利用鱼眼摄像机测量植被叶面积指数动态变化

叶面积指数(LAI)的快速准确测量可以为相关生态过程研究提供关键参数.本研究采用光学鱼眼相机拍摄了黄土高原北部典型植被柠条、沙柳、紫花苜蓿、荒草、大豆和玉米不同生长时期冠层照片,在玉米、大豆和柠条样地固定安装鱼眼摄像机定时拍摄冠层照片,并运用图像处理软件分析获取LAI.结果表明: 鱼眼相机法(DHP)获取的多种植被类型的LAI与LAI-2200测量结果存在显著线性相关关系(R²=0.85,P<0.05),均方根误差为0.256.太阳辐射值直接影响专业软件处理照片时的关键参数,镜头朝下情况下,计算LAI的关键参数——绿色指数随着拍摄照片时太阳辐射强度的增加而增加.但是镜头朝上情况下,亮度参数随着太阳辐射值的增加而减少.通过关键参数的调整,玉米、大豆和柠条样地LAI变化与LAI-2200测量结果一致,很好地反映了这些植物生长期的LAI动态变化,柠条样地镜头朝下测量结果更好.鱼眼摄像机可以用于定位监测LAI动态变化.

Measuring the dynamics of leaf area index of vegetation using fisheye camera

The rapid and accurate measurement of LAI is of great importance for the research of ecological processes. Photos from typical land use types in the northern Loess Plateau, including Caragana, Salix, alfalfa, wild grass, soybean and maize, were measured by digital hemispherical photography (DHP). Meanwhile, photos were daily taken by video camera with fisheye lens and the pictures were analyzed by image processing software to obtain the dynamics of LAI in soybean, maize and Caragana fields. The results showed that a linear correlation existed between the LAI measured by DHP and LAI-2200. The coefficient of determination (R²) was 0.85 (P<0.05) and root mean square error (RMSE) was 0.256. The key parameters of professional software were affected by the local solar radiation. When the downward lens was used, the green index was the key parameter which increased with the increase of solar radiation. However, the brightness index decreased with the increase of solar radiation when the lens was upward. Through the adjustment of the key parameters, the results of LAI of maize, soybean, and Caragana were consistent with the LAI-2200 results, well reflecting LAI dynamics during the plant growth. The downward lens in Caragana field was better. The fisheye camera could be used for monitoring the dynamic LAI of different vegetations.