Optimizing and comparing gap-filling techniques using simulated NDVI time series from remotely sensed global data     

《International Journal of Applied Earth Observation and Geoinformation》2019

NDVI (Normalized Difference Vegetation Index) time series usually suffer from remaining cloud presence, even after data pre-processing. To address this issue, numerous gap-filling (or reconstruction) techniques have been developed in the literature, although their comparison has mainly been local to regional, with only two global studies to date, and has led to sometimes contradictory results. This study builds on these different comparisons, by testing different parameterizations for five NDVI temporal profile reconstruction techniques, namely HANTS (Harmonic Analysis of Time Series), IDR (iterative Interpolation for Data Reconstruction), Savitzky-Golay, Asymmetric Gaussian and Double Logistic, and then comparing them as generally parameterized, and then with the best of the tested parameterizations. These comparisons show that the HANTS reconstruction technique provides lower errors in cloud prone areas, while the IDR method works best with shorter cloud covers. However, the remaining errors in cloud prone areas are still high, and there is room for new reconstruction techniques. Although these results are only applicable to the range of the tested parameterizations, these latter have been chosen within widely used configurations, and should provide interested users with a better understanding of the different methods and the best parameterization for their needs, as well as an estimate of the expected error in the reconstruction of NDVI time series.  相似文献   

中美半干旱区长期地表通量序列的构建及检验     

李杉  符淙斌 《气象科学》2015,35(1):1-8

基于中美半干旱区8个野外试验站点2003—2008年的观测数据,选择最小二乘法线性拟合、多项式拟合、以及双重回归拟合等方法,对NCEP再分析数据集的地表通量数据进行了系统的检验和订正。结果表明,对于日平均值,拟合订正效果相对较差,仅部分站点的土壤含水量以及地表感热和潜热通量可以使用曲线拟合的方法得以改进。对月平均值,3种方案都有不同程度的订正改进效果,订正的序列还原了数据的季节变化趋势。在此基础上,综合线性回归和曲线拟合两种方法的优势,最大程度地还原资料的线性趋势,并减小因截断误差造成的信息损失,构建了中美半干旱区长期的地表通量数据序列。所构建的半干旱区长期地表通量序列也为深入认识中美半干旱区陆气相互作用的基本特征以及模式结果验证,提供了宝贵的基础数据。  相似文献   

考虑实际投影成像平面位置的扇束滤波反投影(FFBP)算法     

裴晓东  张全红 《CT理论与应用研究》2005,14(3):18-23

扇束滤波反投影(Fan-beam Filtered Back Projection- FFBP)算法理论公式中,投影成像平面位于旋转中心;而实际CT扫描系统中,投影成像平面与旋转中心都存在一定距离.考虑到实际投影成像平面位置,本文推导了它的FFBP算法(即IFFBP-Improved Fan-beam Filtered Back Projection算法),比较了此两种情况下(即忽略成像平面与旋转中心距离)FFBP、IFFBP算法重建质量.计算机模拟和实验结果证明了IFFBP算法的正确性.  相似文献   

螺旋CT三维重建在脑血管疾病诊断中的应用     

朱清肖  佟静  郭欣华  李雪 《CT理论与应用研究》2005,14(4):21-23

目的评价螺旋CT三维重建在脑血管疾病诊断中的作用.方法对51例临床脑血管病患者行脑增强CT扫描后三维重建图像进行分析,所有检查采用GE Hispeed NX/I所排CT扫描机,将图像传输至工作站进行三维重建; 图像经2位以上放射科诊断医师阅片分析.结果51例临床脑血管病患者中:脑血管正常14例;单纯变异7例;其他脑血管均有不同程度变窄(30例),其中混合型变窄12例(两支以上含两支脑血管变窄),脑血管变异合并脑血管变窄5例,脑血管单支变窄13例.结论螺旋CT脑增强扫描三维重建是诊断脑血管病变的比较理想且有效的检查方法.  相似文献   

QUATERNARY GEOLOGY & GEOMORPHOLOGY     

《Abstract of Chinese Geological Literature》2014,(4)

正20142336Chen Bishan(Department of Earth Sciences,Sun Yat-Sen University,Guangzhou 510275,China);Zheng Zhuo Sedimentation Rate and Environmental Reconstruction Based on Grain-Size and Pollen-Spores Analysis from Huangdong Reservoir,Huizhou City  相似文献   

