基于虚拟仪器的果树重叠叶片LAI实时检测系统

目前叶面积指数(leaf area index,LAI)检测中重叠叶片的辨别是一个难点。该文提出一种创新的重叠叶片LAI简易检测方法:在室内直射平行光源照射下,通过光电传感器检测叶片透射光能量,传感器信号经过调理,由数据采集卡采集至计算机,利用LabVIEW软件平台进行程序设计,自动判断重叠叶片层数。将叶片层数乘以传感器的接收面积即为该检测位置各层叶片面积,将整个检测过程中的叶片面积累加即为各层叶片的总面积,进而求出LAI。根据试验结果选用近红外作为光源,设计并制作用于检测的近红外光电传感器,其短路电流I1、I2分别与前置放大输出电压U1、主放大输出电压U2均有良好的线性关系,于0.05水平显著。数据采集试验结果表明,在手动进行扫描、定位采集的方式下,以方格法计算的LAI值作为准确值,系统对LAI的计算最大相对误差绝对值为14.8%。初步探讨了叶片间隔对透射辐射量的影响,结果发现乘幂模型的拟合效果较好。

Real-time detection system for LAI of fruiter overlapped leaves based on virtual instruments

At present, distinguishing overlapped leaves is the difficulty of measuring LAI(leaf area index). In this paper, a new method for the detection of LAI of overlapped leaves was proposed. The citrus leaves were put under the direct parallel light and the photoelectric sensor was used to measure the transmitted light energy. The output voltage signal of the sensor was sent into the computer through the data acquisition card. Then, the amount of overlapped layers was determined automatically by LabVIEW software programming. The amount of overlapped layers multiplied by the area of the sensor receiver was the area of the leaves. The total area of the leaves was the cumulative leaf area in the whole testing process and the LAI could be calculated. According to the experimental results, near-infrared was chosen as the photosource and a near-infrared photoelectric sensor was designed. The short circuit current I1 and I2 had a good linear relationship with the preamplifiers output voltage U1 and the main output voltage U2. The significant level of R2 was p<0.05. The data acquisition experimental results showed that the absolute value of the maximum relative error between the value of LAI calculated by this platform and the real value of LAI obtained by grid method was 14.8%, in the mode of manual scanning. Moreover, the LAI with distant leaves was tested in preliminary stage showing a power function with the leaf distance significantly.