低空间分辨率遥感数据亚像元级水华面积提取方法

在对太湖、巢湖等大型湖泊进行业务化蓝藻水华遥感监测工作中,常以250 m空间分辨率的MODIS数据为主,但其像元多为水体和水华的混合像元,若用常规方法进行水华面积提取,势必会严重影响水华监测的精度和实际应用效果。针对上述问题,基于混合像元分解原理,通过混合像元分解得到水华组分在混合像元中的丰度(百分比),实现亚像元级的水华面积提取。该方法可直接根据图像的DN值进行水华面积提取,无需对数据进行辐射校正和大气校正等预处理。与常规水华提取法相比,该方法的水华面积提取精度提高了近30%。     

Monitoring vegetation dynamics with medium resolution MODIS-EVI time series at sub-regional scale in southern Africa

Currently there is a lack of knowledge on spatio-temporal patterns of land surface dynamics at medium spatial scale in southern Africa, even though this information is essential for better understanding of ecosystem response to climatic variability and human-induced land transformations. In this study, we analysed vegetation dynamics across a large area in southern Africa using the 14-years (2000–2013) of medium spatial resolution (250 m) MODIS-EVI time-series data. Specifically, we investigated temporal changes in the time series of key phenometrics including overall greenness, peak and timing of annual greenness over the monitoring period and study region. In order to specifically capture spatial and per pixel vegetation changes over time, we calculated trends in these phenometrics using a robust trend analysis method. The results showed that interannual vegetation dynamics followed precipitation patterns with clearly differentiated seasonality. The earliest peak greenness during 2000–2013 occurred at the end of January in the year 2000 and the latest peak greenness was observed at the mid of March in 2012. Specifically spatial patterns of long-term vegetation trends allowed mapping areas of (i) decrease or increase in overall greenness, (ii) decrease or increase of peak greenness, and (iii) shifts in timing of occurrence of peak greenness over the 14-year monitoring period. The observed vegetation decline in the study area was mainly attributed to human-induced factors. The obtained information is useful to guide selection of field sites for detailed vegetation studies and land rehabilitation interventions and serve as an input for a range of land surface models.     

沿海地区DInSAR形变探测:精度与可应用性分析

卫星合成孔径雷达差分干涉在区域地表形变探测方面已表现出极好的应用前景。以我国沿海地区的2个典型实验区(即香港新机场和台湾西部地震区)作为研究对象,使用卫星ERS-1/2所获取的多幅SAR影像来探测香港填海地基沉降和台湾地震形变,与地面水准和GPS数据比较,评价干涉结果的实际观测精度,最后分析干涉雷达在沿海地区应用的局限性,并指出潜在的解决途径。     

利用DInSAR的东南极极记录和达尔克冰川冰流速提取与分析

目的 利用1996年 ERS-1/2tandem SAR数据,采用 DInSAR方法提取了极记录和达尔克冰川的冰流速,并利用冰流速转换模型和该地区的实测值进行了对比。结果表明,DInSAR结果很好地体现了整个区域的冰流速。对于内陆地区,DInSAR提取的监测点冰流速和实测值非常吻合;对于达尔克冰川的前缘,受时间差异和潮汐等因素的影响,DInSAR推求的冰流速结果略小于实测值。     

邵阳市区域尺度GPS高程异常分析

针对工程测量中GPS大地高代替水准正常高的问题,该文根据邵阳市实测GPS、水准数据,采用二次曲面拟合模型得到了该地区高程拟合参数。通过正常高与拟合高程进行比较,最大拟合残差为3.9cm,最小为0cm,高程异常模型拟合中误差为1.85cm,证明了该区域GPS高程拟合参数可以满足工程建设中大地高代替正常高的要求。根据GPS高程拟合参数得到的邵阳市辖区及周边地区高程异常曲面具有由西北至东南递减且变化梯度逐渐递减的特征,该区域最大高程异常15.65m,最小高程异常14.75m。     

中小比例尺下居民地综合及冲突处理

针对中小比例尺地形图上的散列式居民地较难进行自动化综合缩编的问题,该文对中小比例尺地形图上散列式居民地的综合过程及其冲突处理方法进行了研究。首先,通过探测邻近关系和分析空间特征,对居民地进行合并和选取,减少目标数,控制数量变化;进一步地通过模板匹配对单一的目标进行形状化简,控制表达变化。同时,针对其综合处理和符号化过程中可能出现的空间冲突,提出了基于Delaunay三角网模型的探测和处理方法。最后,给出了一套中小比例尺地形图上居民地要素的综合处理策略。该研究成果可规模化应用于中小比例尺综合缩编生产实践。     

