MODIS卫星数据地表反照率反演的简化模式

以内蒙西部地区的MODIS遥感图像数据和地表野外同步观测的光谱数据为例,在野外数据量较少且有定标数据的条件下反演地表反照率。使用6S大气1辐射传输模型进行大气校正,并通过MODTRAN4.0模型获取各波段地表入射光通量和窄波段的地表反照率;在窄波段反照率与宽波段反照率之间存在线性关系的前提下,以各波段的入射光通量占总入射通量的比例作为反演参数,实现窄波段到宽波段的反演。反演结果证明此方法简便可行。     

Narrowband-to-broadband albedo conversion for glacier ice and snow: equations based on modeling and ranges of validity of the equations

In this paper, we propose equations for narrowband-to-broadband (NTB) albedo conversion for glacier ice and snow for four types of satellite sensors: thematic mapper (TM), advanced very high resolution radiometer (AVHRR), moderate resolution imaging spectroradiometer (MODIS), and multi-angle imaging spectroradiometer (MISR). We do this on the basis of spectral albedos and incident spectral irradiances generated with radiative-transfer models of the (sub-)surface (a two-stream model) and the atmosphere, respectively. First, we establish equations for reference values of atmospheric components and the surface elevation. These equations describe measurements with root-mean-square differences of ∼0.016. We then show that the “reference equations” also perform well when total ozone and aerosol optical depth are changed with respect to the reference. The negative effect of humidity and elevation variations on the performance of the equations can be eliminated by adding a correction term. We argue that narrowband albedos are much less sensitive to variations in the incident spectral irradiance than broadband albedos. Hence, our conclusions about the effects of variations in atmospheric composition and elevation are also valid for equations for NTB conversion proposed in other papers.     

Validation of MISR land surface broadband albedo

Land surface broadband albedo is a critical variable for many scientific applications. Due to the scarcity of spectral albedo measurements of the Earth's surface environments, it is useful to construct broadband albedo from spectral albedo data obtained by multi‐angle satellite observations. The Multi‐angle Imaging SpectroRadiometer (MISR) onboard NASA's Earth Observing System (EOS) Terra satellite provides land surface albedo products from multi‐angular observations; however, the products have not been comprehensively validated. We convert MISR spectral albedos to total shortwave albedos and validate them using ground measurements at different validation sites. For most surface types, a published narrowband to broadband conversion formula was used, but a new conversion formula for snow and ice covered sites is developed in this study where the spectral range of the instrument is different. Several comparisons are made: (1) between MISR directional‐hemispherical reflectance (DHR) or albedo and MODIS (Moderate Resolution Imaging Spectroradiometer) DHR; and (2) between MISR spectral DHR and bi‐hemispherical reflectance (BHR). The results show that: (1) both the value and the temporal trends of the MISR shortwave albedo and the ground measured shortwave albedo are in good agreement, with the exception of the snow and ice sites; (2) the MISR DHR conforms well to MODIS DHR; and (3) the values of MISR DHR and BHR are nearly identical.     

Narrowband to broadband conversion of Landsat TM glacier albedos

In this paper we present an empirical relationship between the broadband glacier albedo (alpha) and the narrowband glacier albedos in Landsat TM bands 2 and 4 (alpha2 and alpha4, respectively). The relationship was established on the basis of multiple linear regression analysis of 112 ground-based simultaneous measurements of alpha, alpha2 and alpha4 made at 32 sites on the tongue of the Morteratschgletscher, Switzerland. The measurements were carried out over a representative set of glacier surface types ranging from completely debris-covered glacier ice (alpha=0.08)to dry snow (alpha=0.86). The regression model explains more than 99% of the variance of the broadband albedo and the root-mean-square value of the residuals is only 0.009. The relationship enables users of Landsat TM data to make an accurate estimate of the broadband albedo on the basis of narrowband albedos without having to classify the glacier surface.     

