基于HJ-1A高光谱的黄河口碱蓬和柽柳盖度反演模型研究

碱蓬和柽柳是黄河口湿地典型的盐生植物类型,是多种保护珍禽的主要栖息地,具有景观尺度较小、分布广且多混生的特点。应用覆盖黄河口北部潮滩的HJ-1A高光谱遥感影像,基于现场测量的端元光谱和从遥感影像中使用顺序最大角凸锥法(SAMCC)自动提取的端元光谱,应用线性光谱分解法(LSU)、正交子空间投影法(OSP)、匹配滤波法(MF)、最小能量约束法(CEM)和自适应一致估计法(ACE)5种不同光谱解混方法进行混合像元光谱解混,对比两种方法得到的端元光谱分别对碱蓬和柽柳盖度的反演能力,并给出相应的反演模型。结果显示:(1)现场测量端元光谱取得了较好的碱蓬和柽柳盖度反演结果,其中应用LSU方法的光谱解混结果与现场测量盖度的决定系数对于碱蓬和柽柳分别达到了0.88和0.95;(2)两种端元获取方式的光谱解混结果中,LSU和OSP方法均获得了较高的相关性,ACE解混方法的相关性都最低;(3)SAMCC方法提取端元光谱对柽柳的分解结果与现场测量盖度的相关性远高于碱蓬。     

The utilization of the double focal transformation for sparse data representation and data reconstruction

In many cases, seismic measurements are coarsely sampled in at least one dimension. This leads to aliasing artefacts and therefore to problems in the subsequent processing steps. To avoid this, seismic data reconstruction can be applied in advance. The success and reliability of reconstruction methods are dependent on the assumptions they make on the data. In many cases, wavefields are assumed to (locally) have a linear space–time behaviour. However, field data are usually complex, with strongly curved events. Therefore, in this paper, we propose the double focal transformation as an efficient way for complex data reconstruction. Hereby, wavefield propagation is formulated as a transformation, where one‐way propagation operators are used as its basis functions. These wavefield operators can be based on a macro velocity model, which allows our method to use prior information in order to make the data decomposition more effective. The basic principle of the double focal transformation is to focus seismic energy along source and receiver coordinates simultaneously. The seismic data are represented by a number of localized events in the focal domain, whereas aliasing noise spreads out. By imposing a sparse solution in the focal domain, aliasing noise is suppressed, and data reconstruction beyond aliasing is achieved. To facilitate the process, only a few effective depth levels need to be included, preferably along the major boundaries in the data, from which the propagation operators can be calculated. Results on 2D and 3D synthetic data illustrate the method's virtues. Furthermore, seismic data reconstruction on a 2D field dataset with gaps and aliased source spacing demonstrates the strength of the double focal transformation, particularly for near‐offset reflections with strong curvature and for diffractions.     

A partial susceptibility approach to analysing the magnetic properties of environmental materials: a case study

An approach to expressing the magnetic properties of environmental materials in terms of the contributions of the magnetic susceptibilities of specific magnetic components is reported. The approach links the partial susceptibilities of discrete particles, domains or mineral fractions with the concentration-dependent parameters by means of multiple linear regression methods. The case study, using the Liverpool street dust data set, demonstrates that the technique is able to model the contributions of the main magnetic components satisfactorily. Several factors may have a significant impact on the regression results. These include the validity of the linear proportional relationships between partial susceptibilities and the relevant concentration-dependent parameters, the adequacy of the variable selection procedure and the regression model, and the suitability of certain magnetic parameters.     

CO2 saturation estimates at Sleipner (North Sea) from seismic tomography and rock physics inversion

CO₂ saturations are estimated at Sleipner using a two-step imaging workflow. The workflow combines seismic tomography (full-waveform inversion) and rock physics inversion and is applied to a two-dimensional seismic line located near the injection point at Sleipner. We use baseline data (1994 vintage, before CO₂ injection) and monitor data that was acquired after 12 years of CO₂ injection (2008 vintage). P-wave velocity models are generated using the Full waveform inversion technology and then, we invert selected rock physics parameters using an rock physics inversion methodology. Full waveform inversion provides high-resolution P-wave velocity models both for baseline and monitor data. The physical relations between rock physics properties and acoustic wave velocities in the Utsira unconsolidated sandstone (reservoir formation) are defined using a dynamic rock physics model based on well-known Biot–Gassmann theories. For data prior to injection, rock frame properties (porosity, bulk and shear dry moduli) are estimated using rock physics inversion that allows deriving physically consistent properties with related uncertainty. We show that the uncertainty related to limited input data (only P-wave velocity) is not an issue because the mean values of parameters are correct. These rock frame properties are then used as a priori constraint in the monitor case. For monitor data, the Full waveform inversion results show nicely resolved thin layers of CO₂–brine saturated sandstones under intra-reservoir shale layers. The CO₂ saturation estimation is carried out by plugging an effective fluid phase in the rock physics model. Calculating the effective fluid bulk modulus of the brine–CO₂ mixture (using Brie equation in our study) is shown to be the key factor to link P-wave velocity to CO₂ saturation. The inversion tests are done with several values of Brie/patchiness exponent and show that the CO₂ saturation estimates are varying between 0.30 and 0.90 depending on the rock physics model and the location in the reservoir. The uncertainty in CO₂ saturation estimation is usually lower than 0.20. When the patchiness exponent is considered as unknown, the inversion is less constrained and we end up with values of exponent varying between 5 and 20 and up to 33 in specific reservoir areas. These estimations tend to show that the CO₂–brine mixing is between uniform and patchy mixing and variable throughout the reservoir.     

