Improving Satellite-Retrieved Cloud Base Height with Ground-Based Cloud Radar Measurements

Cloud base height(CBH) is a crucial parameter for cloud radiative effect estimates, climate change simulations, and aviation guidance. However, due to the limited information on cloud vertical structures included in passive satellite radiometer observations, few operational satellite CBH products are currently available. This study presents a new method for retrieving CBH from satellite radiometers. The method first uses the combined measurements of satellite radiometers and ground-based cloud radars to develop a lookup table(LUT) of effective cloud water content(ECWC), representing the vertically varying cloud water content. This LUT allows for the conversion of cloud water path to cloud geometric thickness(CGT), enabling the estimation of CBH as the difference between cloud top height and CGT. Detailed comparative analysis of CBH estimates from the state-of-the-art ECWC LUT are conducted against four ground-based millimeter-wave cloud radar(MMCR) measurements, and results show that the mean bias(correlation coefficient) is0.18±1.79 km(0.73), which is lower(higher) than 0.23±2.11 km(0.67) as derived from the combined measurements of satellite radiometers and satellite radar-lidar(i.e., Cloud Sat and CALIPSO). Furthermore, the percentages of the CBH biases within 250 m increase by 5% to 10%, which varies by location. This indicates that the CBH estimates from our algorithm are more consistent with ground-based MMCR measurements. Therefore, this algorithm shows great potential for further improvement of the CBH retrievals as ground-based MMCR are being increasingly included in global surface meteorological observing networks, and the improved CBH retrievals will contribute to better cloud radiative effect estimates.

Time-varying baseline error correction method for ground-based micro-deformation monitoring radar

In recent years, ground-based micro-deformation monitoring radar has attracted much attention due to its excellent monitoring capability. By controlling the repeated campaigns of the radar antenna on a fixed track, ground-based micro-deformation monitoring radar can accomplish repeat-pass interferometry without a space baseline and thus obtain highprecision deformation data of a large scene at one time. However, it is difficult to guarantee absolute stable installation position in every campaign. If the installation position is unstable, the stability of the radar track will be affected randomly, resulting in time-varying baseline error. In this study, a correction method for this error is developed by analyzing the error distribution law while the spatial baseline is unknown. In practice, the error data are first identified by frequency components, then the data of each one-dimensional array(in azimuth direction or range direction) are grouped based on numerical distribution period, and finally the error is corrected by the nonlinear model established with each group.This method is verified with measured data from a slope in southern China, and the results show that the method can effectively correct the time-varying baseline error caused by rail instability and effectively improve the monitoring data accuracy of groundbased micro-deformation radar in short term and long term.

Constrained geometry analysis to resolve 3-D deformations from three ground-based radars

When multiple ground-based radars(GB-rads)are utilized together to resolve three-dimensional(3-D)deformations,the resolving accuracy is related with the measurement geometry constructed by these radars.This paper focuses on constrained geometry analysis to resolve 3-D deformations from three GB-rads.The geometric dilution of precision(GDOP)is utilized to evaluate 3-D deformation accuracy of a single target,and its theoretical equation is derived by building a simplified 3-D coordinate system.Then for a 3-D scene,its optimal accuracy problem is converted into determining the minimum value of an objective function with a boundary constraint.The genetic algorithm is utilized to solve this constrained optimization problem.Numerical simulations are made to validate the correctness of the theoretical analysis results.

Application of Interferometric Spaceborne Synthetic Aperture Radar to Morphotectonic Research in the Bengcuo Area of Tibet

Using ELLS-1/2 radar satellite data, we generated a Digital Elevation Model by Interferometric Synthetic Aperture Radar, and the ERS-1/2 DEM that we generated is obviously superior to both the 1/25 ten thousand-scale DEM of the National Fundamental Geographic Information System of China and the 90-m spatial resolution＇s SRTM DEM that America published in 2004 when it showed the characteristics of tiny structure relief. By analyzing the relief characteristics of the Bengcuo fault zone based on ERS-1/2 DEM, we find that the relief on the connection location of the Bengcuo and Pengcuo fault zones has complex characteristics. A structure relief that is similar to the Pengcuo fault zone crosses through the Dazi-Dasha fault on the the Bengcuo fault zone, while the Dazi-Dasha fault crosses through a gully at this place. This indicates that the Dazi-Dasha fault has been active at this place recently. At the same time, the Naka-Naduiduo fault is severed by the gully which was cut through by the Dazi-Dasha fault. Therefore, the Naka-Naduiduo fault was formed earlier than the Dazi-Dasha fault.

