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1.
A Chirp Transform Algorithm for Processing Squint Mode FMCW SAR Data   总被引：2，自引：0，他引：2  
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   

2.
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   

3.
This letter presents a new method, called total Zero Doppler steering, to perform yaw and pitch steering for spaceborne synthetic aperture radar (SAR) systems. The new method reduces the Doppler centroid to theoretically 0 Hz, independent of the range position of interest. Residual errors are only due to pointing inaccuracy or due to approximations in the implementation of the total zero Doppler steering law. This letter compares the new method with currently applied methods. The attitude angles and the residual Doppler centroid frequencies are calculated and depicted exemplarily for the parameters of TerraSAR-X, for which the new method will be implemented and used. The new method provides a number of advantages. The low residual Doppler centroid and the reduced variation of the Doppler centroid over range allow a more accurate Doppler centroid estimation. Due to the low residual Doppler centroid, the synthetic aperture radar (SAR) processing can be alleviated, since the range cell migration is reduced and the Doppler frequencies are low. This facilitates the use of very efficient processing algorithms, which are based on approximations whose quality is better for low Doppler frequencies. The new method will furthermore optimize the overlap of the azimuth spectra of SAR image pairs for cross-track interferometry. Low Doppler centroids will also reduce the impact of coregistration errors on the interferometric phase. Furthermore, scalloping corrections in the ScanSAR processing are alleviated due to the low variation of the Doppler centroid over range.  相似文献   

4.
Estimation of differential shift of image elements between two synthetic aperture radar (SAR) images is the basis for many applications, like digital elevation model generation or ground motion mapping. The shift measurement can be done nonambiguously on the macro scale at an accuracy depending on the range resolution of the system or on the micro scale by employing interferometric methods. The latter suffers from phase cycle ambiguities and requires phase unwrapping. Modern wideband high-resolution SAR systems boast resolutions as small as a few tens of a wavelength. If sufficiently many samples are used for macro-scale shift estimation, the accuracy can be increased to a small fraction of a resolution cell and even in the order of a wavelength. Then, accurate absolute ranging becomes precise enough to support phase unwrapping or even make it obsolete. This letter establishes a few fundamental equations on the accuracy bounds of shift estimation accuracy for several algorithms: coherent speckle correlation, incoherent speckle correlation, split-band interferometry, a multifrequency approach, and correlation of point scatterers in clutter. It is shown that the performance of split-band interferometry is close to the Crame/spl acute/r-Rao bound for a broad variety of bandwidth ratios. Based on these findings, Delta-k systems are proposed to best take advantage of the available radar bandwidth.  相似文献   

5.
In this letter, the fourth-order extended exact transfer function (EETF4) is adapted for spaceborne bistatic synthetic aperture radar (SAR) processing. The problems with high squint and large bistatic Doppler centroid variations are analyzed, and it is shown that if both transmitter and receiver are highly squinted in the same direction, then it may be demanding to achieve perfect quality of the point targets. It is shown that if both transmitter and receiver have high squint in opposite directions with small Doppler centroid variations, then the SAR image can be processed very precisely.  相似文献   

6.
The performance of high-resolution synthetic aperture radar (SAR) systems under degrading conditions such as uncontrolled platform motion can only be analyzed and evaluated by modeling the whole imaging system through simulation. A major scientific problem, however, is the generation of spotlight mode SAR raw data because of the need for high numerical and modeling accuracy, and restricted computer time and space. Taking into account a squinted geometry and platform instabilities, the common generation of raw data in the time domain becomes time inefficient. This letter proposes a raw data generator with which the spotlight mode raw data set of an extended scene can be simulated and which combines the precision obtainable when working in the time domain with the efficiency of work in the frequency domain. The generated raw data are processed and analyzed to quantify the quality of the proposed simulation tool.  相似文献   

7.
徐三元  王建国 《遥感学报》2010,14(2):267-277
建立双基地SAR的单基地等效模型,分析了系统时间同步误差的机理;提出了双基地SAR回波中的直达波数据进行时间同步误差校正的算法;在双基地SAR单站等效模型的基础上,利用时变阶梯变换算法进行成像处理。经过理论分析,实测数据处理验证,这一算法是有效的,能够校正双基地SAR时间同步误差,较好地进行实测数据的成像处理。  相似文献   

