一种机载SAR数据点目标辐射定标方法北大核心CSCD

针对机载平台姿态时变造成的天线波束指向不稳定而导致辐射精度下降的问题,提出了一种新的天线方向图定标方法。该方法基于sinc函数模型,考虑了飞机飞行过程中横滚角的影响,能够有效改善飞机姿态不稳导致辐射精度下降的问题。文章根据点目标响应能量计算、天线方向图定标和定标常数计算等关键步骤开展辐射定标研究,采用多波段机载SAR系统获取的C波段和X波段SAR数据对该方法的有效性进行了验证。积分法和峰值法的对比分析结果表明,结合本文新的天线方向图模型,积分法得到的相对和绝对辐射精度均优于峰值法,说明积分法提取点目标能量与本文改进的天线方向图模型结合的辐射定标方法能够满足高分辨率机载SAR数据辐射定标处理的要求。     

SAR定标中角反射器的研究

角反射器是合成孔径雷达(SAR)定标中使用最为广泛的无源点目标,开展角反射器的研究对于SAR定标有着十分重要的意义。本文采用融入多层次快速多极子算法(MIFMM)的矩量法(MoM),对角反射器的雷达散射截面(RCS)进行计算,对比几种常用角反射器的性能,确定不同尺寸三角面角反射器RCS最大值及相应的入射方向,分析加工尺寸、加工角度误差、入射角度偏差等对三角面角反射器RCS的影响,总结角反射器在设计制作和安装过程中应考虑的问题。本文的分析结果对设计角反射器和SAR定标具有重要的参考价值。     

SAR辐射定标技术研究与应用

针对机载SAR辐射定标问题,该文通过对试验获取SAR图像进行分析处理,分别利用积分法和峰值法计算角反射器的回波响应能量,通过雷达方程推导出回波响应能量和定标常数、理论RCS的关系,由此计算出定标常数,并对结果进行了分析.结果表明,在本文的试验条件下,积分法的相对和绝对定标精度优于峰值法的相对和绝对定标精度.     

点目标的机载SAR辐射定标实验精度分析

辐射定标的精度高低直接关系着后续定量遥感技术应用。鉴于辐射定标工作的重要性,该文利用积分法与峰值法提取点目标能量,计算定标常数,并通过TerraSAR-X和机载SAR数据分别进行定标实验。依照定标实验,分析了影响定标精度的主要因素。其中,定标设备方面,三角形角反射器相比四面角形角反射器定标结果稳定;定标算法方面,积分法比峰值法定标具有更高的稳定性,但也有可能对定标常数高估。实验结果表明,机载SAR定标虽然受到飞行平台稳定性的影响,但依然取得了较高稳定度的结果。     

星载SAR传感器外场定标实验研究—以TerraSAR-X卫星为例

传感器的定标精度是衡量SAR卫星系统性能和数据质量的重要标志。以TerraSAR\|X卫星为例,系统设计了外场定标实验流程,围绕高精度获取参考目标外场实际几何坐标和散射截面积的目标,对角反射器的设计与制作、布设方案、状态参数计算和坐标精密测量等问题进行了研究。基于同步获取的SAR数据和外业数据,进行了TerraSAR\|X几何和辐射定标参数的精度验证。验证结果证明了实验总体设计和关键问题解决的有效性,对于其他星载SAR定标工作具有借鉴意义。
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宽角度扫描反射面天线辐射特性

研究了宽角度扫描时侧馈偏置卡塞格伦反射面天线(SFOC)系统的远场特性.应用几何光学原理,对侧馈偏置卡塞格伦反射面天线的各项参数进行了设计.利用最小二乘法对反射面的最佳馈点位置进行了拟合,得到了最佳馈点位置的曲面图,并给出了馈源对副面的最佳指向.采用几何光学与基于傅立叶一贝塞尔方法的物理光学相结合的方法对扫描状态下给定尺寸的双反射面天线系统进行分析.方法具有分析速度快,精度高的优点.计算出了该天线的宽角扫描辐射特性和增益.计算结果表明,该天线在宽角扫描范围内,辐射方向图无太大畸变,增益损失小,效果好.     

