引入PLSA模型的光学遥感图像舰船检测

提出一种基于概率潜在语义分析(Probabilistic Latent Semantic Analysis,PLSA)的检测算法,首先通过PLSA将目标表述为潜在成分的概率组合,然后利用统计模式识别方法对获取的潜在成分概率进行判别,从而完成最终的检测。其中,生成的潜在成分反映了目标与特征之间相互出现的频率关系,并以潜在成分在目标中概率差异的形式对上述不对应现象给出了直观描述。实验结果表明,所提出的算法对多种复杂情况下的光学图像舰船检测具有很好的准确性和鲁棒性。     

Generalized diffraction‐stack migration and filtering of coherent noise

We reformulate the equation of reverse‐time migration so that it can be interpreted as summing data along a series of hyperbola‐like curves, each one representing a different type of event such as a reflection or multiple. This is a generalization of the familiar diffraction‐stack migration algorithm where the migration image at a point is computed by the sum of trace amplitudes along an appropriate hyperbola‐like curve. Instead of summing along the curve associated with the primary reflection, the sum is over all scattering events and so this method is named generalized diffraction‐stack migration. This formulation leads to filters that can be applied to the generalized diffraction‐stack migration operator to mitigate coherent migration artefacts due to, e.g., crosstalk and aliasing. Results with both synthetic and field data show that generalized diffraction‐stack migration images have fewer artefacts than those computed by the standard reverse‐time migration algorithm. The main drawback is that generalized diffraction‐stack migration is much more memory intensive and I/O limited than the standard reverse‐time migration method.     

Uncertainty assessment of ephemeral gully identification,characteristics and topographic threshold when using aerial photographs in agricultural settings

Manual digitizing on aerial photographs is still commonly used for characterizing gully erosion over large areas. Even when automated detection procedures are implemented, manual digitizing is frequently being resorted to in order to constitute reference datasets used for training and validation. In both cases, manual digitizing entails some subjective decisions on behalf of the operator, which introduces uncertainty into the resulting datasets. To assess the magnitude of this uncertainty, 11 experienced operators were asked to digitize and classify ephemeral gullies (EGs) on cropland following a standardized methodology. The resulting 11 datasets were compared in terms of number, type and location of EGs. Furthermore, for EGs located on a well‐defined runoff flow concentration axis, the slope versus contributing area topographic thresholds required for initiating gully channels were assessed using four thresholding methods, and compared across the 11 datasets. The operators identified 259 different EGs. However, the number (52–139) and sum total length (8.9–23.7 km) of EGs varied widely across operators. Only 34% of the EGs were digitized by more than half of the operators, and 7% were identified by all. Identification of EGs located on a well‐defined flow concentration axis proved least subjective. The longer the EG and the more fields the EG crossed, the larger the number of operators that were able to identify it. EGs were also most easily identified when located in sugar beet fields as compared to other crops. EG classification and topographic threshold lines were also found to be strongly operator‐dependent. Quantile regression appeared to be one of the most robust thresholding methods. Operator subjectivity when digitizing EGs on orthophotographs introduces uncertainty that should be taken into account in future remote sensing‐based studies of EG erosion whenever they rely, in part or in full, on manual photograph interpretation. Copyright © 2014 John Wiley & Sons, Ltd.     

中国3个典型城市气溶胶光学厚度地基观测及其MODIS气溶胶产品精度分析

利用中国太阳分光观测网的观测资料结合MODIS(中分辨率成像光谱仪)的气溶胶产品分析了北京、兰州、上海3个典型区域城市的气溶胶光学特性。结果表明:北京AOD(气溶胶光学厚度)年平均为0.41±0.35,春夏高,秋冬低,Angstrm波长指数α年平均为1.40±0.85表现为细模态粒子,MODIS的光学厚度为0.52±0.39与地面观测相关系数为0.91,存在系统性高估;兰州AOD年平均为0.55±0.21,夏季最低,秋冬较高,α年平均为0.95±0.20表现为粗模态粒子,MODIS光学厚度为0.43±0.21与地面观测相关系数仅为0.07,存在系统性低估;上海AOD年平均为0.55±0.21,无明显季节变化,α平均为1.03±0.25,MODIS光学厚度为0.74±0.30与地面观测相关系数为0.75,存在系统性高估。城市地理位置和复杂地表等原因造成反照率的不确定,MODIS气溶胶产品在这3个城市的反演效果仍有很大提升空间。     

