Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335
- Most Read
- Most Cited
- Most Downloaded
Abstract:Using one band effective mass approximation and shooting method, optimized parameters of quantum well infrared photodetector structure were calculated. Taking into account high order effect of band nonparabolicity, the device structure with a peak detection wavelength of 8 μm were designed. Based on the calculated result, GaAs/AlGaAs multiwell material was grown. Then single-element QWIP device were fabricated and characterized. Symmetrical I-V curves showed very good quality of the material and successful process in device fabrication. Spectral responsivity exhibited peak wavelength of 7.96 and 7.98 μm, which were in excellent agreement with our designed value.
Abstract:Simulation of transport properties in mid-infrared quantum cascade lasers (QCLs) with different structures at different temperatures based on non-local transport model is reported. With this model, drift-diffusion equations are solved with modification of current density by accounting for long-range carrier transport including quantum tunneling, mini-band tunneling and hot carrier transport in the device. The simulation compared the integrated models with experimental data and reasonable agreements with experiments have been obtained with some reasonable fitting parameters.
Abstract:A D-band frequency doubler with quartz substrate is proposed in this paper with commercial planar Schottky diodes DBES105a. The balun in the doubler is implemented by finline-suspended-stripline coupler (FSSC). The waveguide-to-finline transition suit for quartz substrate has only 0.15 dB measured insertion loss. Compared with traditional coupler in balanced doubler and mixer designs, it has the advantage of easier bias for the diodes. Measured results of the doubler showed that the maximum output power is 3.39 mW with 0.4 V reverse bias voltage and 26.3 mW drive power. Its corresponding peak efficiency is 12.9%. The output power of the doubler is reduced from 3.1 mW to 2.0 mW when the bias voltage deviates from its optimum bias condition. The finding shows that proper external DC bias for Schottky varistor multiplier is as important as for schottky varactor diode frequency multiplier.
Abstract:The results of simultaneous-mode 128?128 MW/LW two-color HgCdTe Infrared detector was presented in this paper. The photoresist (PR) spray-coating technology was developed to open the windows of non-planar implantation and metallization of two-color HgCdTe infrared detector. By etching to expose the n-type implantation-region of MW photodiodes, non-planar B -implantation of MW photodiodes and LW photodiodes synchronously, side-wall passivation, side-wall metallization and flip-chip hybridization with Readout Integrated Circuit (ROIC), 128?128 MW/LW two-color HgCdTe Infrared detector was achieved from a triple-layer p3-p2-P1 hetero-junction Hg1-xCdxTe film grown by molecular beam epitaxy. At liquid nitrogen temperature, the cut-off wavelengths of the simultaneous-mode MW/LW two-color Infrared detector were 5.1μm and 10.1μm individually, and the peak detectivities (D?p* ) were2.02?1011cmHz1/2/W and 3.10?1010 cmHz1/2/W respectively. Also the spectral cross-talks of MW-to-LW and LW-to-MW were suppressed to only 3.8% and 4.4% by optimizing the chip structure of the simultaneous-mode two-color infrared detector.
Abstract:In this paper, we reported the growth and fabrication of a 128 ? 128 infrared focal plane array detector made of type-II InAs/GaSb superlattice. The superlattice structure was grown on GaSb substrate using molecular beam epitaxy (MBE) technology. It consisted of 200 periods of 13ML(InAs)/9ML(GaSb) for longwave infrared detection. The pixel of the detector had a conventional PIN structure with a size of 40 μm?40 μm. The device fabrication process consisted of mesa etching, side-wall passivation, metallization and flip-chip hybridization with readout integrated circuit (ROIC). At 77 K, the detector had a 100% cut-off wavelength of 8.0 μm, and a peak detectivity of 6.0?109 cmHz1/2W-1. Concept proof of infrared imaging was also demonstrated with the focal plane array at liquid nitrogen temperature.
