Estimation of snow density using full-polarimetric Synthetic Aperture Radar (SAR) data

In this paper, a new snow density estimation methodology is proposed for full-polarimetric Synthetic Aperture Radar (SAR) data. The generalized four component polarimetric decomposition with unitary transformation (G4U) based generalized volume parameter is utilized to invert snowpack dielectric constant using the Fresnel transmission coefficients. The snow density is then estimated using an empirical relationship. Six Radarsat-2 fine resolution full-polarimetric C-band datasets were acquired over Himachal Pradesh, India. The near-real time in-situ measurements were collected with the satellite pass to validate the proposed method. The mean absolute error (MAE) of the proposed method is 0.027 g cm⁻³ and the root mean square error (RMSE) is 0.032 g cm⁻³. The snow density variation within a season were also analyzed using multi-temporal Radarsat-2 data.     

GB-SAR导轨倾角引起的影像坐标投影变换误差分析

依据GB-SAR传感器运行导轨与成像投影面的空间关系,分别推导了导轨中心线俯仰角和横轴侧倾角所引起的成像投影误差的计算公式。计算结果表明,导轨安装定位时产生的俯仰角通常可以忽略不计,而成像投影误差对导轨横轴的侧倾角更为敏感。在GB-SAR连续变形监测应用中,导轨的横向姿态需做严格控制,确保其水平度。     

一种改进的SAR影像边缘检测方法

由于SAR影像具有乘性相干斑噪声,某些对光学影像有较好检测性能的边缘检测算子,对于SAR影像并不适用,因此本文提出了一种将改进后的Ratio算子与Canny算子相组合的新方法。首先采用多种客观评价指标,得出经典方法中的Lee滤波能有效去除噪声,且最大限度保留了梯度信息,适用于边缘检测;然后对边缘检测具有恒虚警特性的Ratio算子进行改进,改进后的算子更利于影像归一化处理;最后利用改进后的Ratio算子与Canny算子组合成新方法。试验结果证明,组合后的新方法显著提高了边缘检测正确率和定位精度,改善了边缘连续性,具有一定的有效性和实用性。     

Optical Dating Equivalent Dose (De) Comparison of Global Standardised Growth Curve (gSGC) and Single-aliquot Regenerative-dose (SAR) Methods for Quartz Grains

Optical dating is a method of measuring the time since the sample was buried from last thermal event or light exposure. Samples such as quartz and feldspar grains are the most commonly used sediment of measurement. Single-Aliquot Regenerative-dose (SAR) method has become the most acceptable procedure for obtaining the equivalent Dose (D_e) of a sample. The Standardised Growth Curve (SGC) method provides a possible procedure for measuring a large number of samples; the limitation is that the growth curve fitted by different samples or even different aliquots is divergent. The global Standardised Growth Curve (gSGC) method improves the shortage by normalizing the dose response curves using one regenerative dose OSL signal. The gSGC provides a possible method for obtaining the D_e value of the sample efficiently and quickly. However, due to the radiation dose rate, operating procedures and instrument error and the selected regenerative-dose normalized dose value, etc., each laboratory should develop their own gSGC which has unique parameters. This study established the gSGC curve and measurement process of our laboratory, and then compared the consistency of the equivalent Dose (D_e) values from gSGC and SAR methods. In gSGC procedure, the D_e value of an aliquot can be estimated from the nature signal, one regenerative dose signal and their corresponding test dose signal. It will speed up the optical dating measurement rate of our laboratory and provide reference to establish gSGC in other laboratories. It is found that in the low dose range (0~100 Gy) the obtained D_e values were well consistent by gSGC and SAR methods. There were obviously differences in the higher dose range (>100 Gy) compared to the SAR results. It may be due to the insufficient number of older samples used to fit gSGC in this study. It is necessary to gradually accumulate more samples to improve the gSGC parameters in the future work. For some aliquots, individual quartz grains do not follow the global standardised growth curve, which leads to some deviations of D_e from gSGC. However, these two methods could obtain the similar average De value when multiple aliquots measuring.     