基于Terra/MODIS数据的HJ-1B/CCD1交叉定标方法研究

交叉辐射定标是国际上新近发展起来的一种无场地定标方法,它的应用弥补了场地定标成本较高、定标参数更新周期较长的不足。对于我国2008年发射的环境与灾害监测预报小卫星CCD数据而言,探索交叉辐射定标方法的适用性,对及时发现传感器辐射性能的变化,促进CCD遥感数据的定量化应用具有重要意义。本研究以辐射定标精度较高的Terra/MODIS数据为参考,分别使用光线匹配法（RM）和辐射传输模型方法（RTM）对HJ-1B/CCD1数据进行交叉辐射定标,并与相同条件下进行的场地定标结果比较。实验结果表明,使用这两种方法获取的CCD1的第2、3、4波段的定标结果与场地定标结果差异较小,只有第1波段定标结果与场地定标结果差异相对较大,这证明了交叉辐射定标方法的有效性。另外,虽然RTM方法考虑了参考传感器和待定标传感器光谱响应和观测几何的差异,但是由于RTM方法会受到所使用的6S模型本身的误差以及输入的大气参数、地表参数测量误差的影响,该方法并不总是优于RM方法。     

SAR有源编码辐射定标技术研究

在对SAR有源编码辐射定标技术的研究中,首先开展了地物杂波信号对SAR辐射定标精度影响的研究,推出了受地物杂波信号影响的系统总体传递函数的误差公式,其次分析了有源编码辐射定标技术抑制地物杂波的机理和信号处理流程。在不同地物杂波分布情况下,完成了SAR有源编码辐射定标技术的仿真实验。实验结果证明SAR有源编码定标技术能够有效地抑制地物杂波信号的影响,改善SAR辐射定标的精度,特别是提高了定标场地选择的灵活性。     

基于分段辐射校正的星载TDI-CCD成像数据辐射处理方法

文中在分析现有的相对辐射校正方法的局限性基础上,提出了一种基于分段辐射校正的星载TDI-CCD成像数据辐射处理方法.该方法利用实验室定标数据对探元不同感光范围的光电响应模式采用不同的模型进行拟合,从而提高定标系数或者查找表的拟合精度.文中选取资源1号02BHR光学影像进行实验,实验结果表明文中提出的方法与现有的方法相比有较大提高.     

一种EMD的SAR图像自适应辐射均衡方法

针对合成孔径雷达(synthetic aperture radar,SAR)侧视观测模式及天线方向图引起的SAR图像辐射差异严重影响SAR图像的广泛应用问题,根据经验模态分解(empirical mode decomposition,EMD)技术的自适应、自驱动和多尺度等特性,提出了基于EMD技术的SAR图像自适应辐射均衡方法。该方法利用EMD技术获取SAR图像距离向的多阶本征模函数,自适应地确定包含辐射误差的低频信息,并将其优化可获得辐射误差趋势信息和补偿因子,从而均衡SAR图像。将该方法应用到已知误差趋势的仿真数据以及多组机载SAR真实数据,结果表明该方法能够有效地自适应补偿SAR图像的辐射差异,提高了SAR图像的可视化效果和解译能力。     

Calibration and modelling of MAESTRO 1 polarimetric SAR data of a forest area in Les Landes,France

Abstract. The results of an analysis of polarimetric P, Land C-band SAR data from the JPL AIRSAR of a forest area of maritime pine in Les Landes, southwest France, are described and discussed. The data were acquired in connection with the MAESTRO I Campaign organized by ESA and JRC/lspra. Cross-talk and channel imbalance distortions are removed in a calibration process using the SAR data itself and trihedral corner reflectors positioned at the scene. Two calibration methods have been implemented and compared: the iterative Klein algorithm and the non-iterative Quegan algorithm. Quegan's method shows the largest reduction of the cross-talk, and the most stable and easily interpreted results. Also, absolute calibration using the integral method has been performed. The results presented show that P band (and to some extent L band) is very sensitive to trunk biomass using single-polarization radar data, at least at the incidence angles in the range from 38° to 52°, whereas C band is less sensitive. Also, the cylinder model by Durden et al. of the baekseattering from a forest has been implemented and the results show good agreement with the SAR data. The dominant scattering mechanisms have been determined using the model at P and L bands.     

