Abstract:Object extraction is an essential task in remote sensing and geographical sciences. Previous studies mainly focused on the accuracy of object extraction method while little attention has been paid to improving their computational efficiency. For this reason, a partial differential equation (PDE)-based framework for semi-automated extraction of multiple types of objects from remote sensing imagery was proposed. The mathematical relationships among the traditional PDE-based methods, i.e., level set method (LSM), nonlinear diffusion (NLD), and active contour (AC) were explored. It was found that both edge- and region-based PDEs are equally important for object extraction and they are generalized into a unified framework based on the derived relationships. For computational efficiency, the widely used curvature-based regularizing term is replaced by a scale space filtering. The effectiveness and efficiency of the proposed methods were corroborated by a range of promising experiments.

Abstract:0.5μm InP/InGaAs DHBT with 350/533 GHz ft/fmax and two layers of interconnecting technology were developed for ultra high speed digital integrated circuit (IC) application. A static divide-by-2 frequency divider operating at 100 GHz was demonstrated. As the important parameters of gate delay, base-collector capacitance Ccb and Ccb/IC were analyzed. The value of Ccb/IC as low as 0.4 ps/V was achieved, indicating that frequency divider operating above 150 GHz could be potentially realized.

Abstract:A periodic multilayer structure of metal and dielectric layer has been proposed and studied to gain a stop-band filter in the THz range. A broad stop-band has been realized through making use of polarization hybridization. The bandwidth of the stop-band filter can be tunable in a large range through electric-magnetic couplings in silver layers. The influences of the number of metal layer, the lattice constant and the permittivity of dielectric layer on the central frequency and stop-bandwidth have been studied. The central frequency would be blue-shifted and stop-bandwidth can be expanded through selecting these parameters appropriately. The bandwidth tunability which can be worked through the coupling effect provides good guidance for designing broad stop-band filter.

Abstract:In this paper, 2-D numerical simulation was performed on HgCdTe nBn detectors to study the photoelectric characteristics. We changed the parameters of each layer of HgCdTe nBn structure, including thickness, doping concentration and Cd composition, to study the variation of performance of nBn devices. We also proposed an optimal nBn structure for achieving high performance of HgCdTe nBn Detectors.

Abstract:The development of InP based antimony free 2~3 μm band lasers and photodetectors in our laboratory are introduced, including the 2~2.5 μm band type I InGaAs MQW lasers under pseudomorphic triangle well scheme, 2.5~3.0 μm band type I InAs MQW lasers under metamorphic strain compensation well scheme, as well as InGaAs photodetectors with high indium contents with cut-off wavelength larger than 1.7 μm. All device structures were grown using gas source MBE method. CW operation above room temperature has been reached for the lasers with wavelength less than 2.5 μm, which have gained actual applications. Pulse operation of 2.9 μm lasers at TE temperature also has been reached. The dark current of 2.6 μm InGaAs photodetectors has been decreased notably with the inserting of supperlattice electron barriers. These types of epitaxial materials have been used to the development of FPA modules for space remote sensing applications.

Abstract:Up-conversion infrared (IR) photodetectors show great potential in large-array and low dark current IR detection due to the advantages of pixelless imaging and being free from thermal mismatch between photodetectors and read-out integrated circuits. The emission efficiency of near-IR photons is one of the important issues that influence the up-conversion efficiency. In this paper, cascade IR up-converters with different numbers of emission quantum wells were designed and fabricated. Based on the IR response measurement and simulation of carrier distribution, the influence of the number of quantum wells on the emission efficiency of near-IR photons was investigated. The experiment results indicate that the near-IR emission efficiency can be improved by adopting single emission quantum well, which consequently improves the up-conversion efficiency.

Abstract:Thin films of Mn1.95Co0.77Ni0.28O4 with a thickness of 6.5 μm were prepared by the magnetron sputtering method annealed at temperatures of 400℃, 500℃, 600℃, 700℃, 800℃ respectively. The negative temperature coefficient of resistivity (NTCR) of the films at room temperature α295 increases firstly, and then decreases with the growing annealing temperature. However, the resistivity of the films at room temperature ρ295 keeps decreasing with the growing annealing temperature. The sample annealed at 500℃ has the minimal normalized noise spectral density (SV·VR/V2), while that annealed at 700℃ has the maximal. The annealing process produces defects in the films, which lower the thermal conductivity and augment response time τ as well as the detector noise.

