Identification of eroded areas using remote sensing in a badlands landscape on marls in the central Spanish Pyrenees     

L.C. Alatorre  S. Beguería 《CATENA》2009,76(3):182-190

Identification of erosion areas on a regional scale can be very useful for environmental planning, and can help reduce land degradation and sediment yield to streams and reservoirs. Remote sensing techniques were used to determine erosion and erosion risk areas in a badlands landscape in the Ésera River catchment (Spanish Pyrenees). The size, sparse vegetation cover, and high erosion level in the badlands, enabled good visual and digital discrimination relative to other land covers and surfaces. The maximum likelihood algorithm was used for obtaining a spectral distance map to the bare soil signature characteristic of badlands on marls. The ROC (receiver operating characteristic) curve analysis was applied to this map for obtaining an optimum classification of the badlands. Two alternative classification thresholds were set to determine erosion areas and areas at risk of erosion. Two classification performance statistics, the model's sensitivity and specificity, were calculated as a means of expressing the uncertainty–omission and commission errors–associated to both maps. Most erosion risk areas coincided with low vegetation cover surrounding the badland areas.  相似文献   

基于ROC图的油菜生长期光谱敏感波段的研究     

段少新  姜珊  王访  邹锐标  廖桂平 《湖南农业大学学报(自然科学版)》2017,43(6)

测定了直播和移栽油菜的苗期、抽薹期、花期、盛花期和角果期的冠层光谱,构建了比值光谱植被指数(RSI)和归一化光谱植被指数(NDSI)。为了获得区分直播和移栽的最佳RSI和NDSI,利用降采样法和精细采样法相结合的受试者工作特征(ROC)图寻找油菜生长期光谱的敏感波长,直播和移栽油菜各时期RSI和NDSI的最敏感波长分别为:苗期(458 nm,511 nm)和(433 nm,517 nm);抽薹期(997 nm,501 nm)和(990 nm,510 nm);花期(1 235 nm,1 180 nm)和(1 235 nm,1 180 nm);盛花期(478 nm,396 nm)和(484 nm,416 nm);角果期(1 073 nm,1 037 nm)和(1 092 nm,1 024 nm)。用敏感波长下的2种植被指数为特征,以最近邻法为分类器的定性识别模型,结果花期的区分效果最好,最大约登指数分别为0.941 7和0.945 0。  相似文献   

霜冻天气对桂中地区主栽甘蔗品种生长及蔗糖分的影响   总被引：8，自引：0，他引：8  

谭宏伟  李杨瑞  周柳强  谢如林  黄金生  黄美福 《广西农业科学》2010,41(4):326-328

2008年初广西各蔗区甘蔗均遭受严重的寒害冻害,研究霜冻天气对主栽甘蔗品种生长及蔗糖分的影响对确保甘蔗持续生产,选育抗寒甘蔗品种具有重要意义。2009年1月霜冻天气对桂中地区主栽甘蔗品种生长及蔗糖分影响的研究结果表明,这次霜冻天气后甘蔗的受冻害症状明显,蔗糖分下降了0．21％-0．48％（绝对值）,宿根蔗蔗糖分的降幅较新植蔗大;简纯度下降了0．37％～1．48％（绝对值）,新植蔗的降幅较宿根蔗大。  相似文献   

A Bayesian approach to assess the accuracy of a diagnostic test based on plant disease measurement     

David Makowski  Jean-Baptiste Denis  Laurent Ruck  Annette Penaud 《Crop Protection》2008,27(8):1187-1193

