ASAR-antenna synthetic aperture radar imaging

The antenna synthetic aperture radar (ASAR) imaging concept is introduced. We present the ASAR imaging algorithm to pinpoint the locations of secondary scattering off a platform from antenna radiation data. It is shown that a three-dimensional (3-D) ASAR image of the platform can be formed by inverse Fourier transforming the multifrequency, multiaspect far-field radiation data from an antenna mounted on the platform. This concept is demonstrated using the computed radiation data from the code Apatch, which employs the shooting and bouncing ray (SBR) technique. Furthermore, we develop a fast ASAR algorithm specially tailored for the SBR approach. By taking advantage of the ray tracing information within the SBR engine, we demonstrate that the fast approach can result in the same quality of image as the frequency-aspect algorithm at only a fraction of the computation time     

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。     

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     

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     

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.     

Observation of sea-ice dynamics using synthetic aperture radarimages: automated analysis

Two techniques for automated sea-ice tracking, image pyramid area correlation (hierarchical correlation) and feature tracking, are described. Each technique is applied to a pair of Seasat SAR sea-ice images. The results compare well with each other and with manually tracked estimates of the ice velocity. The advantages and disadvantages of these automated methods are pointed out. Using these ice velocity field estimates it is possible to construct one sea-ice image from the other member of the pair. Comparing the reconstructed image with the observed image, errors in the estimated velocity field can be recognized and a useful probable error display created automatically to accompany ice velocity estimates. It is suggested that this error display may be useful in segmenting the sea ice observed into regions that move as rigid plates of significant ice velocity shear and distortion     

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     

Space-time processing for multichannel synthetic aperture radar

Synthetic aperture radar (SAR) provides high-resolution images of a non-moving ground scene, but fails to indicate the presence and position of moving objects. As in airborne MTI (moving-target indication) systems the solution to this problem is to use an array of antennas or subapertures and several receiving channels (`MSAR', or multichannel SAR), and to apply multichannel clutter suppression. One of the most efficient methods is adaptive space-time processing (STAP), which can be simplified to frequency-dependent spatial processing in the Doppler domain. Some of these techniques applied to SAR are reviewed and illustrated with data gathered by the German experimental multichannel SAR system `AER-II'     

Multibeam synthetic aperture radar for global oceanography

A single-frequency multibeam synthetic aperture radar concept for large swath imaging desired for global oceanography is evaluated. Each beam illuminates a separate range and azimuth interval, and images for different beams may be separated on the basis of the Doppler spectrum of the beams or their spatial azimuth separation in the image plane of the radar processor. The azimuth resolution of the radar system is selected so that the Doppler spectrum of each beam does not interfere with the Doppler foldover due to the finite pulse repetition frequency of the radar system.     

Electronic processing for synthetic aperture array radar

A simple method of electronically processing synthetic aperture arrays is presented. The processing technique is based on the fact that synthetic aperture recorded signals are one-dimensional Fresnel zone-plate lenses. By essentially employing unfocussed processing methods on individual Fresnel zone-plates and then appropriately summing the results, a narrow beam "semifocussed" aperture may be formed, using only binary electronics.     

一种改善SAR对舰船目标成像质量的新方法研究

常规合成孔径雷达(SAR)成像技术适用于静止场景目标成像,在对海上舰船等运动目标成像时,由于目标存在自身转动分量,使得积累时间内回波多普勒频率不为常数,导致常规成像处理后,目标出现散焦、分辨力下降的现象.通过分析存在平动、转动分量目标回波的多普勒频率特征,可以把SAR对舰船目标成像问题转化为稀疏信号表示问题,利用信号重构回波散射系数实现二维成像.将基于贝叶斯学习的稀疏信号表示用在SAR对舰船目标成像上,采用该方法处理实测数据可获得较清晰的目标像,通过与传统方法的比较验证了该方法的有效性.     

A tomographic formulation of spotlight-mode synthetic aperture radar

Spotlight-mode synthetic aperture radar (spotlight-mode SAR) synthesizes high-resolution terrain maps using data gathered from multiple observation angles. This paper shows that spotlight-mode SAR can be interpreted as a tomographic reeonstrution problem and analyzed using the projection-slice theorem from computer-aided tomograpy (CAT). The signal recorded at each SAR transmission point is modeled as a portion of the Fourier transform of a central projection of the imaged ground area. Reconstruction of a SAR image may then be accomplished using algorithms from CAT. This model permits a simple understanding of SAR imaging, not based on Doppler shifts. Resolution, sampling rates, waveform curvature, the Doppler effect, and other issues are also discussed within the context of this interpretation of SAR.     

Compact acousto-optic processor for synthetic aperture radar imageformation

A compact implementation of a real-time acousto-optic synthetic aperture radar (SAR) imager is described. The architecture generates SAR imagery by decomposing the required 2D integration into a cascade of two 1D integrations, in a manner similar to that used in computed tomography for medical imaging applications. To achieve low power consumption, the required integrations are performed in the analog optical domain, with a crossed Bragg cell configuration, using a combination of spatial and temporal integration of optical signals. The time integrating and space integrating modules of the architecture are coupled via a common path interferometer. Subimages are formed on a 2D CCD detector array that is rotated during image formation to avoid a computationally difficult digital interpolation operation. The complex-valued subimages are combined in a digital frame buffer for dynamic range enhancement before being displayed. To accommodate needed flexibility, the required filter functions are calculated in a digital controller and downloaded through the Bragg cells. Results of a laboratory demonstration are presented. Performance projections suggest that the architecture may offer an advantage over an all-electronic approach for high-resolution applications which are severely constrained in power consumption     

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     

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     

合成孔径雷达成像Matlab仿真研究

计算机仿真是现代雷达研究中的重要技术之一,针对合成孔径雷达(SAR)成像中影响仿真结果的因素,从分析SAR发射信号和回波信号模型出发,运用Matlab软件对SAR的发射波形以及点目标成像进行了仿真,直观地反应了距离多普勒成像算法原理。最终通过仿真分析,总结了SAR成像中影响仿真结果的5项因素,而这5项因素在运用Matlab仿真过程中对成像质量的优劣有着至关重要的影响。     

分布式小卫星合成孔径雷达的空间编队构形研究

合理的空间编队构形是实现分布式小卫星SAR系统功能的基础.着重讨论分布式小卫星合成孔径雷达(SAR)空间编队构形的设计问题.分析了实现三维地形成像、提高空间分辨率和动目标检测三种系统功能时,空间编队构形设计所需解决的问题,提出了进行分布式小卫星SAR空间编队构形设计的三个最优化准则,给出了空间编队构形的评估方法,并对现有的几种分布式小卫星SAR的空间编队构形进行分析.最后根据分布式小卫星SAR的空间编队构形,通过与单颗星载SAR回波信号相比较,分析了分布式小卫星SAR回波信号的特点,为其数据处理提供参考.     

Time-delayed reflections in L-band synthetic aperture radar imageryof icebergs

In some L-band synthetic aperture radar imagery of icebergs, there are relatively strong reflections which do not exist on the coincident X-band imagery and which do not correspond to attributable surface roughness or features. As these false images appear on the down-range side of the iceberg, they were originally explained as multiple reflections within the iceberg. It is shown that the majority of the observations correspond to the expected positions of a transit to and from the ice-water interface at the bottom surface of the iceberg. Factors governing observation of the bottom surface reflection and its significance in terms of underwater draught are discussed