Developing a dynamic growth model for teak plantations in India

Background： Tectono grandis （teak） is one of the most important tropical timber species occurring naturally in India. Appropriate growth models, based on advanced modeling techniques, are not available but are necessary for the successful management of teak stands in the country. Long-term forest planning requires mathematical models and the principles of Dynamical System Theory provide a solid foundation for these.
Methods： The state-space approach makes it possible to accommodate disturbances and avarying environment. In this paper, an attempt has been made to develop a dynamic growth model based on the limited data, consisting of three annual measurements, collected from 22 teak sample plots in Karnataka, Southern India.
Results： A biologically consistent whole-stand growth model has been presented which uses the state-space approach for modelling rates of change of three state-variables viz., dominant height, stems per hectare and stand basal area. Moreover, the model includes a stand volume equation as an output function to estimate this variable at any point in time. Transition functions were fitted separately and simultaneously. Moreover, a continuous autoregressive error structure is also included in the modelling process. For fitting volume equation, generalized method of moments was used to get efficient parameter estimates under heteroscedastic conditions.
Conclusions： A simple model containing few free parameters performed well and is particularly well suited to situations where available data is scarce.     

Thermal Infrared Radiation for Assessing Crop Water Stress in Wheat

Field studies on differentially irrigated wheat ( Triticum aestivum L.) crops were conducted at Pantnagar for two years to evaluate the use of thermal infrared radiation to detect crop water stress. Data show that the stress-degree-day index (mid day canopy-air temperature difference) is influenced by environmental variability other than soil moisture. Improvement in the stress-degree-day (SDD) index was achieved by including the measurements of vapor pressure deficit and approach was termed as plant water stress index (PWSI). Observations indicated that daily variation in SDD values due to meteorological changes was removed through PWSI. Better correlation was found between soil-induced leaf water potential and plant water stress index than between total leaf water potential and plant water stress index. It is concluded that remote sensing of thermal infrared radiation offers a promising technique which can be incorporated into irrigation management programme.     

Comparison of two ground-based active-optical sensors for in-season estimation of corn (Zea mays,L.) yield

Thirty field experiments were conducted in North Dakota during 2011 and 2012 to compare two ground-based active-optical sensors for their relationship between sensor readings and INSEY (in-season estimate of yield). The experimental design at each site was a randomized complete block with four replications and six nitrogen (N) rate treatments: control, 45, 90, 134, 179, and 224 kg ha^?1 applied pre-plant as ammonium nitrate within five days of planting. The two sensors, GreenSeeker® (Trimble, Sunnydale, CA, USA) (GS) and Crop Circle ACS 470® sensor (Holland Scientific, Lincoln, NE, USA) (CC) were used to scan over the top of the corn at V6 and V12 growth stages. The GS INSEY and the CC INSEY were similarly related to corn yield at V6. The CC using the red-edge lens option improved the INSEY relationship to corn yield compared to the GS or the CC using the red lens option at V12.     

成熟期苹果树冠层器官异源图像配准

为精确构建果树冠层彩色三维空间结构,以成熟期苹果树冠层为研究对象,将PMD摄像机及彩色摄像机相结合获取冠层器官异源图像,开展异源信息配准技术研究。将SIFT算法应用于异源图像特征点提取研究中,并应用目标函数优化RANSAC算法完成同名点提纯以保证特征点匹配的有效性,避免了异源图像尺度变化及果园自然光照的影响;在分析异源图像成像效果基础上,确定了应用双线性映射模型求解异源图像空间映射关系,有效克服了应用仿射变换模型求解异源图像空间映射关系的不精确性。果园不同自然环境下的配准实验表明:提出的混合算法适用于苹果树冠层器官异源图像的配准,晴天顺光环境下的正确配准率为88.2%,晴天逆光环境下的正确配准率为84.2%,阴天环境下的正确配准率为72.7%。     

Water balance, transpiration and canopy conductance in two beech stands

Measurements of sap flow, vapour fluxes, throughfall and soil water content were conducted for 19 months in a young beech stand growing at low elevation, in the Hesse forest. This experiment is part of the Euroflux network, covering 15 representative European forests. Study of the radial variation of sap flow within tree trunks, showed a general pattern of sap flux density in relation to the depth below cambium. Among-tree variation of sap flow was also assessed, in order to determine the contribution of the different crown classes to the total stand transpiration. Stand sap flow and vapour flux, measured with eddy covariance technique, were well correlated, for half hourly as well for daily values, the ratios of the fluxes for both averaging periods being 0.77. A strong canopy coupling to the atmosphere was found, omega factor ranging between 0.05 and 0.20 relative to the windspeed. Canopy conductance variation was related to a range of environmental variables: global radiation, vapour pressure deficit, air temperature and soil water deficit. In addition to the effect of radiation and of vapour pressure deficit often found in various other tree species, here beech exhibited a strong reduction in canopy conductance when air temperature decreased below 17°C. The model of transpiration was calibrated using data measured in the Hesse forest and applied to another beech stand under mountainous conditions in the Vosges mountains (east France). Measured and modelled stand transpiration were in good agreement.     

