Effective soil moisture sampling depth of L-band radiometry: A case study

The aim of this study is to analyze the influence of the soil moisture sampling depth in the parameterization of soil emission in microwave radiometry at L-band. The analysis is based on brightness temperature, soil moisture and temperature measurements acquired over a bare soil during the SMOSREX experiment. A more detailed profile of surface soil moisture was obtained with a soil heat and water flows mechanistic model. It was found that (1) the soil moisture sampling depth depends on soil moisture conditions, (2) the effective soil moisture sampling depth is shallower than provided by widely used field moisture sensors, and (3) the soil moisture sampling depth has an impact on the calibration of soil roughness model parameters. These conclusions are crucial for the calibration and validation of remote sensing data at L-band.     

Effective input order of dynamics learning tree

In this paper, we discuss about the learning performance of dynamics learning tree (DLT) while mainly focusing on the implementation on robot arms. We propose an input-order-designing method for DLT. DLT has been applied to the modeling of boat, vehicle, and humanoid robot. However, the relationship between the input order and the performance of DLT has not been investigated. In the proposed method, a developer is able to design an effective input order intuitively. The proposed method was validated in the model learning tasks on a simulated robot manipulator, a real robot manipulator, and a simulated vehicle. The first/second manipulator was equipped with flexible arm/finger joints that made uncertainty around the trajectories of manipulated objects. In all of the cases, the proposed method improved the performance of DLT.     

L波段海上浮标通信信道传播特性研究

分析了基于L波段浮标海上通信的链路传输损耗特性,以模拟动态海浪曲线为基础,结合射线追踪与数值分析思想,建立了适用于不同海况等级的信道冲激响应模型,给出了信道反射点数目与功率的累积分布概率曲线,最后以浮标-卫星与浮标-舰船两种链路为例,仿真得到了不同海况下的误码率曲线,并与传统两径信道与高斯白噪声信道结果进行对比。分析结果表明,海况恶劣程度与入射波仰角大小对链路误码率影响显著,传统两径模型不足以描述其传播特性,该研究对实际浮标通信链路预算具有重要意义。     

Estimation of tree growth in a conifer plantation over 19 years from multi-satellite L-band SAR

The general capability of synthetic aperture radar (SAR) for monitoring forest ecosystems is well documented. However, the majority of SAR studies of forest dynamics use only imagery acquired by one SAR system and are thus limited to the lifecycle of a particular satellite. The synergistic analysis of SAR data from one of the earliest spaceborne SAR missions, the SEASAT mission, with the Japanese JERS-1 satellite-borne SAR is presented. Biophysical parameters frequently retrieved from SAR are tree biomass using backscatter and tree height from the interferometric phase. One potential application that has not been thoroughly examined is mapping of incremental tree growth from SAR backscatter changes. Tree growth measures biomass changes over time, and is correlated to the amount of carbon sequestered by the trees. This paper examines the retrieval of tree growth from multitemporal spaceborne L-band SAR. A SEASAT SAR image from 1978 and a JERS-1 SAR image from 1997 over Thetford forest, UK are used to retrieve tree growth of Corsican Pine stands. Incremental growth was estimated from the changes in backscatter coefficient, and compared to the expected tree growth from general yield class models used by the UK Forestry Commission. The accuracy of the retrieval algorithm depends on the minimum forest stand size included in the analysis. For managed forest plantations, multitemporal L-band SAR has some potential for detecting incremental biomass to support sustainable forest management.     

