Remote sensing the biochemical composition of a slash pine canopy

Airborne imaging spectrometers can record spatially-explicit information on the absorption features associated with foliar biochemicals in a forest canopy. The spectra of a single species pine canopy were recorded by the National Aeronautics and Space Administration's (NASA) Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). Up to three wavebands were correlated to the concentration of chlorophyll, nitrogen, lignin, and cellulose (R²=0.96,0.94,0.93, and 0.61, respectively) and the content of these four biochemicals (R²=0.98,0.91,0.88, and 0.92, respectively). The AVIRIS data were used, for the first time, to map the content of these biochemicals within the forest canopy and the accuracy was between 3-7% of the mean     

470MHz无线信号在混交林中的传播特性及模型构建

LoRa无线通信技术因其传输距离较远、功耗较低,满足了混交林中大规模节点传输汇聚的要求,可作为林业物联网数据采集的主要通信方式来使用.利用接收信号强度指示(Received Signal Strength Indication,RSSI)分析了470 MHz无线信号传输中的电波路径损耗问题,通过对测得的叶面积指数(Le...     

Estimation of forest parameters through fuzzy classification of TMdata

Several studies have investigated the utility of Landsat 5 TM imagery to estimate forest parameters such as stand composition and density. Regression equations have generally been used to relate these parameters to the radiance responses of the TM channels. Such a method is not feasible in highly complex landscapes, where forest mixtures and terrain irregularities may obscure the existence of simple relationships. A fuzzy approach to the problem is presented based on a multi-step procedure. First, some typical forest plots with known features are spectrally identified. A maximum likelihood fuzzy classification with nonparametric priors is then applied to the study images, so as to derive fuzzy membership grades for all pixels with respect to the typical plots. Finally, these grades are used to compute the estimates of the forest parameters by a weighted average strategy. The method was tested on a complex, rugged area in Tuscany mainly covered by deciduous and coniferous forests. Two TM scenes and accurate ground references taken in spring and summer 1991 were utilized for the testing. The first results, statistically evaluated in comparison with those of a more usual multivariate regression procedure, are quite encouraging. The possible application of the fuzzy approach to other cases of environmental monitoring is finally discussed     

Forest variable estimation from fusion of SAR and multispectral optical data

Radar and optical remote sensing data are used in a unified algorithm to estimate forest variables. The study site is the H. J. Andrews experimental forest in Oregon, which has significant topography and several mature and old-growth conifer stands with biomass values sometimes exceeding 1000 tons/ha. Polarimetric multifrequency Airborne Synthetic Aperture Radar (AIRSAR) backscatter, interferometric C-band Topographic Synthetic Aperture Radar (TOPSAR) coherence, and multispectral Landsat Thematic Mapper (TM) digital numbers are used in a regression analysis that relates them to forest variable measurements on the ground. Parametric expressions are derived and used to estimate the same variables(s) at other locations from the combination of AIRSAR and TM data. It is shown that the estimation accuracy is significantly improved when the radar and optical data are used in combination compared to estimating the same variable from a single data type alone.     

Validity and feasibility of intelligent Walkbot system

The first study to highlight the validity and feasibility of the innovative exoskeletal Walkbot system is presented. The Walkbot is a locomotor retraining robot designed to provide gait impairment for the systematic reacquisition of locomotor skills. Neuromechanical data obtained from kinematic and electromyographic (EMG) measurements yielded excellent validity and consistency. Linear regression analysis for kinematic hip and knee angle data showed R² = 0.8604 and R² = 0.9265, respectively. The coefficient of variation also showed consistent EMG amplitudes in the selected ankle muscles at two independent velocities. The preliminary data provide promising evidence of locomotor retraining.     