Exploring improvement of impervious surface estimation at national scale through integration of nighttime light and Proba-V data

Directly mapping impervious surface area (ISA) at national and global scales using nighttime light data is a challenge due to the complexity of land surface components and the impacts of unbalanced economic conditions. Previous research mainly used the coarse spatial resolution Defense Meteorological Satellite Program’s Operational Linescan System (DMSP OLS) and Moderate Resolution Imaging Spectroradiometer (MODIS), normalized difference vegetation index (NDVI) data for ISA mapping; the improved spatial resolution and data quality in the Suomi National Polar-orbiting Partnership, Visible Infrared Imaging Radiometer Suite’s Day/Night Band (VIIRS DNB) and in Proba-V data provide a new opportunity to accurately map ISA distribution at the national scale, which has not been explored yet. This research aimed to develop a new index – modified impervious surface index (MISI) – based on VIIRS DNB and Proba-V data to improve ISA estimation and to compare the results with those from the combination of VIIRS DNB and MODIS NDVI data. Landsat data were used to develop ISA data for the typical sites for use as reference data. Regression analysis was used to establish the ISA estimation model in which the dependent variable was from the Landsat data and the independent variable was from the MISI, as well as the previously used Large-scale Impervious Surface Index (LISI). The results indicate that the major error is from the very small or very large proportion of ISA in a unit; improvement of spatial resolution through use of higher spatial resolution nighttime light data (e.g., VIIRS DNB) or NDVI (e.g., Proba-V NDVI) data is an effective approach to improve ISA estimation. Although different indices for the combination of nighttime light and NDVI data have been used, the MISI is especially valuable for reducing the estimation errors for the regions with a small or large ISA proportion.     

TerraSAR-X卫星影像中大比例尺测图应用研究

为了研究TerraSAR-X卫星的中大比例尺测图可行性,文章利用成都都江堰市3m、1m分辨率的TerraSAR-X影像、控制点及可见光卫星影像,对TerraSAR-X影像在多云多雨地区的中、大比例尺测图展开了研究和分析。实验表明利用TerraSAR-X影像能够符合中大比例尺基础地图测图或修测的精度要求,可用于困难地区1∶50 000~1∶10 000比例尺的基础测图生产和更新。     

Assessing ground cover at patch and hillslope scale in semi-arid woody vegetation and pasture using fused Quickbird data

The amount and distribution of vegetation and ground cover are important factors that influence resource transfer (e.g. runoff, sediment) in patterned semi-arid landscapes. Identifying and describing these features in detail is an essential part of measuring and understanding ecohydrological processes at hillslope scales that can then be applied at broader scales. The aim of this study was to develop a comprehensive methodology to map ground cover using high resolution Quickbird imagery in woody and non-woody (pasture) vegetation. The specific goals were to: (1) investigate the use of several techniques of image fusion, namely principal components analysis (PCA), Brovey transform, modified intensity-hue-saturation (MIHS) and wavelet transform to increase the spatial detail of multispectral Quickbird data; (2) evaluate the performance of the red and near-infra-red bands (NIR), the difference vegetation index (DVI), and the normalised difference vegetation index (NDVI) in estimating ground cover, and (3) map and assess spatial and temporal changes in ground cover at hillslope scale using the most appropriate method or combination of methods. Estimates of ground cover from the imagery were compared with a subset of observed ground cover estimates to determine map accuracy. The MIHS algorithm produced images that best preserved spectral and spatial integrity, while the red band fused with the panchromatic band produced the most accurate ground cover maps. The patch size of the ground cover beneath canopies was similar to canopy size, and percent ground cover (mainly litter) increased with canopy size. Ground cover was mapped with relative accuracies of 84% in the woody vegetation and 86% in the pasture. From 2008 to 2009, ground cover increased from 55% to 65% in the woody vegetation and from 40% to 45% in the pasture. These ground cover maps can be used to explore the spatial ecohydrological interactions between areas of different ground cover at hillslope scale with application to management at broader scales.     

DInSAR技术对不同方位形变的敏感性研究

以DEM数据为假想的地面目标,只考虑距离对相位的影响,模拟竖直向、距离向和方位向形变的干涉纹图,从而研究DInSAR技术对空间不同方位形变的敏感性。在所有模拟参数和形变位移大小都相同的情况下,三个不同方位形变所产生的相位从0到2π变化的完整干涉环的数目是各不相同的,揭示DInSAR技术对不同方位地表形变的敏感性存在差异,且敏感性由大到小依次为:竖直向、距离向和方位向。     

Evaluation of simulated IRS-1C WiFS data for concurrent monitoring of command areas at disaggregated level

