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:A cylinder shape photoacoustic (PA) cell has been designed and fabricated for midinfrared laser photoacoustic spectroscopy (MIRPAS) gas sensing application. A complete modeling of the acoustic signal transmission and detection in the PA cell using FEM have been performed to simulate its characteristics and compared systemtically with the measured data. Results show that the second longitudinal mode of the PA cell has the highest resonance amplitude around 4.2 KHz with moderate Q value, so this mode is quite suitable for MIRPAS gas sensing purpose.
Abstract:In the present study, midinfrared spectroscopy(MIR) was attempted to apply for quality evaluation of C. deserticola. First of all, IR spectra of the herbal sample and its 3 main extracts including PeGs, Man and Polysaccharides were compared. Characteristic absorption peaks within different wave number range were found in different extracts. Then the authors managed to find the relationships between the intensity of the characteristic peaks and the relative content of the PeGs and Man in herbal sample. The IR spectra of the herbal samples were compared with PeGs and Man using Spectrum v5.02 software (Perkin Elmer) for IR Corrdations. It was found that the content of PeGs (y) and its IR Correlation (x) within herbal sample in the range of 1800~1200cm-1 〖JP2〗were correlative (R2= 0.9927) by the SPSS 11.0 analysis, and the regression equation is y=19.846x + 0.0623. In the same way, the content of Man (y) is correlative with the IR Correlation (x) in the range of 1100~ 600cm-1 (R2 =0.9705), and the regression equation is y=13.855x-0.1714. Therefore, MIR spectroscopy is a fast and effective method in qualitative and semiquantitative analysis of quality evaluation of C. deserticola.
Abstract:A highpower and high beam quality 980nm bottomemitting verticalcavity surfaceemitting laser (VCSEL) with optimized pcontact aperture was reported. A numerical simulation of current density in a large aperture bottomemitting VCSEL with oxidation between the active region and the top ptype mirror was conducted. It is found that the simulated current density profiles of VCSEL are dependent on the oxide aperture diameter and the pcontact diameter. For a fixed oxide aperture diameter, the homogeneous current density of the VCSEL could be realized by optimizing the pcontact diameter. Thus, the edge mode in farfield patterns was suppressed. The farfield divergence angle from a 600 μm diameter VCSEL was suppressed from more than 30° to 15° and no strong sidelobe was observed in farfield pattern when the pcontact diameter decreased from 650 μm to 580 μm. There is a slight rise both in threshold current and optical output power due to the pcontact optimization. The VCSEL device produces the maximum optical output power of 2.01 W with lasing wavelength of 982.6nm by improving the device packaging method.
Abstract:ZrO2 films were prepared at different conditions using electron beam evaporatim. The influences of oxygen pressure, temperature and substrate rotation on the films were analyzed. The relationship of microstructure characteristics and laser induced damage threshold was investigated. There are mostly monoclinic phases in ZrO2 with substrate rotation, and tetragonal phases without rotation. The surface roughness and grain size of ZrO2 films reduce with the increase of oxygen pressure, and the impact is greater for tetragonal phases than monoclinic phases. The increase of oxygen pressure makes the spathic structure change into the amorphism structure, and the damage threshold of spathic structure increases when the grain size reduces. The surface roughness of the film increases with the depositing temperature increasing. The damage threshold of spathic structure is much larger than the amorphism structure's. For ZrO2 films, the laser induced damage threshold and surface roughness (E-σ) approximately accord with Eσα=β(α=1.41, β=2.25).
Abstract:The laser beam induce current (LBIC) characterization on femtosecond laser drilled holes indicates the formation of pn junctions in p-HgCdTe. The influences of laser power and numerical values of focus lens on the morphology of the drilled holes were studied. The diameter of the holes and their inversion layer thickness are both linearly proportional to the power of laser. On the other hand, there were no observable changes in the LBIC signals of the holes as the laser power was changed. In addition, the LBIC signal intensity of the holes was insensitive to the change of focus depth of the drilling laser.
