High sidelobe effects on interferometric coherence for circular SAR imaging geometry

The coherence is a measure for the accuracy of the interferometric phase, and the synthetic aperture radar （SAR） inter- ferometric coherence is affected by several sources of the decor- relation noise. For the circular SAR （CSAR） imaging geometry, the system response function is in the form of the Bessel function which brings a high sidelobe, and the high sidelobe of CSAR will be an important factor influencing the interferometric coherence. The effect of the high sidelobe on the coherence is analyzed and deduced. Based on the interferometric characteristics of the slight difference in the viewing angles and the potential pixel off- set in the interferometric SAR （InSAR） images, a relation between the radar impulse response and the coherence loss function is derived. From the relational model, the coherence loss function due to the high sidelobe of CSAR is then deduced, and compared with that of the conventional SAR. It is shown that the high sidelobe of CSAR focusing signal will severely affect the baseline decorre- lation and coregistration decorrelation. Simulation results confirm the theoretical analysis and quantitatively show the baseline and coregistration decorrelation degradation due to the high sidelobes of CSAR.

An approach to estimate tree height using PolInSAR data constructed by the Sentinel-1 dual-pol SAR data and RVoG model

We estimate tree heights using polarimetric interferometric synthetic aperture radar(PolInSAR)data constructed by the dual-polarization(dual-pol)SAR data and random volume over the ground(RVoG)model.Considering the Sentinel-1 SAR dual-pol(SVV,vertically transmitted and vertically received and SVH,vertically transmitted and horizontally received)configuration,one notes that S_(HH),the horizontally transmitted and horizontally received scattering element,is unavailable.The S_(HH)data were constructed using the SVH data,and polarimetric SAR(PolSAR)data were obtained.The proposed approach was first verified in simulation with satisfactory results.It was next applied to construct PolInSAR data by a pair of dual-pol Sentinel-1A data at Duke Forest,North Carolina,USA.According to local observations and forest descriptions,the range of estimated tree heights was overall reasonable.Comparing the heights with the ICESat-2 tree heights at 23 sampling locations,relative errors of 5 points were within±30%.Errors of 8 points ranged from 30%to 40%,but errors of the remaining 10 points were>40%.The results should be encouraged as error reduction is possible.For instance,the construction of PolSAR data should not be limited to using SVH,and a combination of SVH and SVV should be explored.Also,an ensemble of tree heights derived from multiple PolInSAR data can be considered since tree heights do not vary much with time frame in months or one season.

Detection, Estimation and Compensation of Ionospheric Effect on SAR Interferogram Using Azimuth Shift

An increasing interest in the use of low frequency Synthetic Aperture Radar(SAR)systems,e.g.,L-and P-bands,makes the research of the ionospheric effects on SAR interferograms become urgent and significant.As the most pronounced signature in interferograms,the ionosphere-induced azimuth streak was thoroughly investigated in this study through processing of the 19 L-band Advanced Land-Observing Satellite(ALOS)Phased Array type L-band Synthetic Aperture Radar(PALSAR)images over the Chongqing City,China.The investigations show that the visible ionosphere-induced stripe-shape azimuth shifts with the invariable direction of 26°E,113°N are observed in some interferometric pairs.Relating these anomalous azimuth shifts to the International GNSS Service(IGS)final ionospheric products shows that the detected ionosphere-contaminated SAR images display the relatively large ionospheric variation with time during SAR satellite travelled through the study area,indicating a somewhat correlation between them.After detecting the ionosphere-contaminated interferograms,we estimated the Ionospheric Phase Streak(IPS)based on an approximate linear relationship between IPS and azimuth shift,and then removed them from the original interferograms.The corrected results show that ionospheric phase patterns are largely removed from the ionosphere-contaminated interferograms.The investigation indicates that the direction of the IPS keeps approximately constant in space and time,which provides the potential chance to develop methods to correct the ionospheric effect.Furthermore,this study once more proves that the ionospheric effect on SAR interferogram can be detected,estimated and corrected from azimuth shifts.

IMPACT OF WIDE-BAND I/Q MODULATION ERRORS IN SAR IMAGING ANALYSIS AND COMPENSATION METHOD RESAERCH

Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.

An Efficient Topography Adaptive Filter for Insar Processing

An efficient implementation of the topography adaptive filter based on local frequency estimation is proposed, where chirp z transform is applied to enhance the accuracy of the frequency estimation. As a by product of this adaptive filter, the linear approximated phase model of the interferogram is employed to improve the coherence estimation. The impacts of the adaptive filter on global and local phase unwrapping algorithms are discussed. Finally, aiming at the negative effect that the adaptive filter can bring to local phase unwrapping algorithms, a fusion scheme that takes advantage of least square and several local phase unwrapping algorithms is presented.

AN IMPLEMENTATION METHOD OF ADAPTIVE THRESHOLD TO DETECT MOVING TARGETS BASED ON ATI TECHNOLOGY

AT-InSAR(Along Track Interferometric SAR) is a technique to detect slow-moving targets. However, the detection performance is greatly influenced by noise and clutter. In this paper, the influence of noise and clutter on the detecting performance is analyzed. By simulating different background clutter and noise, the performances of the phase threshold and dual-threshold methods are discussed in detail, and then the adaptive-threshold method is proposed which can greatly improve the detection performance.

基于InSAR技术的中国地表形变一张图研制

地表形变危害巨大且深远,利用合成孔径雷达干涉测量(interferometric synthetic aperture radar,InSAR)技术监测地表形变虽已较为成熟,但是超大范围,甚至全国范围的地表形变快速提取仍充满挑战。为快速获取全国地表形变信息,设计了一种基于超算并行计算的广域地表形变快速提取优化方法,并对干涉集基线组合方法、广域相位解缠算法、大气效应改正方法等进行了改进和创新。基于该方法,采用10157景哨兵1号数据,研制了中国全境2021年度40m分辨率地表形变速率图,经验证形变速率精度为4.82mm/a,有效覆盖度为94.6%,图幅间无明显接边差异。同时对国内典型地表形变区域进行了分析。研究为广域地表形变常态化快速提取提供了参考。