Monitoring seasonal changes of a mixed temperate forest using ERSSAR observations

Temporal variations of environmental research satellite (ERS)-1/2 backscattering coefficients acquired over a mixed deciduous forest are analyzed with an aim toward relating the observed radiometric variations to changes either in the vegetation seasonal cycle or in the structural parameters. Overall, the results are somewhat pessimistic. Temporal σ⁰ plots show chaotic variations, which are difficult to relate to the seasonal changes of forest parameters and particularly to the foliage dynamics. Furthermore, no distinction between stand types or between deciduous species is found to be possible, and nearly identical temporal plots are observed for all the stands, suggesting that the radar signatures are partly under the influence of nonforest parameters. Besides, the effect of meteorological events are difficult to evaluate. Discrimination between deciduous stands and conifers is nevertheless possible, since the radiometric difference between the two species is about 1 dB. With an overall sensitivity to standing biomass of about 0.1 dB/50 tons per hectare, ERS SARs can be considered as almost insensitive to biomass variations. For the young stands, the C-band response is found to be dominated by stand structure, whereas the backscattering coefficient saturates for biomass values higher than 50 and 80 t DM ha^-1 for deciduous and conifers, respectively     

基于改进型双正切变换的高阶近奇异性精确积分方法研究

电磁场表面积分方程方法（SIE）中的高阶近奇异性积分是SIE精确求解的关键技术之一,但现有方法主要是处理平面单元建模中的低阶近奇异性问题,目前还没有一种可用于高阶曲面建模中3阶近奇异性的精确稳定积分方法.本文在前期提出的双正切变换方法（DAT）的基础上,针对高阶曲面建模中含有RR/R⁵、R/R⁴和1/R³等形式积分核的近奇异性问题,通过引入指数变换解决了DAT算法在近奇异点与源单元非常接近时算法不稳定的问题,并通过引入形函数变换解决了DAT近奇异点与源单元边界靠近时积分不稳定的问题,形成改进型双正切变换方法（IDAT）.相对于DAT,所提IDAT更稳定高效.所提IDAT不仅可用于曲面单元中的高阶近奇异性问题的精确积分,同时也适用于低阶近奇异积分问题.理论分析与数值算例验证了本文所提方法的精确性与稳定性.     

Polarization-independent LiTaO3 guided-wave electroopticswitches

Polarization-independent LiTaO₃ optical switches that utilize the off-diagonal electrooptic coefficient r₅₁ are discussed. The waveguides are formed by Zn vapor diffusion. Interguide transfer efficiencies of 84 and 88% for TM and TE polarizations, respectively, have been obtained. Modulation efficiency of 99.8% for TM and 95% for TE have been demonstrated at nearly equal voltages by thermally tuning to 20°C. The relatively high voltage-length product (30-35 V-cm) attained in these initial devices at a 0.633-μm wavelength is attributed to a weak overlap between optical and electrical fields in the periodic electrode structure     

A retrospective of R*: A distributed database management system

This paper discusses the experience gained during the implementation of a prototype distributed database management system. The R^*prototype supports transparent distribution of a relational database which is accessed using the SQL language for data definition and manipulation. While supporting autonomy among the participating sites, R^*also emphasizes good performance for both local and multi-site operations. During the implementation of the R^*prototype, we were guided by a few key objectives and encountered several interesting problems. This paper will discuss the guiding objectives of the R^*effort, as well as several areas of the implementation which presented special difficulties or were simplified by design decisions.     

基于MAX-DOAS观测的淮北冬季NO2变化特征

基于2018年12月8日~12月31日淮北地区多轴差分吸收光谱技术(MAX-DOAS)获得的太阳散射光谱观测数据,反演了该地区NO2对流层柱浓度, 并分析了冬季不同天气下NO$_2$浓度日变化特征。观测结果表明NO2浓度高值出现在12月18日~12月27日期间,日均值最大值6.83×10¹⁶ molecules/cm²出现在12月27日,约为日均值最低值的2.9倍。结合风场轨迹模型研究了不同大气条件下的风场,发现在NO2浓度较低时段主要为 偏北风场, NO2浓度高值时段偏南风场增加,表明城区产生的污染向观测区域进行了输送。将MAX-DOAS结果与OMI卫星结果进行了 对比,发现两者具有较好的一致性(R²=0.88)。     

Deep-depletion breakdown voltage of silicon-dioxide/silicon MOS capacitors

The deep-depletion breakdown voltage of silicon-dioxide/ silicon MOS capacitors is determined by the ionization-integral method, with potential distributions computed by two-dimensional relaxation techniques. Calculations cover the range of substrate doping between 10¹⁴and 10¹⁸cm^-3and oxide thickness between 0.01 and 5.00 µm, providing plots of breakdown voltage versus substrate impurity concentration with oxide thickness as parameter. A universal and normalized criterion is derived for field uniformity in terms of the ratio of oxide thickness to the maximum (breakdown) width of the silicon depletion region: this ratio should be larger than 0.3 in order not to have field concentration around the edges of the metal plate.     