Seismic stratigraphy and structural analysis of the northern East China Sea Shelf Basin interpreted from multi-channel seismic reflection data and cross-section restoration   总被引：1，自引：0，他引：1  

Deniz Cukur  Senay HorozalDae C. Kim  Hyun C. Han 《Marine and Petroleum Geology》2011,28(5):1003-1022

Analysis of multi-channel seismic data from the northern East China Sea Shelf Basin (ECSSB) reveals three sub-basins (Socotra, Domi, and Jeju basins), separated by structural highs (Hupijiao Rise) and faulted basement blocks. These sub-basins show a typical rift-basin development: faulted basement and syn-rift and post-rift sedimentation separated by unconformities. Four regional unconformities, including the top of acoustic basement, have been identified and mapped from multi-channel seismic data. Faults in the acoustic basement are generally trending NE, parallel to the regional structural trend of the area. The depths of the acoustic basement range from less than 1000 m in the northwestern part of the Domi Basin to more than 4500 m in the Socotra Basin and 5500 m in the Jeju Basin. The total sediment thicknesses range from less than 500 m to about 1500 m in the northwest where the acoustic basement is shallow and reach about more than 5500 m in the south.Interpretation of seismic reflection data and reconstruction of three depth-converted seismic profiles reveal that the northern ECSSB experienced two phases of rifting, followed by regional subsidence. The initial rifting in the Late Cretaceous was driven by the NW-SE crustal stretching of the Eurasian Plate, caused by the subduction of the Pacific Plate beneath the Eurasian Plate. Extension was the greatest during the early phase of basin formation; estimated rates of extension during the initial rifting are 2%, 6.5%, and 3.5% in the Domi, Jeju, and Socotra basins, respectively. A regional uplift terminated the rifting in the Late Eocene-Early Oligocene. Rifting and extension, although mild, resumed in the Early Oligocene; while fluvio-lacustrine deposition continued to prevail. The estimated rates of extension during the second phase of rifting are 0.7%, 0.8%, and 0.5% in the Domi, Jeju, and Socotra basins, respectively. A second phase of uplift in the Early Miocene terminated the rifting, marking the transition to the post-rift phase of regional subsidence. Regional subsidence dominated the study area between the Early Miocene and the Late Miocene. An inversion in the Late Miocene interrupted the post-rift subsidence, resulting in an extensive thrust-fold belt in the eastern part of the area. Uplift and subsequent erosion were followed by regional subsidence.  相似文献   

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金双根  朱文耀 《大地测量与地球动力学》2007,27(5):49-53

??GPS???????????????????????????????????????????GPS?????????????????????????????????????????????????????????????????????????GPS??????????????????????????????????????????档?????????ο????(IRI2001)????????????????????GPS????????????????????????￡?????????????????????????????????????????GPS???????????????????????????????о?????????????ü????  相似文献   

Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen     

Stefan Klotz  Joel Guiot  Volker Mosbrugger   《Global and Planetary Change》2003,36(4):277-294

Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the Pinus–Quercetum mixtum–Corylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian Pinus–Picea–Abies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.  相似文献   

Looking for the future in the rubble of Palmyra: Destruction,reconstruction and identity     

《Geoforum》2016

The destruction of the ancient ruins of Palmyra by the terrorist group Islamic State (IS) in September 2015 shocked the world, with some going so far as to decry it as a war crime. This paper explores why the razing of Palmyra resonated so strongly with the international community, demonstrating how the relationship between urban space and collective memory made this event so powerful. Looking to the future, it suggests that the toughest test for Palmyra is yet to come. The challenge of post-conflict reconstruction in sites such as this is inextricably bound up with questions of identity, memory and power, all of which will need to be worked out when the war in Syria eventually comes to an end.  相似文献   

图象重建中的基本定理及其数值计算     

王卫东  包尚联 《CT理论与应用研究》2001,10(3):6-9

本文系统地给出了基于投影的图像重建的6个基本定理及其数值计算方法，研究了变焦束投影的扫描方式主要用于单光子断层扫描（SPECT）中以提高信噪比和分辨力。  相似文献