基于冠层尺度的枣树色素含量的高光谱估算模型

植物冠层色素含量与氮素含量具有高度的相关性,是农业遥感中的关键研究因素。本研究的主要目的是：(1)对比偏最小二乘回归和支持向量机两种建模方法对枣树冠层色素的预测精度;(2)构建基于高光谱数据的枣树冠层色素含量定量反演模型,为枣树冠层色素含量的快速、无损、廉价、环保的测定提供一定的理论依据和技术支持。相关性分析结果表明,枣树冠层色素与高光谱数据之间具有较好的相关性,但叶绿素、叶绿素a要优于叶绿素b和类胡萝卜素。独立样本对模型的预测性能检验结果表明,偏最小二乘回归和支持向量机均能有效的估算枣树色素含量,但不同色素的偏最小二乘回归模型和支持向量机模型的预测精度存在一定的差异,叶绿素和类胡萝卜素的支持向量机模型的预测精度要高于偏最小二乘回归模型,而叶绿素a和叶绿素b则相反。比较不同色素的最佳反演模型的预测精度表明,叶绿素、叶绿素a和类胡萝卜素的预测精度要优于叶绿素b,前三者的决定系数大于0.8,残余预测误差高于2.0,平均相对误差低于13%,而叶绿素b的对应值分别为0.60%,20.79%和1.79%。     

A Kolmogorov-type competition model with multiple coexistence states and its applications to plant competition for sunlight

It is demonstrated that a Kolmogorov-type competition model featuring species allocation and gain functions can possess multiple coexistence states. Two examples are constructed: one in which the two competing species possess rectangular allocation functions but distinct gain functions, and the other in which one species has a rectangular allocation function, the second species has a bi-rectangular allocation function, and the two species share a common gain function. In both examples, it is shown that the species nullclines may intersect multiple times within the interior of the first quadrant, thus creating both locally stable and unstable equilibrium points. These results have important applications in the study of plant competition for sunlight, in which the allocation functions describe the vertical placement of leaves for two competing species, and the gain functions represent rates of photosynthesis performed by leaves at different heights when shaded by overlying leaves belonging to either species.     

高光谱数据的刚竹毒蛾虫害程度检测

刚竹毒蛾虫害检测对毛竹的生长和竹业的发展起着至关重要的作用。根据高光谱冠层光谱信息与刚竹毒蛾虫害程度之间的关系,提取冠层光谱中与虫害紧密相关的特征波长、指数以及光谱参数等,利用Fisher判别分析法建立刚竹毒蛾虫害程度检测模型。分别以原始光谱的400～508,586～693和724～900 nm处的波长、包络线去除光谱的400～756 nm之间的特征波长、9种冠层光谱植被指数和7种冠层特征光谱参数作为Fisher判别函数自变量,构建判别函数。收集300组毛竹叶片虫害样本数据,随机划分为210组建模集与90组验证集,根据检测精度、Kappa系数以及判定系数R2作为检验标准,对建立的判别函数进行效果评价与对比。结果表明,以原始光谱、去包络线光谱、冠层指数、光谱参数为自变量建立的Fisher判别函数的检验精度分别为：84.4%,81.1%,79.7%,78.7%;Kappa系数分别为：0.79,0.74,0.74,0.76;R2分别为：0.89,0.88,0.88和0.85。由此可知,Fisher判别分析模型建立的函数具备很好的刚竹毒蛾虫害程度检测能力,而且基于冠层原始光谱建立的判别函数检测效果最佳。根据高光谱数据的冠层原始光谱建立的判别函数对福建省顺昌县大干镇武坊村的洋门和土垅村的上湖竹林进行刚竹毒蛾虫害程度检测。检测结果为：上湖两个样区的竹林以健康为主。洋门两个样区虫害程度以中度和重度为主。因此基于无人机高光谱遥感对于刚竹毒蛾虫害的大面积检测具有可行性,该方法可为虫害检测的探究提供参考,为基于冠层遥感虫害检测贡献理论支撑。     

农作物冠层光谱信息检测技术及方法综述

相比传统的化学方法及主观视觉测定植物生理信息指标,通过光谱辐射仪对农作物冠层信息的评估更简单、快速和精确。本文结合近年来农作物群体信息的获取方法,综述了不同类型光谱仪尤其以国际上应用最广泛的Cropscan多光谱辐射仪在农作物群体叶面积指数、生物量、氮素及叶绿素的预测,病虫害的监测及产量预测中的应用。总结了不同类型的的植被指数(VIs)、冠层光谱的获取及光谱分析方法,比较了不同农作物建立相关模型的回归系数。总体上建立的数学模型的相关系数较高,能实现对农作物各种生理信息等的检测。此外,将多光谱辐射仪与多种传感器相结合所得到的综合信息对于全面评价农作物生长情况具有重要指导价值。     