An algorithm for the retrieval of 30-m snow-free albedo from Landsat surface reflectance and MODIS BRDF

We present a new methodology to generate 30-m resolution land surface albedo using Landsat surface reflectance and anisotropy information from concurrent MODIS 500-m observations. Albedo information at fine spatial resolution is particularly useful for quantifying climate impacts associated with land use change and ecosystem disturbance. The derived white-sky and black-sky spectral albedos may be used to estimate actual spectral albedos by taking into account the proportion of direct and diffuse solar radiation arriving at the ground. A further spectral-to-broadband conversion based on extensive radiative transfer simulations is applied to produce the broadband albedos at visible, near infrared, and shortwave regimes. The accuracy of this approach has been evaluated using 270 Landsat scenes covering six field stations supported by the SURFace RADiation Budget Network (SURFRAD) and Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) network. Comparison with field measurements shows that Landsat 30-m snow-free shortwave albedos from all seasons generally achieve an absolute accuracy of ±0.02-0.05 for these validation sites during available clear days in 2003-2005, with a root mean square error less than 0.03 and a bias less than 0.02. This level of accuracy has been regarded as sufficient for driving global and regional climate models. The Landsat-based retrievals have also been compared to the operational 16-day MODIS albedo produced every 8-days from MODIS on Terra and Aqua (MCD43A). The Landsat albedo provides more detailed landscape texture, and achieves better agreement (correlation and dynamic range) with in-situ data at the validation stations, particularly when the stations include a heterogeneous mix of surface covers.     

Calibration and on-line data selection of multiple optical flow sensors for odometry applications

This work proposes a calibration method and a computational algorithm to integrate the data of multiple optical flow sensors for two-dimensional trajectory measurements. Optical flow sensors offer a different kind of odometer as compared to the wheel encoder. Using multiple sensors can reduce the effect of measurement uncertainties. Since all sensors are mounted on a rigid body, their measurement data must obey a certain relation, which is utilized in this work. Additionally, mathematical formulae are developed to realize the computation. Analytical results show that the calibration procedure can be cast as an optimization problem given measurement data. Furthermore, the rigid-body relation is formulated as a null-space constraint using the calibrated parameters. Unreliable sensor measurements can be removed during operation by accessing the error distance to the null space. Experimental results are presented to support the proposed methods.     

双足步行机器人的ZMP-CoP检测及研究

ZMP(零力矩点）和CoP(压力中心)是评价双足步行机构行走稳定性的重要参数．本文在研究了ZMP和CoP两者关系的基础上，根据THBIP-I仿人机器人基于ZMP理论的姿态调整要求和六维力/力矩传感器的安装位置，推导了适用于双足机器人的CoP计算公式，建立了采用六维力/力矩传感器的CoP检测系统．进行了THBIP-I仿人机器人行走过程的实际CoP检测实验，并对实验结果进行了讨论．实验证明了该系统的准确性.     

Assessing the coupling between surface albedo derived from MODIS and the fraction of diffuse skylight over spatially-characterized landscapes

In this effort, the MODerate Resolution Imaging Spectroradiometer (MODIS) (Collection V005) Bidirectional Reflectance Distribution Function (BRDF)/Albedo algorithm is used to retrieve instantaneous surface albedo at a point in time and under specific atmospheric conditions. These retrievals are then used to study the role that the fraction of diffuse skylight plays under realistic scenarios of anisotropic diffuse illumination and multiple scattering between the surface and atmosphere. Simulations of the sky radiance using the MODTRAN®5.1 radiative transfer model were performed under different aerosol optical properties, illumination conditions, and surface characteristics to describe these effects on surface albedo retrievals from MODIS. This technique was examined using a validation scheme over four measurement sites with varied aerosol levels and landscapes, ranging from croplands to tundra ecosystems, and over extended time periods. Furthermore, a series of geostatistical analyses were performed to examine the types of spatial patterns observed at each measurement site. In particular, Enhanced Thematic Mapper Plus (ETM+) retrievals of surface albedo were acquired to analyze the change in variogram model parameters as a function of increased window-size. Results were then used to assess the degree to which a given point measurement is able to capture the intrinsic variability at the scale of MODIS observations. Assessments of MODIS instantaneous albedos that account for anisotropic multiple scattering, over snow-free and snow-covered lands and at all diurnal solar zenith angles, show a slight improvement over the albedo formulations that treat the downwelling diffuse radiation as isotropic. Comparisons with field measurements show biases improving by 0.004-0.013 absolute units (root-mean-squared error) or 0.1%-2.0% relative error.     