The proportion of diseased plant organs measured before chemical treatment is often used to make an assessment of the need for crop protection in agricultural plots, but such diagnostic tests are not perfect and sometimes lead to incorrect decisions. The area under the receiver operating characteristic (ROC) curve is a popular index of the overall performance of a test. It can be interpreted as the probability that the test value for a randomly chosen diseased subject will exceed that of a randomly chosen disease-free subject. In this paper, we present a Gaussian/Binomial model to assess the accuracy of diagnostic test based on a measured proportion of diseased plant organs. The model parameters were estimated from a real dataset and the model was used to analyse the accuracy of a diagnostic test based on a measured proportion of oilseed rape flowers contaminated by Sclerotinia sclerotiorum. The results showed that the accuracy of the test depends on the number of collected flowers, but that it is not necessary to collect more than 40 flowers per plot. A simulation study showed that the bias of the estimator of the area under the ROC curve was near zero for all size of dataset and that its mean-square error decreased in function of the number of experimental plots used in the ROC analysis. A major interest of our approach is that it allows one to study the effect of the sample size of the organs on the accuracy of the test. It can also be used to estimate the probability of disease occurrence, and to determine a decision threshold according to the sensitivity and specificity values.  相似文献   

清至民国时期归绥城市绿地研究     

牛淑贞 《干旱区资源与环境》2013,(2):69-76

在清代和民国时期不同的社会历史环境和植树造林观念影响下,归绥城市绿地呈现出不同的规模、类型及功能。清代,由于汉族移民在内蒙古地区的寄民身份及其对所种土地没有所有权,造成归绥城的绿地建设只有少数官员或个人参与,所建绿地多为少数人所享用的花园。与清代形成对照,民国时期由于居民寄民身份的改变,以及政府的大力宣传、组织,全民参与植树,且共享其成果,归绥城市绿地因此获得较为快速的发展,逐渐形成了由花园、公园、林地、林场、苗圃、行道树及沿河绿带等构成的绿色环境体系。尽管民国时期归绥城的城市绿地建设更多地关注防风、防尘、防水等功能,绿地景观的多样性低,建设水平处于较低层次,布局也不均匀。但是,不可否认,它对归绥城的生态环境和空间景观产生了一定的优化作用,也在一定程度上改变了归绥城以往荒寒的城市形象。  相似文献   

基于生态位模型的石蒜适生区预测     

毛志远  张兆金  周坚 《林业科技开发》2014,28(6)

运用预设预测规则的遗传算法(GARP)和最大熵(MaxEnt)两种生态位预测模型,以及受试者工作曲线(ROC)分析方法,预测石蒜属石蒜潜在适生区.结果表明,GARP和MaxEnt模型ROC曲线下面的面积AUC(area under the ROC curve)均值分别为0.910和0.988,MaxEnt模型的AUC值更大,预测结果更准确,运行速度更快,更适合用于石蒜的适生区预测.对环境变量进行刀切法表明,在所有环境变量中,最冷季度平均温度对于石蒜分布的影响(贡献)最大,其次是年均温、最冷月的最低温度和最暖季度降水量,而海拔、降水量变化方差对石蒜分布的影响比较小.预测结果显示,石蒜在世界范围内主要分布在亚洲东部以及亚洲中部一小部分,另外北美洲的东部,欧洲南部一小部分地区也适合其生长.在中国范围内主要分布在云南、贵州、福建、江苏、浙江、安徽、江西、重庆、湖北、湖南等省,以及山东、河南、陕西、甘肃等省南部;四川东部和广东、广西(除了南部沿海地区)均预测为适生区,海南、台湾、西藏部分地区也是适生区.  相似文献   

EXPERT INTERPRETATION COMPENSATES FOR REDUCED IMAGE QUALITY OF CAMERA‐DIGITIZED IMAGES REFERRED TO RADIOLOGISTS     

ALLISON L. ZWINGENBERGER  JENNIFER L. BOUMA  H. MARK SAUNDERS  CALVIN F. NODINE 《Veterinary radiology & ultrasound》2011,52(6):591-595

