Modeling and Analysis of the Impacts of Temporal-Spatial Variant Troposphere on Ground-Based SAR Imaging of Asteroids

The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth,so it is crucial to monitor asteroids.Ground-based synthetic aperture radar(SAR)is an observation technique for high resolution imaging of asteroids.The ground-based SAR requires a long integration time to achieve a large synthetic aperture,and the echo signal will be seriously affected by temporal-spatial variant troposphere.Traditional spatiotemporal freezing tropospheric models are ineffective.To cope with this,this paper models and analyses the impacts of temporal-spatial variant troposphere on ground-based SAR imaging of asteroids.For the background tropo-sphere,a temporal-spatial variant ray tracing method is proposed to trace the 4D(3D spatial+temporal)refractive index network provided by the numerical weather model,and calculate the error of the background troposphere.For the tropospheric turbulence,the Andrew power spectral model is used in conjunction with multiphase screen theory,and varying errors are obtained by tracking the changing position of the pierce point on the phase screen.Through simulation,the impact of temporal-spatial variant tropospheric errors on image quality is analyzed,and the simulation results show that the X-band echo signal is seriously affected by the troposphere and the echo signal must be compensated.

3D Target Localization Based on FrFT from Spaceborne Curve SAR

Synthetic aperture radar(SAR)three-dimensional(3D)imaging technology can reconstruct the complete structure of observed targets and has been a hot topic.Compared with tomographic SAR,array interferometric SAR,and circular SAR,curve SAR can use less data to achieve 3D positioning of targets.Most existing algorithms for estimating Doppler frequency modulation(FM)rate are based on sub aperture partitioning,resulting in low computational efficiency.To address this,this article establishes a target height estimation model,which reflects the relation-ship between the height and the residual Doppler FM rate for spaceborne curve SAR.Then,a fast SAR 3D localization processing flow based on fractional Fourier transform(FrFT)is proposed.Experimental verification demonstrates that this method can estimate the Doppler FM of the target column by column,and the 3D position error for non-overlapping targets is controlled within 1 m.For overlapping points with an intensity ratio greater than 1.5,the root mean square error(RMSE)of the estimation results is around 5 m.If the separation between overlapping points is greater than 35 m,the RMSE decreases to approximately 2 m.

Skeleton-aware implicit function for single-view human reconstruction

The aim is to reconstruct a complete and detailed clothed human from a single-view input.Implicit function is suitable for this task because it represents fine shape details and varied topology.Current methods,however,often suffer from artefacts such as broken or disembodied body parts,missing details,or depth ambiguity due to the ambiguity and complexity of human articulation.The main issue observed by the authors is structureagnostic.To address these problems,the authors fully utilise the skinned multi-person linear(SMPL)model and propose a method using the Skeleton-aware Implicit Function(SIF).To alleviate the broken or disembodied body parts,the proposed skeleton-aware structure prior makes the skeleton awareness into an implicit function,which consists of a bone-guided sampling strategy and a skeleton-relative encoding strategy.To deal with the missing details and depth ambiguity problems,the authors’body-guided pixel-aligned feature exploits the SMPL to enhance 2D normal and depth semantic features,and the proposed feature aggregation uses the extra geometry-aware prior to enabling a more plausible merging with less noisy geometry.Additionally,SIF is also adapted to the RGB-D input,and experimental results show that SIF outperforms the state-of-the-arts methods on challenging datasets from Twindom and Thuman3.0.

Simulation and Analysis of the Impacts of Anisotropic Ionospheric Scintallition on Geosynchronous Synthetic Aperture Radar

The impacts of ionospheric scintillation on geosynchronous synthetic aperture radar(GEO SAR)focusing is studied based on the multiple phase screen(MPS)theory.The power spectrum density of electron irregularities is first modified according to the ionospheric anisotropy.Then propagation wave equations in random medium are deduced in the case of oblique incidence in GEO SAR.The amplitude and phase errors induced by the random electron fluctuations are generated by the iterated MPS simulations and are superimposed into the GEO SAR signals.Through the following imaging and evaluation,the effects of the anisotropic ionospheric scintallition on GEO SAR are assessed.At last,the optimized integration time under different ionospheric scintillation conditions are recommended through Monte Carlo experiments.It is concluded that,greater ionospheric fluctuations and longer integration time will result in more severe deterioration,even no focus at all in the worst case.

SAR Tomography with Improved Non-Local Means Filtering Based on Adaptive Window

In order to mitigate speckle noise in synthetic aperture radar(SAR)images and enhance the accuracy of SAR tomography,non-local means(NL-means)filtering has been proven to be an effective method for improving the quality of SAR interferograms.Apart from considerations like noise type and the definition of similarity,the size and shape of filtering windows are critical factors influencing the efficacy of NL-means filtering,yet there has been limited research on this aspect.This paper introduces an enhanced NL-means filtering method based on adaptive windows,allowing for the automatic adjustment of filtering window size according to the amplitude information of the SAR interferogram.Simultaneously,a directional window is incorporated to align SAR interferograms,achieving the dual objective of preserving filtering standards and retaining detailed information.Experimental results on interferogram filtering and tomography,based on TerraSAR-X data,demonstrate that the proposed method effectively reduces phase noise while maintaining texture accuracy,thereby improving tomography quality.

