1961-2014年焉耆盆地霜冻气候分析     

隆永兰  刘濛濛  夏玉莲 《沙漠与绿洲气象(新疆气象)》2017,11(1):81-86

利用焉耆盆地3个气象站1961-2014年的初终霜冻日、无霜期资料,采用线性倾向估计法、多项式趋势、M-K检测等统计方法,分析焉耆盆地54a来霜冻气候变化特征。结果表明：(1)焉耆盆地平均初、终霜冻整体均呈显著线性后推趋势,平均分别后推了3d和21d,终霜冻推后速率大于初霜冻,无霜期呈缩短趋势,平均缩短了18d,具有明显的年代际特征。(2)平均初、终霜冻及无霜期分别于1987年、1985年、1967年发生了气候突变,初、终霜冻均表现为由提前转为明显推迟,无霜期表现为由延长转为缩短.(3)焉耆盆地特早、偏早初霜冻发生频率分别为7%和22%,发生在60年代到90年代,特晚、偏晚终霜冻发生频率分别为4%和11%,多发生在70年代和90年代,21世纪各出现一次。(4)终霜日显著推后,无霜期缩短,是今后焉耆盆地农业生产结构优化关注的重点。  相似文献   

Does the High School Geography Experience Influence Enrollment in University Geography Courses?     

Joseph Leydon  Christina McLaughlin  Heather Wilson 《The Journal of geography》2017,116(2):79-88

The literature suggests that owing to profound difficulties with high school geography curricula, teachers play a vital role in stimulating student interest and in providing a platform for continuation in the study of geography at university. Yet, with little empirical evidence offered in support, it is unclear why students select geography at university and if their high school experience informs their decision. Through a survey of students enrolled in an introductory geography course at an Ontario university, this research questions the relationship between students' high school experience and their enrollment in the course and ponders the implications for the health of the discipline.  相似文献   

Quantification winter wheat LAI with HJ-1CCD image features over multiple growing seasons     

《International Journal of Applied Earth Observation and Geoinformation》2016

Remote sensing images are widely used to map leaf area index (LAI) continuously over landscape. The objective of this study is to explore the ideal image features from Chinese HJ-1 A/B CCD images for estimating winter wheat LAI in Beijing. Image features were extracted from such images over four seasons of winter wheat growth, including five vegetation indices (VIs), principal components (PC), tasseled cap transformations (TCT) and texture parameters. The LAI was significantly correlated with the near-infrared reflectance band, five VIs [normalized difference vegetation index, enhanced vegetation index (EVI), modified nonlinear vegetation index (MNLI), optimization of soil-adjusted vegetation index, and ratio vegetation index], the first principal component (PC1) and the second TCT component (TCT2). However, these image features cannot significantly improve the estimation accuracy of winter wheat LAI in conjunction with eight texture measures. To determine the few ideal features with the best estimation accuracy, partial least squares regression (PLSR) and variable importance in projection (VIP) were applied to predict LAI values. Four remote sensing features (TCT2, PC1, MNLI and EVI) were chosen based on VIP values. The result of leave-one-out cross-validation demonstrated that the PLSR model based on these four features produced better result than the ten features’ model, throughout the whole growing season. The results of this study suggest that selecting a few ideal image features is sufficient for LAI estimation.  相似文献   

A systematic comparison of different object-based classification techniques using high spatial resolution imagery in agricultural environments     

《International Journal of Applied Earth Observation and Geoinformation》2016

Geographic Object-Based Image Analysis (GEOBIA) is becoming more prevalent in remote sensing classification, especially for high-resolution imagery. Many supervised classification approaches are applied to objects rather than pixels, and several studies have been conducted to evaluate the performance of such supervised classification techniques in GEOBIA. However, these studies did not systematically investigate all relevant factors affecting the classification (segmentation scale, training set size, feature selection and mixed objects). In this study, statistical methods and visual inspection were used to compare these factors systematically in two agricultural case studies in China. The results indicate that Random Forest (RF) and Support Vector Machines (SVM) are highly suitable for GEOBIA classifications in agricultural areas and confirm the expected general tendency, namely that the overall accuracies decline with increasing segmentation scale. All other investigated methods except for RF and SVM are more prone to obtain a lower accuracy due to the broken objects at fine scales. In contrast to some previous studies, the RF classifiers yielded the best results and the k-nearest neighbor classifier were the worst results, in most cases. Likewise, the RF and Decision Tree classifiers are the most robust with or without feature selection. The results of training sample analyses indicated that the RF and adaboost. M1 possess a superior generalization capability, except when dealing with small training sample sizes. Furthermore, the classification accuracies were directly related to the homogeneity/heterogeneity of the segmented objects for all classifiers. Finally, it was suggested that RF should be considered in most cases for agricultural mapping.  相似文献   