8.
This letter derives a 2-D point target spectrum for general bistatic synthetic aperture radar (SAR). For the bistatic configuration, the contributions of the transmitter and the receiver to the overall instantaneous Doppler are unequal due to the different slant range histories. In this letter, an instantaneous Doppler contribution ratio is proposed to represent the difference between the instantaneous Doppler contributions of the transmitter and the receiver, which varies with instantaneous Doppler and range frequency. Then, the 2-D spectrum is obtained by using the stationary phase principle and Taylor series expansion for general bistatic SAR. The accuracy of the spectrum is verified with a point target simulation of different general bistatic configurations.   相似文献   

9.
Efficient synthetic aperture radar (SAR) processing algorithms are unable to exactly implement the aperture- and topography-dependent motion compensation due to the superposition of the synthetic apertures of several targets having different motion errors and potentially different topographic heights. Thus, during motion compensation, a reference level is assumed, resulting in residual phase errors that impact the focusing, geometric fidelity, and phase accuracy of the processed SAR images. This letter proposes a new short fast Fourier transform-based postprocessing methodology capable of efficient and precise compensation of these topography- and aperture-dependent residual phase errors. In addition to wide beamwidth (very high resolution) SAR systems, airborne repeat-pass interferometry especially benefits from this approach, as motion compensation can be significantly improved, especially in areas with high topographic changes. Repeat-pass interferometric data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach.  相似文献   

10.
Inverse synthetic aperture radar (ISAR) is an imaging technique that is dependent on an object's rotational motion over a coherent processing interval. Maritime vessels and aircraft possess 3-D rotational motion, whereas it is only their ISAR contributing motion that is useful to the ISAR imaging process; the contributing motion consists of the Doppler generating axis and the effective angle of rotation. This letter presents a quaternion-based transformation that converts measured attitude and position data into an object's Doppler generating axis and effective angular rotation rate. This transformation is significant since it isolates the component of the motion that directly influences the ISAR image. It provides an alternative approach that can be used to understand the causes of blurring of most ISAR images of sea vessels as well to identify good imaging intervals for applications such as cooperative ISAR for radar cross section measurement purposes.   相似文献   

11.
This letter presents a new motion compensation algorithm to process airborne interferometric repeat-pass synthetic aperture radar (SAR) data. It accommodates topography variations during SAR data processing, using an external digital elevation model. The proposed approach avoids phase artifacts, azimuth coregistration errors, and impulse response degradation, which usually appear due to the assumption of a constant reference height during motion compensation. It accurately modifies phase history of all targets before azimuth compression, resulting in an enhanced image quality. Airborne L-band repeat-pass interferometric data of the German Aerospace Center experimental airborne SAR (E-SAR) is used to validate the algorithm.  相似文献   

12.
This letter deals with the problems of retrieving height and synthetic aperture radar (SAR) reflectivity of layovered terrain using multibaseline SAR interferometry (InSAR). In particular, we focus on the wideband array problem caused by practically large InSAR arrays and high-resolution SAR images, i.e., the problem of signal envelope misalignment, which is neglected in the work by Gini We propose two methods to eliminate or mitigate the effect of envelope misalignment, one called the aligning method and the other called the joint range cell processing method. In the aligning method, we align each signal envelope for each searched height of the layovered components (i.e., ground resolution cells with different altitudes) during searching procedure. The joint range cell processing method jointly processes the neighboring cells in range to estimate the parameters of layovered components so that the effect of the envelope misalignment can be mitigated. Theoretical analysis and computer simulation results show that both methods have the ability to provide accurate estimation of the heights and radar reflectivities of multiple layovered resolution cells in the presence of large envelope misalignments.   相似文献   

13.
张毅  周成英 《遥感学报》2004,8(5):419-424
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   

14.
A new high-resolution Ku-band Doppler radar for meteorological applications has been developed. With the new system design, the radar can accurately measure the radar reflectivity factor with 4-m resolution over a range from 40 m to several kilometers for 100-mW power using a pulse compression technique. Details of the system design, signal processing algorithm, and data acquisition procedures are described. To demonstrate the accuracy of the system, the radar reflectivity measurements are compared with the Joss-Waldvogel disdrometer measurements, and fairly good agreement is shown. The ability of the system to capture the backscattered signal and Doppler spectrum from rain volume at low altitude with high resolution is demonstrated for both convective- and stratiform-type rain events.  相似文献   

