共查询到20条相似文献，搜索用时 15 毫秒
1.
Maneesha Gupta Anuja Sharma B. Kartikeyan 《Journal of the Indian Society of Remote Sensing》2017,45(2):195-207
The single-frequency Radar Imaging Satellite-1 (RISAT-1) Synthetic Aperture Radar (SAR) (launched in April, 2012) is designed to provide a wide variety of imaging options compared to the prevailing SAR missions. The scale of the calibration task for the RISAT-1 mission is increased with the inclusion of multiple beams and polarizations (single, dual and quad) along with circular/hybrid polarization capabilities, for the first time from space. Significant efforts have been made in the evolution of SAR processor for the provision of radiometrically and geometrically calibrated products to the users. After the commissioning phase, RISAT-1 was put into routine operations in Oct. 2012. Since then extensive beam coverage of Amazon rainforest in various modes was carried out to evaluate the calibration parameters and SAR processor performance. Subsequently, the processor version 1.2.0 was improved to version 1.3.0 and with further modifications to version 1.4.0. This article details the analysis carried out at each processor version, by quality evaluation team, to quantify the parameter behaviour and to give feedback on the processor performance to the SAR processor team. The various radiometric quality parameters evaluated and monitored are shape of the antenna pattern, gamma-naught, backscattering coefficient (sigma-naught), speckle index, radiometric resolution and Noise Equivalent Sigma Zero (NESZ). Data studied for the analysis is in Single Look Complex (SLC) for stripmap mode and multilook (Ground range) for ScanSAR and stripmap mode in dual and circular polarizations. The performance of version 1.4.0 for all the beams (near-to-far) is found to be consistent and meeting the mission specifications for the product. 相似文献
2.
结合SAR成像原理,在提出了基于DGPS/IMU数据的机载InSAR系统DEM三维坐标求解的基础上,推导出了基线长度、基线倾角、相位差、雷达天线到地面目标点的距离、雷达天线位置、中心多普勒频率及飞机飞行速度等因素误差对DEM精度的影响公式,分析讨论了机载InSAR系统影响精度的主要因素及系统可实现的性能情况,提出了机载InSAR系统部分设计建议,并使用实际的机载InSAR数据进行了试验。结果表明,本方法结果与实际试验统计的精度基本一致,影响精度的分析结论正确。 相似文献
3.
Unambiguous SAR signal reconstruction from nonuniform displaced phase center sampling 总被引：4，自引：0，他引：4
The displaced phase center (DPC) technique will enable a wide-swath synthetic aperture radar (SAR) with high azimuth resolution. In a classic DPC system, the pulse repetition frequency (PRF) has to be chosen such that the SAR carrier moves just one half of its antenna length between subsequent radar pulses. Any deviation from this PRF will result in a nonuniform sampling of the synthetic aperture. This letter derives an innovative reconstruction algorithm and shows that an unambiguous reconstruction of a SAR signal is possible for nonuniform sampling of the synthetic aperture. This algorithm will also have great potential for multistatic satellite constellations as well as the dual receive antenna mode in Radarsat 2 and TerraSAR-X. 相似文献
4.
Tong Wang Zheng Bao 《Geoscience and Remote Sensing Letters, IEEE》2006,3(3):297-301
As we know, a multiple-aperture radar carried by a group of formation-flying satellites can be used to improve the coverage and azimuth resolution of spaceborne synthetic aperture radar (SAR) simultaneously. However, in the case of the reconstruction of azimuth signal from a periodic nonuniform sampling sequence, the sidelobe clutter and noise may be amplified by tens of decibels in some cases, which makes the final SAR image blurry. In this letter, we present the analytical result of the amplification factor of sidelobe clutter and noise for the evaluation of the reconstruction performance. According to the result, we propose a method to reduce the sidelobe clutter and noise, which considerably improves the quality of SAR image. Computer simulation results confirm the effectiveness of the method. 相似文献
5.
An optimal power and antenna height determination over a wide range of incidence angles is proposed for in-orbit operations of the spaceborne stripmap synthetic aperture radar (SAR) with variable antenna height and variable radiating element power. The antenna height and the average transmitted radio-frequency power of a radiating element for each incidence angle are determined so that the mapping area can be maximized with the constraints on the signal-to-noise ratio, ambiguities, and swath width, given the SAR geometry (an altitude and incidence angles) and radar wavelength. With the receive-chain power consumption of one transmit/receive module (P/sub r/=10 mW) and the SAR instrument power consumption without the phased array antenna (P/sub I/=5 W), the illustrative design example shows that the mapping area of the proposed SAR for the maximum incidence angle (/spl eta//sup max/=75/spl deg/) is about 269.1% of that resulted from utilizing only the variable antenna height. The proposed optimization would have a more beneficial effect on applications that need the high-incidence-angle operations. 相似文献
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8.