Evapotranspiration Estimation Based on MODIS Products and Surface Energy Balance Algorithms for Land （SEBAL） Model in Sanjiang Plain, Northeast China

In this study,the Surface Energy Balance Algorithms for Land(SEBAL) model and Moderate Resolution Imaging Spectroradiometer(MODIS) products from Terra satellite were combined with meteorological data to estimate evapotranspiration(ET) over the Sanjiang Plain,Northeast China.Land cover/land use was classified by using a recursive partitioning and regression tree with MODIS Normalized Difference Vegetation Index(NDVI) time series data,which were reconstructed based on the Savitzky-Golay filtering approach.The MODIS product Quality Assessment Science Data Sets(QA-SDS) was analyzed and all scenes with valid data covering more than 75% of the Sanjiang Plain were selected for the SEBAL modeling.This provided 12 overpasses during 184-day growing season from May 1st to October 31st,2006.Daily ET estimated by the SEBAL model was misestimaed at the range of-11.29% to 27.57% compared with that measured by Eddy Covariance system(10.52% on average).The validation results show that seasonal ET from the SEBAL model is comparable to that from ground observation within 8.86% of deviation.Our results reveal that the time series daily ET of different land cover/use increases from vegetation on-going until June or July and then decreases as vegetation senesced.Seasonal ET is lower in dry farmland(average(Ave):491 mm) and paddy field(Ave:522 mm) and increases in wetlands to more than 586 mm.As expected,higher seasonal ET values are observed for the Xingkai Lake in the southeastern part of the Sanjiang Plain(Ave:823 mm),broadleaf forest(Ave:666 mm) and mixed wood(Ave:622 mm) in the southern/western Sanjiang Plain.The ET estimation with SEBAL using MODIS products can provide decision support for operational water management issues.     

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应用三分量浅层地震反射方法探测隐伏活动断裂

多波多分量地震勘探方法在油气田勘探开发中日益受到重视,但在工程和活动断裂探测中过去还没有开展多波多分量地震勘探的先例.本文简要介绍了在北京黄庄—高丽营断裂上开展的三分量浅层地震反射试验数据采集和资料处理方法,以及取得的初步结果.试验结果表明,采用纵波震源或横波震源激发、三分量接收的浅层地震勘探方法,可获得较高信噪比的浅层地震纵波、横波和转换波剖面,特别是水平分量采集的横波和转换波可提供很有意义的地下结构和构造信息.综合利用纵波、横波和转换波剖面特征进行的地质分层和断层解释结果取得了与跨断层的钻孔联合地质剖面结果较好的一致性.     

裂步法最小二乘偏移

最小二乘偏移的核心思想是用正向传播算子的逆算子代替其共轭转置算子进行偏移.它克服了常规偏移方法用共轭转置算子偏移的缺点.本文详细地描述了裂步法最小二乘偏移的原理,实现算法,并通过两个模型展示了裂步法最小二乘偏移的可行性和有效性.并且通过研究发现最小二乘较容易被扩展到基于其它波场延拓算子的最小二乘偏移.     

基于SOM的海表温度遥感数据集的EOF算法重构

针对海表温度数据集的数据缺失,提出了一种基于自组织映射算法(SOM)和经验正交函数算法(EOF)有机结合的重构缺失值的新方法。该方法应用了SOM的非线性估计,能够很好的反映数据集的非线性结构,并把SOM估计的结果用于EOF算法的初始化,克服了EOF对数据集初始化敏感的问题。在处理过程中,对奇异值分解使用了lanczos算子分解矩阵,提高了程序运行效率。此外,该方法还引入蒙特卡罗交叉校正集,确定最佳重构的EOF模态数,最终高精度计算出重构误差。使用AQUA遥感卫星海表温度数据进行实验,结果表明该方法能够很好地重构出缺失率高达83.23%的数据集,且重构精度高。     

数字海图的成果质量评测系统研究

总结归纳了海图要素数据存在的主要质量问题,阐述了评测采用的方法和依据,建立了基于质量评测算子库的海图数据要素检测引擎,初步检测出了海图数据成果质量是否存在问题,存在哪些问题,存在问题的性质、数量、位置,通过对成果的总体质量进行分析评价,最终给出了海图数据成果质量分析检测报告。