短波监测站测向准确度的检验

全国短波监测网的一期工程有4个固定监测站:北京站、哈尔滨站、乌鲁木齐站和成都站.后3个站由成都华日通讯技术有限公司负责系统集成.设备安装就绪,在国家无线电监测中心的主持下,对成都站、乌鲁木齐站和哈尔滨站做了验收测试.各监测站所配备的测向装置的测向准确度的测量是验收测试中的一个主要检测项目.在该项检测中,我们充分利用了当代科学技术的最新成果,拟定了极具操作性的、科学的、经济的和便捷的测量方法,获得了准确可靠的测量结果.下面介绍该测量方法的要点,以供同行参考运用.     

Calibration of the AIRS microwave instruments

Aqua carries three microwave radiometers that form an integral part of the Atmospheric Infrared Sounder (AIRS) sounding suite. Two Advanced Microwave Sounding Unit-A modules, one operating with two channels in the 23-31-GHz range and one operating with 12 channels in the 50-60-GHz range and one channel at 89 GHz, provide all-weather temperature soundings and cloud information. The Humidity Sounder for Brazil operates with four channels in the 150-190-GHz range and provides all-weather humidity and cloud soundings. All are cross-track scanners, as is AIRS. While there are significant differences between these three instruments, they are sufficiently alike that a common approach can be used to calibrate them. We describe the instruments and their heritage, the onboard calibration system, and the ground-based calibration processing.     

Accurate boresight measurements of large antennas and radomes

A laser-mirror system incorporated into an antenna pattern range is capable of aligning the antenna tower to measure the radome boresight error of large antennas to within 0.1 mrad angular accuracy. The simplicity of the alignment system makes it relatively easy to position the antenna, with or without its radome to a preestablished mechanical reference plane. Hence, deflection of the antenna tower system due to different loadings can be determined which otherwise would be undetected with most range facilities.     

Improving the accuracy of volumetric segmentation using pre-processing boundary detection and image reconstruction

The concentration edge -detection and Gegenbauer image-reconstruction methods were previously shown to improve the quality of segmentation in magnetic resonance imaging. In this study, these methods are utilized as a pre-processing step to the Weibull E-SD field segmentation. It is demonstrated that the combination of the concentration edge detection and Gegenbauer reconstruction method improves the accuracy of segmentation for the simulated test data and real magnetic resonance images used in this study.     

相控阵天线的光电轴匹配探讨

详细分析引起相控阵光电轴不一致的各种误差来源，给出解决这一问题的方法，并把理论计算结果与某一相控阵天线的测试结果做了比较，验证了此方法的正确性及可行性，为提高其它各指向角的指向精度奠定了基础。     

An overview of the AIRS radiative transfer model

The two main elements of the Atmospheric Infrared Sounder radiative transfer algorithm (AIRS-RTA) are described in this paper: 1) the fast parameterization of the atmospheric transmittances that are used to perform the AIRS physical retrievals and 2) the spectroscopy used to generate the parameterized transmittances. We concentrate on those aspects of the spectroscopy that are especially relevant for temperature and water vapor retrievals. The AIRS-RTA is a hybrid model in that it parameterizes most gases on a fixed grid of pressures, while the water optical depths are parameterized on a fixed grid of water amounts. Water vapor, ozone, carbon monoxide, and methane profiles can be varied, in addition to the column abundance of carbon dioxide.     

Optimization of two-dimensional radome boresight error performanceusing simulated annealing technique

A systematic approach to radome design is presented. The problem is formulated as a global optimization procedure such that the radome performance is optimized by properly adjusting the thickness of the radome layer over the entire radome surface. In this approach the thickness profile is parameterized via B-splines representation. Simulated annealing technique is applied to finding the best thickness profile so that the maximum boresight error is reduced to as small as possible over the entire range of the antenna look angle. A two-dimensional design example is given. The best possible thickness profile is found and the boresight error is reduced considerably compared to that due to a uniform layer. The method is general and can be applied without difficulty to other realistic three-dimensional radomes of arbitrary shapes     

Coalignment and synchronization of the AIRS instrument suite

Previous multispectral sounders have consisted of infrared and microwave instruments operated asynchronously, with the data interpolated during ground processing to common fields of view (FOVs) for geophysical retrieval processing. To help achieve the high retrieval accuracy required for the Atmospheric Infrared Sounder (AIRS) system, the four instruments making up the AIRS suite are aligned and synchronized in such a way as to achieve common FOVs without interpolation. We describe the system, how the alignment is accomplished, and the plans to verify performance after launch and compensate for misalignments that might be revealed then.     

