基于极化干涉SAR 反演植被高度的改进三阶段算法

利用极化干涉合成孔径雷达(Polarimetric Interferometry SAR, PolInSAR)数据反演森林参数问题为当前PolInSAR 研究的热点问题。经典的森林参数反演算法是基于随机散射体模型(Random Volume over Ground, RVoG)的阶段反演算法,该算法中直线拟合误差和体散射估计误差会严重影响反演精度。为了提高树高估计精度,该文使用整体最小二乘法直线拟合得到更精确的地表相位估计结果,并提出以Gamma 函数为线性度量自适应地估计体散射去相干,得到了改进的PolInSAR 三阶段反演算法,实验结果表明改进算法可靠有效。      

合成孔径雷达简缩极化干涉数据的植被高度反演技术研究

该文提出了一种利用合成孔径雷达简缩极化干涉数据进行植被高度反演的三阶段方法。将全极化干涉数据处理中的相干最优方法引入简缩极化干涉数据处理,由相位最优相干系数对应的最优相位获得体去相干系数和地表相位的初始估计,利用相干区域边界提取方法更新体去相干系数,得到精确的植被高度估计值。采用欧空局提供的L波段的模拟全极化干涉数据构造简缩极化数据集,将该数据用于植被反演,反演结果验证了提出方法的有效性。     

基于PolInSAR的植被区高精度数字表面模型反演方法

针对传统方法无法估计电磁波在植被中的穿透深度导致植被数字表面模型(DSM)反演误差较大的问题,该文提出一种高精度DSM估计方法。该方法首先通过极化干涉相干最优中最大化相位差法分离得到电磁波在植被中高、低散射相位中心的干涉相位。然后提出一种归一化高、低散射相位中心高度随消光系数变化的模型,基于该模型搜索得到电磁波在植被中的最浅穿透深度。最后利用干涉处理方法得到高散射相位中心的高程,将最浅穿透深度补偿到该高程中,从而提升植被区DSM估计精度。利用PolSARpro软件在不同植被种类和不同植被高度下进行仿真试验以及机载全极化数据进行实测数据试验,试验结果表明该方法能有效提高植被区DSM反演精度。

     

单基线PolInSAR反演算法研究

极化干涉合成孔径雷达(PolInSAR)测量是一种集极化雷达(PolSAR)和干涉雷达(InSAR)测量技术于一体的新的对地观测技术,利用极化干涉雷达数据反演地表植被参数特别是森林的垂直结构参数是当前极化干涉研究的热点问题。经典的单基线PolInSAR反演算法是Cloude和Papathanassiou提出的三阶段反演算法,但是该算法在相干值估计、直线拟合和散射体去相干估计等方面都存在着误差,直接影响反演精度。该文提出了一种新的基于统计特征和PolInSAR相位最优化算法的反演算法,并采用PolInSAR模拟数据验证了该算法的有效性。     

Microwave Biomedical Data Inversion Using the Finite-Difference Contrast Source Inversion Method

We present a contrast source inversion (CSI) technique which is based on a finite-difference (FD) solver for use in microwave biomedical imaging. The algorithm is capable of inverting complex-permittivity biomedical data sets without the explicit use of a forward solver at each iteration. The FD solver is based in the frequency domain, utilizes perfectly matched layer (PML) boundary conditions, and the stiffness matrix is solved via an LU decomposition and Gaussian elimination. An important feature of the FD-CSI algorithm is that the stiffness matrix associated with the FD solver depends only upon the background medium and frequency, and thus the LU decomposition is only performed once, before the iterative inversion process. Unlike the usual Integral Equation (IE) based inversion techniques, the FD-CSI algorithm is readily capable of utilizing an arbitrary background medium for the inversion process.      