基带数字信号源是合成孔径雷达 (SAR)系统中的关键设备 ,开发基带数字信号源对于满足SAR向多分辨率、多模式的发展具有重要的意义。随着SAR信号处理的完全数字化 ,基带数字信号源已经替代以往使用的声表面波器件 (SAW ) ,成为SAR数字线性调频产生单元的一部分 ,能够为雷达提供所需发射的各种波形信号。同时 ,面对复杂的SAR系统 ,如何测试和验证SAR设备的功能是开发人员所必须面对的重要环节。高速数字信号源的研制 ,对测试雷达视频信号处理设备有着十分重要的意义。该文首先简要介绍了数字信号源在SAR中的作用 ,然后 ,从理论上详细分析了基带数字线性调频信号的产生原理和设计过程 ;讨论并提出了数字信号源作为雷达视频信号处理测试设备的作用 ;给出了按照上述两种功能研制的高速基带数字信号源的性能、组成及其设计方案。 相似文献
9.
结合了圆迹SAR(CSAR)和地球同步轨道SAR(GEOSAR)的特点,地球同步轨道圆迹SAR(GEOCSAR)具有大面积区域观测、可获得目标三维信息、可对目标区域连续监测等优点。但GEOCSAR合成孔径时间长,完成整个圆周孔径测量的时间为24小时,而大气变化的时间尺度经常表现为数分钟到数小时,因此大气折射率时间变化将会对GEOCSAR方位向聚焦成像产生重要影响。本文考虑L波段GEOCSAR,因此对流层和电离层效应均不可忽略。文中建立了对流层和电离层折射率时间变化引起的相位误差模型,分析和推导了折射率时间变化对GEOCSAR方位向聚焦性能的影响,计算了引起L波段GEOCSAR聚焦性能退化的最小对流层折射率和电离层电子含量随机时间变化量,并通过仿真进行了验证。 相似文献
10.
Generation of wide-swath and high-resolution SAR images from multichannel small spaceborne SAR systems 总被引：9，自引：0，他引：9
Zhenfang Li Hongyang Wang Tao Su Zheng Bao 《Geoscience and Remote Sensing Letters, IEEE》2005,2(1):82-86
Future spaceborne synthetic aperture radar (SAR) systems will be required to produce high-resolution imagery over a wide area of surveillance. However, the minimum antenna area constraint makes it a contradiction to simultaneously obtain both unambiguous wide-area and high azimuth resolution. To overcome this limitation, a technique has been suggested that combines a broad illumination source with multiple receiving channels. Then, the coherent combination of the recorded multichannel signals will allow for the unambiguous SAR mapping of a wide ground area with fine azimuth resolution. This letter first gives an overview of current research work carried out about the generation of wide-swath and high-resolution SAR images from multichannel small spaceborne SAR systems, and then a space-time adaptive processing (STAP) approach combined with conventional SAR imaging algorithms is presented, which could be of help to overcome the existing difficulties in data processing. The main idea of the approach is to use a STAP-based method to properly overcome the aliasing affect caused by the lower pulse repetition frequency and thereby retrieve the unambiguous azimuth wide (full) spectrum signal from the received signal. Following this operation, conventional SAR data processing tools can be applied to fully focus the SAR images. The performance of the approach is also discussed in this letter. The approach has the advantages of simplicity, robustness, and high efficiency. 相似文献
11.
