WCDMA卫星移动通信RAKE接收机性能分析

研究了基于WSSUS模型的UHF频段卫星移动信道模型,利用该模型在四种典型的信道环境下进行相干RAKE接收,在搭建的RAKE接收仿真平台上,比较了三种不同RAKE合并方式下的误码率性能.仿真结果表明,公共导频符号信道估计能有效地克服传统数据符号中时分插入导频符号传输方式在高速运动和快速变化信道中估计不准确的问题,特别在机载信道环境下,接收机性能有明显提高,同时不会产生多余的时隙延迟,信道跟踪实时性强,算法简单.     

Automatic registration of SeaWiFS and AVHRR imagery

An automatic approach for integrating images from multitemporal and multisensor remote sensing is outlined based on coastlines derived from satellite images. One point on a coastline is taken as a candidate point of ground control points (GCPs). A correlation-relaxation (CR) technique is used to search for the corresponding point in the second image. A decision rule is used to guarantee the correctness of GCPs which are used to compute a polynomial equation for registering two images. The relationship between the accuracy of registration and the number of GCPs indicates that a large number of GCPs will lead to more accurate image registration. The correctness of GCPs can also improve the accuracy of geometric registration. The approach can be used particularly well to register images of coastal areas. Examples are given for registration of SeaWiFS and AVHRR imagery.     

Inverting a forest canopy reflectance model to retrieve the overstorey and understorey leaf area index for forest stands

In this article, the Kuusk–Nilson forest reflectance and transmittance (FRT) model was inverted to retrieve the overstorey and understorey leaf area index (OU-LAI) of forest stands in the Longmenhe forest nature reserve in China. Data from detailed sample sites were collected in 30 forest stands representing the typical vegetation community in the study area. An uncertainty and sensitivity matrix (USM) was used to analyse the sensitivity of the FRT model parameters based on these data. The results indicated that overstorey LAI strongly influenced stand reflectance, whereas understorey LAI had a much lower impact. To predict OU-LAI in forest stands, FRT model inversion is carried out by minimizing a merit function that provides a measure of the difference between the reflectance simulated by the FRT model and the reflectance originating from optimal band selection of Hyperion data. Various combinations of Hyperion bands were tested to evaluate the most effective wavelengths for the inversion of OU-LAI. The best estimates from 17 Hyperion bands (5 VIS, 8 NIR, 4 SWIR) by the FRT model inversion showed an R ²?=?0.41 and RMSE/mean?=?0.21 for overstorey LAI and R ²?=?0.49 and RMSE/mean?=?0.91 for understorey LAI. Advantages and disadvantages of FRT inversion for retrieval OU-LAI combined with Hyperion data are discussed.     

Image‐object detectable in multiscale analysis on high‐resolution remotely sensed imagery

Landscapes are complex systems composed of a large number of heterogeneous components as well as explicit homogeneous regions that have similar spectral character on high‐resolution remote sensing imagery. The multiscale analysis method is considered an effective way to study the remotely sensed images of complex landscape systems. However, there remain some difficulties in identifying perfect image‐objects that tally with the actual ground‐object figures from their hierarchical presentation results. Therefore, to overcome the shortcomings in applications of multiresolution segmentation, some concepts and a four‐step approach are introduced for homogeneous image‐object detection. The spectral mean distance and standard deviation of neighbouring object candidates are used to distinguish between two adjacent candidates in one segmentation. The distinguishing value is used in composing the distinctive feature curve (DFC) with object candidate evolution in a multiresolution segmentation procedure. The scale order of pixels is built up by calculating a series of conditional relative extrema of each curve based on the class separability measure. This is helpful in determining the various optimal scales for diverse ground‐objects in image segmentation and the potential meaningful image‐objects fitting the intrinsic scale of the dominant landscape objects. Finally, the feasibility is analysed on the assumption that the homogeneous regions obey a Gaussian distribution. Satisfactory results were obtained in applications to high‐resolution remote sensing imageries of anthropo‐directed areas.     

A method for retrieving soil moisture in Tibet region by utilizing microwave index from TRMM/TMI data

According to simulation analysis of the advanced integral equation model (AIEM), there is a good linear relationship between emissivity and soil moisture under conditions of given roughness. The normalized difference of emissivities at 19.35 GHz and 10.65 GHz with vertical polarization can partly eliminate the influence of roughness and the squared correlation coefficient is about 0.985. This paper uses the normalized brightness temperature for retrieving soil moisture in Tibet from TRMM/TMI data. This method avoids parametrizing the land surface temperature which is a key parameter for the computation of emissivity. We make some sensitivity analysis for the atmosphere which is the main influence factor for our method. The analysis results indicate that our method is very good for clear days but is not very good when there is rainfall. We evaluate our algorithm by using the ground truth data obtained from GAME‐Tibet and the retrieval error of soil moisture is about 0.04m³ m^?3 relative to experimental data. The analysis indicates that the relationship obtained from the theoretical model should be revised through the local ground measurement data because the method is still influenced by roughness and vegetation. After making a regression revision, the retrieval error of soil moisture is under 0.02m³ m^?3. Finally, we retrieve the soil moisture in Tibet from TRMM/TMI data, and the distribution trend of retrieval results is consistent with the real world.     

太仓市县级基础水信息平台设计与建设

建立统一高效的基础水信息平台是基层水利单位信息化建设的重点任务。结合水利工作不断发展的业务需求,以太仓市水利基础水信息平台建设为基础,探讨利用 SOA架构并运用云计算的新理念,Web GIS 和Web Services技术,深入研究1个数据库,1套标准,1张图,1个平台,1个门户--“五个一”的县级基础水信息平台的搭建,对提高水利业务的管理水平和效率具有重要的意义。     

Multi-directional model validity tests for non-linear system identification

New multi-directional model validation tests are derived to provide improved statistical validation test procedures for a wide class of non-linear modelling methods.     

An improved model for adhesively bonded DCB joints

An improved analytical model is proposed for characterizing the fracture behavior of an adhesively bonded double cantilever beam joint under Mode I loading. Novel interfacial normal stress distribution function is used with a key parameter c that is determined using continuum mixture theory. In addition to the mechanical and sectional properties of the adherends, crack length, and overlap area, the model also incorporates the adhesive thickness and material properties as well as the crack tip rotation. Model prediction of the fracture toughness of the joint is entered into finite element analysis to simulate crack propagation under peel loading. The effect of various parameters on the joint fracture properties is discussed. Results show that the proposed model provides better correlation with published experimental data.     

Thermal modelling of new Li-ion cell design modifications

The effects of material and design modifications on the temperature distribution of Li-ion cells are simulated numerically. A two-dimensional anisotropic cylindrical coordinate model with linear triangular finite elements is used to simulate the steady-state temperature distribution within the cell. The cell’s material and geometry are changed. New cell materials are investigated for thermal performance: a negative electrode of variously-oriented carbon nanotubes, as well as separators made of Separion, of Al₂O₃ containing Cr particles or of BeO containing Be and Si particles. The cell’s diameter and length are varied. A new cell design with an internal cooling tube is proposed. The effect of cooling tube diameter upon cell temperature and the energy efficiency of cooling are investigated. This simple design change significantly improves the temperature distribution at marginal cost.