Trimmed L-moments (1,0) for the generalized Pareto distribution

Abstract

Statistical analysis of extremes is often used for predicting the higher return-period events. In this paper, the trimmed L-moments with one smallest value trimmed—TL-moments (1,0)—are introduced as an alternative way to estimate floods for high return periods. The TL-moments (1,0) have an ability to reduce the undesirable influence that a small value in the statistical sample might have on a large return period. The main objective of this study is to derive the TL-moments (1,0) for the generalized Pareto (GPA) distribution. The performance of the TL-moments (1,0) was compared with L-moments through Monte Carlo simulation based on the streamflow data of northern Peninsular Malaysia. The result shows that, for some cases, the use of TL-moments (1,0) is a better option as compared to L-moments in modelling those series.

Citation Ahmad, U.N., Shabri, A. & Zakaria, Z.A. (2011) Trimmed L-moments (1,0) for the generalized Pareto distribution. Hydrol.Sci. J. 56(6), 1053–1060.     

模拟退火算法在江苏及邻区地震定位中的应用

使用模拟退火算法,以2019年4月6日江苏溧水M_L 3.3地震为典型震例,进行地震定位反演试算,确定适用于江苏及邻区地震定位的最佳初始温度、降温策略和扰动函数。设置初始温度为25,降温策略为T = 0.96T,选用效率较高的局部收敛加强型方法产生随机模型,对2019年江苏及周边地区105次M_L≥1.8地震进行重新定位,结果表明,76%的事件震中经、纬度定位误差绝对值在0.1°以内,但深度定位误差较大。鉴于该算法对P波到时信息及地震台站空间分布的依赖性,认为模拟退火算法在江苏及邻区陆地地震定位中效果较好,对于海域地震,则定位误差较大。     

模拟摩擦接触问题的新型无网格数值方法

针对摩擦接触问题,给出一种新型的无网格数值方法。该方法基于单位分解思想,在标准无网格Galerkin法的位移模式中嵌入不连续函数和裂尖奇异函数,分别反映接触面的不连续性和接触面端点的奇异性;结合接触摩擦定律,继而构造出求解摩擦接触问题的无网格线性互补模型。在该方法中,接触面方程使用接触点对离散,全局离散系统方程则转化为标准的线性互补问题,可以很方便地使用Lemke算法求解。算例分析证明,本文方法的正确性和有效性。     

海底天然气渗漏形成水合物量的线性动力学模型:以墨西哥湾GC185区块Bush高地为例

世界许多地区如墨西哥湾，存在着大量天然气渗漏并形成水合物的现象，出于科学，生态，气候和安全的需要。人类有必要弄清存在于海底以水合成形式存在的天然气的比例。因此，构建了水合物形成量的线性动力学模型，以分析墨西哥湾GC185块区Bush高地海底渗漏天然气的地质过程和行为。Bush高地渗漏的天然气来源于附近的Jolliet气藏，结果表明，渗漏天然气中约有9％的海底形成了水合物。     

宽观测带SAR图像入射角效应量化研究与校正

针对宽观测带SAR图像,在对入射角效应量化研究的基础上,提出了一种入射角效应按类校正方法。利用分水岭分割和区域标记技术实现地物取样,基于结合线性回归估计的余弦朗伯定律,实现对地物后向散射值的按类辐射校正。针对Envisat ASAR C波段HH极化数据的实验结果表明,入射角效应对雷达后向散射有明显的影响,含水量越高的地物类型,入射角效应越明显。利用本文方法进行入射角效应校正的效果优于绝对定标和一阶余弦校正的效果。     

AVHRR 1B定位数据经验插值模型的误差分析

确定像元地理坐标是几何纠正及卫星数据应用的基础。经验插值方法常用于计算高分辨率辐射计AVHRR1B定位数据,研究插值模型的定位误差具有重要意义。该文分析了AVHRR像元空间位置和像元大小,利用AVHRR扫描线的圆心角θ表示像元的位置,建立了像元位置θ和像元大小Δθ的表达模型;根据分段线性插值模型,计算插值后的像元位置θafter和像元大小Δθafter,获得分段线性插值模型的像元位置和大小的误差模型。