ScanSAR的Scalloping辐射误差研究

由于在观测带内采用了多波束扫描的工作模式,使得ScanSAR产生了固有的周期性的scalloping效应,影响了ScanSAR的辐射特性。该文基于ScanSAR工作模式的特点,研究了scalloping产生的机理和性质,定量地分析了scalloping引起的辐射误差以及多普勒中心误差与scalloping的关系,并研究了对scalloping进行校正后的剩余误差问题。     

基于环境星CCD数据的山区大气校正研究

山区地形崎岖，高程变化较大，遥感影像地形效应明显，地物的光谱特征容易受到干扰，导致在分类过程中对遥感影像出现误分，不利于遥感信息的提取。基于辐射传输原理，利用Python开发了针对山区的大气校正算法。所提算法充分考虑了太阳直接辐射、天空散射辐射及邻近地表反射辐射对卫星入瞳处目标辐亮度的影响，可以有效地消除地形阴影的影响。利用所提算法，结合数字高程模型（DEM），对环境减灾二号01组卫星的CCD传感器的山区数据进行大气校正研究。分析结果表明：校正后的图像地形效应减弱，图像质量得到了明显的改善，反演得到的地表反射率与实地测量的地物光谱数据比较吻合，为进一步开展定量遥感研究提供了数据质量保障。     

基于改进Kalman滤波模型的扫描合成孔径雷达图像扇贝效应校正方法

星载扫描合成孔径雷达(ScanSAR)采取Burst工作模式,该模式在获得宽幅测绘能力的同时,也导致图像中产生了固有的扇贝效应,严重影响图像的视觉效果和定量应用。该文结合对ScanSAR图像方位向统计特性的分析,针对现有滤波模型稳定性差和时间复杂度高等缺点,提出了一种改进的Kalman滤波模型,对图像方位向标准差和均值进行滤波以校正扇贝条纹。在高分三号(GF-3)卫星获取的真实ScanSAR图像上的校正结果验证了改进算法的有效性和高效性,此外在建筑群和海陆交界等复杂场景图像上的实验结果表明,改进算法具有较强的鲁棒性。     

基于改进Kalman滤波模型的扫描合成孔径雷达图像扇贝效应校正方法

星载扫描合成孔径雷达(ScanSAR)采取Burst工作模式,该模式在获得宽幅测绘能力的同时,也导致图像中产生了固有的扇贝效应,严重影响图像的视觉效果和定量应用。该文结合对ScanSAR图像方位向统计特性的分析,针对现有滤波模型稳定性差和时间复杂度高等缺点,提出了一种改进的Kalman滤波模型,对图像方位向标准差和均值进行滤波以校正扇贝条纹。在高分三号(GF-3)卫星获取的真实ScanSAR图像上的校正结果验证了改进算法的有效性和高效性,此外在建筑群和海陆交界等复杂场景图像上的实验结果表明,改进算法具有较强的鲁棒性。     

星载ScanSAR干涉处理研究

星载ScanSAR干涉测量是一种宽测绘带的三维测高模式。该文结合ScanSAR工作原理,研究该模式干涉信号的频谱特点及ScanSAR干涉处理中特有的方位扫描同步;分析ENVISAT卫星ASAR Wide Swath模式单视复图像数据的特点,提出ScanSAR干涉数据处理的具体实现方案,并通过处理真实数据验证该方法的有效性。     

星载ScanSAR成像处理技术研究

由于天线在不同的子带进行扫描,星载扫描模式不能像条带模式那样,获得连续的方位向相位历史,利用条带模式高精度处理算法（如距离一多普勒算法）处理ScanSAR数据,通过在脉冲扫描间隔中填零,把扫描数据看成中间填零的相干脉冲串序列,等效成条带SAR数据,利用条带模式的处理算法进行成像。针对填零后的数据,数据量大,可以采用基于通用图形处理单元的并行处理技术,加快处理速度。对填零处理形成的栅瓣调制,通过滤波进行消除。这样处理的图像和条带模式的图像具有相同的辐射和几何分布特性,有效抑制扇贝效应带来的影响。对实测星栽ScansAR数据进行成像处理,试验结果表明该方法的有效性。     