Abstract:In order to improve the infrared stealth of water surface object, the attenuation character of water spray on infrared radiation was numerically investigated. The infrared attenuation and temperature response of the composite test board were measured before and after the water sprayed. The numerical and experimental results show that water spray with a certain concentration can decrease infrared transmission efficiently and change the infrared radiation feature of the test board quickly. According to the detective model of infrared system, the detective distance and image distance were analyzed with and without water spray between infrared imager and water surface object. The analysis result demonstrates that the detective distance of water surface object decreases about 25% and image distance decreases about 19% after water spray system was turned on, which tells that water spray is an effective method for infrared stealth and it can be widely used in the infrared stealth of water surface object.
Abstract:Seasonal variation in spectral characteristics of Moss Soil Crust (MSC) under different moisture conditions highly affects the application of remote sensing on determining the fraction cover and productivity of MSC. However, relatively little research has focused on it. This study thus aimed to fill the gap by analyzing in situ measurements of spectral reflectance of dry and wet MSC as well as bare soil. Results show that the spectral response curve of dry MSC is similar to that of bare soil，while the wet MSC alive demonstrates a similar spectral characteristic with higher plants. Similar to higher plants, the spectral reflectance of wet MSC varies seasonally indicated by a large difference in July and October, and so does that of dry MSC. In addition, the spectral reflectance of MSC changes as soil moisture changes. Hence, the applicability of remote sensing approaches developed only based on the difference of the spectral response curve of MSC from other ground objects under certain condition is much reduced. Besides, the similarity in the spectral reflectance curves of wet MSC and higher plants may result in the misinterpretation of vegetation indices and the overestimation of vegetation productivity in an area covered by abundant mosses. The misinterpretation of vegetation indices could be more severe due to the Maximum Value Composite (MVC) technique used to compose the global vegetation maps in the study of vegetation dynamics.
Abstract:Basic applicable conditions and upper limits for improving spatial resolution of image restoration and superresolution reconstruction were researched theoretically by using discretetodiscrete imaging model. The quantitative indices of applicable conditions based on image processing were given. Experiments on restoration and SRR were carried out by simulating different sampling frequencies and SNR lowresolution images, and the results were analyzed in detail. The perfect consistence was obtained between the theory and experiment.
Abstract:The theoretical analysis of emergence mechanism and linear unmixing model of mixed pixel was presented. A novel compact field hyperspectral imaging system was setup, and high accurate spectrum of endmembers was collected directly. Based on these endmembers, the model of linear unmixing of the mixed pixels was studied. The weighted spectrum obtained with the model for endmember with different abundance in the whole nonthreedimensional space was compared with the practical mixing spectrum. The accuracy of the model was verified.
Abstract:Fusion method of subdivision band images of midwave infrared is presented based on both morphology processing and support value transform (SVT). Local process of two subdivision band MWIR images is implemented with erosion, dilation and weighted stacking method, in order to eliminate saturating regions in the first subdivision band image that are formed by sun irradiation. Fusion between local processed image and the second subdivision band image is achieved by SVT, in order to combine detailed information of two images and to get legible results. The experimental results show that the saturating regions of image obtained by proposed method, compared with image fused by wavelet packet transform, are removed effectively. The sun effect parameter decreased by 60.05%, local standard deviation and local coarseness increased by 2.59% and 3.39% respectively, and elapsed time decreased by 66.77%. The validity of fusion method proposed is proved.
Abstract:To correct measurement errors in spectral emissivity measurement based on FTIR in the vacuum ambient, the emissivity calibration model has been constructed, including radiation thermal losses, one dimension heat transfer and radiation thermometry. The emissivity error has been quantitatively analyzed. The results show that the higher the sample temperature is, the lower is the value of the emissivity. This result is induced by thermal losses, material thermal conductivity and sample thickness. To reduce the error induced by these factors, the system should be calibrated. The calibrated spectral emissivity of highpurity graphite sample at 2000℃ agrees very well with the results reported by G. Neuer and G. JaromaWeiland.
