An improved building detection approach using L-band POLSAR two-dimensional time-frequency decomposition over oriented built-up areas     

Lei Deng  Ying He  Zhi-hui Mao  Jie Yu 《地理信息系统科学与遥感》2019,56(1):1-21

The objective of this study is to efficiently extract detailed information about various man-made targets in oriented built-up areas using polarimetric synthetic aperture radar (POLSAR) images. This paper develops an improved approach for building detection by utilizing Two-Dimensional Time-Frequency (2-D TF) decomposition. This method performs outstandingly in distinguishing between man-made and natural targets based on the isotropic behaviors, frequency-sensitive responses, and scattering mechanisms of objects. The proposed method can preserve the spatial resolution and exploit the advantages of TF decomposition; specifically, the exact outlines of buildings can be effectively located, and more types of features (e.g., flat roofs, roads, and walls that are oblique to the radar illumination) can be distinguished from forests in complex built-up areas by 2-D TF decomposition. The coarser-resolution subaperture images that are produced in the azimuth direction, which correspond to different looking angles, are beneficial for detecting man-made structures with main scattering centers oriented at oblique angles with respect to the radar illumination. In the range direction, the obtained subaperture images, which correspond to various observation frequencies, can be helpful in distinguishing flat roofs and roads from forests. This method was successfully implemented to analyze both NASA/JPL L-band AIRSAR and L-band EMISAR data sets. The building detection results of the proposed method exhibit a significant improvement over those of other methods and reach an overall accuracy over 80%, with approximately 20% higher than the accuracies of K-means clustering and the entropy/alpha-Wishart classifier and approximately 10% higher than the accuracy of the support vector machine method. Moreover, building details can be precisely detected, obliquely oriented buildings can be identified, and the distinction between buildings and forests is significantly improved, as both visually and statistically indicated. This method is highly adaptable and has substantial application value.  相似文献   

Simulation of landscape spatial layout evolution in rural-urban fringe areas: a case study of Ganjingzi District   总被引：2，自引：0，他引：2  

Jun Yang  Andong Guo  Yonghua Li  Yuqing Zhang  Xueming Li 《地理信息系统科学与遥感》2019,56(3):388-405

In recent years, the rapid expansion of urban spaces has accelerated the mutual evolution of landscape types. Analyzing and simulating spatio-temporal dynamic features of urban landscape can help to reveal its driving mechanisms and facilitate reasonable planning of urban land resources. The purpose of this study was to design a hybrid cellular automata model to simulate dynamic change in urban landscapes. The model consists of four parts: a geospatial partition, a Markov chain (MC), a multi-layer perceptron artificial neural network (MLP-ANN), and cellular automata (CA). This study employed multivariate land use data for the period 2000–2015 to conduct spatial clustering for the Ganjingzi District and to simulate landscape status evolution via a divisional composite cellular automaton model. During the period of 2000–2015, construction land and forest land areas in Ganjingzi District increased by 19.43% and 15.19%, respectively, whereas farmland, garden lands, and other land areas decreased by 43.42%, 52.14%, and 75.97%, respectively. Land use conversion potentials in different sub-regions show different characteristics in space. The overall land-change prediction accuracy for the subarea-composite model is 3% higher than that of the non-partitioned model, and misses are reduced by 3.1%. Therefore, by integrating geospatial zoning and the MLP-ANN hybrid method, the land type conversion rules of different zonings can be obtained, allowing for more effective simulations of future urban land use change. The hybrid cellular automata model developed here will provide a reference for urban planning and policy formulation.  相似文献   

灰关联GM(1,N)模型在建筑物沉降分析中的应用     

成枢  周龙飞  郭祥琳 《测绘与空间地理信息》2019,42(5):10-13

针对建筑物沉降变形中各监测点相互关联、相互影响的情形,可将灰色系统理论中的GM(1,N)模型引入到建筑物沉降分析中。本文利用灰度关联方法确定相关因子的关联度,建立GM(1,N)模型,并与回归分析、GM(1,1)模型比较。通过工程实例,得出灰关联GM(1,N)模型预测精度明显高于另外两种模型,验证了该模型在进行建筑物沉降分析预测中应用的可行性。  相似文献   