Enhanced predictive modelling process of broadband services adoption based on time series data

In this paper, the importance of the predictive modelling process of broadband services adoption is described. A detailed overview of different analytical models used for prediction, i.e., fitting and forecasting processes of broadband services adoption are presented. Furthermore, a comparison of several analytical models commonly used for prediction of broadband adoption is conducted. In order to more accurately fit to the existing broadband adoption time series data, and to forecast the future broadband services adoption paths, the features of the most accurate common predictive models have been identified for different phases of broadband services adoption. Considering the given results, usage of additional models in the predictive modelling process is analyzed. The objective of these analyses is set to improve the accuracy of the existing predictive modelling process. The accuracy of the predictive modelling process using additional models is tested and compared in different phases of broadband adoption. The model which gives the most accurate results is identified. Finally, in order to enable the usage of this model within a whole broadband service life cycle, as well as to include a greater number of explanatory parameters in predictive modelling process, an enhanced predictive modelling process is proposed.     

On the computation of the temperature distribution at the combustion chamber of a diesel engine using adinat

This paper reports on the computation of the temperature distribution at the surface of the combustion chamber of a direct-injection diesel engine. The aim of these computations with ADINAT is to determine the temperature distribution, perturbated by the presence of measurement sensors, for the numerical calibration of these sensors. In addition, the temperature deviations caused by soot deposits on the surface are investigated; here the ADINAT results are compared to an analytical solution by a Fourier series approach.

Furthermore software aspects are discussed that arise from the relatively large problems analysed here. A software environment for the new program system ADINAT in connection with existing pre- and postprocessors is described, the special requirements of large-scale problems and the resulting necessary modifications in the program are summarized, and finally the performance of ADINAT with respect to computational costs is studied in test computations.     

NURBS曲线和曲面的递推矩阵及其应用

本文运用Ｔｏｅｐｌｉｔｚ矩阵，导出了任意非均匀Ｂ样条的递推矩阵公式；提出了一个计算非均匀Ｂ样条基矩阵的新方法，该递推矩阵公式即可以用于ＮＵＲＢＳ曲线和曲面的分析计算，也可以用于Ｂｅｚｉｅｒ，均匀和非均匀Ｂ样条曲线及曲面的分析计算。     

一种单载波宽带信号非线性均衡技术

针对单载波宽带信号均衡难以收敛的问题,研究了一种基于子带分解与重构的宽带非线性均衡技术。综合利用复数子带滤波器组与判决反馈均衡器理论,给出了两种具有模式切换功能的宽带非线性均衡结构,基于最小均方算法推导了它们的均衡权值迭代更新公式,分析比较了两种结构在不同均衡模式下的收敛特点。仿真证明基于子带技术的宽带非线性均衡能适用于群时延较严重的信道,且比传统全频带均衡具有更好的收敛效果和更低的计算复杂度。     

电容式传感器和电容的测量

本文介绍部分电容式传感器的构造和测量方法,并对此进行了讨论。内容涉及位移测量、平板电容式压力测量、液位测量和物质含水量测量等。介绍了专用集成电路CAV444对电容式传感器的电容电压线性转换的应用。     

基于二次曲面拟合的二维传感器数据处理技术研究

针对温度、湿度传感器在测量系统中相互干扰所导致的测量误差问题,提出了基于二次曲面拟合理论的数据处理模型,实验以温湿度集成传感器为例,采用传感器标定系统对二维传感器进行多点温度、湿度标定,基于二次曲面拟合方程对数据进行处理,结果表明:该方法有效地提高了温度、湿度传感器的测量精度,具有很高的实用价值。     

On the Earth's surface energy exchange determination from ERS satellite ATSR data. Part I: Long-wave radiation

This is the first in a series of papers which addresses the determination of the Earth's surface energy exchange using data from the Along-Track Scanning Radiometer (ATSR). This paper focuses on long-wave radiation from sea and land surfaces and a technique is proposed for the derivation of land surface temperature (LST) and land surface emissivity retrieval using ATSR data in a new simultaneous split-window method. Two points regarding net long-wave radiation are also considered. Firstly, over land and sea, differences in several previously published are discussed. Secondly, over sea, the effect on the net longwave radiation of using sea surface skin temperatures, which can be derived accurately from satellite thermal band data, as input to the empirical formulae is compared to the use of bulk water temperature taken from in situ measurements. Finally, a new formula is developed for the calculation of net long-wave radiation at the surface. The equivalent sky temperature, T, is used and the results agree sky with those obtained using the Oberhuber formula. Both of these formulae are useful for the calculation of net long-wave radiation over wet areas such as sea, with a high relative humidity. Initial tests of the formulae were carried out using ATSR sea surface temperatures (SSTs) and LSTs in the United Kingdom. The formulae were also tested using TOGA-TAO data and ATSR sea surface temperatures over the Pacific Ocean. From our results, the net long-wave radiation showed the magnitude and spatial variability to be (15-35 W m 2). The absolute difference of net long-wave radiation by using ATSR SST and TOGA SST is around 3 W m 2 for most areas, but the maximum difference is up to 7W m 2. The relative difference is more than 10% and up to 30%.     

