Wind vector retrieval using ERS-1 synthetic aperture radar imagery

An automated algorithm intended for operational use is developed and tested for estimating wind speed and direction using ERS-1 SAR imagery. The wind direction comes from the orientation of low frequency, linear signatures in the SAR imagery that the authors believe are manifestations of roll vortices within the planetary boundary layer. The wind direction thus has inherently a 180° ambiguity since only a single SAR image is used. Wind speed is estimated by using a new algorithm that utilizes both the estimated wind direction and σ ₀ values to invert radar cross section models. The authors show that: 1) on average the direction of the roll vortices signatures is approximately 11° to the right of the surface wind direction and can be used to estimate the surface wind direction to within ±19° and 2) utilizing these estimated wind directions from the SAR imagery subsequently improves wind speed estimation, generating errors of approximately ±1.2 m/s, for ERS-1 SAR data collected during the Norwegian Continental Shelf Experiment in 1991     

一种改进的舰船合成孔径雷达图像分割方法

针对舰船合成孔径雷达(SAR)图像识别中的图像分割问题,运用数理统计领域的方法,以舰船合成孔径雷达图像为研究对象,在深入分析经典K–Means聚类算法以及高斯混合模型之后,提出一个改进的高斯混合模型,用来对舰船合成孔径雷达图像进行分割。该方法采用马氏距离对经典K–Means方法进行改进,同时,将传统高斯混合模型的每一个概率分布,进一步再细分成单个的概率成分,在辅助变量计算过程中,采用梯度上升算法。仿真实验结果显示,研究得到了比使用经典K–Means算法和普通高斯混合模型的分割方法精确度更高、稳定性更好的分割结果。     

Segmentation of polarimetric synthetic aperture radar data

A statistical image model is proposed for segmenting polarimetric synthetic aperture radar (SAR) data into regions of homogeneous and similar polarimetric backscatter characteristics. A model for the conditional distribution of the polarimetric complex data is combined with a Markov random field representation for the distribution of the region labels to obtain the posterior distribution. Optimal region labeling of the data is then defined as maximizing the posterior distribution of the region labels given the polarimetric SAR complex data (maximum a posteriori (MAP) estimate). Two procedures for selecting the characteristics of the regions are then discussed. Results using real multilook polarimetric SAR complex data are given to illustrate the potential of the two selection procedures and evaluate the performance of the MAP segmentation technique. It is also shown that dual polarization SAR data can yield segmentation resultS similar to those obtained with fully polarimetric SAR data     

An optical processor for synthetic aperture radar

In this paper a 3-lens optical processor is described. It has the features of quick and easy adjustment, wide adaptability, easy assembly and disassembly. It is a good optical processor for processing synthetic aperture radar signals while working in the field.     

Feature-enhanced synthetic aperture radar image formation based onnonquadratic regularization

We develop a method for the formation of spotlight-mode synthetic aperture radar (SAR) images with enhanced features. The approach is based on a regularized reconstruction of the scattering field which combines a tomographic model of the SAR observation process with prior information regarding the nature of the features of interest. Compared to conventional SAR techniques, the method we propose produces images with increased resolution, reduced sidelobes, reduced speckle and easier-to-segment regions. Our technique effectively deals with the complex-valued, random-phase nature of the underlying SAR reflectivities. An efficient and robust numerical solution is achieved through extensions of half-quadratic regularization methods to the complex-valued SAR problem. We demonstrate the performance of the method on synthetic and real SAR scenes.     

一种新的星载SAR图像定位求解方法

目前对于无地面控制点的R-D构像方程的求解方法多为采用繁杂的坐标参数变换后进行解析处理.为使求解方法简化,首先将R-D构像方程中的星地距离矢量作为变元进行泰勒级数展开导出误差方程,然后利用最小二乘平差原理迭代求解目标点的位置信息.利用苏州地区ERS-2 SAR图像产品和该地区1:10万地形图对该方法进行了实验验证,结果表明该方法平面定位精度达到200m量级,可以满足无控制点条件下中分辨率星载SAR图像中目标像元定位的需求.     