Data of Wide Field Sensor (WiFS) to go onboard Indian Remote Sensing Satellite, IRS-1C, in December 1995, is simulated mainly from IRS IB LISS I data of Bhadra command area, Karnataka (India) during 1993–94 summer season, to evaluate its capability in concurrent monitoring of irrigated crops at disaggregated level Crop area, crop-growth profiles of homogeneous crops like paddy, as obtained from both simulated WiFS data and LISS I data are very close for almost all the distributary commands of Bhadra project Though non-paddy-crop groups could also be classified satisfactorily, the Workability with small-extent-individual crops like groundnut, garden and sugarcane is found to be less due to coarse resolution of WiFS data and hence the individual crops could not be separated out. This study proves the potential of WiFS in concurrent monitoring of fairly-large-extent irrigated crops at distributary level. The basic feasibility of WiFS had been established in an earlier work at broad level and this study demonstrates the feasibility of information extraction at distributary command level from WiFS data.     

Using Sentinel-1A DInSAR interferometry and Landsat 8 data for monitoring water level changes in two lakes in Crete,Greece

Differential Interferometric Synthetic Aperture Radar (DInSAR) methodology has been successfully employed to detect water level changes and produce corresponding water level variation maps. In this study, Agia and Kournas lakes, located in Western Crete, Greece, were used as pilot areas to monitor water level change with means of SAR interferometry and auxiliary Earth Observation (EO) data. The water level variation was monitored for the period 2015–2016, using Sentinel-1A imageries and corresponding stage water level data. Landsat 8 data were additionally used to study vegetation regime and surface water extent and how these parameters affect interferograms performance. The results highlighted the fact that the combination of SAR backscattering intensity and unwrapped phase can provide additional insight into hydrological studies. The overall analysis of both interferometric characteristics and backscattering mechanism denoted their potential in enhancing the reliability of the water-level retrieval scheme and optimizing the capture of hydrological patterns spatial distribution.     

POS数据用于双介质水下地形摄影测量的研究

本文以双介质摄影测量的基本公式为基础、海水为介质,利用POS数据进行双介质水下地形摄影测量研究。文中介绍了机载POS系统及双介质摄影测量基本公式,论述了海水折射率和由折射引起的高程改正系数的求解,提出了双介质相对定向和直接定向的计算方法,最后用模拟数据进行验证。     

Mapping spatio-temporal flood inundation dynamics at large river basin scale using time-series flow data and MODIS imagery

Flood inundation is crucial to the survival and prosperity of flora and fauna communities in floodplain and wetland ecosystems. This study tried to map flood inundation characteristics in the Murray-Darling Basin, Australia, utilizing hydrological and remotely sensed data. It integrated river flow time series and Moderate Resolution Imaging Spectroradiometer (MODIS) images to map inundation dynamics over the study area on both temporal and spatial dimensions. Flow data were analyzed to derive flow peaks and Annual Exceedance Probabilities (AEPs) using the annual flood series method. The peaks were linked with MODIS images for inundation detection. Ten annual maximum inundation maps were generated for water years 2001–2010, which were then overlaid to derive an inundation frequency map. AEPs were also combined with the annual maximum inundation maps to derive an inundation probability map. The resultant maps revealed spatial and temporal patterns of flood inundation in the basin, which will benefit ecological and environmental studies when considering response of floodplain and wetland ecosystems to flood inundation.     

云南及周边地区GNSS数据处理方法优化

采用麻省理工学院开发的GAMIT／GLOBK软件,将2015年-2016年全球347个IGS站观测数据分七个子网解算,得到一个固定的参考框架来解算云南及周边地区的35个全球卫星导航系统（GNSS）基准站的坐标,测站坐标均方根误差水平方向在0.7 mm以内,垂直方向在0.3 mm以内,水平方向的坐标重复性精度在5 mm以内,垂向坐标的重复性精度大多数在2.5 cm以内;与在ITRF2014下解算的测站坐标、基线长度、水平速度场结果对比表明:测站坐标存在系统误差,水平方向上的差异在8.5 mm以内,垂直方向上在3 cm以内;基线长度差异在2 mm以内,水平速度场在数值上存在毫米级的差异,方向上基本一致．      

Multiple-entity based classification of airborne laser scanning data in urban areas

