坡度对应用机载激光雷达估测人工针叶林单木参数的影响

以黑龙江省佳木斯市桦南县孟家岗林场为研究对象,利用2017年的机载激光雷达(ALS)数据构建冠层高度模型(CHM),探索坡度对单木参数估测的影响。研究区域内坡度分为4级,Ⅰ级为平坡:坡度<5°;Ⅱ级为缓坡:坡度5°~14°;Ⅲ级为斜坡:坡度15°~24°;IV为陡-急-险坡:坡度≥25°。每一级选取8块高郁闭度的人工针叶林样地(50 m×50 m),应用基于区域的分层横截面分析法(RHCSA)进行单木树冠提取,估测单木位置、树高和冠幅信息,利用目视解译的单木树顶和树冠作为参考数据进行精度检验(包括单木树冠提取精度和单木参数估测精度检验)。结果表明:不同坡度下单木树冠提取和单木定位估测均有显著差异(p<0.05)。其中,平坡上的单木树冠提取总体精度最高(均值为84.61%),陡-急-险坡上的总体精度最低(均值为41.31%);缓坡上的单木定位精度最高,平均的均方根误差为1.16 m,陡-急-险坡上单木定位精度最低,平均均方根误差为1.58 m。但是,不同坡度下单木树高和冠幅的估测结果差异并不显著(p>0.05)。因此,应用CHM进行单木参数估测时,虽然进行了地形标准化,但还是需要考虑坡度对单木树冠提取和单木定位的影响,而其对树高和冠幅的影响不大。

Effects of Slope on the Estimates of Individual Tree Parameters for Coniferous Plantation Using Airborne Laser Scanner

We applied airborne laser scanner(ALS) data captured in 2017 to build canopy height model(CHM) for exploring the effects of slope on the estimates of individual tree parameters in Mengjiagang Forest Farm located in Huanan County, Jiamusi City, Heilongjiang Province. The slope was divided into four categories(Class I: flat, <5°;Class II: gentle, 5°-14°;Class III: incline, 15°-24°;Class IV: steep-rapid-dangerous: ≥25°). We selected eight plots(50 m×50 m) of coniferous plantation with high density within each class and employed region-based hierarchical cross-section analysis(RHCSA) to conduct individual tree crown delineation, and estimate tree locations, and tree height and crown diameter. Reference treetops and tree crowns were manually interpreted and delineated for accuracy assessment of individual tree delineation and parameter estimations. There was significant difference(p<0.05) of individual tree crown delineation and tree location estimates among different slope classes. The overall accuracy of individual tree delineation on the flat slope and steep-rapid-dangerous were the highest(mean is 84.61%) and the lowest(mean is 41.31%), respectively. The accuracy of individual tree positioning on the gentle class and steep-rapid-dangerous were the highest(average RMSE(Root Mean Square Error) is 1.16 m) and the lowest(average RMSE is 1.58 m), respectively. However, the estimation of individual tree height and crown diameter with various slopes were notsignificantly different(p>0.05). Thus, although terrain normalization is performed when applying CHM for estimating individual tree parameters, it is still necessary to consider the effects of slope on individual tree crown delineation and positioning, whereas there is little influence on the estimation of tree height and crown diameter.