Mitigating Uncertainty from Vegetation Spatial Complexity with Highly Portable Lidar

Abstract:

To fully utilize the excellent spatial coverage and temporal resolution offered by satellite resources for estimating ecological variables, fine-scale observations are required for comparison, calibration and validation. Lidar instruments have proved effective in estimating the properties of vegetation components of ecosystems, but they are often challenged by occlusion, especially in structurally complex and spatially fragmented ecosystems such as tropical forests. Increasing the range of view angles, both horizontally and vertically, by increasing the number of scans, can mitigate occlusion. However these scans must occur within the window of temporal stability for the ecosystem and vegetation property being measured.

The Compact Biomass Lidar (CBL) is a TLS optimized for portability and scanning speed, developed and operated by University of Massachusetts Boston. This 905nm wavelength scanner achieves an angular resolution of 0.25 degrees at a rate of 33 seconds per scan. The ability to acquire many scans within narrow windows of temporal stability for ecological variables has facilitated the more complete investigation of ecosystem structural characteristics, and their expression as a function of view angle. The lightweight CBL has facilitated the use of alternative deployment platforms including towers, trams and masts, allowing analysis of the vertical structure of ecosystems, even in highly enclosed environments such as the sub-canopy of tropical forests where aerial vehicles cannot currently operate.

We will present results from view angle analyses of lidar surveys of tropical rainforest in La Selva, Costa Rica where the CBL was deployed at heights up to 10m in Carbono long-term research plots utilizing a portable mast, and on a 25m stationary tower; and temperate forest at Harvard Forest, Massachusetts, USA, where the CBL has been deployed biannually at long-term research plots of hardwood and hemlock, as well as at heights of up to 25m utilizing a stationary tower.