Ecosystem structure (DP3.30015.001)

Forests store and sequester a considerable proportion of the terrestrial global carbon budget. Forest canopy metrics are directly measurable with LiDAR sensors because laser pulses will be reflected from the uppermost canopy layers and remaining energy will penetrate to, and reflect from, under-story and the ground surface. The near simultaneous direct measurement of ground and canopy elevation allows the canopy height to be estimated through differencing. The CHM is generated by creating a continuous surface of canopy height estimates across the entire spatial domain of the LiDAR survey. The CHM is derived directly from the LiDAR point cloud. The LiDAR point cloud is produced from LiDAR return signals from both surface features and the true-ground as LiDAR pulses will be reflected from the uppermost layers of the canopy, as well as the underlying ground surface. To produce the CHM, the point cloud is separated into classes representing the ground and vegetation returns. The ground classified points allow calculation of a height normalized point cloud to provide a relative estimate of vegetation elevation. A surface is then generated using the height normalized vegetation points to produce the CHM. Any canopy heights less than 2m are set to zero. Latency: AOP data will be available 60 days after the final collection day at a site.

森林储存并固存了全球陆地碳预算中相当大的一部分。森林冠层指标可通过激光雷达（LiDAR）传感器直接测量，因为激光脉冲会从冠层最上层发生反射，剩余能量则会穿透并从林下植被层与地表反射。对地表和冠层高程进行近乎同步的直接测量后，可通过差值运算估算冠层高度。冠层高度模型（Canopy Height Model, CHM）通过在激光雷达测绘的整个空间范围内生成连续的冠层高度估算表面而得到，其直接由激光雷达点云衍生而来。激光雷达点云由来自地表特征和真实地表的激光雷达回波信号生成，因为激光脉冲既会从冠层上层反射，也会从下方地表反射。为生成冠层高度模型，需将点云划分为分别代表地表回波与植被回波的类别。经分类的地表点云可用于计算高度归一化点云，以提供植被高程的相对估算值。随后利用高度归一化后的植被点云生成表面，进而得到冠层高度模型。所有低于2米的冠层高度均被设为0。数据延迟说明：航空观测平台（Airborne Observation Platform, AOP）数据将在某一站点的最终采集日结束后60天内开放获取。