Effect of digital elevation models on monitoring slope displacements in open-pit mine by differential interferometry synthetic aperture radar

Displacement monitoring in open-pit mines is one of the important tasks for safe management of mining processes.Differential interferometric synthetic aperture radar(DInSAR),mounted on an artificial satellite,has the potential to be a cost-effective method for monitoring surface displacements over extensive areas,such as open-pit mines.DInSAR requires the ground surface elevation data in the process of its analysis as a digital elevation model(DEM).However,since the topography of the ground surface in open-pit mines changes largely due to excavations,measurement errors can occur due to insufficient information on the elevation of mining areas.In this paper,effect of different elevation models on the accuracy of the displacement monitoring results by DInSAR is investigated at a limestone quarry.In addition,validity of the DInSAR results using an appropriate DEM is examined by comparing them with the results obtained by global positioning system(GPS)monitoring conducted for three years at the same limestone quarry.It is found that the uncertainty of DEMs induces large errors in the displacement monitoring results if the baseline length of the satellites between the master and the slave data is longer than a few hundred meters.Comparing the monitoring results of DInSAR and GPS,the root mean square error(RMSE)of the discrepancy between the two sets of results is less than 10 mm if an appropriate DEM,considering the excavation processes,is used.It is proven that DInSAR can be applied for monitoring the displacements of mine slopes with centimeter-level accuracy.

An approach to wide-field imaging of linear rail ground-based SAR in high squint multi-angle mode

Ground-based synthetic aperture radar(GB-SAR) has been successfully applied to the ground deformation monitoring.However, due to the short length of the GB-SAR platform, the scope of observation is largely limited. The practical applications drive us to make improvements on the conventional linear rail GB-SAR system in order to achieve larger field imaging. First, a turntable is utilized to support the rotational movement of the radar.Next, a series of high-squint scanning is performed with multiple squint angles. Further, the high squint modulation phase of the echo data is eliminated. Then, a new multi-angle imaging method is performed in the wave number domain to expand the field of view. Simulation and real experiments verify the effectiveness of this method.

AN ALGORITHM FOR INTERFEROMETRIC SAR DATA PROCESSING

In this paper, an algorithm of generating INSAR unwrapped phase image from SAR single-look complex images is presented. Besides the general processing technique, this article focuses on the methods of flat-earth phase removal, phase noise reduction and phase unwrapping. The availability is tested by the results of processing ERS-1/2 SAR images.

Frequency Domain Filtering SAR Interferometric Phase Noise Using the Amended Matrix Pencil Model

Interferometric phase filtering is one of the key steps in interferometricsynthetic aperture radar (InSAR/SAR). However, the ideal filtering results are difficult toobtain due to dense fringe and low coherence regions. Moreover, the InSAR/SAR datarange is relatively large, so the efficiency of interferential phase filtering is one of themajor problems. In this letter, we proposed an interferometric phase filtering methodbased on an amended matrix pencil and linear window mean filter. The combination ofthe matrix pencil and the linear mean filter are introduced to the interferometric phasefiltering for the first time. First, the interferometric signal is analyzed, and theinterferometric phase filtering is transformed into a local frequency estimation problem.Then, the local frequency is estimated using an amended matrix pencil at a window. Thelocal frequency can represent terrain changes, thus suggesting that the frequency can beaccurately estimated even in dense fringe regions. Finally, the local frequency is filteredby using a linear window mean filter, and the filtered phase is recovered. The proposedmethod is calculated by some matrices. Therefore, the computational complexity isreduced, and the efficiency of the interferometric phase filtering is improved.Experiments are conducted with simulated and real InSAR data. The proposed methodexhibits a better filtering effect and an ideal efficiency as compared with the traditionalfiltering method.