Abstract:For separating two wavelengths of 810nm and 850nm polarized light into two optical beams, keeping their polarization directions and pursuing the maximal degree of polarization, a dichroic beam-splitter at incidence angle of 45?is designed and fabricated, and it makes 810nm beam passed and 850nm beam reflected. Selected an apposite initial film configuration to control the separation of s- and p-polarization components, and optimized the the film configuration by the Global Modified LM method in Film Wizard software, and the phase and energy parameters meet the design target. TiO2 and SiO2 have been chosen as high- and low-refractive index layer materials respectively. Ion beam-assisted deposition, optical extreme value method, and quartz crystal oscillator have been used to control the thickness of films . The extinction ratio of obtained sample reaches 7000:1 in 810nm beam and 20000:1 in 850nm beam. This work realized phase and energy control of optical thin films to meet the demands of polarization states coding communication experiment.
Abstract:The cold fluid model theory are used for the transport and its instability for the sheet electron beam in the uniform magnetic field, which are indicated that, if the focusing magnetic field and the filling factor of the beam in tube are increased, the Diocotron instability will be decreased to achieve the transportation in long distance. Then, the 3D simulation method is developed to obtain the electron optics system for the W-band sheet beam klystron. Furthermore, a 2D macro-particle model for sheet electron beam is proposed to develop a beam-wave interaction simulation program code for SBK, named SBK2D. And the beam wave interaction processes for the W-band SBK with 8 multi-gap cavities are calculated using the SBK2D, the 69kW high frequency output with the efficiency of 24% , gain of 37 dB and 3dB bandwidth of 100MHz are observed. Finally, the w-band sheet beam tube is manufactured. The transmission rate and cross-section experiments are performed with the beam voltage of 20-82 kV, beam current of 0.5-4.27A, and the length of tunnel of 100mm，and more than 98% transmission rate with the beam cross-section about 10mmx0.5mm are obtained.
Abstract:This paper proposes an optimized method for in-flight spectral calibration of UAV (Unmaned Aerial Vehicle) hyperspectral imager covering visible and near infrared band. Taking simulated radiance as reference spectrum, the method uses spectrum matching technique to retrieve the most important spectral parameters center wavelength and bandwidth. With the data in Urad Front Banner, Inner Mongolia on November 14th, 2010, hyper-spectral camera on UAV was calibrated based on the laboratory spectral calibration result. The efficiency of data process was 100 times that of normal algorithm. A method of accuracy evaluation with ground targets was also developed. The in-flight spectral calibration accuracy for a sensor with bandwidth of 7nm was proved to be better than 0.5nm.
Abstract:Considering the Moon as a reference source for thermal emissive band (TEB) calibration without any knowledge of lunar surface’s emissivity or temperature, the quantitative relationship of the measured radiances between different TEBs is established by introducing the parameter universal dual-band emissivity ratio (UDER) and further used to deduce a novel cross-calibration approach between different bands. Meanwhile, selecting the thermal infrared band with the higher radiometric accuracy as a baseline, the on-orbit radiometric calibration for water-vapor band of FY-2E satellite is basically realized by using multi-bands lunar observations without any space-borne full-path blackbody. The radiometric calibration accuracy has been averagely improved by about 3.5K in the lower temperature region between 200K and 220K, which greatly benefits to the enhancement of some quantitative products significantly, i.e. cloud classification.
Abstract:The multiple scattering effect between heterogeneous non-isothermal surfaces is described rigorously using the configuration factor in engineering thermophysics, based on which a directional thermal radiance model is built, and the numerical calculation of the model is discussed. The model is is integrated with the the gap probability model and applied to a row structure to simulate the change of Directional Brightness Temperature (DBT). The results show that the modeled DBT hold high correspondence with the observed DBT, especially in the condition that the gap probability is very low. It is also shows that the DBT is aggrandized because of the multiple scattering effects, whereas the change range of DBT is smoothed. The temperature difference, spatial distribution, emissivity of the components can all lead to the change of DBT, that is to say, the higher of the temperature difference, the craggier of the surface and the lower of the emissivity, the more exquisite DBT changes along with the viewing zenith. The model advanced in this paper can explain “hot spot effect” of thermal radiance, and it is confirmed that the existence of “hot spot” is mainly related to the spatial distribution of components’ temperature. This model can be used for the study of directional effect on emissivity, the LST retrieval over urban areas and the adjacency effect of thermal remote sensing pixels.
