不同植被指数和无人机航高对草地盖度估测精度的影响

搭载高清数码相机的无人机在草地资源调查等方面具有成本低廉、机动性高、观察范围大等突出优势,拥有广阔的发展前景.本研究使用小型无人机(unmanned aerial vehicle,UAV)、手机相机等设备获取草地盖度数据,选用植被因子指数(vegetative index,VEG)、超绿指数(excess green index,ExG)、超绿超红差分指数(excess green minus excess red index,ExGR)和绿叶指数(green leaf index,GLI)4种基于可见光的植被指数提取草地盖度信息,从无人机航高、草地盖度水平等方面分析各植被指数的适用性.结果表明:1)VEG和ExG方法估测草地盖度的效果较好,平均精确度均在93％以上.ExGR与GLI方法的估测效果较差,平均精度仅75％～80％.2)4种方法的估测精度均随盖度增加而降低.VEG方法估测草地盖度的精度受盖度水平影响最小,ExG方法次之,ExGR和GLI方法对高盖度草地的估测效果较差.3)VEG方法在高、中盖度水平下的最适航高为100 m,在低盖度水平下为40 m;ExG和ExGR方法在高、中盖度水平下的最适航高为100 m,在低盖度水平下为80 m;GLI方法在高盖度水平下的最适航高为100 m,在中、低盖度水平下为20 m.

Influence of different vegetation indices and heights of UAVs on the accuracy of grassland coverage estimation

Unmanned aerial vehicles (UAVs) equipped with high-definition digital cameras have various advantages such as low cost, high mobility, and large observation range in the field of grassland resource surveys and have a developmental potential. In this study, small UAVs and mobile phone cameras were used to obtain grassland coverage data. The vegetative index (VEG), excess green index (ExG), excess green minus excess red index (ExGR), and green leaf index (GLI) were selected to extract the grassland coverage information based on the visible light vegetation index, and the applicability of each vegetation index was analyzed from the viewpoint of UAV flight height and grassland coverage level. The results showed that (1) VEG and ExG can effectively estimate grassland coverage, with an average accuracy of more than 93%. The estimation results of ExGR and GLI were poor, with an average accuracy of only 75%～80%. (2) The estimation accuracy of the four methods reduced with increasing coverage. VEG had the worst performance in terms of accuracy of grass coverage estimation, followed by ExG. ExGR and GLI were less effective in estimating high-coverage grasslands. (3) The optimal UAV heights for VEG were 100 m for the high and middle coverage levels and 40 m for the low coverage level. The optimal UAV heights for ExG and ExGR were 100 m for the high and middle coverage levels and 80 m for the low coverage level. The UAV optimum heights for GLI were 100 m for the high coverage level and 20 m for the middle and low coverage levels.