基于分类统计的PolInSAR植被高度最大似然估计

极化干涉SAR是一种集极化和干涉SAR优势于一体的新型遥感技术.结合两层植被随机体散射模型和极化分解技术,基于极化干涉SAR数据的概率分布统计特征,提出一种利用参数迭代求解预测模璎和测量值最小似然距离的植被高度反演方法.该方法克服了传统最大似然估计方法需已知地表散射特征参数的约束,减少了计算复杂性.最后通过极化干涉SAR仿真数据实验分析,文中算法相对于三阶段反演算法提高了植被高度估计的精度.验证了算法的有效性.     

Characterization of Quantum-Cascade Lasers Using Single-Pass Transmission Spectroscopy

The study of the electron distribution and intersubband transitions in quantum cascade (QC) lasers provides fundamental insights into the laser operation. Measurements on intersubband transitions are often performed on QC lasers under nonoperating conditions, i.e., at zero electric field. In this study, a single-pass transmission technique that allows for probing of QC lasers under operating conditions was used. The measurements and analysis were done on QC lasers with vertical and diagonal transition active region designs operating at $lambdasim 10 mu{hbox {m}}$. The single-pass modal gain coefficients, extracted for the vertical transition design, were 24.04 cm/kA at 100 K, 21.36 cm/kA at 125 K, 14.25 cm/kA at 150 K, and 5.26 cm/kA at 175 K.      

Evaluating the Impacts of Using Different Digital Surface Models to Estimate Forest Height with TanDEM-X Interferometric Coherence Data

In our previous studies, we demonstrated the usefulness of TanDEM-X interferometric bistatic mode with single polarization to obtain forest heights for the purposes of large area mapping. A key feature of our approach has been the use of a simplified Random Volume Over Ground(RVOG) model that locally estimates forest height. The model takes TanDEM-X interferometric coherence amplitude as an input and uses an external Digital Surface Model(DSM) to account for local slope variations due to terrain topography in order to achieve accurate forest height estimation. The selection of DSM for use as a local slope reference is essential, as an inaccurate DSM will result in less accurate terrain-correction and forest height estimation. In this paper, we assessed TanDEM-X height estimates associated with scale variations in different DSMs used in the model over a remote sensing supersite in Petawawa, Canada. The DSMs used for assessments and comparisons included ASTER GDEM, ALOS GDSM, airborne DRAPE DSM, Canadian DSM and TanDEM-X DSM. Airborne Laser Scanning(ALS) data were used as reference for terrain slope and forest height comparisons. The results showed that, with the exception of the ASTER GDEM, all DSMs were sufficiently accurate for the simplified RVOG model to provide a satisfactory estimate of stand-level forest height. When compared to the ALS 95th height percentile, the modeled forest heights had R2 values greater than 80% and Root-Mean-Square Errors(RMSE)less than 2 m. For a close similarity in slope estimation with the ALS reference, coverage across Canada and open data access, the 0.75 arc-second(20 m) resolution Canadian DSM was selected as a preferred choice for the simplified RVOG model to provide TanDEM-X height estimation in Canada.     

Analysis of Forest Structure Using Thematic Mapper Simulator Data

Remotely sensed data from forested landscapes contain information on both cover type and structure. Structural properties include crown closure, basal area, leaf area index, and tree size. Cover type and structure together are useful variables for designing forest volume inventories. The potential of Thematic Mapper Simulator (TMS) data for sensing forest structure has been explored by principal components and feature selection techniques. Improved discrimination over multispectral scanner (MSS) data proved possible in a mixed conifer forest in Idaho for estimating crown closure and tree size (saplings/seedlings, pole, sawtimber). Classification accuracy increased monotonically with the addition of new channels up to seven; the four optimum channels were 4, 7, 5, and 3. The analysis of TMS data for 123 field sites in Sequoia National Park indicated that canopy closure could be well estimated by a variety of bands or band ratios (r = 0.62-0.69) without reference to forest type. Estimation of basal area was less successful ( r = 0.51 or less) on average, but improved for certain forest types when data were stratified by floristic composition. To achieve such a stratification, sites were ordinated by a detrended correspondence analysis (DECORANA) based on the canopy of dominant species. Within forest types, canopy closure continued to be the best predictor of spectral variation. Total basal area could be predicted in certain forest types with improved or moderate reliability using various linear ratios of TMS bands (e. g., red fir, 5/4, r = 0.76; lodgepole pine, 4/3, r = 0.82).     