提高过零点检测精度的方法

为提高过零点检测精度,减小漏电保护器的拒动作和误动作,本文介绍了过零点检测的基本原理,理论论述零点检测误差存在的原因,提出一种新的过零点检测方法;给出电路设计图及仿真结果。经验证,该电路将过零检测的时间误差减小到了6.423μs,大大提高漏电保护的可靠性和有效性,同时也可以应用于工频检测,谐波分析等。     

The sun as a test source for boresight calibration of microwave antennas

Although the diameter of the sun at microwavelengths is a little over half a degree, the sun can be used for establishing, say between 3 and 30 cm, the pointing corrections (boresight calibration) of microwave antennas, with high precision. There is, however, a discrepancy between the position of the microwave sun on any given day and the position of the center of the solar disc as tabulated in [16]. Over the period 1966-1969 this discrepancy had an rms value of 1.6' east-west and 1.2' north-south and a range of 11.4' east-west and 9.2' north-south. These conclusions are based on sun maps, made at 9.1 cm with an antenna having a beamwidth of approximately 3', which are published regularly. From such a map the microwave centroid can be determined with an error less than 1'. In the absence of such a map, the centroid can be estimated to within 2' or slightly better by taking account of optical data such as sunspots or plages. The correction on any one day is strongly correlated with that of the day before, but the correlation is small after about 5 days. The correlation returns in part after 27 days.     

Vertical Resolution Estimates in Version 5 of AIRS Operational Retrievals

In this paper, we present an overview of averaging-kernel computations from the Atmospheric Infrared Sounder (AIRS) Version 5 product retrieval software. Temperature and moisture retrievals form the focus of this paper; however, some results for all other retrieved gas amounts are presented. The theory and methodology required to utilize the averaging kernels for comparison of AIRS retrievals with correlative measurements are given. The averaging kernels are used to transform correlative measurements to AIRS effective resolution and are used to assess and derive the vertical resolution of Version 5 temperature and moisture retrievals in different atmospheric conditions. We find that depending on the scene, AIRS Version 5 tropospheric temperature (moisture) retrieval resolution, which is as determined by the full-width at half-maximum of the averaging kernels, ranges between 2.5 km (2.7 km) near the surface and 7.1 km (4.3 km) near the tropopause.      

基于阵元相位调控的天线罩瞄准误差快速优化

提出了一种通过调节相控阵单元激励相位来实现带罩天线瞄准误差快速优化的方法.基于粒子群算法,实现了连续可变相位以及数字离散相位的调节优化.在数字优化编码中结合相位偏移优选技术,有效降低了低位移相器的数字量化误差.结合先验信息,改进瞄准误差优化的速度更新公式,提高了优化收敛速度.分析建立代表场源关系的预计算矩阵,降低适应度函数求解计算量,节约了数值计算时间.通过对16元4位移相阵列天线——正切卵形罩系统的优化设计,验证了该方法的正确性与有效性.     

提高波前探测精度的高阶矩方法

夏克-哈特曼波前传感器测量畸变波前的探测精度主要取决于光斑质心的测量精度。提出了一种提高光斑质心探测精度的新方法,在优化的探测窗口内使用高阶矩方法计算光斑的质心。首先,在整个子孔径内,通过一阶矩方法获得光斑的近似中心,然后以这个近似中心为中心,包含整个光斑,建立一个矩形窗口,并在该窗口内通过高阶矩方法重新计算光斑的质心。通过该改进的方法,在优化的探测窗口外,噪声的影响基本被消除;在优化的探测窗口内,噪声的影响也因为光斑权值比重的增大而削弱。实验结果证明:与传统方法相比,新方法提高了光斑质心测量的精度、重复性和稳定性。     

Nature of the electromagnetic field reflected from a coastline

In a recent publication, Millar considered the field variation near a coastline when an H- polarised plane wave is incident from the sea or land. He stated that disagreement exists between his results and those of Wait. In this communication, it is shown that Millar's conclusions are in error.     