基于自注意力机制和CycleGAN的高分三号ScanSAR图像的扇贝效应抑制

高分三号卫星是我国首颗分辨率达到1 m的C波段 多极化合成孔径雷达(synthetic aperture radar,SAR) 卫星,其中扫描 式合成孔径雷达(scan synthetic aperture radar,ScanSAR)模式是高分三号卫星重要的工 作模式之一,由于该模式的工作机制导致生成的图像可能发生扇贝效应,一般呈现为明暗相 间的条纹。本文针对高分三号卫星ScanSAR模式下存在的扇贝效应,提出自注意力机制与循 环一致对抗网络(cycle-consistent adversarial networks,CycleGAN)结合的模型对Scan S AR图像进行处理,从而抑制扇贝效应产生的条纹现象。本文所示方法与传统扇贝效应抑制方 法和深度学习相关算法进行比较,并通过亮度均值、平均梯度等指标进行分析。实验结果表 明,本文方法可以对高分三号ScanSAR图像存在的扇贝效应进行较好的处理,有效抑制图像 的条纹现象,使得图像质量得到提升,具有较大的实用意义。     

星载ScanSAR工作模式研究与设计

该文系统地阐述了星载ScanSAR系统的基本工作原理,由ScanSAR系统的空间几何模型,确定了ScanSAR系统各子条带的空间位置,研究了ScanSAR系统的方位分辨率问题,确定了ScanSAR系统工作的时间关系,各子条带的脉冲重复频率的选择及每个burst的样本数,为系统设计提供了依据。重点研究了 ScanSAR系统的信噪比及距离模糊问题,提出了一种新的 ScanSAR系统特有的模糊概念ARASR,并提出新的分析方法,对其影响做了定量的计算,最后对 ScanSAR系统的数据下载格式提出了建议。     

地形条件对空间目标细致光谱辐射特性的影响

随着多光谱、高光谱和超光谱探测技术的发展,探测识别目标发出的细致光谱辐射特性技术日益成熟。建立了一种空间目标细致光谱有效辐射的计算模型,考虑了地形条件和大气环境对目标的光谱有效辐射影响,分别计算了传统方法和两种设置的典型地形条件下空间目标各表面的温度和细致光谱有效辐射,分析了3~5 m和8~14 m波段下导致目标有效辐射强度随波长变化的主要影响因素,最后分析了在不同地形条件下空间目标在8.69~9.00 m探测波段内的辐射特性。结果表明,地形条件对空间目标的温度和有效辐射有较大影响,尤其是地表反照率对地球反射太阳辐射的影响较大,特别是空间目标朝向地球的面,在两种典型条件下的最大温差可以达到69.2 K,光谱有效辐射出射度偏差达到7.002 W/（m2m）。     

基于MNMP的ScanSAR并行成像系统设计

该文对星载ScanSAR成像并行处理进行了详细的研究。首先,针对ScanSAR成像机制的特殊性,给出了基于传统主-从模式的并行实现流程。根据主-从模式的不足,该文提出了一种基于多节点-多进程的异步并行模式的星载ScanSAR并行处理的技术。实验结果表明,相对于传统的并行处理方法,该文所采用方法的成像时间得到了较好的改善,具有一定的优越性。     

Optimal range and Doppler centroid estimation for a ScanSAR system

This paper presents a new range and Doppler centroid estimation algorithm for a ScanSAR system. This algorithm is based on processing the image data in the overlapped region of two bursts of the same beam or adjacent beams. It leads to highly accurate radar pointing angles that are paramount to achieving good radiometric performance in ScanSAR imagery. The achievable accuracy is derived theoretically and verified by tests performed using SIR-C ScanSAR data and ERS data. This algorithm is computationally efficient and easy to implement. The proposed Doppler centroid estimation algorithm is also an excellent candidate for a strip mode SAR system     

ScanSAR focusing and interferometry

The authors discuss an efficient phase preserving technique for ScanSAR focusing, used to obtain images suitable for ScanSAR interferometry. Given two complex focused ScanSAR images of the same area, an interferogram can be generated as for conventional repeat pass SAR interferometry. However, due to the nonstationary azimuth spectrum of ScanSAR images, the coherence of the interferometric pair and the interferogram resolution are affected, both by the possible scan misregistration between two passes and by the terrain slopes along the azimuth. The resulting decorrelation can be significantly reduced by means of an azimuth varying filter, provided that some conditions on the scan misregistration are met. Finally, the SAR-ScanSAR interferometry is proposed: here the decorrelation can always be removed. With no resolution loss by means of the technique presented     

Optimum look weighting for burst-mode and ScanSAR processing

Burst-mode and ScanSAR systems record only short pieces of Doppler histories; the energy contained in each echo ensemble and, hence, the intensity in the final burst image (look) depends on the scatterer's position relative to the time of the burst event according to the azimuth antenna pattern, an effect known as scalloping. Most systems employ a burst period short enough that adjacent looks overlap allowing for individual weighting of the looks before summation. The paper introduces a new class of look weighting functions for burst-mode and ScanSAR processing that correct for scalloping while simultaneously keeping the S/N ratio constant over azimuth and maximizing the equivalent number of looks. The achievable radiometric resolution and the sensitivity to Doppler centroid estimation errors are discussed. A 3-look example using ASAR parameters illustrates the proposed weighting functions     