Japanese Earth Resources Satellite-1 synthetic aperture radar

The spaceborne synthetic aperture radar (SAR) to be launched on the Japanese Earth Resources Satellite-1 is described. The SAR is operated in the L-band. The mission is mainly dedicated to geological applications. The ground resolution of the processed image is designed as 18 m and the off-nadir angle required to meet geological applications is 35°. The design and performance of the key system parameters are discussed, along with the reasons for choosing such design parameters. The antenna is a thin-flat-foldable configuration that has a 11.9-m by 2.2-m aperture when extended in orbit. The transmitter, receiver, and signal processor are all of the solid-state type to achieve high reliability of operation. They transmit an 1100-W peak (minimum) chirp pulse and receive the return echos and process the echo signals into in-phase and quadrature data streams     

Repeat-pass interferometry with airborne synthetic aperture radar

It is shown that interference can be observed by coherently combining pairs of either X- or C-band airborne synthetic aperture radar (SAR) images from separate passes over the same test site. Coherence between separate images is obtained only if the aircraft is flown, and the data are processed in such a way that each resolution cell in the two images is viewed with very nearly the same geometry. Successful repeat-pass interferometric results were obtained from those passes flown by the CCRS Convair 580 aircraft with flight-line offsets of less than a few tens of meters. A summary of the experiment, the phase correction of nonrectilinear aircraft motion, and the subsequent data processing is provided     

机载SAR重复轨道干涉成像试验结果

该文描述了中科院电子所机载L-SAR系统的重复轨道干涉试验,通过对得到的观测数据进行处理和分析,得到了中国第一幅与实际地形图基本吻合的数字高程图,高程精度在10m左右。同时,该文提出一种适用于轨道有夹角的图像配准方法,并在处理过程中验证了算法的有效性。     

New applications of transponder in focusing distributed synthetic aperture radar data

High-precision phase synchronisation or compensation techniques must be provided for distributed synthetic aperture radar (DiSAR), which operates with separate transmitters and receivers. The use of a novel transponder that was proposed for calibrating high-resolution imaging radars to compensate oscillator frequency instability is investigated here. This transponder modulates the radar pulses in a manner that the retransmitted signal shows two additional Doppler frequencies, which enables their separation from the scene echoes. In this way, DiSAR frequency synchronisation errors can be compensated. Thereafter, the DiSAR raw data is focused by using a derived image formation algorithm. The originality of this text lies in the phase compensation technique via transponder for DiSAR systems, as well as an image formation algorithm with integrated synchronisation compensation.     

Reconnaissance with ultra wideband UHF synthetic aperture radar

The author addresses the problem of detecting and identifying stationary and moving targets with foliage penetrating UHF synthetic aperture radar (SAR). The role of a target's coherent SAR signature, which varies with the radar's frequency and aspect angle, in forming the Fourier space of the SAR signal is analyzed. The resultant relationship is the basis of an algorithm which, after extracting (digital spotlighting) the target's coherent SAR signature in the reconstruction domain, could be used to differentiate man-made structures from foliage. Methods for blind-velocity moving target indication are discussed. The main tool of the work is a signal theory based analysis of SAR signal via Fourier transform. However, the theory is at most as good as the collected SAR data     

An analytical presentation of the monochromatic ocean wave image bya regular or an interferometric synthetic aperture radar

An asymptotic expansion of the theoretical model for simulation of a monochromatic ocean wave imaging by either regular synthetic aperture radar (SAR), or by along-track interferometric SAR (INSAR), and its analytical approximation are considered. The model takes into account the so-called velocity bunching imaging mechanism. The domains of validity of the simplified asymptotic and analytical expressions for both SAR and INSAR imaging of the ocean waves are established by comparing those solutions with the corresponding full numerical simulations. The analytical presentations of the SAR and the INSAR wave imaging obtained in the present study are used to understand better the limitations and the relative advantages of both techniques and to define the dimensionless parameters which govern the imaging process     

An application of L-band synthetic aperture radar to tide height measurement

A method for measuring the tide height near the coast from L-band synthetic aperture radar (SAR) data is presented. Twenty-one coherent interferograms have been successfully constructed from Japanese Earth Resources Satellite 1 (JERS-1) SAR data obtained over oyster sea-farming structures. A coherence analysis of the 21 interferometric pairs showed that a perpendicular baseline of less than 3 km, with a temporal baseline within 500 days, are required to obtain a coherent pair, with a coherence higher than 0.25, in the study area. The coherent phases preserved in the interferograms showed a close relation with the sea level. The problem of phase unwrapping to restore an absolute tide height was overcome by introducing normalized image intensities. The radar measurements estimated by the proposed method were verified using tide gauge data, and comparison of the two datasets yielded a correlation coefficient R/sup 2/ of 0.91, with a root mean square error of 5.76 cm. The results demonstrate that radar interferometry can be applied for a tide height measurement near the coast given sufficient structures that return off-nadir radar pulses to the antenna. The multipolarized L-band SAR system will provide better results, using only double-bounced signals, in the future.     