基于PolInSAR相干区域的最优正规矩阵近似解的地形与树高估计

森林区域林下地形及树高的反演是极化干涉雷达的一个重要应用。该文首先对极化干涉SAR数据的相干区域进行建模及运用最优正规矩阵近似干涉互相关矩阵,得到白化正规干涉互相关矩阵。白化正规干涉互相关矩阵的相干区域为一条直线,任意求得两个不同极化状态下的相干系数进行直线拟合,完成地表的估计,再结合体散射去相干与树高之间的关系,运用查表方法完成树高的估计。该方法回避了传统方法中求解所有极化状态下的相干系数估计及相干区域边缘提取的步骤,在简化参数反演提升估计效率的同时获得正确地表与树高估计,最后运用仿真数据完成算法有效性与可靠性的验证。     

Voltage-Controlled Ku-Band and X-Band Tunable Combline Filters Using Barium-Strontium-Titanate

Tunable X-band and Ku-band combline bandpass filters using barium-strontium-titanate capacitors fabricated on alumina substrates with through-substrate CuW vias are reported. Under a 0–100 V bias, the X-band filter changes center frequency from 8.75 GHz to 10.96 GHz with 4–8 dB of loss while the Ku-band filter changes center frequency from 11.7 GHz to 14.3 GHz with 6–10 dB of loss. Advances in processing and integration related to the filter fabrication and design are discussed.      

A Low-Noise X-Band Parametric Amplifier Using a Silicon Mesa Diode

This paper summarizes a cooperative effort to develop silicon mesa variable-capacitance diodes and to evaluate their potential for achieving low-noise amplification in the high microwave frequency range. Cutoff frequencies of about 70 kMc at zero-bias voltage (corresponding to 140 kMc at maximum reverse bias voltage) with a total permissible voltage swing in excess of 5 volts have been obtained. A versatile degenerate X-band parametric amplifier was developed which, when used in conjunction with these silicon mesa diodes, achieved a radiometer noise temperature of 130°K at 8.5 kMc with a 50-Mc bandwidth at 17-db gain. The measured performance of the diode (figure of merit) is compared with the first-order theory in an operating radar system. The over-all performance of the amplifier improved the observed system sensitivity by 6 db.     

Coniferous Forest Classification and Inventory Using Landsat and Digital Terrain Data

Accurate cost-effective stratification of forest vegetation and timber inventory is the primary goal of a Forest Classification and Inventory System (FOCIS) developed at the University of California, Santa Barbara, and the Jet Propulsion Laboratory, Pasadena. Conventional timber stratification using photointerpretation can be time-consuming, costly, and inconsistent from analyst to analyst. FOCIS was designed to overcome these problems by using machine-processing techniques to extract and process tonal, textural, and terrain information from registered Landsat multispectral and digital terrain data. FOCIS was developed in northern California's Klamath National Forest (KNF), where the rugged terrain and diverse ecological conditions provided an excellent area for testing Landsat-based inventory techniques. The FOCIS procedure was further refined in the Eldorado National Forest (ENF), where the portability and flexibility of FOCIS was verified. Using FOCIS as a basis for stratified sampling, the softwood timber volume of the western portion of the Klamath (944 833 acres; 422 340 ha) was estimated at 3.83 x 109 ft3 (1.08 x 108 m3), with a standard error of 4.8 percent based on 89 sample plots. For the Eldorado, the softwood timber volume was estimated at 1.88 x 109 ft3 ( 0.53 x 108 m3) for an area of 342 818 acres (138 738 ha) with a standard error of 4.0 percent, based on 56 sample plots. These results illustrate the power of FOCIS methods to produce timely accurate large-area inventories with comparable accuracies and reduced costs when compared to conventional timber inventory methods.     