Abstract:An exact maximum likelihood error estimation algorithm based on unbiased converted measurements (UCMEML) was proposed in order to estimate systematic errors of a MMW radar/IR imaging composite system accurately. An error estimation model was formulated based on measurement noises in polar coordinates, then the criterion function and the corresponding negative log likelihood function were given. The algorithm was implemented using a recursive twostep optimization that involves a modified GaussNewton procedure. Simulation results show that the UCMEML algorithm is better than the exact maximum likelihood (EML) algorithm and the modified exact maximum likelihood (MEML) algorithm on performance and convergence rate.
Abstract:A new mixed kernel function weighted RX algorithm for anomaly detection in hyperspectral imagery was proposed. First, each spectral pixel was mapped into a highdimensional feature space by a nonlinear mapping function. Second the nonlinear information between different spectral bands of the hyperspectral imagery was exploited with the RX algorithm in the feature space. In order to optimize the covariance matrix, each pixel in the covariance matrix was weighted according to its centroid distance. In this way the weighted covariance matrix could represent the background distribution better. Finally, the dot product computation in the highdimensional feature space were converted into the kernel computation in the low dimensional input space. The new spectral kernel function and the radial basis kernel function were composited according to the characteristic of hyperspectral data to improve the performance of the proposed algorithm. To validate the effectiveness of the proposed algorithm, experiments were conducted on real hyperspectral data. The results show that the proposed method can detect more anomaly targets than the RX algorithm in the feature space.
Abstract:An unsupervised change detection method based on fast expectationmaximization (EM) algorithm and fuzzy fusion for multiband remote sensing images was proposed. First, fast EM iteration algorithm based on histogram of image difference in each band was used to obtain the change class threshold and change information. Second, the fuzzy theory and relationship matrix were adopted to integrate the classification information of all bands, and the final changed and unchanged map of the bitemporal remote sensing images were obtained. Thus, the change detection image was formed. The real bitemporal SPOT5 and Landsat TM satellite imagery were performed to evaluate the effectiveness of the proposed method. The results show that the proposed method reduces the processing time and gets better detection effectiveness comparing with other methods.
Abstract:The effect of line defects on photonic band gap was investigated for the two dimensional photonic crystal consisting of square lattices of dielectric cylinder by means of plane wave expansion method. The result shows that both the radius and the width of defect layer in photonic crystal have an obvious effect on photonic band gap. The first band gap width of the TE wave was a maximum with the increase of the radius of the defect cylinders. The centre of the band gap shifts down and the numbers of band gap are changed well with increase of the radius of the defect cylinders. In addition, the band gap width is reduced as the difference between the width of defect layer and that of normal layer increases.
Abstract:A variation approach for SAR image feature enhancement is proposed. By analyzing the diffusion coefficient of PM diffusion, it was found that it is the nonCFAR character of Canny detector that blurs the edges in the filtered SAR image. Further more, the ROA detector can detect edges in the image, but it lacks the ability of detecting the strong scatters. Based on the Rayleigh distribution of speckle in the amplitude image, the variation model for feature enhancement was established by combining the ROA detected version and the amplitude of SAR image from the MAP estimator. Experiments〖JP〗 on the real SAR image demonstrated that the proposed method can suppress speckle efficiently in the homogeneous areas and preserve or even enhance edges and strong targets in the image.
Abstract:Data of the UV absorption spectra from the water samples with a certain concentration of the nitrogen and phosphorus is very large. Wavelet transformation (WT), based on the softthreshold, can be effectively used to compress the spectrum signal of UV absorption spectra. High correlation often exists among the spectral intensity for the water samples with different concentration of the nitrogen and phosphorus. Partial least square regression (PLSR) can be used to decrease such correlation and to build an effective regression model for the sampled water. The detection precision is also increased in this way. Simulation of the tested water samples showed that the maximum relative error in the concentrations of nitrogen and phosphorus was 8.9%. The model can fully meet the requirements of detection precision.
Editor in chief：Jun-Hao CHU
International standard number：ISSN 1001-9014
Unified domestic issue：CN 31-1577
Domestic postal code：4-335