Spectral band selection for vegetation properties retrieval using Gaussian processes regression     

《International Journal of Applied Earth Observation and Geoinformation》2016

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像元与对象特征融合的高分辨率遥感影像道路中心线提取     

曹云刚  王志盼  慎利  肖雪  杨磊 《测绘学报》2016,45(10):1231-1240

提出了一种融合像元-多尺度对象级特征的高分辨率遥感影像道路中心线提取方法。首先在像素级上提取影像的纹理和形状结构特征,在构建的多尺度分割集影像上提取对象的区域光谱特征。然后,将像元级特征与多尺度对象特征进行决策级融合,完成道路网的粗提取。最后,结合本文所提出的非道路区域自动去除算法和张量投票算法,实现道路中心线的精提取。不同场景、不同分辨率数据下开展的试验结果表明,该方法可有效改善传统道路提取方法易产生的"盐噪声"和非道路地物粘连现象。  相似文献   

基于邻域投票和Harris-SIFT特征的低空遥感影像匹配     

胡小青  程朋根  陈晓勇  何海清  聂运菊 《测绘工程》2016,25(2):33-37

文中提出一种基于邻域投票和改进的Harris-SIFT特征的低空遥感影像匹配方法。首先用NMS算法提取多尺度的Harris-SIFT特征并对其进行方向描述,然后根据最近邻与次近邻特征点距离之比确定初始匹配点对,最后通过近邻域选择投票的方法剔除候选点中的虚假匹配点,进而实现低空遥感影像的配准。实验表明该算法在获得充足匹配点且保证匹配精度的同时,明显提高影像匹配的效率。  相似文献   

联合光谱和纹理特征的支持向量机滩涂分类方法研究     

赵亮  孟立轲  张艳  冯伍法  张继领 《测绘工程》2016,25(1):43-46

滩涂作为海岸带的重要组成部分,是重要的土地资源。针对遥感影像滩涂分类的提取,文中提出一种联合光谱和纹理特征支持向量机(SVM)滩涂分类的方法。首先介绍纹理特征影像获取方法,通过灰度共生矩阵分析得到滩涂纹理特征影像;然后将光谱影像与纹理影像叠加形成一幅多维特征影像,用SVM分类算法中的OAR分类器进行分类实验,对分类结果进行实验分析。实验结果表明,该算法对提高海岸带地理信息获取能力,提升海洋遥感测绘信息化保障水平有积极意义。  相似文献   

混合智能优化算法的SAR图像特征选择   总被引：1，自引：0，他引：1  

张琴  谷雨  徐英  赖晓平 《遥感学报》2016,20(1):73-79

为提高SAR图像自动目标识别的准确率及实时性,提出了一种基于混合智能优化的SAR图像特征选择算法。首先,采用分形特征对SAR图像进行增强,基于分割后的图像提出了一种基于图像矩的方位角估计方法。然后基于未校正和校正后的图像分别提取Zernike矩、Gabor小波系数和灰度共生矩阵构成候选特征集合,使用遗传算法结合二值粒子群的混合优化算法实现SAR图像特征选择。最后,采用MSTAR数据库验证本文算法的有效性。实验结果表明,优化后的特征集合具有一定泛化能力,一方面提高了SAR目标识别的准确率,另一方面减小了SAR图像目标识别的时间。  相似文献   

基于多尺度模型的数据库影像特征匹配     

高翔  徐柱 《测绘科学》2016,41(2):121-125,162

针对传统的遥感影像数据库中影像特征匹配效率低下的问题,该文提出一种基于多尺度模型的数据库影像特征匹配方法。为遥感影像数据库构建多尺度模型,能较高效率地在数据库中快速定位候选的匹配影像;基于搜索得到的候选影像,采用快速排序算法逐层筛选最佳匹配影像,从而实现了数据库匹配影像的精确定位。实验结果表明:所提算法不仅能高效地完成影像间特征点匹配运算,还能从数据库中精确地筛选得到最佳的匹配影像;且随着数据库中影像总数的增加,该方法的优势表现得更加明显。这一研究将为遥感影像数据库的高效、实时及动态匹配提供可能性。  相似文献