Forest Biophysical Parameter Estimation Using L- and P-Band Polarimetric SAR Data

L- and P-band airborne polarimetric synthetic aperture radar (SAR) data acquired by the RAMSES system over different height maritime pine (Pinus Pinaster Ait.) stands of the Nezer forest (Landes, France) have been evaluated for forest biophysical parameter estimation. A pseudolinear correlation has been brought to evidence at P-band between polarimetric anisotropy and mean tree height, which is also linked to other biophysical parameters in the Nezer forest, meaning that SAR polarimetry constitutes a promising tool for forest parameter retrieval at low frequency. The spatial conditions have been evaluated through the quantification of the impact of signal-to-noise ratio diminution and resolution degradation on the forest height inversion. It has been shown that the inversion accuracy remains acceptable for N Esigma₀, representing the noise level of the SAR image, which is lower than -15 dB, and for spatial resolution increasing up to 15 m.     

Data on the Temperature Dependence of X-Band Fluorescent Lamp Noise Sources

This paper is concerned primarily with the performance of fluorescent lamps as microwave noise sources at 9,000 mc. In particular, it deals with the temperature dependence of the excess noise ratio of an 8-watt lamp running at a lamp current of 150 ma in a 10° E-plane holder. It was found that 1) the bulb temperature is much higher than that with a lamp current of 75 ma encountered in the 90° H-plane circuit investigated previously at 4,000 mc, hence the temperature coefficient of excess noise versus waveguide temperature obtained in the 4,000 mc circuit does not apply, 2) anomalous and unreproducible inversions in the temperature coefficient at these higher bulb temperatures have been observed, 3) these anomalies can be avoided by operating the bulb at lower temperatures, 40°C to 50°C, where the lamps appear to be just as uniform and stable and probably just as noisy as they are at 4,000 mc.     

Optical Feedback Height Control System Using Laser Diode Sensor for Near-Field Data Storage Applications

We demonstrated a laser diode position sensor for a near-field height control system. The feedback signal of the laser diode sensor that resulted from self-mixing interferometry was characterized and modeled by a simplified method. Due to the fine spatial resolution of the laser sensor, an active height control system with nanoscale position precision was designed and realized under a spinning disk for near-field applications.     

X-Band Microstrip-Inserted Puck Circulator Using Arc-Plasma-Sprayed Ferrite (Short Papers)

Experimental circulators using ferrite pucks which have been sprayed into cavities in dielectric substrates by an arc-plasma spray (APS) process are described.     

自然反型层硅光电二极管

自然反型层光电二极管是利用在P型硅片上生长热氧化层时形成的自然反型层作为感应的NP结的一侧而制得的。本文报导作者试制的IL90型自然反型层光电二极管的初步结果。器件暗电流小于7×10~(-10)A(在100mV下测试,有效光敏面积1cm~2);光谱响应峰值向短波方向明显移动;光谱响应与人眼视见函数相近;对短波长光有较高的绝对响应度,例如,在365um处,为0.293μA/μW;在254um处,为0.113μA/μW。     

Inversion of Phaseless Total Field Data Using a Two-Step Strategy Based on the Iterative Multiscaling Approach

In this paper, a new approach for the quantitative electromagnetic imaging of unknown scatterers located in free space from amplitude-only measurements of the total field is proposed and discussed. The reconstruction procedure splits the problem into two steps. The method is based on the use of an inverse source algorithm to first complete the scattering data by estimating the distribution of the radiated field in the investigation domain. The object's function profile is then retrieved from the phaseless data via an iterative multiresolution procedure integrated with an effective minimization technique based on the particle swarm algorithm. Numerical examples are provided to assess the effectiveness of the whole two-step strategy in the presence of synthetic noise-corrupted data as well as in dealing with experimental data sets. Comparisons with full-data and "bare" approaches are reported as well