Parallel implementation of synthetic aperture radar algorithms

Two sequences of operations necessary for implementation of high resolution image formation in strip and spotlight modes of the synthetic aperture radar (SAR) are presented. The sequences are mapped onto a mesh-connected SIMD architecture. The mapping includes not only parallel implementation of all the basic computation steps, but also all the necessary data transformation and communication operations. Detailed estimates of the processing times are provided for Hughes Research Laboratories Systolic/Cellular architecture.This work was partially supported by NSF grant No MIP-8714689     

干扰合成孔径雷达的统一方程

合成孔径雷达(SAR)是当前的一种新型雷达体制,它既能测定目标的座标位置又能对目标成像,不论在军用还是在民用都有广泛的应用和广阔的发展前景,当然也就成了雷达干扰研究的重点对象。我们应用了几年的时间,分析了对SAR的干扰原理;推导出对SAR的干扰方程;做了多种仿真干扰试验,室内小功率模拟干扰试验和实际飞行干扰试验,获得大量干扰数据和干扰图像,证明了推导的干扰方程的正确性。还证明了常规脉冲雷达的干扰方程与SAR的干扰方程可以统一成一种方程。只是在计算干扰等效功率时,取不同的干扰压制系数即可。     

Fast algorithm for a near-field synthetic aperture radar processor

A radar image can be formed by coherently integrating the backscattered fields over the measured frequency band and cross-range scan. This coherent integration can be seen as a convolution of the measured data and a focusing function, which only depends on the geometry of the measurement. Thus, by applying fast Fourier transform (FFT) techniques and computing a product in the Fourier domain one can efficiently reconstruct the target image. On the other hand, in the particular case of indoor synthetic aperture radar (SAR) measurements with the same geometry, the focusing operator must be computed just once and may be reused when processing the different datasets, reducing drastically the computing time     

多视角聚束合成孔径雷达成像

在介绍聚束合成孔径雷达高分辨率成像机理、其获得更高分辨率的难点所在、以及空间分辨率与观测空间频谱关系原理的基础上,提出利用多视角观测增加对目标的观测角,从而增加目标观测的空间频率范围,进而提高空间分辨率的思想.通过对每一视角观测采用波数域成像算法获得每次观测的频谱,利用空间频谱与空间域的对应关系进行频谱融合,对融合后的频谱进行逆傅立叶变换获得方位向分辨率提高的图像.计算机模拟验证了多视角聚束合成孔径雷达成像提高成像分辨率的有效性.     

Snow mapping in alpine regions with synthetic aperture radar

Active microwave sensors can discriminate snow from other surfaces in all weather conditions, and their spatial resolution is compatible with the topographic variation in alpine regions. Using data acquired with the NASA AIRSAR in the Otztal Alps in 1989 and 1991, the authors examine the usage of synthetic aperture radar (SAR) to map snow- and glacier-covered areas. By comparing polarimetric SAR data to images from the Landsat Thematic Mapper obtained under clear conditions one week after the SAR flight, the authors found that SAR data at 5.3 GHz (C-band) can discriminate between areas covered by snow from those that are ice-free. However, they are less suited to discrimination of glacier ice from snow and rock. The overall pixel-by-pixel accuracies-74% from VV polarization alone with topographic information, 76% from polarimetric SAR without any topographic information, and 79% from polarimetric SAR with topographic information-are high enough to justify the use of SAR as the data source in areas that are too cloud-covered to obtain data from the Thematic Mapper. This is especially true for snow discrimination, where accuracies exceed 80%, because mapping of a transient snow cover during a cloudy melt season is often difficult with an optical sensor. The AIRSAR survey was carried out in summer during a heavy rainstorm, when the snow surfaces were unusually rough. Even better results for snow discrimination can be expected for mapping in the spring, when snow is usually smoother     

Theory of synthetic aperture radar imaging of a moving target

Two novel image processing techniques have been developed to refocus a moving target image from its smeared response in the synthetic aperture radar (SAR) image which is focused on the stationary ground. Both approaches may be implemented with efficient fast Fourier transform (FFT) routines to process the Fourier spatial spectrum of the image data. The first approach utilizes a matched target filter that is derived from the signal history along the range-Doppler migration path mapped onto the SAR image from the moving target trajectory in real space. The coherent spatial filter is specified by the apparent target range in the image and the magnitude of the relative target-to-radar velocity. The second approach eliminates the range-dependence by reconstructing the moving target image from a spectral function that is obtained from the SAR image data spectrum via a spatial frequency coordinate transformation