Abstract:In this study, hypespectral data was used to estimate leaf and canopy nitrogen content. First, improved model based on the Gaussian error function of BP neural network, Erf-BP was used to develop remote sensing models for estimating leaf nitrogen content; then the scaling conversion function during downscales from canopy to leaf spectral was derived according to principles of geometric optics model. Furthermore, these relations were used during downscales from the canopy reflectance of Hyperion image to leaf spectral for leaf nitrogen content estimation. Finally, forest structural parameter LAI (Leaf Area Index) was used to obtain canopy nitrogen content from leaf level. The results showed that the best Erf-BP neural network model with testing accuracy of 76.8597% includes 8 hidden layers. Using scaling conversion function to estimate canopy spectra at 670nm and 865nm, R2 of the relations between modeling spectra and measurements were 0.5203 and 0.4117 respectively. And correlation coefficient between estimated leaf nitrogen content and measurements was 0.7019. It can be found that this method provides a good reference for more rapid and accurate estimation of leaf and canopy nitrogen.
Abstract:Based on the thermal infrared data obtained from environmental mitigation satellite, the sea surface temperature (SST) was retrieved using generalized single-channel method to get the quantitative information about the diffusion of the thermal discharge around the Tianwan Nuclear Power Plant. It indicated that the retrieved SST was consistent with the MODIS SST product. Based on the retrieved SST distribution map, the thermal field variations in different seasons and tides were analyzed. The area where the SST has increased more than 3℃ in winter was much larger than that in summer. During the winter months, the thermal discharge extended to a sector area around the power station, while in summer it was limited to a longer and narrower area in one side of the bay. The thermal fields at low tide were rather larger than that at high tide, with the area where the SST has increased more than 3℃ four times larger than that at high tide.
Abstract:Traditional method for retrieving precipitable water vapor was evaluated with the data obtained from series of long time in-situ measurements of CE-318. The results show that the method has a low accuracy and is not suitable for applications over this region. In this paper, the theory of precipitable water vapor detection with NIR channels was introduced. Equations of precipitable water vapor remote sensing were derived and analyzed. Retrieving method for FY-3A/MERSI（Medium Resolution Spectral Imager）was proposed. Comparing with the results of CE-318 in-situ measurements in the studied area, it was concluded that precision of the method relied so much on reflectance of the underlying surface. The method of three-channel ratio had better performance than that of two-channel ratio by reducing the errors from 16.1% to 14.3%.
Abstract:A simulated database build with the Dobson semi-empirical model was fitted to the Hallikainen formula by the least square regression method. The coefficients at key frequency points of the L/S/C/X-band were calibrated with some improvement. The simplified model between the real part of the dielectric constant and the soil volumetric moisture content was established. It was validated and compared with other models. The results show that the simplified model has better accuracy than the Hallikainen empirical model, and also has good accuracy and practicality compared with the complex Dobson semi-empirical model.
Abstract:Disadvantages of the active contour model with high computation cost, slow speed, and especially low efficiency are carefully researched and a novel active contour model is presented. The presented model replaces the real symbol distance function with the virtual symbol distance function, and the evolution of the active contour in presented model depends on the averages inside and outside the object. The gradient of the virtual distance function form a narrow band, where the active contour evolutes by simply adding and simply subtracting. Thus, the evolution has the following advantages: simple calculation, high-efficiency segmentation, free topology, and global property. The virtual symbol distance function is re-initialized with sign function after the virtual symbol distance function is regularized by the Gaussian function within a narrow band. In addition, a simple condition is given for the active contour convergence within the narrow band and it is easy to judge whether the object is detected.
Abstract:Reconstructions of the 3-D model of buildings from single high-resolution SAR (Synthetic Aperture Radar) image were studied. After a detailed analysis on the electromagnetic backscattering model of buildings, the methods on how to calculate the backscattering coefficient of different reflectivity areas and on how to create a simulated SAR image from the CAD model of a building was proposed. The outlines and orientations of buildings were extracted using the double-bounce structures. The building height was estimated based on the iterative simulation and matching. The simulated SAR images are divided into different kinds of scattering areas. The Kullback-Leibler divergence between these areas was treated as a measurement of the matching degree. The tested height, at which the simulation SAR image obtains the best matching degree, is taken as the final estimated height. The above methods were evaluated on two real high-resolution SAR images. The reconstruction results are satisfying and prove the feasibility of 3-D reconstruction of building from single high resolution SAR image and the validity of the proposed approach.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335