AIRS near-real-time products and algorithms in support of operational numerical weather prediction

The assimilation of Atmospheric InfraRed Sounder, Advanced Microwave Sounding Unit-A, and Humidity Sounder for Brazil (AIRS/AMSU/HSB) data by Numerical Weather Prediction (NWP) centers is expected to result in improved forecasts. Specially tailored radiance and retrieval products derived from AIRS/AMSU/HSB data are being prepared for NWP centers. There are two types of products - thinned radiance data and full-resolution retrieval products of atmospheric and surface parameters. The radiances are thinned because of limitations in communication bandwidth and computational resources at NWP centers. There are two types of thinning: (1) spatial and spectral thinning and (2) data compression using principal component analysis (PCA). PCA is also used for quality control and for deriving the retrieval first guess used in the AIRS processing software. Results show that PCA is effective in estimating and filtering instrument noise. The PCA regression retrievals show layer mean temperature (1 km in troposphere, 3 km in stratosphere) accuracies of better than 1 K in most atmospheric regions from simulated AIRS data. Moisture errors are generally less than 15% in 2-km layers, and ozone errors are near 10% over approximately 5-km layers from simulation. The PCA and regression methodologies are described. The radiance products also include clear field-of-view (FOV) indicators. The residual cloud amount, based on simulated data, for FOVs estimated to be clear (free of clouds) is about 0.5% over ocean and 2.5% over land.     

Verification of CDM circuit simulation using an ESD evaluation circuit

In this work, the capability of circuit simulation to predict CDM robustness of integrated circuits and to determine weak circuit elements is studied. The applicability is demonstrated for an ESD evaluation circuit designed to enable the analysis and optimization of ESD protection strategies in an early design phase during the introduction of a new technology. CDM circuit simulation is compared to the measurement results of variations of this circuit in two different package types. Failure locations are verified with physical failure analysis. The failure locations and CDM failure levels were reproduced accurately with circuit simulation for all circuit and package variations.     

Prelaunch spectral calibration of the atmospheric infrared sounder (AIRS)

The Atmospheric Infrared Sounder (AIRS) is a high-resolution infrared sounder launched aboard the National Aeronautics and Space Administration's Aqua satellite on May 4, 2002. AIRS is a grating spectrometer with 2378 channels located between 15 and 3.8 /spl mu/m, with nominal resolving powers of /spl nu///spl Delta//spl nu/=1200. As the first of a new generation of upcoming infrared instruments with similar spectral coverage and resolution, there will be much interest in the performance of AIRS. The ability to retrieve good atmospheric profiles from AIRS observations will depend in part upon our knowledge of the spectral response of AIRS to the upwelling radiance. This paper discusses the spectral calibration of AIRS based upon an extensive set of laboratory test data generated by the instruments prime contractor, BAE. In particular, we describe the calibration of the AIRS spectral response functions, showing that our requirement for accuracies of "1% of a width" have been achieved.     

Measuring image edge detector accuracy using realisticallysimulated edges

Edge detector tests using edges derived from the acquisition system's edge spread function are described. The test edges used are the most difficult that could exist in a practical system. The results were significantly different to those obtained by traditional methods, indicating that simpler detectors may suffice for some applications     

EEG localization accuracy improvements using realistically shapedhead models

A model of the head must be used in making estimates of the locations of electrical sources in the brain using electroencephalograms (EEGs) measured on the scalp. In part, the accuracy of these estimates is dependent on how accurately the model represents the actual head. In most work performed to date, spherical models of the head have been used. This paper presents results in which the estimates of source location are made in realistically shaped head models. Techniques for accurately and conveniently developing realistically shaped head models from CTs, MRIs, X-rays, and/or physical measurements are also presented. Realistically shaped head models are developed for three subjects with electrical sources implanted at known locations in the brain. Localization accuracy is found to be significantly better in the realistically shaped bead models than in spherical models if EEGs with good signal-to-noise ratio are used