Profile-based roughness discrimination with pen-type texture sensor

Tactile discriminations of surface roughness using artificial sensors have been challenging. The modeling methods and parameters that have been using to describe the mechanical properties of rough surface are insufficient for haptic roughness. This paper proposes a method to characterize surface roughness based on the profiles of the surface. A compact handheld pen-type texture sensor with a right probe is developed for the measurement of surface profiles. Based on the contact force and the motion of the senor, profiles in the paths of scanning are estimated. The height variations of a profile are converted to a series of tactile stimuli to represent the contact stimulations in haptic explorations. The mean and the standard deviation of the amplitudes of stimuli are identified as haptic features that indicate the required tangential force to slide on the rough surface and how rough the surface is, respectively. Experiments show that the roughness on four kinds of sandpapers can be clearly distinguished by the proposed discrimination method.     

Conversion and evaluation for two types of parametric surfaces constructed by NTP bases

In this paper, a new generalized Ball basis, normalized totally positive (NTP) basis given by Delgado and Peña, is investigated. The conversion formulae between the basis and the Bernstein basis are derived. We also prove that these formulae not only are valuable for studying the geometric properties, such as subdivision, of the curves and surfaces constructed by this generalized Ball basis, but also can improve the computational speed of the Bézier curves and surfaces. After the Bézier surface (curve) is converted into the generalized Ball surface (curve), the time complexity for evaluation can be reduced from cubic to quadratic, of the degree of the surface (curve). However, the intrinsic property, such as shape-preserving property, is not changed. So, the generalized Ball surface and curve have a great future in application of geometric design.     

光纤高温传感器表面镀膜技术研究

在高温测试中,光纤高温传感器具有独特的优势,在制作光纤高温传感器过程中,镀膜技术是一个关键的环节。根据高温测试需要,选取了合适的镀膜材料,对氧化锌（ZnO）和氧化镁铝（MgAl2O4）的物理化学性质进行了介绍,同时根据材料特性选择了适合的镀膜方法,分别适用于黑体腔温度传感器的头部镀层和光纤光栅传感器表面镀膜,取得了良好的效果,达到了温度测量的要求。     

Retrieval of surface directional reflectance properties using ground level multiangle measurements

Knowledge of the directional reflectance properties of natural surfaces such as soils and vegetation canopies is essential for classification studies and canopy model inversion. Atmospheric correction schemes, using various levels of approximation, are described to retrieve surface bidirectional reflectance factors (BRFs) and directionalhemispherical reflectances (albedos) from multiangle radiance measurements taken at ground level. The retrieval schemes are tested on simulated data incorporating realistic surface BRFs and atmospheric models containing aerosols. Sensitivity of the atmospherically corrected BRFs and associated directional-hemispherical reflectances to various aerosol properties and the sun-view geometry is illustrated. A measurement strategy for obtaining highly accurate surface reflectance properties also is examined in the context of instrument radiometric calibration, knowledge of the atmospheric properties, and sun-view angular coverage.     

Generating global surface albedo products from multiple geostationary satellites

Operational weather geostationary satellites have acquired data for more than two decades and offer thus the possibility to generate long time series of Essential Climate Variables like surface albedo as suggested by GCOS. This paper investigates the possibility to generate consistent global, to the exception of the polar regions, surface broadband albedo product from these satellites. In this context, the paper addresses two specific issues. Firstly, the spatial consistency of surface albedo derived from five different geostationary satellites is examined in detail. Secondly, this product is compared with the equivalent MODIS one to define the temporal consistency between surface albedo derived with old geostationary instruments and technologically advanced radiometers like MODIS. The analysis of the surface albedo products has revealed a good agreement between the products derived from the various geostationary satellites. Comparison of this global product with the one routinely derived from MODIS shows that on the average, the mean relative difference between these two data sets agree within 10%. These first encouraging results open therefore a new avenue for the exploitation of the archived data for the generation of long time series, covering the last 25 years or so, of global surface albedo from geostationary weather satellites.