Radiometric calibration stability assessment for the RISAT-1 SAR sensor using a deployed point target array at the Desalpar site,Rann of Kutch,India

Synthetic aperture radar (SAR) data used for quantitative temporal and/or spatial analysis requires calibration to ensure that observed pixel values of amplitude and phase can be related to the geophysical parameters of interest. The process of radiometric calibration of SAR images involves comparison of the backscattered radar reflectivity signal from a ground resolution element containing a calibration target of known signal response, such as a corner reflector. In this study, absolute radiometric calibration of RISAT-1 intensity data of fine resolution stripmap-1 (FRS-1) and medium resolution ScanSAR (MRS) mode was carried out by utilizing array of standard point targets of various types (triangular trihedral, square trihedral, and dihedral) with known radar cross-section deployed prior to satellite overpass with precise azimuth and elevation angles in Desalpar, Rann of Kutch in western India. The derived calibration constants using the integral method were then compared with the values provided in the header file. Deviations in the results are reported in this article. The results obtained show that the difference between the estimated average calibration constants for FRS-1 and MRS mode data with the provided value was found to be within the absolute radiometric accuracy specification of Radar Imaging SATellite (RISAT-1). Near-range to far-range difference of 0.1–0.2 dB for HH (Horizontal transmit, Horizontal receive) polarization and 0.1–0.3 dB for HV (Horizontal transmit, Vertical receive) polarization was estimated for the same scene using distributed target analysis indicating the stability of calibration for the same scene. This study also concluded that Desalpar site in Rann of Kutch has the potential of being an operational SAR calibration site.     

机载SAR天线稳定平台的DSP数字控制器设计

机载SAR(airborne Synthetic Aperture Radar,合成孔径雷达)中,用三轴稳定平台隔离载机的姿态变化及机械振动来稳定天线波束指向是关键的运动补偿技术之一。本文提出用TMS320LF2407DSP芯片设计机载SAR三轴陀螺稳定平台的数字控制器,介绍了机载SAR对稳定平台的要求和TMS329LF2407DSP芯片用于运动控制器设计的优点,给出了控制系统的原理方框图、数学模型和DSP数字控制器结构图。     

SAR图像目标方位角联合估计方法研究

为了精确估计任意角度的目标方位角,融合主导边界法与峰值拟合法,提出一种SAR目标方位角的联合估计方法。通过计算投影比以及目标区域同外接矩形面积之比,初步判断目标是否位于水平或垂直方位附近,自适应选择相应的估计算法进行处理。移动与静止目标获取与识别(MSTAR)公共数据库实测数据的仿真结果表明,该方法估计误差较小,可获得较高的估计准确度。方位角联合估计方法有利于增强目标方位角估计的适应性,提高目标分类和识别的效率。     

Evaluation of calibration methods for a helicopter-borne microwave scatterometer

The French frequency modulated continuous waves (FMCW) scatterometer ERASME mounted on small helicopter or aircraft has been designed as dualfrequency (C and X bands) and dualpolarization (HH, VV) to investigate simultaneously the vegetation and the soil responses in radar backscattering. It is operated as a forward looking radar with a large elevation beamwidth (± 10° at 3 db) to observe easily the same surface target over a large range of incidence angles during a single flight. By this ability, ERASME is a complementary research tool for intercalibration of airborne and spaceborne imaging Synthetic Aperture Radars like Radarsat and ASAR and has to be well calibrated in every configuration, both absolutely and relatively for comparisons at different incidence angles.

This paper evaluates different calibration methods to be applied to such an instrument. Absolute calibration within 1 dB is easily obtained by external calibration using metallic corner reflectors. But this method remains insufficient to get the antenna elevation aperture which is essential on natural distributed targets for antenna pattern correction, due to the severe constraint of a narrow azimuthal beam and flight parameters (pitch, roll, altitude) varying quickly in time and range.