Modelling skin pelvic landmark coordinates into corresponding internal bone for wheelchair users

The purpose of this study was to investigate the relationships, by linear regression, between internal and external pelvic landmarks identified by two techniques: manual digitization or skin markers. It was hypothesized that the body mass index or the skinfold thickness are significant variables in these relationships. The internal pelvic landmarks were obtained with a stereoradiographic method. Results showed that the external coordinates are generally statistically different from the internal ones; manual digitization of the landmark reduces the soft tissue artifacts compared to the use of skin markers. Different regression models were obtained according to the external acquisition method. Body mass index or skinfold thickness was generally included as a significant variable in models along the direction of the soft tissue thickness: postero-anterior direction for the anterior-superior iliac spine, medio-lateral direction for the apex of the iliac crests. With the use of skin markers, models obtained for a specific internal landmark coordinate include generally many variables, such as the other two coordinates of the landmark, body mass index, or skinfold measurements. This study presented preliminary results on the relationships between internal and external pelvic landmark coordinates. More research is needed before the full relationships are understood and adequate models are developed.     

基于AMBE～2000^TM的高质量语音通信系统

介绍了AMBE-2000^TM声码器语音压缩解压芯片的工作原理及其应用；给出了语音通信系统中AMBE-2000^TM与PCM编解码器AD73311的A／D-D／A接口电路。该系统可以在低速率下保持声音自然、语音清晰，并且在选择语音速率和误码率中提供了很高的灵活性，能实现全双工、实时语音压缩解压等功能，此外还具有低成本、低功耗等优点。因此在卫星通信、数字移动通信、保密通信、语音邮件等方面都有广泛的应用。     

Significance in adding a queuing subsystem to the R/sup 3/T random access OCDMA protocol

A queuing subsystem is proposed to the round robin receiver/transmitter (R³T) optical code-division multiple-access (OCDMA) protocol. The corresponding state diagram and its mathematical model are outlined. We prove that significant improvement in terms of system throughput and blocking probability can be achieved by only adding a single buffer at each user node. Furthermore, the modified R³T protocol can support higher traffic loads with acceptable delay and good efficiency.     

Lasing mode behavior of a single-mode MQW laser injected with TMpolarized light

The lasing mode behavior of a multiple quantum well (MQW) distributed feedback (DFB) laser was measured when intensity-modulated orthogonally polarized transverse magnetic (TM) mode light was injected. The 3-dB bandwidth of the frequency response shows a trend different from that observed with conventional bias current modulation: at high bias currents, it decreases with increasing bias current. The maximum bandwidth of 3 dB was observed when the normalized bias current was 4, and it reached 16 GHz at this bias current. The gain saturation coefficients for the transverse electric (TE) and TM modes estimated from these results were ∈_p^E; 2.5×10^-17 cm³ and ∈_q^E 5.7×10^-18 cm³ for the TE mode, and ∈_p^M: 6.0×10^-17 cm³ and ∈_q^M: 2.0×10^-14 cm³ for the TM mode     

Development of a TiW plasma etch process using a mixture experimentand response surface optimization

The characteristics of SF₆/He plasmas used to etch TiW have been studied with statistically designed experiments using a Tegal 804 single wafer system. Two processes were developed using both positive and negative photoresist as the mask material for etching TiW. The goal was to consolidate both processes into one. A two-phase experimental approach was taken to generate the processes. In phase 1 a fractional factorial screening experiment was used to identify key factors, and in phase 2 a mixture experiment was used for process optimization. The fractional factorial experiment was initially used to study the effects of reactor pressure, RF power, SF₆/He gas ratio, overetch time, and hard bake. The results of this initial experiment were used to identify the appropriate levels for the main process parameters. Then, at these parameter levels, a mixture experiment was conducted using the partial pressures of SF₆, He, and the nitrogen ballast as the design variables. Since the total pressure in the system is fixed, these three variables are the components of a mixture, and thus form a constrained design space for the experiment. Quadratic and special cubic response surface models were generated for the following responses: TiW etch rate, photoresist etch-rate, selectivity between the TiW and photoresist, uniformity of all etch rates and selectivities, and critical dimension control for the photoresist and TiW. Contour plots for all responses as a function of the partial pressure of SF₆, He, and nitrogen ballast were generated. The contours from these empirical models were analyzed jointly to optimize the processes     