Relating the X-band opacity of a tropical tree canopy to sapflow, rain interception and dew formation

During summer and autumn 2007, a 11 GHz microwave radiometer was deployed in an experimental tree plantation in Sardinilla, Panama. The opacity of the tree canopy was derived from incoming brightness temperatures received on the ground. A collocated eddy-covariance flux tower measured water vapor fluxes and meteorological variables above the canopy. In addition, xylem sapflow of trees was measured within the flux tower footprint. We observed considerable diurnal differences between measured canopy opacities and modeled theoretical opacities that were closely linked to xylem sapflow. It is speculated that dielectric changes in the leaves induced by the sapflow are causing the observed diurnal changes. In addition, canopy intercepted rain and dew formation also modulated the diurnal opacity cycle. With an enhanced canopy opacity model accounting for water deposited on the leaves, we quantified the influence of canopy stored water (i.e. intercepted water and dew) on the opacity. A time series of dew formation and rain interception was directly monitored during a period of two weeks. We found that during light rainfall up to 60% of the rain amount is intercepted by the canopy whereas during periods of intense rainfall only 4% were intercepted. On average, 0.17 mm of dew was formed during the night. Dew evaporation contributed 5% to the total water vapor flux measured above the canopy.     

基于SNMP的MIB构结树高效算法研究

简单网络管理协议是一套定义管理信息存储、传递的应用层协议标准,它使得各种网络设备可以被统一的管理,而SNMP软件的主要性能瓶颈在于保存和查找MIB(管理信息库)对象的效率.考虑到其资源利用率和执行效率的高低对被管系统的整体性能有着直接的影响,对基于SNMP的MIB库的访问进行了研究.分析了MIB树的构造原理,提出了两种算法,并对它们进行了比较,结果表明了该方法的可行性.     

一种基于事务规则树的高效关联规则挖掘算法

提出了基于事务规则树改进的关联规则快速挖掘算法--FG算法.该算法不需要查找频繁项集,可直接求出所有无冗余的关联规则;将FG算法与其他算法进行实验比较,结果表明,FG算法在效率上优于其他算法,是有效的、可行的关联规则挖掘算法.     

Effective solution for unhandled exception in decision tree induction algorithms

This paper deals with some improvements to rule induction algorithms in order to resolve the tie that appear in special cases during the rule generation procedure for specific training data sets. These improvements are demonstrated by experimental results on various data sets. The tie occurs in decision tree induction algorithm when the class prediction at a leaf node cannot be determined by majority voting. When there is a conflict in the leaf node, we need to find the source and the solution to the problem. In this paper, we propose to calculate the Influence factor for each attribute and an update procedure to the decision tree has been suggested to deal with the problem and provide subsequent rectification steps.     

Analysis of the applicability of multi-temporal full polarimetric airborne L-band SAR scattering to paddy rice field mapping

ABSTRACT

A Synthetic Aperture Radar (SAR) is an all-weather imaging system that is often used for mapping paddy rice fields and estimating the area. Fully polarimetric SAR is used to detect the microwave scattering property. In this study, a simple threshold analysis of fully polarimetric L-band SAR data was conducted to distinguish paddy rice fields from soybean and other fields. We analysed a set of ten airborne SAR L-band 2 (Pi-SAR-L2) images obtained during the paddy rice growing season (in June, August, and September) from 2012 to 2014 using polarimetric decomposition. Vector data for agricultural land use areas were overlaid on the analysed images and the mean value for each agricultural parcel computed. By quantitatively comparing our data with a reference dataset generated from optical sensor images, effective polarimetric parameters and the ideal observation season were revealed. Double bounce scattering and surface scattering component ratios, derived using a four-component decomposition algorithm, were key to extracting paddy rice fields when the plant stems are vertical with respect to the ground. The alpha angle was also an effective factor for extracting rice fields from an agricultural area. The data obtained during August show maximum agreement with the reference dataset of estimated paddy rice field areas.     

Semi-empirical regressions at L-band applied to surface soil moisture retrievals over grass

The L-band brightness temperature of natural grass fields is strongly influenced by rainfall interception. In wet conditions, the contribution of the soil, mulch, and vegetation to the overall microwave emission is difficult to decouple, thus rendering the retrieval of surface soil moisture from a direct emission model difficult. This paper investigates the development and assesses the performances of statistical regressions linking passive microwave measurements to surface soil moisture in order to assess the potential of soil moisture retrievals over natural grass. First, statistical regressions were analytically derived from the L-Band Emission of the Biosphere model (L-MEB). Single configuration (1 angle, 1 polarisation), and multi-configuration regressions (2 angles, or 2 polarisations) were developed. Second, the performance of statistical regressions was evaluated under different rainfall interception conditions. For that purpose, a modified polarisation ratio at L-band was used to build three data sets with different interception levels. In the presence of interception, a regression based on one observation angle (50°) and two polarisations was able to reduce the effects of vegetation and soil roughness on the soil moisture retrievals. The methodology presented in this study is also able to provide estimates of the vegetation and soil roughness contribution to the brightness temperature.     

