The SIR-C/X-SAR synthetic aperture radar system

The SIR-C/X-SAR synthetic aperture radar, a three-frequency radar to be flown on the Space Shuttle in September 1993, is described. The SIR-C system is a two-frequency radar operating at 1250 MHz (L-band) and 5300 MHz (C-band), and is designed to get four-polarization radar imagery at multiple surface angles. The X-band synthetic aperture radar (X-SAR) system is an X-band imaging radar operating at 9600 MHz. The discussion covers the mission concept; system design; hardware; RF electronics; digital electronics; command, timing, and telemetry, and testing     

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。     

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     

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     

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     

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     

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     

Preliminary observations of volcanoes with the SIR-C radar

The two flights of the Shuttle Imaging Radar (SIR-C/X-SAR) in April and October 1994 provided a wealth of new image data over many of the world's volcanoes, including 13 of the 15 International Decade Volcanoes. A first look at these data shows that mapping of remote volcanoes (e.g., Nyiragongo and Nyamuragira in Africa) will now be easier, especially when aided by the collection of multi-parameter radar data over better known analogous volcanoes such as Kilauea, HI. The utility of the radar to identify different types of lava flows is shown for Fernandina volcano, Galapagos Islands. Growth of mudflow deposits (“lahars”) that were emplaced on Mount Pinatubo, Philippines, during the six months between the two missions is also illustrated. Additionally, interferometric radar data were collected over several active volcanoes; the potential uses of these data for topographic mapping and ground deformation studies are discussed     

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.     

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'     

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.     

W波段机载视频合成孔径雷达系统

合成孔径雷达(SAR)能够全天时全天候工作,在对地遥感领域具有广泛和深入的应用。视频SAR将SAR成像获得的空间维度信息拓展到时-空维度,可以获取更加丰富的遥感信息。传统SAR频段较低,导致合成孔径时间长,数据计算量大,高帧频输出难度很大;而低频段太赫兹波对目标细节感知能力强,合成孔径短,特别适合于微弱目标的视频感知。本文设计了一种工作在W波段的视频SAR系统,采用收发分置连续波固态前端体制,输出峰值功率1 W,最大发射带宽可达1 GHz;采用极坐标格式算法(PFA)结合GPU架构实现高帧率低延时成像。仿真试验表明,系统成像分辨力可达0.15 m,成像帧率约5 Hz。     

Bistatic synthetic aperture radar inversion with application indynamic object imaging

An inversion method is presented for bistatic synthetic aperture radar imaging. The method is based on a Fourier analysis (Doppler processing) of the bistatic synthesized array's data followed by a phase modulation analysis of the Doppler data. The approach incorporates the phase information of the wavefront curvature in the transmitted waves as well as the resultant echoed signals. The Doppler data are shown to provide samples of the reflectivity function's spatial Fourier transform within a band that depends upon the bistatic angles and ranges. Associated resolution, reconstruction, and sampling constraints for the imaging problem are discussed. The bistatic SAR inversion is also utilized to formulate an inversion for multistatic measurements made along a physical linear array due to a single transmission to image a dynamic object     

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.     

稀疏孔径和大转角下ISAR对目标转动的估计

逆合成孔径雷达（inverse synthetic aperture radar，ISAR）对非合作目标做成像时图像质量依赖于对目标运动参数的准确估计.针对在稀疏孔径和非均匀转动条件下现存的参数估计方法计算量过大或者方法适用条件不满足，提出了一种基于神经网络的参数估计方法.此方法以成像问题的模型知识指导数据的生成过程，然后训练通用的神经网络，最终实现将数据中隐含的知识转化为转动估计器.从仿真实验结果来看，所得到的网络对满足一定信噪比要求的回波数据可以提供较准确的估计，所得参数可以帮助成像算法提高聚焦效果，大量的样例表明网络可以部分学习到回波与转动之间的关系.     

Image processing of synthetic aperture radar range ambiguoussignals

If wide-range swath scenes are illuminated by a synthetic aperture radar with high-pulse repetition frequencies, ambiguous scattered signals from an undesired range may appear in its receiver at the same time from consecutive transmitted pulses. This simplified analysis shows that range ambiguous signal returns result in a defocused image because they are convolved with the phase history of the desired range signal. A satellite borne SAR example is presented     

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