The external calibration is strongly improved by using a statistical analysis of data obtained over natural targets which analyses the correlation between the processed data and the recorded flight parameters. This method appears promising, but its application on natural targets with random variations need specific statistical properties of the data set. It is operative for high antenna setting (here 38° incidence angle) and mostly over bare soils, with low of σ⁰ variances and σ² correlation length of the order of the correlation length of pitch. It provides the aperture range around the antenna axis and an accuracy of 0.5 dB upon erσ⁰ is achieved providing the antenna pattern correction are done.     

Differentiating sonar reflections from corners and planes byemploying an intelligent sensor

A multitransducer, pulse/echo-ranging system is described that differentiates corner and plane reflectors by exploiting the physical properties of sound propagation. The amplitudes and ranges of reflected signals for the different transmitter and receiver pairs are processed to determine whether the reflecting object is a plane or a right-angle corner. In addition, the angle of inclination of the reflector with respect to the transducer orientation can be measured. Reflected signal amplitude and range values, as functions of inclination angle, provide the motivation for the differentiation algorithm. A system using two Polaroid transducers is described that correctly discriminates between corners and planes for inclination angles within ±10° of the transducer orientation. The two-transducer system is extended to a multitransducer array, allowing the system to operate over an extended range. An analysis comparing processing effort to estimation accuracy is performed     

Coaxial cavity waveguide antennas excited by stacked circular microstrip patches for use as prime‐focus reflector feeds

A coaxial cavity antenna excited by a stacked circular microstrip antenna is investigated as a feed for prime‐focus parabolic reflector antennas. The radiation pattern of the proposed cavity‐backed antenna is saddle shaped, which widens the ?10 dB beamwidths and increases the reflector efficiency especially for deep reflectors with small focal length‐to‐diameter ratios. With a single‐probe feed, the co‐polar radiation pattern is slightly asymmetric in the E‐plane, but is made symmetric by a differential feeding technique, using two probes. The impedance bandwidth of the proposed feed antenna is 20%. The antenna was fabricated and tested, and it exhibited good agreement between simulation and measurement results. The gain factor of the feed was also studied with a circular‐symmetric reflector and provided a gain factor of 79% at f/D = 0.375. This type of feed can be used as an alternative to conventional horn or waveguide feeds, where reduced size and light‐weight are desirable with added advantage of easy integration with electronics.     

干涉型超光谱成像仪的星上定标技术研究

根据干涉型超光谱成像仪的原理、特点以及对星上定标的要求,介绍了几种星上定标技术,分析了几种定标方案的结构和优缺点。在一次像面上引入定标结构的方法是利用一次像面上狭缝两端的边视场或在狭缝旁开孔,引入定标光源实现定标。根据聚光结构的不同,定标光源使用聚光镜和自聚焦镜两种方案;全系统定标方法是通过摆镜旋转90°引入定标光源,可分为朗伯板定标系统和积分球定标系统。在实际设计中,根据光学系统、结构总体的实现可能性,选择了积分球定标系统的方案。经过分析对比,后者结构紧凑、光能量大,可实现全系统、全口径、部分视场定标。     

干涉型超光谱成像仪的星上定标技术研究

根据干涉型超光谱成像仪的原理、特点以及对星上定标的要求,介绍了几种星上定标技术,分析了几种定标方案的结构和优缺点。在一次像面上引入定标结构的方法是利用一次像面上狭缝两端的边视场或在狭缝旁开孔,引入定标光源实现定标。根据聚光结构的不同,定标光源使用聚光镜和自聚焦镜两种方案;全系统定标方法是通过摆镜旋转90°引入定标光源,可分为朗伯板定标系统和积分球定标系统。在实际设计中,根据光学系统、结构总体的实现可能性,选择了积分球定标系统的方案。经过分析对比,后者结构紧凑、光能量大,可实现全系统、全口径、部分视场定标。