On the SAR derived alert in the detection of oil spills according to the analysis of the EGEMP

Satellite services that deliver information about possible oil spills at sea currently use different labels of “confidence” to describe the detections based on radar image processing. A common approach is to use a classification differentiating between low, medium and high levels of confidence. There is an ongoing discussion on the suitability of the existing classification systems of possible oil spills detected by radar satellite images with regard to the relevant significance and correspondence to user requirements. This paper contains a basic analysis of user requirements, current technical possibilities of satellite services as well as proposals for a redesign of the classification system as an evolution towards a more structured alert system. This research work offers a first review of implemented methodologies for the categorisation of detected oil spills, together with the proposal of explorative ideas evaluated by the European Group of Experts on satellite Monitoring of sea-based oil Pollution (EGEMP).     

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非均布列车荷载作用下软土路基的振动分析

基于实测资料,假设列车轮载经钢轨传递下来的荷载由5根枕木承担。根据分担比,获得了道渣层表面非均布荷载的表达式。将道渣层视为单相弹性介质,软土地基被看成是考虑水土耦合作用的饱和多孔介质。借助势函数,利用Helmholtz矢量分解法及Fourier变换技术分别对弹性土体和饱和半空间土体进行求解,得到非均布移动荷载作用下软土地基位移、应力及孔压响应在变换域内的精确解答。利用FFT算法得到了数值结果,详细分析了荷载分布形式、观察点位置、道渣性质以及软土地基渗透系数对动力响应的影响。研究结果表明：高速情况下动力响应与低速情况有很大不同;对于软土路基,应特别注意列车高速运行时路基浅层范围内产生的孔压响应。     

基于拉格朗日分解算法的SAR图像混合像元分解

为解决与光学遥感图像不同的合成孔径雷达(SAR)图像中存在大量混合像元的问题,本文提出了一种基于拉格朗日分解算法的SAR图像混合像元分解的方法,结合相关内容中具体定理的证明,文中给出拉格朗日分解算法用于SAR图像混合像元分解的系统的求解方法.用人工模拟SAR图像和ENVISAT SAR图像进行实验,结果表明拉格朗日分解算法的混合像元分解结果明显优于非约束类神经网络(文中实验以BP神经网络为例)的分解结果.     

不同钠吸附比含水介质中胶体迁移-沉积动力学

以滨海含水介质中天然胶体为研究对象,采用自行设计的室内土柱装置,研究不同钠吸附比胶体在滨海含水介质中迁移动态特征,测定了胶体沉积动力学曲线,计算了胶体总沉积率和沉积速率常数,最后对胶体迁移沉积机理进行了探讨。研究结果表明,胶体的穿透曲线与示踪离子相比,存在一个临界孔隙体积数(临界点),在临界点之前胶体的迁移速度大于示踪离子,之后则相反;胶体未发生完全穿透,钠吸附比SAR为0,2.85和∞;出水胶体最大相对浓度为0.65,0.16和0.70;胶体在含水介质迁移过程中发生了沉积,沉积量随孔隙体积数的增加而增加。胶体在含水介质中迁移的总沉积率分别为50.96%、87.95%和54.24%。钠吸附比SAR=2.85时沉积动态曲线为直线,沉积速率常数为0.151h-1,而钠吸附比SAR为0和∞时胶体沉积动态曲线为分段直线,拐点前后胶体沉积速率常数分别为0.072 h-1、0.048h-1和0.211 h-1、0.194 h-1。研究结果用双电子层理论可以很好地解释。     

机载SAR影像时空模型重构因子及3D特征提取

时空模型有助于人们获取类似于真实世界的时间及空间信息 ,对于城市工程设计、灾害预防决策及军事应用具有重要意义。本文探讨了机载SAR影像重构时空模型的潜力及方法 ,研究了时空模型重构因子、基于机载SAR影像的建筑物、植被的三维提取 ,以及相应的机载SAR影像时空建模一般方法