Abstract:The infrared detector module is the key device of target detection and imaging system. Its spatial resolution directly affects imaging quality of detection system. When evaluating the spatial resolution of detector modules, researchers usually adopt modulation transfer function (MTF), which is influenced by the different structures of the detector modules. The basic principle and configuration of infrared micron-spot test system with an optical dispersion diameter of 30 μm was introduced. MTF of detectors with different structures was measured by scanning slit technique. The results show that the profile of overlap electric region is photosensitive. This is the main factor to widen the line spread functions(LSF), cause the secondary peak, and so on. The MTF is thus deteriorated. Meanwhile, the different distance of chip and filter with 0.17 mm and 0.30 mm influences slightly the optical crosstalk of the detector module. These results are used for optimizing design of infrared detector modules for stray light control.

Abstract:As the extension of optical and microwave imaging, THz imaging has now attracted broad attention and showed many unique advantages in areas such as characterizations of semiconductor materials, diagnoses of biological tissues, nondestructive tests and security inspections. According to the diffraction limit, traditional THz imaging is subjected to the shortcoming of its long wavelength that results in a low spatial resolution. However, THz near-field imaging is one of the research highlights to surpass the limit and obtain images with spatial resolutions up to sub-micrometer or even nanometer scale. In this paper, the schemes and basic principles of THz near-field imaging were introduced. Then, four kinds of typical methods, as well as their recent progress and existing problems, were reviewed in detail, including aperture based, tip based, sub-wavelength THz source based, and microstructure control based techniques. Finally, developing prospects were discussed.

Abstract:The imaging technology of Infrared focal plane array(FPA) detector is a method which converts the thermal radiation of the target into the visible image. It is widely used in target seeking, missile guidance and space exploration, etc. For the requirements of small volume and fast cool-down application in missile guidance, an infrared FPA imaging guidance system was designed, including the catadioptric infrared lens, fast cool-down IRFPA detector, and low noise image circuit. The whole system satisfies the imaging requirements of the missile guidance.

Abstract:The temperature data measured with the microwave thermometer in the ground vacuum experiment suffer from a high-order nonlinearity, which cannot be properly calibrated with the traditional method. The origin of this high-order term was analyzed with the diode equation expressed in the form of Maclaurin expansion. A method combining the two-point linear correction with the cubic equation nonlinear correction was proposed to calibrate the deviation of the temperature data from the actual one. The method was verified through the cross-comparison of data from O-B and ATMS for the FY-3C microwave thermometer. The calibration precision reaches up to 4 K higher than that achieved using the U parameter correction method.

Abstract:Bi0.9Ce0.1Fe1-xNixO3(xBCFNO, x=0, 0.03, 0.05, 0.07)thin films were fabricated on SiO2 substrates by sol-gel process.X-ray diffraction patterns indicate that all films exhibit a distorted pseudo-tetragonal perovskite structure with a high degree of (012/110) preferred orientation and peak position deviation. The intensity of(012/110)peak changes with the change of x with a maximum value at x=0.05. Furthermore, the grain size become the biggest at x=0.05 revealed by scanning electron microscopy (SEM). The smallest band gap of xBCFNO films is 2.14 eV at x=0.03 measured by the optical transmission spectra. The magnetic hysteresis (M-H) loops show that the room-temperature ferromagnetism was enhanced with Ce and Ni co-doping.

Abstract:Residual stress matching is critical for elimination of deformation for terahertz (THz) microbolometer with micro-bridge structure. Finite element simulation model of micro-bridge was built with a pixel size of 35 μm×35 μm. Intellisuite was used for mechanics simulation based on orthogonal experimental design. A minimum deformation of 0.0385 μm was obtained with an optimized stress combination when the residual stresses of support layer, passivation layer, electrode layer, sensitive layer and absorption layer were +200 MPa, +200 MPa, +200 MPa, 0 MPa and -400 MPa, respectively. 320×240 THz focal plane array was fabricated with the optimized stress combination. A minimal deformation was achieved, which agreed well with the simulation.

Abstract:Leaf area index (LAI) is an important indicator of wetland ecosystem health. Poyang Lake wetland vegetations grow densely, with LAI of large dynamic range. Considering the complex scattering mechanisms of radar data, a radar vegetation index was defined. To overcome the saturation of the optical vegetation indices, a new integrated vegetation index using GF-1 and Radarsat-2 data was established for estimation of wetland vegetation LAI. The validation of measured data and theoretical model simulation showed that this integrated vegetation index is a good alternative to that using only the optical or radar observation. The best fitting models were built with optical vegetation indices, radar vegetation index, and the integrated vegetation index, respectively. The result indicates that the integrated vegetation index can improve predication accuracy for wetland vegetation LAI.

