利用波形去噪算法的森林最大冠顶高估测研究

针对大光斑激光雷达回波信号噪声影响森林冠顶高估测精度,且回波分析法判定回波位置受限于平坦地区的问题,利用高斯低通滤波和小波去噪两种方法对GLAS波形进行去噪处理,提出了结合均方根倍差法和回波分析法来判定回波位置的有效算法。经小波去噪后信号的信噪比23.360 704,均方根误差为0.000 233 3,经均方根倍差法和回波分析法相结合来判定回波位置估测的冠顶高结果与实测结果相关性系数r值为0.864,效果均优于高斯低通滤波去噪。基于GLAS回波数据实验结果表明:小波去噪较好地实现了对回波信号的去噪处理,均方根倍差法和回波分析法相结合,实现了对坡度相对较大地区的GLAS波形的回波开始位置和地面回波位置的准确判定,对森林冠顶高的精确估算具有重要意义。     

An improved method for estimating forest canopy height using ICESat-GLAS full waveform data over sloping terrain: A case study in Changbai mountains,China

Light Detection And Ranging (LiDAR) has a unique capability for estimating forest canopy height, which has a direct relationship with, and can provide better understanding of the aboveground forest carbon storage. The full waveform data of the large-footprint LiDAR Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat), combined with field measurements of forest canopy height, were employed to achieve improved estimates of forest canopy height over sloping terrain in the Changbai mountains region, China. With analyzing ground-truth experiments, the study proposed an improved model over Lefsky's model to predict maximum canopy height using the logarithmic transformation of waveform extent and elevation change as independent variables. While Lefsky's model explained 8–89% of maximum canopy height variation in the study area, the improved model explained 56–92% of variation within the 0–30° terrain slope category. The results reveal that the improved model can reduce the mixed effects caused by both sloping terrain and rough land surface, and make a significant improvement for accurately estimating maximum canopy height over sloping terrain.     

全波形LiDAR数据分解的可变分量高斯混合模型及RJMCMC算法

传统激光雷达(light detection and ranging,LiDAR)数据处理均采用固定数的波形分解方法,容易遗漏部分重叠的返回波,降低波形拟合精度。为了实现可变数波形分解,本文提出了一种自动确定波形分解数的方法。假定波形数据服从混合高斯分布,并以此建立理想的波形模型;定义用于控制理想模型与实际波形拟合程度的能量函数,用吉布斯分布构建或然率;根据贝叶斯定理构建刻画波形分解的后验概率模型;设计可逆跳转马尔科夫链蒙特卡洛(reversible jump Markov chain Monte Carlo,RJMCMC)算法模拟该后验概率模型,以确定波形分解数并同时完成波形分解。为了验证提出算法的正确性,分别对不同区域的ICESat-GLAS波形数据进行了波形分解试验,定性和定量分析结果验证了本文方法的有效性、可靠性和准确性。