压缩金字塔树:有效的高维数据索引结构

提出了一种压缩金字塔树,基本思想是,首先将d维数据空间划分为2d个金字塔,由于在低维空间中无效的信息在高维数据空间中往往无效,采用γ划分策略对低维空间中的数据进行压缩,减小索引结构,解决了金字塔技术的缺点,给出了压缩金字塔树的插入、查询、删除算法。最后经实验证明,压缩金字塔树是一种有效的空间划分策略,在高维稀疏空间有良好的性能。     

L波段海水辐射率模型综述

全球海洋盐度的分布和变化对于海洋生态系统和海洋气候系统都是非常重要的参数。盐度的被动微波辐射遥感虽然在L波段灵敏度最高,但是其在L波段的灵敏度低于其它许多变量,因此对盐度反演模型精度要求很高。通过介电常数模型、海表粗糙表面波谱模型和电磁散射模型的融合,并经过实验数据的比较,可以获得描述海表辐射率的理论模型表达式。概述了目前常见的L波段描述海表辐射率的理论模型和几种半经验模型,利用不同的组合模型Two-scale与Durden &Vesecky x 2结合、SSA与Elfouhaily结合和利用亮温依靠速度的Hollinger和Camps等人的半经验线性模型以及Gabarro等人的半经验模型,归纳了Gabarro等人利用WISE试验数据和EuroSTARRS数据反演盐度的结果,并依据盐度反演的质量对这些模型进行了评估。     

Influence of sea surface emissivity model parameters at L-band for the estimation of salinity

In order to prepare the Soil Moisture and Ocean Salinity (SMOS) mission, we present sensitivity studies on a two-scale sea surface emissivity model used to compute brightness temperatures ( T B ) from the Sea Surface Temperature (SST), the wind vector, the incidence angle and the Sea Surface Salinity (SSS). We analyse the impact of uncertainties of the model on T B at 1.4 GHz ( u 0 = 21 cm), namely we determine the influence of the parametrization of the sea surface permittivity and of the cutoff wavelength u d (the limit which separates the short scales of the wave spectrum from the large scales). Using two existing permittivity parametrizations we find differences on T B ranging from 0.4 to 1.1 K. For SST warmer than 12°C and incidence angles smaller than 35°, the difference on T B is a bias independent of SSS and weakly dependent on SST. For these small incidence angles, the choice of the cutoff wavelength does not lead to significant differences on T B . For incidence angles larger than 40°, the permittivity parametrization and the choice of u d are more critical, resulting in a variation of T B of several tenths of a Kelvin.     

Effective fragment potentials and spectroscopy at enzyme active sites

Spectroscopy at a biochemical active site is influenced by local fields and hydrogen-bonds. Quantum calculations of the electronic structure of the entire biomolecule is, of course, impossible, but the chemical system can be modeled by dividing it into an active region (A) described quantum mechanically, and a spectator region (S) that influences A with strong fields and hydrogen-bonds. The all-electron interaction between A and S is replaced by an effective fragment potential (EFP) which represents the interaction as electrostatic, polarization and exchange repulsion terms. The EFP are derived entirely by ab initio model calculations of the S electronic properties and interactions and have been implemented in the quantum chemistry code, GAMESS. Spectroscopic analysis of enzyme active sites using the EFP will examine rhodanese and glutathione bound to glutathione S-transferase. The effect of specific hydrogen-bonds and local helices on spectral shifts is determined.     

