Boreal Forest Aboveground Biomass Estimation with ICESat-2

Abstract:

Aboveground biomass is a critical element of the global carbon cycle, both in terms of the large magnitudes of carbon stored in aboveground woody material, and the ecological carbon-climate feedbacks related to disturbances from pests and fire which are particularly important for carbon cycling in the boreal system. Optical satellite data and modeling has demonstrated a capacity for forest structure mapping over large areas, but accuracies are limited and spaceborne lidar has higher sensitivity for forest structure at the spatial scales of boreal forest processes (~30 – 100 m). ICESat-2 has produced forest height products at a 100-m segment resolution openly available via the ATL08 product, but the mission does not have an official biomass requirement or product. This research presents early results from two recently funded NASA projects (one through NASA’s ABoVE program, and one through the ICESat-2 Science Team). These projects focus on using height data from ICESat-2 to estimate and map woody aboveground biomass for the boreal domain. We explore the transference of models developed for NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission that translate height measurements into estimates of biomass based on a global field and airborne lidar campaign. This approach has been extended into the boreal domain with field and airborne lidar datasets from Canada, Alaska, Finland, Sweden, Norway and the UK. We test the sensitivity of biomass estimation to the spatial segment length of ATL08, applying GEDI-like models to 30-m, 50-m and 100-m segment lengths, and test against airborne lidar biomass maps, and compare predictor height metrics between the two sensors to adjust for biases. The biomass estimates presented here can extend the biomass mapping activities of GEDI which collects forest structure measurements from the ISS for tropical and temperate forests between ~51.6 degrees North and South. Together, the boreal wide estimates from this work will be combined with GEDI’s products for a global baseline forest biomass map representative of ~2020 conditions.