Three-dimensional bistatic interferometric ISA Rimaging

An approach based on interferometry technique is proposed for three-dimensional （3D） bistatic inverse synthetic aperture radar （ISAR） imaging. It is converted to a monostatic problem by using the theory that a bistatic radar equals a monostatic radar located on the bisector of bistatic an- gle. Then, interferometric phases extracted from a pair of cross shaped antennas are used to esti- mate the height and associated rotational velocity. Finally, numerical simulations are provided to e- valuate this method.

A Review on Applications of Imaging Synthetic Aperture Radar with a Special Focus on Cryospheric Studies

The cryosphere is the frozen part of the Earth’s system. Snow and ice are the main constituents of the cryosphere and may be found in different states, such as snow, freshwater ice, sea ice, perma-frost, and continental ice masses in the form of glaciers and ice sheets. The present review mainly deals with state-of-the-art applications of synthetic aperture radar (SAR) with a special emphasize on cryospheric information extraction. SAR is the most important active microwave remote sensing (RS) instrument for ice monitoring, which provides high-resolution images of the Earth’s surface. SAR is an ideal sensor in RS technology, which works in all-weather and day and night conditions to provide useful unprecedented information, especially in the cryospheric regions which are almost inaccessible areas on Earth. This paper addresses the technological evolution of SAR and its applications in studying the various components of the cryosphere. The arrival of SAR radically changed the capabilities of information extraction related to ice type, new ice formation, and ice thickness. SAR applications can be divided into two broad classes-polarimetric applications and interferometric applications. Polarimetric SAR has been effectively used for mapping calving fronts, crevasses, surface structures, sea ice, detection of icebergs, etc. The paper also summarizes both the operational and climate change research by using SAR for sea ice parameter detection. Digital elevation model (DEM) generation and glacier velocity mapping are the two most important applications used in cryosphere using SAR interferometry or interferometric SAR (InSAR). Space-borne InSAR techniques for measuring ice flow velocity and topography have developed rapidly over the last decade. InSAR is capable of measuring ice motion that has radically changed the science of glaciers and ice sheets. Measurement of temperate glacier velocities and surface characteristics by using airborne and space-borne interferometric satellite images have been the significant application in glaciology and cryospheric studies. Space-borne InSAR has contributed to major evolution in many research areas of glaciological study by measuring ice-stream flow velocity, improving understanding of ice-shelf processes, yielding velocity for flux-gate based mass-balance assessment, and mapping flow of mountain glaciers. The present review summarizes the salient development of SAR applications in cryosphere and glaciology.

一种天基双基地InSAR系统的相位同步方法及验证情况

以德国的TanDEM-X双星编队干涉合成孔径雷达(InSAR)卫星系统为背景,提出了基于点频连续波同步信号双向对传,实现编队卫星InSAR系统相位同步的方法。文中给出了该同步方法实现的框架,对该相位同步方法的原理进行了理论推导,得出了补偿相位差的表达式,并对影响同步精度的因素进行了初步的分析。该方法可用于天基双/多基地合成孔径雷达系统相位同步链路的设计,仿真分析的结果验证了该方法的理论可行性。此外,通过搭建实物系统对系统的工程可实现精度进行了验证,结果表明获取的载波频率相位同步精度与倍频器件的频率精度和一致性密切相关。该相位同步方法为与TanDEM-X相近InSAR系统的设计提供参考。

MCJ-UNet:一种双/多通道联合InSAR相位解缠网络

干涉合成孔径雷达(InSAR)可实现地表高程的高效获取,在地形测绘中应用广泛。双/多通道InSAR技术可借助不同通道(基线、频点)的高程模糊度差异,解决相位欠采样问题,完成高程陡变区域的干涉相位解缠,实现InSAR技术在测绘困难区域的有效应用。该文即面向高效高精度相位解缠需求,利用深度学习这一有力工具,结合不同通道的相位特征及相互约束关系,提出了一种双/多通道联合干涉相位解缠网络:Multi-Channel-Joint-UNet(MCJ-UNet)。该网络的构建以双通道(双频、双基线)InSAR为基本观测构型,并可实现向多通道构型的扩展,其构建的核心思路主要包括3点:首先,将干涉相位解缠中的模糊数估计问题转化为语义分割问题,并采用UNet网络完成分割处理;其次,引入挤压激励模块(SE)动态调整信息权重,以增强网络不同通道对其所需信息的感知能力;最后,利用多通道联合约束下的相位残差优化损失函数,实现网络调谐。此外,为避免语义分割结果的边缘细节误差对解缠效果的影响,该文还提出了一种基于多通道联合约束的解缠误差自修正方法,以保证解缠质量。模拟地形仿真数据、真实地形仿真数据以及TerraSAR-X实测数据验证了所提方法的有效性。