Recent studies have demonstrated the usefulness of global positioning system (GPS) receivers for relative positioning of formation-flying satellites using dual-frequency carrier-phase observations. The accurate determination of distances or baselines between satellites flying in formation can provide significant benefits to a wide area of geodetic studies. For spaceborne radar interferometry in particular, such measurements will improve the accuracy of interferometric products such as digital elevation models (DEM) or surface deformation maps. The aim of this study is to analyze the impact of relative position errors on the interferometric baseline performance of multistatic synthetic aperture radar (SAR) satellites flying in such a formation. Based on accuracy results obtained from differential GPS (DGPS) observations between the twin gravity recovery and climate experiment (GRACE) satellites, baseline uncertainties are derived for three interferometric scenarios of a dedicated SAR mission. For cross-track interferometry in a bistatic operational mode, a mean 2D baseline error (1σ) of 1.4 mm is derived, whereas baseline estimates necessary for a monostatic acquisition mode with a 50 km along-track separation reveal a 2D uncertainty of approximately 1.7 mm. Absolute orbit solutions based on reduced dynamic orbit determination techniques using GRACE GPS code and carrier-phase data allows a repeat-pass baseline estimation with an accuracy down to 4 cm (2D 1σ). To assess the accuracy with respect to quality requirements of high-resolution DEMs, topographic height errors are derived from the estimated baseline uncertainties. Taking the monostatic pursuit flight configuration as the worst case for baseline performance, the analysis reveals that the induced low-frequency modulation (height bias) fulfills the relative vertical accuracy requirement (σ<1 m linear point-to-point error) according to the digital terrain elevation data level 3 (DTED-3) specifications for most of the baseline constellations. The use of a GPS-based reduced dynamic orbit determination technique improves the baseline performance for repeat-pass interferometry. The problem of fulfilling the DTED-3 horizontal accuracy requirements is still an issue to be investigated. DGPS can be used as an operational navigation tool for high-precision baseline estimation if a geodetic-grade dual-frequency spaceborne GPS receiver is assumed to be the primary instrument onboard the SAR satellites. The possibility of using only single-frequency receivers, however, requires further research effort.Deutsche Forschungsgemeinschaft (DFG) research fellow until Sept. 2004 at the Microwaves and Radar Institute, Deutsche Zentrum für Luft- und Raumfahrt (DLR) e.V., 82234 Weßling, Germany 相似文献
12.
Curvilinear synthetic aperture radar (SAR), as a more practicable 3-D SAR imaging system, utilizes parametric target feature estimates extracted from the received data to reconstruct the target image. The reconstructed image quality is then impacted by the estimation accuracy of the features. In this letter, through discussing the correlation between the system parameters and the estimation performance of the curvilinear SAR, a conclusion can be drawn on how the overall location accuracy of a target is determined by the correlation between the azimuth and elevation coordinates of the flight path, compactly characterizing the curvilinear aperture. Consequently, a new index, determined only with the aperture parameters, is proposed as an aperture evaluator, which is referred to as the feature-independent aperture evaluator (FAE). FAE can be used for guiding the operational aperture design 相似文献
13.
《Geoscience and Remote Sensing Letters, IEEE》2009,6(1):102-106
Azimuth ambiguity occurs in synthetic aperture radar (SAR) systems due to the well-known constraint of minimum antenna area, particularly at high resolutions and wide swaths. A space time domain method can be utilized to remove this ambiguity if the multiple-channel data are available. In this letter, a modified approach is presented to determine the filter weight vectors. This approach was successfully applied to the real data, which were collected by an experimental airborne multiple-channel SAR system. The channel imbalance and the error in antenna phase center position are analyzed in detail. 相似文献
14.
Praveen K. Thakur Pradeep K. Garg Shiv P. Aggarwal Rahul D. Garg Sneh Mani 《Journal of the Indian Society of Remote Sensing》2013,41(4):933-945
The current study has used Synthetic Aperture Radar (SAR) satellite data to estimate the Snow Cover Area (SCA) in Manali watershed of Beas River in Northwest Himalayas of Himachal Pradesh, India. SAR data used in this study is of Radarsat-2 (RS2) and Environmental Satellite (ENVISAT), Advanced Synthetic Aperture Radar (ASAR). The SAR preprocessing was done with SAR image processing tools for converting raw SAR images into calibrated geo-coded backscatter images. Maps for forest, built area, layover and shadow were created and used for masking snow cover in these areas. The backscattering ratio of wet snow to reference image threshold method with value range from ?2 to ?3 db was used to estimate wet SCA for study area. In this technique, if the threshold is too high (≥-2 db) wet SCA is overestimated and if it is too low (≤-3db), this method underestimates the SCA. The wet SCA is under/over estimated (+6 % to?8 % on average) in late spring season due to the inherent terrain and SAR imaging effects of layover/foreshortening and shadow and also due to the masking of forest areas. Overall, the SCA derived from SAR data matches well when compared with total SCA derived from cloud free optical remote sensing data products, especially during wet season. 相似文献
15.
Bistatic synthetic aperture radar (SAR) is an extension of traditional monostatic SAR, which increases the flexibility in designing SAR missions. We describe a scheme for the computation of integration time and azimuth coverage of bistatic SARs based on space-time diagrams. A classification of bistatic SAR configurations is introduced in terms of size and velocity on the ground of antenna footprints. Bistatic SAR regimes are also identified. 相似文献
16.
张植民 《武汉大学学报(信息科学版)》1989,(3)
本文应用局部等效性原理分析无限长圆锥等角螺旋天线中的波型模式,论述了T_(-1)波的有效辐射区。提出适当压缩T_(-1)波的有效辐射区,把小锥角双臂圆锥等角螺旋天线应用于GPS天线的设计思想。文章阐述了该天线的工程设计方法,并给出了其实测指标及使用情况。为GPS正式投入运行,提供了一种性能良好的接收天线。 相似文献
17.