We compared the accuracy of five veterinary radiologists when reading 20 radiographic cases on both analog film and in camera‐digitized format. In addition, we compared the ability of five veterinary radiologists vs. 10 private practice veterinarians to interpret the analog images. Interpretation accuracy was compared using receiver operating characteristic curve analysis. Veterinary radiologists' accuracy did not significantly differ between analog vs. camera‐digitized images (P=0.13) although sensitivity was higher for analog images. Radiologists' interpretation of both digital and analog images was significantly better compared with the private veterinarians (P<0.05).  相似文献   

应用ROC曲线对肉鸡腹水综合征的血常规分析     

郭坤  林华源  郭小权  胡国良  曹华斌  张彩英  杨菲  宋雅露  刘佩  刘平 《江西农业大学学报》2016,(4):717-722

用ROC曲线对肉鸡腹水综合征(AS)的血常规分析,探讨血常规指标在肉鸡腹水综合征诊断的临床价值。购买22日龄健康、体质量相近的白羽肉鸡75羽,随机分为对照组和造病组,对照组为30羽饮自来水,造病组为45羽饮0.3%Na Cl高盐水,其它饲养条件相同,饲喂到35日龄分别进行采血,测血常规;并剖杀取心脏,计算右心室(RV)比全心室(TV)的比值,同时,利用SPSS软件进行t检验和ROC曲线分析。结果表明:造病组的RV/TV比值极显著高于对照组(P0.01);在造病组中的中间细胞(MID)、中间细胞比率(MXD)、粒细胞(GRAN)、红细胞总数(RBC)均显著高于对照组(P0.05),而白细胞总数(WBC)、血小板分布宽度(PDW)极显著高于对照组(P0.01)。根据RV/TV将血常规分为无病组(RV/TV≤0.219)和有病组(RV/TV0.219),进行ROC曲线分析且曲线下面积(AUC)均大于0.5,两组均差异显著(P0.05)。血常规的MID、MXD%、WBC、GRAN、RBC、PDW%的ROC曲线分析的结果,可为肉鸡腹水综合症临床诊断提供参考价值。  相似文献   

Thresholds in nesting habitat requirements of an old forest specialist, the Brown Creeper (Certhia americana), as conservation targets     

Jean-Franois Poulin  Marc-Andr Villard  Mattias Edman  Pierre J. Goulet  Anna-Maria Eriksson 《Biological conservation》2008,141(4):1129-1137

Many bird species respond to forestry, even at moderate intensities. In New Brunswick, Canada, the Brown Creeper exhibits a negative, threshold response to harvesting intensity. This study aimed to determine whether (a) the threshold found in Brown Creeper occurrence is lower than eventual thresholds in its nesting requirements, and whether (b) the conservation of this species could be achieved through moderate-intensity harvest systems. Creepers are particularly sensitive to forestry because they nest on snags with peeling bark and they mainly forage on large-diameter trees. In northern hardwood stands, we compared habitat structure at local- (r = 80 m) and neighbourhood-scales (r = 250 m) around nest sites and sites not used by creepers. Over two years, we found 76 nests, 66 of which were paired with unused sites for comparison. At the local scale, densities of trees 30 cm dbh and snags 10 cm dbh, and the probability of presence of potential nest sites were significantly higher near nests than at sites where no creepers were detected. At the neighbourhood scale, the area of untreated mature forest was significantly higher around nests. Variance decomposition indicated that habitat variables at the local scale accounted for the majority of explained variation in nest site selection. We also found significant thresholds in the densities of large trees (127/ha) and snags (56/ha), and in the area of mature forest (10.4 ha). The conservation of breeding populations of Brown Creepers may thus require densities of large trees nearly twice as high as those associated with its probability of presence. Such a target seems to be incompatible even with moderate-intensity harvesting.  相似文献   

Diagnostic characteristics of refractometry cut-off points for the estimation of immunoglobulin G concentration in mare colostrum     

Elisa Rampacci  Karen Mazzola  Francesca Beccati  Fabrizio Passamonti 《Equine veterinary journal》2023,55(1):102-110

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