不同耐热型春玉米品种对高温的光谱特征响应

运用两种光谱仪（SPAD-502叶绿素仪与Sunscan植物冠层分析仪）分析了华北平原不同耐热型春玉米品种的光合性能对灌浆期高温的光谱学特征响应。田间试验于2011年—2012年在河北省吴桥县进行。品种选用天玉198、兴玉998与天润606,设置2个播种期（4月15日与4月25日）,于灌浆期测定3个光谱特征值,即叶绿素相对含量（SPAD）、叶面积指数（leaf area index, LAI）与光合有效辐射（photosynthetically active radiation, PAR）。结果表明,播种期4月15日与4月25日相比,春玉米灌浆期≥33 ℃日最高气温的天数与日均温分别增加了3.5 d和0.8 ℃,而日照时数、降雨量、气温日较差及生育期长短均相似; 天玉198与兴玉998、天润606相比,耐热指数（stress tolerance indices, STI）分别高2.9%,11.0%; 根据STI由大到小的顺序,将天玉198、兴玉998与天润606分别定为耐热型、较耐热型与不耐热型品种; 播种期4月15日,天玉198比兴玉998、天润606的产量分别高4.1%,13.7%,SPAD分别高12.5%,19.6%,LAI分别高5.3%,5.6%,PAR分别高4.0%,14.0%; 播种期4月25日,产量分别高1.3%,2.8%; SPAD分别高3.5%,6.0%,LAI分别高1.7%,4.1%,PAR分别高-4.4%,0.9%; 三个品种在高温胁迫环境下产量差异显著,耐热型品种具有显著的产量、SPAD与LAI优势（p＜0.05）。播种期4月15日相对于4月25日,天玉198、兴玉998、天润606的产量分别降低了3.2%,5.9%,12.6%; SPAD分别降低了8.6%,12.4%,15.7%; LAI分别降低了11.7%,17.6%,19.8%; PAR分别降低了3.4%,11.3%,14.5%; STI与SPAD的降幅（r=-0.883,p＜0.05）、LAI的降幅（r=-0.853,p＜0.05）均呈显著负相关,与PAR的降幅（r=-0.923,p＜0.01）呈极显著负相关; SPAD的降幅与PAR的降幅（r=0.872,p＜0.05）呈显著正相关; LAI的降幅与PAR的降幅（r=0.943,p＜0.05）呈极显著正相关。综上所述,耐热型春玉米品种在灌浆期受高温胁迫时,能够在个体层面保持相对较高的叶绿素含量,在群体层面保持相对较高的叶面积,进而保持了较高的光能截获与利用,削弱了高温对光合的抑制程度,缩小了产量降幅,实现了高产与稳产; 品种的耐热性可以通过其光谱特征（SPAD,LAI和PAR）对高温的响应作为鉴定与评价的主要指标之一,为利用光谱特征研究玉米耐热性提供了依据。     

运用光谱参数冠层覆盖度建立作物长势及氮营养状态模型

为了探索运用数码照片中光谱(红、绿、蓝)的像素计算得到的冠层覆盖度(canopy cover, CC)对玉米长势及氮素营养状态进行非破坏性监测的技术。通过获取玉米冠层的数码照片图像,定量化数码照片色彩参数与作物叶面积指数(leaf area index, LAI)、冠层干重(shoot dry matter weight, DM)、叶片氮素含量(leaf nitrogen content percentage, N%)之间的关系。试验于2012年和2013年在中国农业科学院试验田进行,运用基于Visual Basic Version 6.0研发的玉米冠层图像分析系统,分析了玉米品种中单909在3个氮素水平条件下分别于9叶展时期、抽雄期和灌浆期的CC、11种色彩指数与植株LAI,DM,N%及产量之间的相关性,并对相关性显著的指标进行了拟合与建模。结果表明,CC与LAI(r=0.93, p＜0.01),DM(r=0.94, p＜0.01),N%(r=0.82, p＜0.01)之间均达到了极显著水平;用CC估算LAI,DM和N%的模型均为幂函数,方程式分别是y=3.281 2x0.763 9,y=283.658 1x0.553 6,y=3.064 5x0.932 9;用与建模相独立的数据对模型验证,结果表明,CC估算LAI模型的实测值与模拟值基于1∶1直线的R2,RMSE和RE分别是0.996,0.035和1.46%;CC估算DM模型的R2,RMSE和RE分别是0.978,5.408 g和2.43%;CC估算N%模型的R2,RMSE和RE分别是0.990,0.054和2.62%。综上所述,模型能够较准确的通过CC估算不同氮肥水平条件下玉米9叶展时期、抽雄期和灌浆期的LAI,DM与N%,表明应用数码相机的光谱信息可实现对玉米生长过程中的生长状况及氮素营养状态进行实时无损快速监测与预测。     