TOPSAR: Terrain Observation by Progressive Scans

In this paper, a novel (according to the authors' knowledge) type of scanning synthetic aperture radar (ScanSAR) that solves the problems of scalloping and azimuth-varying ambiguities is introduced. The technique employs a very simple counterrotation of the radar beam in the opposite direction to a SPOT: hence, the name terrain observation with progressive scan (TOPS). After a short summary of the characteristics of the ScanSAR technique and its problems, TOPSAR, which is the technique of design, the limits, and a focusing technique are introduced. A synthetic example based on a possible future system follows.     

Noise-Related Radiometric Correction in the TerraSAR-X Multimode SAR Processor

Synthetic aperture radar (SAR) image intensity is disturbed by additive system noise. During SAR focusing, pattern corrections that are adapted to the characteristics of the wanted signal, but not to the characteristics of the noise, influence the spatial distribution of the noise power. Particularly in the case of ScanSAR, a distinct residual noise pattern in low backscatter areas results. This necessitates a noise-adapted radiometric correction of the focused image for almost all applications except interferometry. In this paper, we thoroughly investigate this topic. Based on signal theoretical and stochastic considerations, we develop a radiometric correction scheme. Simulations and the application of the algorithm to TerraSAR-X datatakes support the theoretical results.      

ScanSAR processing using standard high precision SAR algorithms

Processing ScanSAR or burst-mode SAR data by standard high precision algorithms (e.g., range/Doppler, wavenumber domain, or chirp scaling) is shown to be an interesting alternative to the normally used SPECAN (or deramp) algorithm. Long burst trains with zeroes inserted into the interburst intervals can be processed coherently. This kind of processing preserves the phase information of the data-an important aspect for ScanSAR interferometry. Due to the interference of the burst images the impulse response shows a periodic modulation that can be eliminated by a subsequent low-pass filtering of the detected image. This strategy allows an easy and safe adaptation of existing SAR processors to ScanSAR data if throughput is not an issue. The images are automatically consistent with regular SAR mode images both with respect to geometry and radiometry. The amount and diversity of the software for a multimode SAR processor are reduced. The impulse response and transfer functions of a burst-mode end-to-end system are derived. Special attention is drawn to the achievable image quality, the radiometric accuracy, and the effective number of looks. The scalloping effect known from burst-mode systems can be controlled by the spectral weighting of the processor transfer function. It is shown that the fact that the burst cycle period is in general not an integer multiple of the sampling grid distance does not complicate the algorithm. An image example using X-SAR data for simulation of a burst system is presented     

A new algorithm for scansar processing

In this paper, a new phase preserving algorithm-the short IFFT algorithm for the burst-mode ScanSAR processing is presented. Analysis and simulation are done to verify the phase accuracy of this algorithm. Finally, the phase accuracy of this algorithm by making interferogram with simulated burst-mode INSAR data is illustrated. The results show that this new algorithm works well for interferometric application of ScanSAR data.     

Improved multilook techniques applied to SAR and SCANSAR imagery

The multilook processing used in SAR (synthetic aperture radar) image formation to reduce the speckle noise is considered. Two multilook techniques are proposed for improving the radiometric resolution without altering the geometric resolution and the characteristics of the impulse response. These techniques are based on the formation of looks with different bandwidths. The final image is formed by giving each look a proper size and weighting, and by adding them incoherently. The looks with wide bandwidth contribute to an improvement of the overall geometric resolution, while the looks with narrow bandwidth improve the overall radiometric resolution. The equivalent number of looks is more than 2.3 times the number of independent looks and is superior to conventional multilook processing with overlapping. Finally, using the proposed techniques, an algorithm for efficient SAR and ScanSAR processing is presented, and its validity is proved by image comparison and analysis     

一种基于最小二乘法的星载ScanSAR滚动角迭代估计算法

该文对于ScanSAR辐射定标中的滚动角估计问题进行了研究,重点分析了波束间相对偏差对于滚动角估计算法的影响.在此基础上提出了一种改进算法,该算法的估计模型中不仅考虑了波束间的相对增益偏差,而且考虑了波束间的相对角度偏移.对估计模型进行线性化处理后,可利用最小二乘法来迭代求解滚动角.通过仿真实验,分析了该算法在不同信噪比情况下的估计精度,并将其与Dragosevic的算法进行了比较,证明了该算法的优良性能.