A semi-empirical backscattering model at L-band and C-band for asoybean canopy with soil moisture inversion

Radar backscatter measurements of a pair of adjacent soybean fields at L-band and C-band are reported. These measurements, which are fully polarimetric, took place over the entire growing season of 1996. To reduce the data acquisition burden, these measurements were restricted to 45° in elevation and to 45° in azimuth with respect to the row direction. Using the first order radiative transfer solution as a form for the model of the data, four parameters were extracted from the data for each frequency/polarization channel to provide a least squares fit to the model. For inversion, particular channel combinations were regressed against the soil moisture and area density of vegetation water mass. Using L-band cross-polarization and VV-polarization, the vegetation water mass can be regressed with an R ²=0.867 and a root mean square error (RMSE) of 0.0678 kg/m ². Similarly, while a number of channels, or combinations of channels, can be used to invert for soil moisture, the best combination observed, namely, L-band VV-polarization, C-band HV- and VV-polarizations, can achieve a regression coefficient of R²=0.898 and volumetric soil moisture RMSE of 1.75%     

Quantitative estimation of SiO2 content in igneous rocksusing thermal infrared spectra with a neural network approach

Develops a method for estimating the SiO₂ content of igneous rocks using thermal infrared reflectance spectra, aiming to utilize it in the remote sensing of thermal spectral emission. Silicate minerals, which are the major components of the Earth's surface, display their strongest fundamental molecular vibration bands in the thermal infrared region (8-12 μm). The wavelengths of these so-called “reststrahlen bands” are systematically related to the SiO ₂ content of rocks. Pattern matching (using a back-propagating neural network approach) between simulated remotely sensed data and the SiO₂ content was performed. This approach was evaluated by comparing the spectrally estimated SiO₂ content with the chemically determined SiO₂ content for a separate set of rock samples. The estimated error between the spectrally estimated and chemically determined SiO₂ contents for most samples was within 7%. Future multiband satellite sensors of the Earth's thermal emission will have much higher spectral and spatial resolution than existing ones, and should be able to detect these spectral trends     

Regularized integral equations and curvilinear boundary elementsfor electromagnetic wave scattering in three dimensions

The boundary integral equations (BIEs), in their original forms, which govern the electromagnetic (EM) wave scattering in three-dimensional space contain at least a hypersingularity (1/R³ ) or a Cauchy-singularity (1/R²), usually both. Thus, obtaining reliable numerical solutions using such equations requires considerable care, especially when developing systematic numerical integration procedures for realistic problems. Regularized BIEs for the numerical computation of time-harmonic EM scattering fields due to arbitrarily-shaped scatterers are introduced. Two regularization approaches utilizing an isolation method plus a mapping are presented to remove all singularities prior to numerical integration. Both approaches differ from all existing approaches to EM scattering problems. Both work for integral equations initially containing either hypersingularities or Cauchy-singularities, without the need to introduce surface divergences or other derivatives of the EM fields on the boundary. Also, neither approach is limited to flat surfaces nor flat-element models of curved surfaces. The Muller linear combination of the electric- and magnetic-field integral equations (EFIE) and (MFIE) is used to avoid the resonance difficulty that is usually associated with integral equation-based formulations. Some preliminary numerical results for EM scattering due to single and multiple dielectric spheres are presented and compared with analytical solutions     

Practical Design and Evaluation of a 1 kW PFC Power Supply Based on Reduced Redundant Power Processing Principle

Using the reduced redundant power processing (R²P²) principle, a single-phase power-factor correction (PFC) power supply can achieve a higher overall efficiency as a result of the use of a noncascading structure that involves less repeated processing of the input power. This paper investigates a single-phase noncascading PFC power supply based on the R²P² principle. The circuit employs a current-fed full-bridge converter as the PFC preregulator, and a buck-boost converter as the voltage regulator. This paper addresses the design of this noncascading PFC power supply and in particular the relationships between the gained efficiency, the transient response and the size of the energy storage. Experimental results obtained from a 1 kW laboratory prototype are presented.