基于自适应趋近律的采摘机器人关节滑模控制研究

利用离散趋近律设计的滑模控制可有效抑制滑模控制中的抖动现象,但其抑制抖动的效果与离散趋近律的设计参数及系统的采样时间有着密切的关系。为此,在分析指数趋近律抖动的基础上,提出了一种自适应滑模控制器,Mat LAB能够进一步的提高基于趋近律的滑模控制器的抖动抑制能力。为了验证本文所提出方法的有效性,在Mat LAB中实现了该算法,并利用其来控制采摘机器人关节的伺服电机。仿真结果表明:本文所提的算法具有较好的位置跟踪能力,进一步地抑制了指数趋近律滑模控制中存在的抖动现象,提高了系统的性能。     

车载式土壤光-电特性参数采集系统研究

土壤电导率是衡量土壤传导电流能力的一种固然属性,除了能够反映土壤质地外,还能够反映土壤的含水率、含盐量、有机物含量等特性。利用土壤光谱数据可以分析出土壤含水率、养分等,且测量过程中无需采样、搅动土壤。通过土壤电导率数据和光谱数据的综合、校正,能够提高系统的精度。基于嵌入式技术开发了土壤电导率和光谱反射率综合检测系统。土壤电导率测量系统采用基于改进的电流-电压四端法原理,使用深松犁的尖端作为电极传感器,能够在测量的同时完成松土的作用。光谱测量系统使用微型光谱传感器采集光谱数据,并进行实时处理。在采集土壤电导率、光谱数据的同时,系统同步采集GPS信息,并和土壤电导率、光谱数据一起保存,供进一步绘制土壤特性分布图使用。系统能够实时综合处理多种数据,并进行显示、保存等操作,具有良好的应用 前景。     

黄淮冬麦区晚霜冻易发时段冠层内最低气温分布及估算

利用2016年和2017年3月中旬?4月下旬两次典型低温过程中,冬小麦田间不同高度逐小时气象观测数据,分析晚霜冻易发时段冬小麦冠层内最低气温出现高度及其变化规律,构建基于150cm高度处气象因子和地表0cm温度的冠层内最低气温估算模型。结果表明：（1）与150cm高度相比,两次典型低温过程中0℃以下气温在冠层高度附近出现时间更早,持续时间更长且温度更低;（2）最低气温总是出现在4/5冠层高度附近,并在2：00?6：00时段,尤以5：00左右发生频率最高;（3）冠层内最低气温与150cm高度处相对湿度、风速的相关性通过了0.01水平的显著性检验,与不同高度气温、不同土壤深度地温的相关性也通过了0.001水平的显著性检验,与地温的相关性随着土壤深度的增加而逐渐降低;（4）冠层内最低气温与150cm高度处气温、风速、相对湿度,以及0cm地温的偏相关系数大小排序表现为,气温＞风速＞地温＞相对湿度;利用以上因子构建基于多元线性回归函数的冠层内最低气温估测模型,其估测值与实测值拟合结果的决定系数达到0.967,均方根误差为0.915。说明基于气象台站常规观测数据构建冠层内最低气温估测模型具备一定可行性,可为冬小麦晚霜冻害的监测预报提供数据支持。     

棉铃着生位置对棉花主要经济性状的影响

选用新品系８９５作试材进行了棉铃着生位置对其经济性状的影响研究。结果表明，棉铃在植株上的着生部位不同，其相应的产量构成因素以及纤维物理性能指标也存在同株差异，如铃重、衣分、子指和绒长、强力、细度等，并表现出一定的规律性。各果枝的第１节结铃性最强，铃重最大，随着果枝从下到上，相同节位棉铃重和衣分呈现出抛物曲线变化趋势，同一果枝上的棉铃，随着节位的外延，铃重和衣分分别表现出降低和增高的直线变化趋势，纤     

应用基于红外热画像技术的CWSI简化算法判断作物水分状态

以不同水分处理下的冬小麦为研究对象,通过基于红外测温技术的Jackson理论模式和Jones简化模式分别计算作物水分胁迫指数（CWSI）,并以理论模式计算值为参考,对Jones模式反映华北地区冬小麦水分胁迫的表现进行初步分析.结果表明,两种计算模式得出的CWSI值与不同水分处理下的冬小麦根层土壤含水量均有较好的相关性,但Jones模式可更好地指示作物缺水状态,对叶片气孔导度的变化更敏感.根据研究结果初步确定了冬小麦高产条件下的CWSI阈值.本研究显示Jones简化模型能准确反映作物水分状态,并易于实现田间多点观测,可用于准确指导农田灌溉.