IU Cancri:a solar-type contact binary with mass transfer     

Hui-Yu Yuan  Hai-Feng Dai  Yuan-Gui Yang 《天文和天体物理学研究(英文版)》2019,(6):89-96

We present new CCD photometry of the solar-type contact binary IU Cnc, which was observed from November 2017 to March 2018 with three small telescopes in China. BV light curves imply that IU Cnc is a W-type contact binary with total eclipses. The photometric solution indicates that the mass ratio and fill-out factor are q = 4.104 ± 0.004 and f = 30.2%± 0.3%, respectively. From all available light minimum times, the orbital period may increase at a rate of dP/dt =+6.93(4)× 10^-7 d yr^-1, which may result from mass transfer from the secondary component to the primary one. With mass transferring,IU Cnc may evolve from a contact configuration into a semi-detached configuration.  相似文献   

Search for H I emission from superdisk candidates associated with radio galaxies     

Abhijeet Anand  Nirupam Roy  Gopal-Krishna 《天文和天体物理学研究(英文版)》2019,(6):71-78

Giant gaseous layers(termed “superdisks”) have been hypothesized in the past to account for the strip-like radio emission gap(or straight-edged central brightness depression) observed between twin radio lobes, in over a dozen relatively nearby powerful Fanaroff-Riley Class II radio galaxies. They could also provide a plausible alternative explanation for a range of observations. Although a number of explanations have been proposed for the origin of the superdisks, little is known about their material content. Some X-ray observations of superdisk candidates indicate the presence of hot gas, but a cool dusty medium also seems to be common. If they are entirely or partly composed of neutral gas, then it may be directly detectable and we report here a first attempt to detect/image any neutral hydrogen gas present in the superdisks that are inferred to be present in four nearby radio galaxies. We have not found a positive H I signal in any of the four sources, resulting in tight upper limits on the H I number density in the postulated superdisks,estimated directly from the central rms noise values of the final radio continuum subtracted image. The estimated ranges of the upper limit on neutral hydrogen number density and column density are 10^-4-10^-3 atoms per cm3 and 10^19-10^20 atoms per cm^2, respectively. No positive H I signal is detected even after combining all the four available H I images(with inverse variance weighting). This clearly rules out an H I dominated superdisk as a viable model to explain these structures, however, the possibility of a superdisk being composed of warm/hot gas still remains open.  相似文献   

New photometric investigation of the low-mass-ratio contact binary star V1853 Orionis     

Jia-Jia He  Sheng-Bang Qian  Boonrucksar Soonthornthum  Amornrat Aungwerojwit  Niang-Ping Liu  Thawicharat Sarotsakulchai 《天文和天体物理学研究(英文版)》2019,(4):77-88

Four-color charge-coupled device(CCD) light curves in the B, V, Rc and I c bands of the totaleclipsing binary system V1853 Orionis(V1853 Ori) are presented. By comparing our light curves with those published by previous investigators, it is determined that the O'Connell effect on the light curves has disappeared. By analyzing those multi-color light curves with the Wilson-Devinney code(W-D code),it is discovered that V1853 Ori is an A-type intermediate-contact binary with a degree of contact factor of f = 33.3%(3.7%) and a mass ratio of q = 0.1896(0.0013). Combining our 10 newly determined times of light minima together with others published in the literature, the period changes of the system are investigated. We found that the general trend of the observed minus calculated(O-C) curve shows a downward parabolic variation that corresponds to a long-term decrease in the orbital period with a rate of d P/dt =-1.96(0.46)×10^-7 d yr^-1. The long-term period decrease could be explained by mass transfer from the more-massive component to the less-massive one. By combining our photometric solutions with data from Gaia DR_2, absolute parameters were derived as M_1 = 1.20 M⊙, M_2 = 0.23 M⊙, R_1 = 1.36 R⊙and R_2 = 0.66 R⊙. The long-term period decrease and intermediate-contact configuration suggest that V1853 Ori will evolve into a high fill-out overcontact binary.  相似文献   

ALMA observations of the circumstellar envelope around EP Aqr     

Pham Thi Tuyet Nhung  Do Thi Hoai  Pham Tuan-Anh  Thibaut Le Bertre  Pierre Darriulat  Pham Ngoc Diep  Nguyen Thi Phuong  Nguyen Thi Thao  Jan Martin Winters 《天文和天体物理学研究(英文版)》2019,(3):97-110

Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained.  相似文献   

CCD astrometric observations of 2017 VR12, Camillo and Midas     

Zhen-Jun Zhang  Yi-Gong Zhang  Xiang-Ming Chen  Jian-Cheng Wang  Jie Su 《天文和天体物理学研究(英文版)》2019,(5):91-100

We have observed three near-Earth objects(NEOs), 2017 VR12, Camillo and Midas, during 2018.The observations were made with the 1-m telescope, operated by Yunnan Observatories, over two nights.Their precise astrometric positions are derived from 989 CCD observations. The theoretical positions of asteroids are retrieved from the Jet Propulsion Laboratory(JPL) Horizons System and Institut de M′ecanique C′eleste et de Calcul des ′Eph′em′erides(IMCCE). The positions of three asteroids are measured with respect to stars in the Gaia DR2 star catalog. For 2017 VR12, the means(O-C) of right ascension and declination are -0.090′′and-0.623′′respectively based on the published JPL ephemeris, but the corresponding means(O-C) are 3.122′′and-0.636′′based on the published IMCCE ephemeris. The great difference in declination could be explained by several factors.(1) The degraded CCD images caused by the fast apparent motion of the objects lead to a reduction in positioning accuracy.(2) The poor timing system may introduce systematic errors, especially in the high speed direction.(3) The asteroid may be perturbed by Earth when it approaches the Earth too closely. These astrometric results demonstrate that the centroid centering method can reduce the dispersion of non-Gaussian images as compared with the PSF modeling method.For Camillo and Midas, the astrometric results are consistent based on the two ephemerides. Implementing a high-precision timing system, and analyzing some astronomical effects and geometric distortions in CCD images should be carefully considered in future works.  相似文献   

Transition-region explosive events produced by plasmoid instability     

Dong Li 《天文和天体物理学研究(英文版)》2019,(5):43-52

Magnetic reconnection is thought to be a key process in most solar eruptions. Thanks to highresolution observations and simulations, the studied scale of the reconnection process has become smaller and smaller. Spectroscopic observations show that the reconnection site can be very small, which always exhibits a bright core and two extended wings with fast speeds, i.e., transition-region explosive events.In this paper, using the PLUTO code, we perform a 2-D magnetohydrodynamic simulation to investigate small-scale reconnection in double current sheets. Based on our simulation results, such as the line-of-sight velocity, number density and plasma temperature, we can synthesize the line profile of SiIV 1402.77? which is a well known emission line used to study transition-region explosive events on the Sun. The synthetic line profile of Si IV 1402.77? is complex with a bright core and two broad wings which can extend to nearly 200 km s^-1. Our simulation results suggest that the transition-region explosive events on the Sun are produced by plasmoid instability during small-scale magnetic reconnection.  相似文献   

Numerical simulation and preliminary analysis of typhoon waves during three typhoons in the Yellow Sea and East China Sea     

WANG Ning  HOU Yijun  LI Shuiqing  LI Rui 《海洋湖沼学报（英文）》2019,(6):1805-1816

In this study,typhoon waves generated during three typhoons(Damrey(1210),Fung-wong(1416),and Chan-hom(1509))in the Yellow Sea and East China Sea were simulated in a simulating waves nearshore(SWAN)model,and the wind forcing was constructed by combining reanalyzed wind data with a Holland typhoon wind model.Various parameters,such as the Holland fitting parameter(B)and the maximum wind radius?,were investigated in sensitivity experiments in the Holland model that affect the wind field construction.Six different formulations were considered and the parameters determined by comparing the simulated wind results with in-situ wind measurements.The key factors affecting wave growth and dissipation processes from deep to shallow waters were studied,including wind input,whitecapping,and bottom friction.Comparison with in-situ wave measurements suggested that the KOMEN scheme(wind input exponential growth and whitecapping energy dissipation)and the JONSWAP scheme(dissipation of bottom friction)resulted in good reproduction of the significant wave height of typhoon waves.A preliminary analysis of the wave characteristics in terms of wind-sea and swell wave revealed that swell waves dominated with the distance of R to the eye of the typhoon,while wind-sea prevailed in the outer region up to six to eight times the R values despite a clear misalignment between wind and waves.The results support the hypothesis that nonlinear wave-wave interactions may play a key role in the formation of wave characteristics.  相似文献