There are two main challenges when it comes to classifying airborne laser scanning (ALS) data. The first challenge is to find suitable attributes to distinguish classes of interest. The second is to define proper entities to calculate the attributes. In most cases, efforts are made to find suitable attributes and less attention is paid to defining an entity. It is our hypothesis that, with the same defined attributes and classifier, accuracy will improve if multiple entities are used for classification. To verify this hypothesis, we propose a multiple-entity based classification method to classify seven classes: ground, water, vegetation, roof, wall, roof element, and undefined object. We also compared the performance of the multiple-entity based method to the single-entity based method.Features have been extracted, in most previous work, from a single entity in ALS data; either from a point or from grouped points. In our method, we extract features from three different entities: points, planar segments, and segments derived by mean shift. Features extracted from these entities are inputted into a four-step classification strategy. After ALS data are filtered into ground and non-ground points. Features generalised from planar segments are used to classify points into the following: water, ground, roof, vegetation, and undefined objects. This is followed by point-wise identification of the walls and roof elements using the contextual information of a building. During the contextual reasoning, the portion of the vegetation extending above the roofs is classified as a roof element. This portion of points is eventually re-segmented by the mean shift method and then reclassified.Five supervised classifiers are applied to classify the features extracted from planar segments and mean shift segments. The experiments demonstrate that a multiple-entity strategy achieves slightly higher overall accuracy and achieves much higher accuracy for vegetation, in comparison to the single-entity strategy (using only point features and planar segment features). Although the multiple-entity method obtains nearly the same overall accuracy as the planar-segment method, the accuracy of vegetation improves by 3.3% with the rule-based classifier. The multiple-entity method obtains much higher overall accuracy and higher accuracy in vegetation in comparison to using only the point-wise classification method for all five classifiers.Meanwhile, we compared the performances of five classifiers. The rule-based method provides the highest overall accuracy at 97.0%. The rule-based method provides over 99.0% accuracy for the ground and roof classes, and a minimum accuracy of 90.0% for the water, vegetation, wall and undefined object classes. Notably, the accuracy of the roof element class is only 70% with the rule-based method, or even lower with other classifiers. Most roof elements have been assigned to the roof class, as shown in the confusion matrix. These erroneous assignments are not fatal errors because both a roof and a roof element are part of a building. In addition, a new feature which indicates the average point space within the planar segment is generalised to distinguish vegetation from other classes. Its performance is compared to the percentage of points with multiple pulse count in planar segments. Using the feature computed with only average point space, the detection rate of vegetation in a rule-based classifier is 85.5%, which is 6% lower than that with pulse count information.     

利用高分辨率立体测绘影像进行中小比例尺地貌要素更新

利用高分辨率立体测绘卫星遥感影像进行地貌更新,因其覆盖面积大、更新周期短等优势,在中小比例尺地貌要素更新中具有极大的应用潜力.本文分别利用WorldView-2和资源三号卫星影像,探索基于高分辨率立体测绘卫星影像的中小比例尺地貌更新技术方案流程,并在不同的试验区开展试验验证.试验结果表明:本文方法能够满足1:50000...     

ADS40相机用于海岛(礁)大比例尺成图的试验

本文利用ADS40相机进行航空摄影,对海岛(礁)区域1∶2000比例尺成图精度进行了分析,比较了差分GPS与精密单点定位技术应用于ADS40航摄的精度。试验结果表明,ADS40相机可满足海岛(礁)大比例尺成图航摄的精度要求,缩短成图周期,精密单点定位技术的平面精度与差分GPS方法相当,高程精度较差,从工程角度考虑,海岛(礁)大比例尺成图时架设地面GPS基站比较稳妥。     

面向对象的成都平原多源遥感影像分割尺度研究

要对高分辨率遥感影像进行分类,采用面向对象的遥感影像分析技术比传统的面向像元的遥感影像分析技术优越。要使用面向对象的遥感影像分析技术,关键的第一步是要对遥感影像进行分割,以便得到一系列与地物有密切联系的影像对象。分割的准确性与分割的尺度选择有关。本文针对成都平原高分辨率卫星影像分割尺度选择进行试验和研究,采用不同尺度对试验区不同分辨率遥感影像进行影像分割,并比较分割结果,得出成都平原高分辨率遥感影像数据分割最佳尺度与影像对象亮度均值标准差最大值所对应的分割尺度一致;并且遥感影像空间分辨率越高,最佳分割尺度越大,反之亦然。     

Radargrammetric registration of airborne multi-aspect SAR data of urban areas

In this paper, the registration of decimeter-resolution airborne multi-aspect SAR (MASAR) data of inner city areas by application of the radargrammetric range-Doppler equations is investigated. The geometrical model is adapted to linear flight trajectories and zero-Doppler processed SAR data, whereas the observed trajectory parameters are adjusted using a strict Gauss–Helmert model and known ground control points. The significance of the estimated corrections is examined and the most suitable set of free parameters is determined. Finally, the methodology is applied to real test data of an airborne campaign over the city of Munich, Germany, and the feasability of the proposed radargrammetric registration method is shown.