15.
Migration through resolution cell compensation in ISAR imaging   总被引：5，自引：0，他引：5  
Range-Doppler (RD) processing is widely used in conventional inverse synthetic aperture radar (ISAR) imaging. The unwanted translational motion of moving targets is compensated by envelope alignment and autofocus. For existing ISAR imaging algorithms, the scatterers' migration through resolution cells (MTRC) caused by the rotational motion is usually ignored. With the improvement of resolution or the increase of target size, MTRC cannot be neglected. In this letter, the keystone formatting algorithm developed in SAR is used for the MTRC compensation in ISAR. Before the keystone formatting, coherent processing must be performed on the raw phase history data. An effective approach is proposed for this kind of coherent processing. Numerical examples are provided to demonstrate the performance of the proposed approach.  相似文献   

16.
高分辨率合成孔径雷达的相干斑是由雷达信号的干性引起的，并存在于所有相干图像中。根据SAR成橡机理，分析了产生的原因特征，给出了SAR相干斑的确切定义、统计方法。实验表明统计结果与传统方法相比更加精确。  相似文献   

17.
In this letter, a synthetic aperture radar (SAR) data reformatting approach named Doppler Keystone transform (DKT) is proposed to correct the range migration of a moving target. By using the DKT, the SAR imaging program, i.e., the 2-D matched filtering, can be transformed into separate 1-D operations along range or azimuth direction, and therefore, the DKT is suitable for the parallel implementation of SAR imaging of the moving target. Our simulations show that by combining the DKT and the Doppler phase compensation methods, the moving target can be well imaged in high signal–clutter-ratio case.   相似文献   

18.
机载合成孔径雷达图像几何处理是机载合成孔径雷达图像后续处理的基础,同时也是机载合成孔径雷达大规模测绘应用的基础。本文根据机载合成孔径雷达图像的成像机理,基于距离多普勒模型,考虑到合成孔径雷达成像时斜视角与多普勒频率的关系,在影像纠正时,将斜视角作为一个变量处理来减小雷达成像时零多普勒误差的影响。试验证明,此种方法比将斜视角作为零处理时的纠正精度有明显提高。详细地分析了利用此方法进行几何纠正时控制点的个数和分布对纠正精度的影响。  相似文献   

19.
合成孔径雷达（ＳＡＲ）是一种重要的微波遥感工具。其关键技术是成像处理,即把接收到的雷达信号转换成雷达图像。事实上,合成孔径就是通过成像处理来实现的。该文在总结目前星载ＳＡＲ各种成像处理算法的基础上,提出一种匹配滤波与ＣｈｉｒｐＳｃａｌｉｎｇ相结合的处理方法。处理过程无需插值便可进行距离迁移校正,还可获得好的聚焦与相位保持性能。所得图像质量超过现有的其它ＳＡＲ成像处理方法所得图像质量。  相似文献   

20.
Synthetic aperture radar (SAR) image formation processing assumes that the scene is stationary, and to focus an object, one coherently sums a large number of independent returns. Any target motion introduces phases that distort and/or translate the target's image. Target motion produces a smear primarily in the azimuth direction of the SAR image. Time-frequency (TF) modeling is used to analyze and correct the residual phase distortions. An interactive focusing algorithm based on TF modeling demonstrates how to correct the phase and to rapidly focus the mover. This is demonstrated on two watercraft observed in a SAR image. Then, two time-frequency representations (TFRs) are applied to estimate the motion parameters of the movers or refocus them or both. The first is the short-time Fourier transform, from which a velocity profile is constructed based on the length of the smear. The second TFR is the time-frequency distribution series, which is a robust derivative of the Wigner-Ville distribution that works well in this SAR environment. The smear is a modulated chirp, from which a velocity profile is plotted and the phase corrections are integrated to focus the movers. The relationship between these two methods is discussed. Both methods show good agreement on the example.  相似文献   

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