融合长短基线的干涉图解缠错误自动改正

合成孔径雷达干涉测量(interferometric synthetic aperture radar,InSAR)技术因具有全天时、全天候、大范围的独特优势,已被广泛应用于地球科学研究、自然灾害监测和环境管理等领域。然而,受地表失相干、干涉条纹密集等因素影响,InSAR数据处理关键的步骤——干涉图相位解缠常出现错误,进而影响高程反演和地表形变监测精度。为此,文章提出了一种融合长短基线干涉相位闭合环的解缠错误自动探测与改正方法,并利用湖南省-江西省高植被覆盖区的Sentinel-1雷达影像开展了算法验证。实验结果表明,该方法可有效地改正干涉相位解缠错误,这对InSAR技术提升高程反演和形变监测精度具有重要意义。

基于InSAR技术的大跨桥梁温度变形监测研究

以国内某高速铁路钢拱桥为研究对象,选取2017—2018年期间59幅C波段Senti⁃nel-1号雷达卫星影像,利用PS-InSAR技术处理影像获得桥梁的视线向(Line of Sight,LOS)位移,根据SAR成像空间几何关系解算出支座的纵向位移.研究结果表明:支座纵向位移的时空特性与实际桥梁结构相符合,验证了PS-InSAR技术观测桥梁结构位移的可行性.建立支座纵向位移与温度的线性相关模型,并与结构健康监测系统的实测结果进行对比.两者吻合良好,相对误差控制在10%以内,验证了PS-InSAR测量桥梁结构位移的可靠性.利用有限元模拟温度作用下桥梁支座的位移变化,并与PS-InSAR位移时间序列进行对比.两者趋势基本一致,LOS向位移误差在[-10,10]mm,验证了PS-InSAR测量桥梁结构位移的准确性.

基于时序InSAR技术的山区高速公路挖方边坡监测

针对传统人工水准监测风险高、难度大的问题,以本桓高速公路挖方边坡为例,提出一种利用SBAS-InSAR与PS-InSAR相结合的技术对挖方边坡进行形变监测。首先,采用SBAS-InSAR技术处理2023年4月—2024年1月获取的22景Sentinel-1A数据,生成小基线差分干涉对,反演得出边坡形变值与形变趋势。然后,选取相同监测时间的水准点测量结果与PS点进行验证,并通过灰色关联度分析降雨量与边坡形变的关联度。监测结果显示,边坡沉降速率集中在10.15~30.27 mm/a,沉降分析结果显示此路堑边坡整体较为稳定,时序InSAR相对水准测量具有全天时、全天候、全维度的特点,并具有可回溯性,表明时序InSAR技术对山区高速公路挖方边坡监测具有可行性与可靠性,确保高速公路挖方边坡安全稳定。

采空区地表InSAR形变监测与安全稳定性评价

为探明河南省平顶山市某变电站拟建场地的安全稳定性,避免采空区地表沉降或倾斜给变电站造成安全隐患,采用永久散射体(PS)合成孔径雷达干涉测量(InSAR)研究平顶山市2015—2022年间的45景Sentinel-1A数据,精细化分析拟建场地的9个代表位置的时序形变特征,进而建立基于InSAR监测的采空区地表场地安全稳定性评价机制,完成对场地的安全稳定性评价。研究结果表明:基于模糊数据集的模糊PS选点法可克服PS点密度低的弊端,有效增加分析可用数据,提升监测结果的准确性;依据基准点校正拟建区内代表点的时序形变后发现,拟建场地整体形变较小且逐渐呈现趋于稳定的趋势,最大沉降量为13.05 mm,最大沉降速度为5.73 mm/a,最大倾斜为0.070 mm/m。基于安全稳定性评价机制分析可知:采空区地表场地移动变形处于稳定状态,变电站地基基础处于安全状态,采空区地表沉降对拟建变电站的影响程度小,综合3种评价指标进行分析,采空区地表场地安全稳定性等级为高,具备建设变电站的可行性。