Abstract:For quantitative remote sensing, instrument calibration precision should be monitored from time to time. To monitor the accuracy of cross calibration of FY-3C satellite Infrared Atmospheric Sounder(IRAS), a platform was set up based on a cross comparison of IRAS with standard infrared high spectral resolution instruments- Infrared Atmospheric Sounding Interferometer (IASI). Calibration precision monitoring analysis using IRAS data in the year of 2014 shows results as the following. For all the 20 infrared channels the correlation coefficients of IRAS with IASI were above 0.98. The mean bias for most channels are less than 1K except that channels 9 and 16 are nearly 1.4 K and channels 1 and 18 are larger than 2 K. The standard deviation for most channels is less than 1.5 K, while for surface sounding bands of 8, 9, 18, 19, and 20, it ranges from 1.5 to 3 K. The latter is probably due to that the channels which detect atmosphere of near boundary layer were more susceptible to the time and location differences. The calibration bias variation trend with target brightness temperature was flat for channel 2, 3, 4, 10 to 13, while an obvious trend can be seen for channels of 14 to 20 and the difference between maximum bias and minimum bias can reach 5 K. Time series analysis of calibration bias indicates that for most channels the calibration bias were stable in one year and the variation magnitude was less than 0.3 K. It is about 1 K for channel 15, 19, and 20. The calibration bias variation reached 2 to 4 K in one year for channel 1, 14, 16, 17, 18. In a word, IRAS cross calibration accuracy monitoring system provide a tool for real time monitoring of calibration precision change.

Abstract:A novel type of asymmetric elliptical-hole photonic crystal fiber (PCF) with a central defect hole was proposed. The full vector finite element method was adopted to investigate its birefringence, dispersion and non-linear characteristics. By changing angle of the first layer of the elliptic hole, birefringence properties of the structure are strengthened, which also can improve the dispersion performance of the structure at the same time. The analysis results demonstrated that fibers with a value of 305×10-2 for birefringence at the wavelength of 1.55 μm can be obtained by setting suitable structure parameters, meanwhile with high nonlinear coefficients in both X and Y polarization directions. Furthermore, while maintaining the high birefringence, the proposed PCF also has negative flat dispersion of nearly 550 nm from 1 000 nm to 1 550 nm. The photonic crystal fiber with the new structure has wide applications for the polarization control, nonlinear optics and optical fiber communication.

Abstract:Using the complex function and the image method, thermal wave scattering in the slab of functionally graded materials with a cylindrical subsurface inclusion was investigated. Based on the Non-Fourier’s heat conduction equation, the temperature field in the slab of FGM with a cylindrical subsurface inclusion was analyzed. The analytical solution of the scattered field of thermal waves in the slab of FGM was obtained. The temperature wave is excited at the surface of FGM by the periodically modulated beam. The upper and lower temperatures are the environmental temperature. The influence of the geometrical and thermophysical parameters of the cylindrical inclusion on the temperature at the frontal surface of FGM was calculated. The results of this paper are expected to provide calculation methods and reference data for infrared thermal wave nondestructive testing of functionally graded materials.

Abstract:Modulation linearity and modulation range of the tunable laser are the major factors limiting the resolution of FMCW laser ranging. When using a tunable laser with a small modulation range to measure the distance of a single target, the measuring resolution can be improved by fusing signals of multiple measurements sampled with equal optical frequency interval. This method can greatly reduce the FMCW laser range’s demands on modulation range of the tunable laser. This method is easy to achieve and the structural is simple. This system has a wide application in industrial large scale measurement, space technology, and surveying.

Abstract:Millimeter wave communication system is widely used in SATCOM due to the characteristics of wide bandwidth and miniaturization application. Optimal link supportability of multi-carrier millimeter-wave SATCOM systems for improving the system capacity faces tradeoff issues among many performance metrics, such as reducing the uplink EIRP demand, improving the transponder power utility, and strengthening the robustness of the links. This paper introduced the concept of multi-objective optimization to the link supportability of millimeter-wave SATCOM modeling. A Constrained Nondominated Neighbor Immune Algorithm (C-NNIA) was presented. Results show that the Pareto-optimal solutions obtained with the algorithm are better than that derived with Direct Solution (DS) algorithm and single objective optimization based Variable Neighborhood Search (VNS) algorithm. It has better constraint handling, convergence and diversity performance as well. Several design guidelines were obtained through the statistics and analysis on design variables and performance metrics within the Pareto-optimal solutions.

Abstract:To process the data from 94/220 GHz dual-band radar, the single scattering and attenuation characteristics of ice crystals with different shapes by the two bands were analyzed. The echo characteristics of ice clouds based on single shape ice crystals or a refined model were discussed. The backscatter and attenuation of the larger particles are sensitive to the particle shape. They are the largest for hexagonal ice crystals, greater for bullet, and the least for snow. The radar reflectivity factor (Ze) of ice clouds based on single shape ice crystals are sensitive to the shapes of ice crystals, ice water content and the median dimension of particles size distribution (PSD). The attenuation coefficient of 220 GHz wave is about 5-25 times than that of 94 GHz at the same PSD. Ze of the refined model increases with the particle concentration, ice water content, and median dimension. It is less sensitive to the shape parameters of the PSD.