Zhi-Hong Jiang Kan Huang-Fu Jian-Wei Wan 《Geoscience and Remote Sensing Letters, IEEE》2007,4(3):377-381
Frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) is a lightweight cost-effective high-resolution airborne imaging radar. In squint case, the frequency scaling algorithm, which is suitable for processing nonchirped raw data, cannot be used directly in FMCW SAR data processing because of low system sampling frequency. On the other hand, the continuous antenna motion of FMCW SAR can cause serious distortions in the reconstructed images. In this letter, an improved algorithm called the chirp transform algorithm is proposed. When the effects of the residual video phase are negligible, the algorithm uses a chirp transform to perform the time scaling operation to alleviate the sampling frequency problem. It requires only fast Fourier transforms and multiplications. The range cell migration introduced by the continuous motion is also compensated completely in range-Doppler domain. The algorithm performances are analyzed and are supported by point target simulation experiments. 相似文献
18.
Vijay Kumar Gopalan Venkataraman 《Journal of the Indian Society of Remote Sensing》2012,40(2):325-334
In this study an attempt is made for studying the Himalayan glacier features using TerraSAR-X and Indian Remote Sensing Satellite,
Linear Imaging Self Scanning System III (IRS LISS –III) images. New generation, synthetic aperture radar (SAR) data from TerraSAR-X
(TS-X) sensor provide opportunity for glacier feature studies in Himalayan rugged terrain. Spot Light High resolution mode
TS-X data give idea about glacial features which remained untraceable from other existing SAR system. However, presence of
speckle noise in SAR images degrades the interpretability of the glacier features. Speckle suppression filters (Lee, Frost,
Enhanced Lee, Gamma-Map) are applied on SAR intensity images. On the basis of field sight seeing and insitu observations it
is observed that still features are not clear. Hence attempt has been made for fusing multitemporal multispatial speckle reduced
TS-X SAR data and multispectral IRS LISS-III data for extracting the glacial features such as crevasses, exposed ice and superaglacier
lakes. Principal component analysis (PCA) represents the high spectral resolution data in a linear subspace with minimum information
loss. Herein, PCA based image fusion technique is adopted for this study and comparison is made between IHS fusion technique
and PCA based technique for glacier studies in the Himalayan region. 相似文献
19.
作为多通道合成孔径雷达(SAR)的一种高效便捷的抗干扰方法,SAR多通道对消技术可有效抑制包括散射波干扰在内的多种干扰类型,于是提出采用方位向余弦调相散射波干扰方法来对抗SAR双通道对消的干扰抑制能力。该方法通过对传统散射波干扰慢时间域进行余弦调相,不仅实现了干扰信号的方位向扩展,更使得干扰信号到达各通道之间的相位关系发生严重改变。这种相位差变化会影响干扰对消过程中的自动相位搜索环节,扰乱对消时所需补偿相位的估计结果,进而严重破坏对消后的真实场景成像。以SAR双通道对消系统为例分析了该干扰方法的影响效果,理论分析与实验结果表明:余弦调相散射波干扰可使得补偿相位的估计结果在慢时间上近似正弦分布;在双通道对消成像中,该干扰使得真实场景在方位向上被重复搬移,造成严重的影像重叠,同时在方位向上伴随着密集的明暗条纹;干扰效果可通过设定余弦调制频率、调制指数等参数进行控制。 相似文献
20.
Carrier phase multipath error characterization and reduction in single aircraft relative positioning
This paper describes GPS carrier phase (CP) multipath characterization and error reduction techniques and their application
in single aircraft relative positioning. In particular, the single aircraft relative positioning scenario has applications
for high-accuracy multi-sensor stabilization where CP multipath is a major error source that limits system performance. We
will briefly review the requisite multipath theory and discuss models for quantifying the error characteristics. Field-test
data will be used to validate the multipath models considering the underlying assumptions. A basic geometric reflection point
theory will be presented to demonstrate the physical environmental sensitivity of CP multipath to parameters such as surface
flatness and antenna height. Several different quantities will be described as multipath indicators for time-domain detection
and will be compared with a frequency-domain technique. A new multipath detection approach will be introduced that is suitable
to track multipath from time-varying reflection/diffraction points. Finally, the narrow-lane antenna baseline processing technique
will be presented as a real-time approach to mitigate CP noise and multipath errors that is well suited for a very short baseline
single aircraft high accuracy relative positioning system. Field-test results and analysis will be used to illustrate the
key concepts in this paper and to help characterize the total navigation system performance. 相似文献