边坡雷达在重大突发性滑坡应急监测中的应用研究

西南地区突发性重大地质灾害常发生于深切河谷区,在应急抢险过程中,存在人员难到达、地面调查与监测困难、灾害持续变形破坏造成的危害大等问题。以西藏自治区江达县白格滑坡和四川丹巴县阿娘寨滑坡应急抢险为例,应用边坡雷达对白格滑坡残留体和阿娘寨滑坡复活体进行应急监测和变形特征研究。结果表明:通过边坡雷达获取各测点的累计视向变形量、变形速率、变形加速度等监测数据绘制监测区变形云图和监测曲线,判识滑坡区变形破坏及发展趋势、研判各变形区所处的变形演化阶段,快速对临滑破坏区进行识别与预报。边坡雷达能对突发性重大地质灾害开展非接触式全天候实时监测,既能实时掌握灾害变形特征,也保证了监测人员安全,对今后类似的突发性地质灾害应急监测和预警预报具有参考借鉴意义。

星载分布式SAR双频乒乓模式测高精度分析

星载分布式合成孔径雷达(SAR)系统用于干涉测绘,凭借其基线灵活、时间去相关很小的特点得到了快速发展。与传统模式相比,双频乒乓模式能够同时得到两种频率的多幅SAR图像,可以实现更高精度的高程测量。本文首先简单介绍了双频乒乓模式的工作原理,然后深入研究了该模式下SAR干涉对的相位比例关系和相关性,理论上分析了其干涉相位估计精度和对应的测高精度,从而为系统设计和干涉处理方法研究提供理论依据。最后仿真分析结果直观展示了双频乒乓模式相较于传统模式的优越性,由于该模式增加了不同频率的干涉相位数据,干涉相位估计精度和测高精度均显著提升。

2024年新疆乌什Ms 7.1地震InSAR同震形变探测与断层滑动分布反演

2024年1月23日,新疆维吾尔自治区乌什县发生Ms 7.1地震,快速查明其同震形变场与发震断层滑动特征,有助于科学认识此次地震发震机理。利用Sentinel-1卫星升、降轨雷达影像,采用合成孔径雷达差分干涉测量技术获取了本次地震的同震形变场,进而基于Okada弹性位错模型,确定了本次地震的震源参数,并基于分布式滑动模型反演了本次地震断层面上的滑动分布。结果表明,升、降轨同震形变场沿视线向最大形变量分别为75 cm和48 cm,断层最大滑动量为4.2 m,主要集中在地下3~20 km区域;模型正演结果表明,此次地震在垂直方向最大抬升约53 cm,最大沉降约12 cm;发震断层运动以逆冲为主,兼具少量左旋走滑,根据InSAR结果及地质资料综合判断,本次发震断层为迈丹断裂。

星载InSAR基线构型测量误差模型与灵敏度分析

为避免双天线InSAR系统基线测量动态监测过程中引入误差,影响基线测量精度,对基线长度与角度测量过程中的可能误差进行定性与定量分析。采用坐标变换法建立系统误差数学模型,明确测量系统的误差来源。提出误差灵敏度概念,对误差项进行定量计算,并对每一自由度的误差源进行灵敏度分析,进一步形成综合误差定量合成结果。根据误差灵敏度系数给出一组精度反演误差分配案例。最后,依据蒙特卡洛法在MATLAB平台闭环验证精度量化分配方法的可行性与稳定性。仿真分析结果表明,激光视觉三轴位置的测量精度要求为300μm(3σ),三轴角度的测量精度要求为50″(3σ),即可满足基线长度精度1 mm(1.6σ),基线角度精度2″(1.6σ)。通过本方法可由测量环境条件输入直接获得基线测量的精度,根据灵敏度系数对误差分配进行反演可以得到系统最优布局,其结果可为测量系统的方案设计与精度分解提供有效指导。