Estimating ionospheric reflection height from Doppler measurements

A method is described which allows estimating an ionospheric reflection height from Doppler measurements made over an oblique CW radio transmission. This method requires the presence of multihop signals. The assumptions pertaining to the method's validity are delineated and an example is illustrated.     

Metamer density estimated color correction

Color correction is the transformation of response values of scanners or digital cameras into a device- independent color space. In general, the transformation is not unique due to different acquisition and viewing illuminants and non-satisfaction of the Luther–Ives condition by a majority of devices. In this paper we propose a method that approximates the optimal color correction in the sense of a minimal mean error. The method is based on a representative set of reflectance spectra that is used to calculate a special basic collection of device metameric blacks and an appropriate fundamental metamer for each sensor response. Combining the fundamental metamer and the basic collection results in a set of reflectances that follows the density distribution of metameric reflectances if calculated by Bayesian inference. Transforming only positive and bounded spectra of the set into an observer’s perceptually uniform color space results in a point cloud that follows the density distribution of device metamers within the metamer mismatch space of acqcuisition system and human observer. The mean value of this set is selected for color correction, since this is the point with a minimal mean color distance to all other points in the cloud. We present the results of various simulation experiments considering different acquisition and viewing illuminants, sensor types, noise levels, and existing methods for comparison.     

电离层电波传播相位污染校正

电离层电波传播相位污染使天波超视距雷达（OTHR）接收的回波信号谱扩展。采用合成孔径雷达（SAR）成像中的相位梯度算法（PGA）来校正相位污染，PGA算法要求所处理的各个分辨单元（这里包括方位和距离单元）具有相同的相位误差，但当对于电离怪空间变化剧烈，或OTHR距离和方位分辨率比较粗时，相邻单元的相位污染不完全相同，这里PGA方法不适用。针对这种情况，考虑相位变化不可能非常剧烈。可用低次多项式表示时，采用最小熵搜索方法，分别校正各单元的电离层相位污染。最后采用我国录取的OTHR实测数据验证，表明这两方法的校正效果良好。     

影响地面雷达测高精度的因素

针对某型三坐标地面雷达,对影响地面雷达测高精度的主要因素进行了分析。基于阵地地形、电磁环境、杂波环境、大气环境和人为导致的系统异常等因素,分析了地面雷达测高误差产生的原因,评估了多种因素对测高精度的影响程度,提出了在实际应用中规避影响因素以改善地面雷达测高精度的建议。     

Estimation of noise error when measuring virtual height during diffusivity of ionospheric F layer

It is shown that during diffusivity of ionosphere its bandwidth of coherence may shrink to hundreds of hertz. Frequency-selective fading appears in these cases and the noise error when measuring ionospheric virtual height increases by 1–2 orders if compared to the normal ionospheric conditions.     

MTD对比相测高的精度影响

比相测高雷达是利用多个天线馈源分别接收目标的回波信号,根据不同馈源接收回波信号时产生的相位差,再结合已知的目标距离,从而获取目标高度信息。但在实际的杂波环境中,信杂比往往很低,使得高度误差太大,影响雷达的测高精度。     

MODIS imagery geometric precision correction based on longitude and latitude information

Moderate resolution imaging spectrum-radiometer (MODIS) imagery is an important remote sensing source, whose goal is to research and forecast the earth changes. In order to provide high precision imagery for MODIS application, geometric correction is one of the most important steps in the image preprocessing. The principle and procedure of geometric correction are introduced in this paper. The appropriate selection method of ground control points (GCPs) is very crucial for geometric correction. Because there are much useful latitude and longitude information in MODIS data, these geographic data are used as GCP to realize geometric precision correction. Through selecting the proper map projection, the original image is transformed from original image coordinate system to map coordinate system. Using the polynomial transformation and the inverse distance weighted interpolation, the corrected imagery can be obtained at last. Experimental results indicate that the quality and precision of the corrected imagery can meet the requirements.     

TOPEX/Poseidon microwave radiometer (TMR). III. Wet troposphererange correction algorithm and pre-launch error budget

For pt.II see ibid., vol.33, no.1, p.138-46 (1995). The sole mission function of the TOPEX/Poseidon microwave radiometer (TMR) is to provide corrections for the altimeter range errors induced by the highly variable atmospheric water vapor content. The three TMR frequencies are shown to be near-optimum for measuring the vapor-induced path delay within an environment of variable cloud cover and variable sea surface flux background. After a review of the underlying physics relevant to the prediction of 5-40 GHz nadir-viewing microwave brightness temperatures, the authors describe the development of the statistical, two-step algorithm used for the TMR retrieval of path delay. Test simulations are presented which demonstrate the uniformity of algorithm performance over a range of cloud liquid and sea surface wind speed conditions. The results indicate that the inherent algorithm error (assuming noise free measurements and an exact physical model) is less than 0.4 cm of retrieved path delay for a global representation of atmospheric conditions. An algorithm error budget is developed which predicts an overall algorithm accuracy of 0.9 cm when modeling uncertainties are included. When combined with expected TMR antenna and brightness temperature accuracies, an overall measurement accuracy of 1.2 cm for the wet troposphere range correction is predicted     

EGNOS test bed ionospheric corrections under the October and November 2003 storms

Two severe geomagnetic storms were experienced on October 29-31 and November 20, 2003, degrading significantly the European Geostationary Navigation Overlay Service (EGNOS) Test Bed (ESTB) performance in Europe. Such storms reached extreme values of Kp=9 during the most severe periods. The analysis of the ESTB ionospheric corrections and their effect on the ESTB integrity and accuracy is presented in this work. The ESTB performance during those storms was monitored from a network of global positioning system (GPS) receivers widely distributed over Europe, including the ESTB reference stations, and the geographical degradation of the accuracy is analyzed in this paper. The correlation between the Kp index and the misleading information (MI) events is also shown. During the most severe stormy periods, the errors in the ESTB ionospheric corrections and its integrity bounds are analyzed to explain the peaks in the navigation system error, which produces MIs. This analysis has been carried out by comparing with direct dual-frequency GPS measurements and global ionospheric maps.     

