Biomass Inventory Using Small Footprint Lidar: Preliminary Results in Two Maryland Counties

The Carbon Monitoring System (CMS) project started in September 2010 with a mandate from the U.S. Congress to NASA (NASA, 2010). The primary goal of the project is the estimation of above-ground biomass stocks and carbon fluxes, the appraisal of error budgets and the delivery of cartographic products and other geo-referenced information for selected locations at a scale that is ecologically meaningful and relevant for forest management. The project is incrementally planning to marry carbon monitoring efforts firstly at both local and federal scale and then globally. As part of the local component of this effort, small footprint LiDAR data from archive have been analysed for two counties in Maryland. LiDAR metrics, such as the percentile distribution of heights and density deciles, were generated for each National Land Cover Database (NLCD) pixel at 30 m resolution. Field data for validation and training of models consisted of variable plot sizes with BAF 10, 20 and 30. Training of models was based on a previous stratification of woodland types into evergreen, broadleaves, mixed, wetlands and non-wooded areas. The biomass models were derived by means of empirical fits between ground-measured biomass and the LiDAR metrics generated for each stratum. The results showed coefficients of determination ranging above 0.70 for all the strata with the exception of mixed woodlands (0.48). The distribution of the residuals showed a bias for plots with largest biomass levels measured in the field, due to the unintended inclusion of boundary trees. The final results were converted into a 30m raster map showing the spatial distribution of biomass in Mg ha-1. Further research within the CMS initiative will concentrate on further validation and error analysis in addition to replicating this methodology in other monitoring areas in order to ensure this methodology is consistent and widely applicable. REFERENCE NASA, 2010. NASA Carbon Monitoring System Initiative. Available online at: http://cce.nasa.gov/cce/cms/index.html.