雷达改善因子与相位噪声及阿伦方差之间的关系

由于电子对抗技术的发展 ,对雷达提出越来越高的要求。雷达工作时经常会遇到来自致周围环境的有源或无源干扰 ;现代雷达应该具备抗各种有源和无源干扰的能力 ,作为雷达核心的频率源既要具备频率捷变能力 ,又要具备很高的频率稳定性。从而促进现代雷达频率源向着捷变频、低相噪方向发展 ,重点分析频率源的技术指标对雷达改善因子影响。     

介质参数对吸收体电磁散射影响的研究

二维周期渐变微波吸收体由金属基体和涂敷有耗介质构成。有耗介质的厚度、介电常数和磁导率是影响吸收体电磁散射特性的主要因素,因此有必要分析这些参数对吸收体电磁散射特性的影响。根据吸收体的二维周期性结构特点,把分析介质参数对吸收体雷达散射截面(RCS)的影响简化成分析介质参数对涂敷导体二面角RCS的影响。利用矩量法给出涂敷导体二面角的RCS随介质参数变化的计算例子,并结合天线阵列技术算出最佳介质厚度时吸收体的RCS。     

极区中层惯性重力波临界层的VHF雷达观测

本文采用移动式ＳＯＵＳＹＶＨＦ雷达１９８７年６月在挪威Ａｎｄφｙａ（６９°Ｎ，１０°Ｅ）的观测数据，研究中层惯性重力波在临界层的传播特征．数据分析结果表明，在临界层附近波动会突然衰减，波能量被背景风所吸收，惯性重力波的水平传播方向和垂直传播方向在通过临界层后会迅速发生改变，说明临界层附近会产生向下传播的能量源．并且在临界层，回波强度达到峰值，表明临界层对产生雷达回波起着重要作用．     

Characterizing slope correction methods applied to satellite radar altimetry data: A case study around Dome Argus in East Antarctica

Slope correction is important to improve the accuracy of satellite radar elevation measurements by mitigating the slope-induced error (SE), especially over uneven ground surfaces. Although several slope correction methods have been proposed, guidance in the form of stepwise algorithm on how to implement these methods in processing radar altimetric data at the coding level, and the differences among these methods need to be presented and discussed systematically. In this paper, three existing types of slope correction methods—the direct method (DM), intermediate method (IM), and relocation method (RM, further divided into RM1 and RM2)—are described in detail. In addition, their main differences and features for various scientific applications are analyzed. We conduct a systematic experiment with CryoSat-2 Low Resolution Mode (LRM) data in a physically stable area around Dome Argus in East Antarctica, where in-situ measurements were available for comparison. The slope correction is implemented separately using the three methods, with the latest high-accuracy Reference Elevation Model of Antarctica (REMA) as the a-priori topography model. The bias and precision of the slope-corrected CryoSat-2 data results from the RM2 is ?0.18 ± 0.86 m based on the comparison with the field Global Navigation Satellite System (GNSS) data. The results from the RM2 indicate higher precision compared to those from the RM1. According to the correlation analysis of the slope-corrected CryoSat-2 data results (RM1 and RM2), the bias enlarges and the precision becomes worse when the surface slope increases from 0 to 0.85°. After a comprehensively comparative analysis, we find that the results from the RM1 and RM2 are superior in precision (0.93 m and 0.86 m) with respect to the GNSS data. The relatively low precision (1.22 m) from the IM is due to the potential error from the a-priori digital elevation model (DEM). The DM has the lowest precision (2.66 m). Another experiment over rough topography in West Antarctica is carried out for comparison, especially between the RM1 (precision of 15.27 m) and RM2 (precision of 16.25 m). In general, the RM is recommended for the SE elimination among the three methods. Moreover, the RM2 is firstly considered over smooth topography due to the superior performance in bias and precision, while the RM1 is more suggested over the rough topography because of the slightly smaller bias and better precision. The IM relies much on the accuracy of the a-prior DEM and is not usually recommended, because of the strict requirement in the sampling time between the radar altimetry data and the a-priori DEM to avoid any surface change over time.     

Debris flux comparisons from the Goldstone Radar,Haystack Radar,and Hax Radar prior,during, and after the last solar maximum

The continual monitoring of the low Earth orbit (LEO) debris environment using highly sensitive radars is essential for an accurate characterization of these dynamic populations. Debris populations are continually evolving since there are new debris sources, previously unrecognized debris sources, and debris loss mechanisms that are dependent on the dynamic space environment. Such radar data are used to supplement, update, and validate existing orbital debris models. NASA has been utilizing radar observations of the debris environment for over a decade from three complementary radars: the NASA JPL Goldstone radar, the MIT Lincoln Laboratory (MIT/LL) Long Range Imaging Radar (known as the Haystack radar), and the MIT/LL Haystack Auxiliary radar (HAX). All of these systems are highly sensitive radars that operate in a fixed staring mode to statistically sample orbital debris in the LEO environment. Each of these radars is ideally suited to measure debris within a specific size region. The Goldstone radar generally observes objects with sizes from 2 mm to 1 cm. The Haystack radar generally measures from 5 mm to several meters. The HAX radar generally measures from 2 cm to several meters. These overlapping size regions allow a continuous measurement of cumulative debris flux versus diameter from 2 mm to several meters for a given altitude window. This is demonstrated for all three radars by comparing the debris flux versus diameter over 200 km altitude windows for 3 nonconsecutive years from 1998 to 2003. These years correspond to periods before, during, and after the peak of the last solar cycle. Comparing the year to year flux from Haystack for each of these altitude regions indicate statistically significant changes in subsets of the debris populations. Potential causes of these changes are discussed. These analysis results include error bars that represent statistical sampling errors.     

合成孔径雷达方程

导出适用于合成孔径雷达（SAR）的基本方程，用于决定回波信号功率、检测前后的信噪比、平均发射功率和噪声等效后向散射系数。考虑了地物目标特性、信号相干积累和多视处理效应，并对各种参数的影响进行讨论。     

星载ScanSAR天线指向稳定度对辐射校正的影响

基于均匀加权天线模型,推导星载ScanSAR天线指向不稳定引起的多普勒中心频率估计误差,建立多普勒中心频率估计误差与图像辐射校正精度之间的数学模型,进而提出星载ScanSAR辐射校正对天线指向稳定度的要求。最后,通过计算机仿真,验证了理论分析的正确性。     

星载激光测高仪辅助卫星摄影测量浅析

激光测高仪可以快速高精度获取地面高程信息,弥补卫星光学遥感影像三维信息获取能力的不足。采用高精度激光测高数据作为控制信息,符合卫星摄影测量尽量减少地面控制点的发展趋势。文章首先介绍了实际卫星立体测绘中难以解决的问题,结合激光测高的特点,设计了星载激光测高仪辅助空中三角测量立体测绘的方案。根据摄影测量观测方程和激光测高仪对地观测方程,以及卫星影像和激光测高数据外方位元素之间的联系,由光束法平差原理建立观测误差方程。对星载激光测高仪进行定位精度理论分析,采用高精度激光测高数据可以作为高程控制,提高高程观测精度。最后对卫星摄影测量数据与星载激光测高数据联合平差仿真实验,实验结果表明定位精度明显提高。     

基于NURBS曲面的雷达散射截面物理光学算法研究

文章实现了一种使用物理光学（PO）计算雷达散射截面的算法。目标模型用非均匀有理B样条（NURBS）曲面建立，并使用等参数等弦长方法剖分为Ⅳ个四边形面元。在剖分面元上，使用Gordon方法将物理光学积分转化为闭合区域线积分。整个算法在保持计算精度的前提下有较高的计算速度。