泥沙动力学研究方法、技术、进展及沉积学意义

分析水沙运动规律是沉积动力学与泥沙动力学面对的共同课题。泥沙动力学研究为解决江河治理和水利工程建设中的泥沙问题提供了重要思路和手段。本文介绍了泥沙动力学的研究方法、试验技术和研究进展。从沉积动力学角度借鉴泥沙动力学领域的研究方法、试验技术和理论成果,从动态观点研究沉积动力过程中各种变量与条件之间的定量关系进而研究沉积物搬运和沉积的动力机制,建立和完善受水动力约束的沉积环境标志,将拓展沉积动力学研究的理论视野和思路,提高沉积环境研究的精度,推动沉积模式的建立和学科概念的形成,丰富沉积动力学的内涵。

Feasibility study of inclined geosynchronous SAR focusing using Beidou IGSO signals

Dear editor,Geosynchronous synthetic aperture radar(GEO SAR)[1,2]has an inclined geosynchronous orbit of around 36000 km,which leads to its short revisit time of around 24 hours and a wide coverage of up to approximately one third of the Earth surface.Its long integration time guarantees the fine resolution.Thus,GEO SAR owns the promising capability of providing images with the high resolution,

Horizontal gene transfer:Driving the evolution and adaptation of plants

About 1.5 billion years ago, the ancestor of photosynthetic eukaryotes evolved from primitive eukaryotes in the ocean by engulfing and integrating a cyanobacterium, resulting in the primary endosymbiosis event that gave rise to the plastids. These ancestral photosynthetic eukaryotes subsequently became separated into Viridiplantae (green plants), Rhodophyta (red algae), and Glaucophyta (glaucophytes)(Dagan et al., 2013;Ponce-Toledo et al., 2019).

偶氮苯作用的核酸开关在生物体内的可逆光调控

随着人们对偶氮苯分子光异构化机理和特性认识的深入,偶氮苯在核酸分子中的引入及其相关过程的可逆调控也受到了大量关注.偶氮苯分子作为光响应元件不仅用于合成智能材料或分子机器,而且正迅速渗透到化学生物学体系的分析和调控.考虑到核酸分子包含的信息多样性,小分子偶氮化合物引入到核酸分子中,可实现开关核酸的结构、RNA沉默、基因表达、适配体识别、酶活性等,也可用作核酸探针了解结构信息和分子之间的作用机理.因而,功能核酸的光可逆调控及其在生物领域中的应用,成为核酸化学领域的热门课题.本文主要阐述了偶氮苯与核酸结合的4种不同方式的设计原理及特点,通过筛选一些有代表性的例子,介绍偶氮苯类光敏分子的光异构化性能及其对核酸结构和功能的可逆调控在生物领域的研究进展,并列举出现阶段可能存在的问题,及对未来的发展前景进行展望.

Photo-controllable room-temperature phosphorescence of organic photochromic polymers based on hexaarylbiimidazole

Pure organic room-temperature phosphorescent(RTP)materials have been attracting widespread attention due to the unique properties and broad applications.However,RTP materials with the adjustable photochromic property are still a challenge.Based on this,two polymers containing hexaarylbiimidazole are strategically designed with dual emission of both fluorescence and phosphorescence.Furthermore,both polymers show sensitive photochromic responses from faint yellow to brown upon exposure to ultraviolet light.This study can enrich pure organic luminescent systems and provide new ideas for functional RTP materials.

Research progress on geosynchronous synthetic aperture radar

Based on its ability to obtain two-dimensional(2D)high-resolution images in all-time and all-weather conditions,spaceborne synthetic aperture radar(SAR)has become an important remote sensing technique and the study of such systems has entered a period of vigorous development.Advanced imaging modes such as radar interferometry,tomography,and multi-static imaging,have been demonstrated.However,current in-orbit spaceborne SARs,which all operate in low Earth orbits,have relatively long revisit times ranging from several days to dozens of days,restricting their temporal sampling rate.Geosynchronous SAR(GEO SAR)is an active research area because it provides significant new capability,especially its much-improved temporal sampling.This paper reviews the research progress of GEO SAR technologies in detail.Two typical orbit schemes are presented,followed by the corresponding key issues,including system design,echo focusing,main disturbance factors,repeat-track interferometry,etc,inherent to these schemes.Both analysis and solution research of the above key issues are described.GEO SAR concepts involving multiple platforms are described,including the GEO SAR constellation,GEO-LEO/airborne/unmanned aerial vehicle bistatic SAR,and formation flying GEO SAR(FF-GEO SAR).Due to the high potential of FF-GEO SAR for three-dimensional(3D)deformation retrieval and coherence-based SAR tomography(TomoSAR),we have recently carried out some research related to FF-GEO SAR.This research,which is also discussed in this paper,includes developing a formation design method and an improved TomoSAR processing algorithm.It is found that GEO SAR will continue to be an active topic in the aspect of data processing and multi-platform concept in the near future.

Polymer-Stretching Photoluminescent Regulation by Doping a Single Fluorescent Molecule

Photoluminescent materials play an essential part in the application of polymer systems.However,intrinsic polymer systems have rarely been intuitively interpreted based on photoluminescent regulation.A novel photoluminescent mechanism called vibration-induced emission(VIE)has recently garnered considerable attention due to its multicolor fluorescence from a single molecular entity.