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Aquatic flow over a submerged vegetation canopy is a ubiquitous example of flow adjacent to a permeable medium. Aquatic canopy flows, however, have two important distinguishing features. Firstly, submerged vegetation typically grows in shallow regions. Consequently, the roughness sublayer, the region where the drag length scale of the canopy is dynamically important, can often encompass the entire flow depth. In such shallow flows, vortices generated by the inflectional velocity profile are the dominant mixing mechanism. Vertical transport across the canopy–water interface occurs over a narrow frequency range centered around f _v (the frequency of vortex passage), with the vortices responsible for more than three-quarters of the interfacial flux. Secondly, submerged canopies are typically flexible, coupling the motion of the fluid and canopy. Importantly, flexible canopies can exhibit a coherent waving (the monami) in response to vortex passage. This waving reduces canopy drag, allowing greater in-canopy velocities and turbulent stresses. As a result, the waving of an experimental canopy reduces the canopy residence time by a factor of four. Finally, the length required for the set-up and full development of mixing-layer-type canopy flow is investigated. This distance, which scales upon the drag length scale, can be of the same order as the length of the canopy. In several flows adjacent to permeable media (such as urban canopies and reef systems), patchiness of the medium is common such that the fully developed condition may not be representative of the flow as a whole. This paper has previously been published in Transp Porous Med (2009) 78: 309–326; DOI .     

The Canopy Graph and Level Statistics for Random Operators on Trees

For operators with homogeneous disorder, it is generally expected that there is a relation between the spectral characteristics of a random operator in the infinite setup and the distribution of the energy gaps in its finite volume versions, in corresponding energy ranges. Whereas pure point spectrum of the infinite operator goes along with Poisson level statistics, it is expected that purely absolutely continuous spectrum would be associated with gap distributions resembling the corresponding random matrix ensemble. We prove that on regular rooted trees, which exhibit both spectral types, the eigenstate point process has always Poissonian limit. However, we also find that this does not contradict the picture described above if that is carefully interpreted, as the relevant limit of finite trees is not the infinite homogenous tree graph but rather a single-ended ‘canopy graph.’ For this tree graph, the random Schrödinger operator is proven here to have only pure-point spectrum at any strength of the disorder. For more general single-ended trees it is shown that the spectrum is always singular – pure point possibly with singular continuous component which is proven to occur in some cases.     

Estimation of Winter Wheat Biomass Using Visible Spectral and BP Based Artificial Neural NetworksSCIEI北大核心CSCD

The objective of this study was to evaluate the feasibility of using color digital image analysis and back propagation (BP) based artificial neural networks (ANN) method to estimate above ground biomass at the canopy level of winter wheat field. Digital color images of winter wheat canopies grown under six levels of nitrogen treatments were taken with a digital camera for four times during the elongation stage and at the same time wheat plants were sampled to measure above ground biomass. Canopy cover (CC) and 10 color indices were calculated from winter wheat canopy images by using image analysis program (developed in Microsoft Visual Basic). Correlation analysis was carried out to identify the relationship between CC, 10 color indices and winter wheat above ground biomass. Stepwise multiple linear regression and BP based ANN methods were used to establish the models to estimate winter wheat above ground biomass. The results showed that CC, and two color indices had a significant correlation with above ground biomass. CC revealed the highest correlation with winter wheat above ground biomass. Stepwise multiple linear regression model constituting CC and color indices of NDI and b, and BP based ANN model with four variables (CC, g, b and NDI) for input was constructed to estimate winter wheat above ground biomass. The validation results indicate that the model using BP based ANN method has a better performance with higher R-2 (0.903) and lower RMSE (61.706) and RRMSE (18.876) in comparation with the stepwise regression model.     

Shallow Flows Over a Permeable Medium: The Hydrodynamics of Submerged Aquatic Canopies

Aquatic flow over a submerged vegetation canopy is a ubiquitous example of flow adjacent to a permeable medium. Aquatic canopy flows, however, have two important distinguishing features. Firstly, submerged vegetation typically grows in shallow regions. Consequently, the roughness sublayer, the region where the drag length scale of the canopy is dynamically important, can often encompass the entire flow depth. In such shallow flows, vortices generated by the inflectional velocity profile are the dominant mixing mechanism. Vertical transport across the canopy–water interface occurs over a narrow frequency range centered around f _v (the frequency of vortex passage), with the vortices responsible for more than three-quarters of the interfacial flux. Secondly, submerged canopies are typically flexible, coupling the motion of the fluid and canopy. Importantly, flexible canopies can exhibit a coherent waving (the monami) in response to vortex passage. This waving reduces canopy drag, allowing greater in-canopy velocities and turbulent stresses. As a result, the waving of an experimental canopy reduces the canopy residence time by a factor of four. Finally, the length required for the set-up and full development of mixing-layer-type canopy flow is investigated. This distance, which scales upon the drag length scale, can be of the same order as the length of the canopy. In several flows adjacent to permeable media (such as urban canopies and reef systems), patchiness of the medium is common such that the fully developed condition may not be representative of the flow as a whole.