Characterizing global forest canopy cover distribution using spaceborne lidar
Characterizing global forest canopy cover distribution using spaceborne lidar
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DOI：
10.1016/j.rse.2019.111262
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发表时间：
2019-09
影响因子：
13.5
通讯作者：
Hao Tang;J. Armston;Steven Hancock;S. Marselis;Scott Goetz;R. Dubayah
中科院分区：
文献类型：
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作者：
Hao Tang;J. Armston;Steven Hancock;S. Marselis;Scott Goetz;R. Dubayah
全球森林动态的详细描述需要精确测量树冠覆盖范围，而不仅仅是估计森林面积的范围。尽管被动光学遥感技术在识别全球森林覆盖丧失热点方面取得了显著成功，但仍不能完全满足地块或树冠级别的观测要求。信号饱和和算法不确定性等关键问题限制了使用卫星图像生成的标准产品捕获微妙的树冠覆盖变化，特别是在基本完好的茂密热带森林上。星载激光雷达遥感可以通过提供 3D 冠层结构的直接测量来填补当代地球观测网络中的这一空白。在这里，我们利用美国宇航局冰、云和陆地高程卫星 (ICESat-1) 上的地球科学激光测高系统 (GLAS) 的观测结果来分析全球树冠覆盖分布。我们发现，即使在覆盖率超过 80% 的茂密森林中，基于 ICESat 的覆盖估计对冠层覆盖动态也很敏感，并且与传统光学遥感衍生的现有产品相比，能够更好地表征生物群落水平梯度和冠层覆盖分布。在足迹层面，ICESat-1 与机载估计值相比几乎没有偏差，并且 RMSE 值约为 20% 的覆盖范围。基于激光雷达改进的覆盖产品应该能够在景观尺度上全面分析森林结构的细微变化，并为森林的生物物理分层和垂直冠层结构的变化提供独特的信息。鉴于国际空间站最近安装了全球生态系统动力学调查（GEDI）激光雷达，这一点尤其正确，该激光雷达将以比迄今为止更高的采样密度获取更高分辨率的激光雷达数据。
Detailed characterization of global forest dynamics requires accurate measurements of canopy cover beyond estimating the extent of forested area. Passive-optical remote sensing techniques, despite remarkable success in identifying global hotspots of forest cover loss, cannot fully satisfy observation requirements at the plot or canopy crown level. Critical issues including signal saturation and algorithm uncertainty impose limitations on capturing subtle canopy cover changes using standard products generated from satellite imagery, particularly over largely intact dense tropical forests. Spaceborne lidar remote sensing can fill this gap in contemporary Earth observation networks by providing direct measurements of 3-D canopy structure. Here we analyze global canopy cover distributions using observations from the Geoscience Laser Altimetry System (GLAS) onboard of NASA's Ice, Cloud, and land Elevation Satellite (ICESat-1). We found ICESat-based cover estimates were sensitive to canopy cover dynamics even over dense forests with cover exceeding 80% and were able to better characterize biome-level gradients and canopy cover distributions than the existing products derived from conventional optical remote sensing. At the footprint level, ICESat-1 produced almost no bias when compared with airborne estimates, and had RMSE values on the order of ~20% cover. Improved cover products based on lidar should allow comprehensive analysis of subtle forest structure changes at landscape scales, and provide unique information for biophysical stratification of forests and changes in vertical canopy structure. This is particularly true given the Global Ecosystem Dynamics Investigation (GEDI) lidar recently installed on the International Space Station, which will acquire higher resolution lidar data at greater sampling densities than has been available to date.