Effective fragment potentials and spectroscopy at enzyme active sites

Spectroscopy at a biochemical active site is influenced by local fields and hydrogen-bonds. Quantum calculations of the electronic structure of the entire biomolecule is, of course, impossible, but the chemical system can be modeled by dividing it into an active region (A) described quantum mechanically, and a spectator region (S) that influences A with strong fields and hydrogen-bonds. The all-electron interaction between A and S is replaced by an effective fragment potential (EFP) which represents the interaction as electrostatic, polarization and exchange repulsion terms. The EFP are derived entirely by ab initio model calculations of the S electronic properties and interactions and have been implemented in the quantum chemistry code, GAMESS. Spectroscopic analysis of enzyme active sites using the EFP will examine rhodanese and glutathione bound to glutathione S-transferase. The effect of specific hydrogen-bonds and local helices on spectral shifts is determined.     

一种L波段低噪声放大器的设计与仿真

研究射频电路前端的天线信号放大和抑制噪声,进行了加快低噪声放大器的设计,提出了一种利用史密斯圆图和ADS软件快速设计和仿真LNA的方法.设计时输入端采用最佳噪声匹配,以获得较小的噪声系数;输出端采用输出共扼匹配,以获得较高的功率增益和较好的输出驻波比.通过对一个L波段低噪声放大器的噪声系数、功率增益、输入输出驻波比等参数进行仿真,结果验证了上述的方法.经反复调整后放大器在L波段内噪声系数小于1dB,增益达30dB,输出驻波比小于1.5,满足了设计要求,对从事LNA的设计来说有着重要的参考价值.     

Soil moisture retrievals at L-band using a two-step inversion approach (COSMOS/NAFE'05 Experiment)

COSMOS (Campaign for validating the Operation of Soil Moisture and Ocean Salinity), and NAFE (National Airborne Field Experiment) were two airborne campaigns held in the Goulburn River catchment (Australia) at the end of 2005. These airborne measurements are being used as benchmark data sets for validating the SMOS (Soil Moisture and Ocean Salinity) ground segment processor over prairies and crops. This paper presents results of soil moisture inversions and brightness temperature simulations at different resolutions from dual-polarisation and multi-angular L-band (1.4 GHz) measurements obtained from two independent radiometers. The aim of the paper is to provide a method that could overcome the limitations of unknown surface roughness for soil moisture retrievals from L-band data. For that purpose, a two-step approach is proposed for areas with low to moderate vegetation. Firstly, a two-parameter inversion of surface roughness and optical depth is used to obtain a roughness correction dependent on land use only. This step is conducted over small areas with known soil moisture. Such roughness correction is then used in the second step, where soil moisture and optical depth are retrieved over larger areas including mixed pixels. This approach produces soil moisture retrievals with root mean square errors between 0.034 m³ m^− 3 and 0.054 m³ m^− 3 over crops, prairies, and mixtures of these two land uses at different resolutions.     

A computer program for nuclear scattering at intermediate and high energies

A computer program is presented which calculates the elastic and inelastic scattering in intermediate and high energy nuclear collisions. A coupled-channels method is used for Coulomb and nuclear excitations of E1, E2, E3, M1, and M2 multipolarities, respectively. The program applies to an arbitrary nucleus, specified by the spins and energies of the levels and by reduced matrix elements. For given bombarding conditions, the angular distribution of elastic and inelastic scattered particles and angular distributions of gamma-rays from the excited nucleus are computed.     

一种子阵划分方法及子阵级STAP性能分析

对于幅度锥削的均匀线性阵列,本文首先提出了一种有效的基于遗传算法的子阵划分方法,在遗传算法中利用罚函数法避免子阵结构中出现阵元交叉项。然后对子阵级权值进行归一化,使得各子阵级噪声电平相等。最后通过计算机仿真分析了子阵级STAP处理器的性能。仿真结果表明,该子阵结构的天线方向图无明显栅瓣,其STAP杂波抑制性能接近于阵元级STAP处理性能。