Adjusting software failure rates that are estimated from test data

Software test environments are often different from field environments. Using test data exclusively to estimate a field failure rate will not usually give a very accurate estimate. In this paper, we extend an empirical calibration methodology for adjusting the failure rate estimate obtained from analysing test data. In addition to scaling the estimated failure rate of a fault, we propose scaling the estimated number of residual faults as well. We also derive likelihood ratio tests to formally determine (from previous releases of the software) if test, and field environments are significantly different. We illustrate our new results with two telecommunications case studies. The combination of the likelihood ratio test, and the calibration methodology offers a practical way to extend the application of software reliability growth models to less formal test environments.     

折射率公式对电波折射修正精度的限制

电波折射误差修正精度主要取决于大气折射率剖面精度,而大气折射率是由温度、气压和湿度通过计算得到的。计算大气折射率的公式有两种,一种为常用公式,另一种为改进型公式。由于两种公式是由统计得到的,因此存在一定的误差。假设大气参数的测量是准确的,则经过对两种公式误差引起电波折射误差的计算可知,如果要求距离折射误差精度小于0．1m,则常用大气折射率计算公式不实用,最好采用改进型折射率计算公式,如果要求距离折射误差精度为0．3m,则常用大气折射率计算公式可以使用。如果采用精度较差的59型探空仪测量大气参数,则只用常用公式计算大气折射率剖面即可。     

精密测量雷达常规标校误差校正参数研究

采用AE类型天线座的精密测量雷达在角度标校过程中涉及轴系及误差校正参数的定义、术语、标定方法、校正模型及参数符号等在不同文献、不同型号雷达、不同研制单位存在较大差异。针对这一实际情况,本文具体介绍了轴系和标校误差项的概念,明确了各校正误差的校正思路,简单分析了各误差项产生原理,详细阐述了各误差校正参数符号与校正模型的关系。针对两种校正模型提出了对应的误差校正参数的符号约束,避免了由于误差校正参数标定方法及符号装订错误引起测角超差故障。最后分析并给出了自动化标校中各校正参数的简化计算模型。     

压力测试系统修正方法的研究

冲击波信号的上升沿很陡,要求测试系统的动态特性要好,对测试系统尤其是传感器提出了较高的要求,本文针对用于爆炸超压测试的压力测试系统激波管动态校准实验数据建立数学模型,研究了基于动态补偿数字滤波器和神经网络的以传感器为主要因素的测试系统补偿修正方法,通过仿真表明:前者可以明显缩短测试系统动态响应时间,并且工作频带也可以得...     

基于PTP授时的同步精度测试方法研究

随着现代武器打击精度的提高,指控系统对时间同步的要求也随之提高,这就对系统授时方案中的网络架构、主时钟以及授时板卡的时间同步精度提出了新的要求。本文主要针对PTP授时方案中的对时精度给出测试方案。测试结果表明,PTP授时模式可满足系统对时间同步精度的需求。     

Experimental error correction results for optical digital pulse-position modulation

Original practical and theoretical results are presented for the detection and correction of errors in a direct detection optical ( lambda =1.523 mu m) digital pulse-position modulation (digital PPM) system. These results show the degradation in system performance due to interframe interference and an original method of correcting this type of error is presented. This error correcting method was then used to enhance the performance of a Reed-Solomon (RS) coded, digital PPM system.<>     

IPS面临市场考验, 精确阻断水平成关键

1.深层防御必须实现精确阻断纵观当前网络安全的局势,可以用两个“日益”来总结,一是攻击日益增多,另一个是手段日益复杂。据统计数据显示,70%以上的攻击行为发生暴露在应用层,我们称之为深层攻击行为。这种攻击     

雷达精度试验中GPS数据坐标转换及误差分析

介绍了应用GPS载波相位定位技术测量得到的GPS数据为精度试验提供标准值的坐标转换数学模型,并利用误差传递法得到GPS坐标转换后的误差公式。借助三个航路误差理论计算,对转换后的GPS数据进行量化分析,得出在试验中规避标准值大误差的方法。     

基于高精度定位的卫星导航板卡性能对比路测

高精度定位与精细化导航的实现,至少需要具备两个条件:高精度定位网络、终端定位芯片或板卡。在高精度定位网络准备之际,终端板卡的能力成了重要关注点。基于此,文章依托中移智行的高精度定位精品网络,选择了三款主流板卡进行测试,对板卡接入中国移动高精度定位网后的功效与性能进行验证。测试表明,在中国移动高精度定位网络的良好支撑下,K700(三系统单频)、K706(三系统六频)、K803(四系统十三频)均能很好地支撑交通参与者获得良好的高精度定位服务。