth observation and so on, we focus on the detection and tracking technology of weak infrared target under complex environment, photoelectric image registration and information fusion technology, feature extraction of target based on image and software and hardware implementation system,etc. That is how we can meet the requirements of the corresponding application systems and provide an
3.3 New Photoelectric Information Processing and System
(1)New Theories and Technologies for Photoelectric Information Acquisition
When exploring new systems, new methods and new theories of multi-dimensional optoelectronic imaging, we have made breakthroughs in key technologies such as large aperture light optical system design, new spectral spectroscopic imaging technology, and multi-aperture integrated imaging. Researches on working mechanism, system composition and key technologies of the new photoelectric detection methods are made, such as THtz imaging and quantum imaging. We investigate optical properties of the field and matters, and take the interaction of light with matter into account. We work for a new imaging optical system and a new imaging method by a new physical mechanism that is different from the traditional one, including computational imaging and imaging through random scattering media.
(2) Design and Application of Photoelectric System
We give priorities to the high-performance measurement system of photoelectricity parameter (such as high-precision CCD chip testing, infrared imaging system testing, fusion optical fiber measurement and analysis systems, etc.), driving system for photoelectric information acquisition component (such as infrared laser power stabilization system, high-performance infrared focal plane array drive system, etc.), photoelectric panoramic imaging system design, photoelectric tracking system design, multi-spectral imaging system construction, infrared warning system, photoelectric guidance system, integrated display, etc.
