Complementary Use of Airborne LiDAR and Terrestrial Laser Scanner to Assess AboveGround Biomass/Carbon in Ayer Hitam Tropical Rain Forest
Cora Jane C. Lawas1, Yousif Ali Hussin2, Evert Henk Kloosterman3
Abstract
This study aimed to develop a method of assessing the AGB/carbon stock of a tropical lowland
rainforest with a vertically complex structure. The method utilizes the complementary strengths of airborne LiDAR and terrestrial laser scanning system to assess the upper and lower canopies of the forest to achieve reasonable results. The method was implemented in Ayer Hitam Forest Reserve in Malaysia. The upper canopy layer was assessed by generating tree parameters using airborne LiDAR to obtain height from CHM and segmenting the Orthophoto to obtain CPA. DBH was modelled through multiple regression using the derived parameters as independent variables and the field DBH as the dependent variable. The modelled DBH achieved an R2 value of 0.90 and RMSE of 0.02 cm for the 16 plots. To estimate the AGB an allometric equation was applied to the modelled DBH together with LIDAR derived height. The modelled AGB was validated using the field DBH and LiDAR derived height. The derived model has an R2 of 0.98 and RMSE of 69.44 Kg for the 16 plots.
The lower canopy layer was assessed using the registered scene from the TLS. This is to complement the trees that were not identified from the upper canopy layer. Scanned trees in the plot were extracted. Then DBH and height parameters were measured using RiSCAN Pro software interface. These parameters were then used for the allometric equation to estimate the AGB for the lower canopy. The correlation of the TLS measured DBH and field measured DBH was established and achieved an R2 value of 0.99 and RMSE of 1.03 cm. The modelled AGB was estimated using the TLS measured height and DBH by applying the allometric equation. The model was validated using the field measured DBH and TLS derived height. The result was a model with an average R2 value of 0.99 and RMSE of 19.23 Kg for the 16 plots. The derived AGB from the upper and lower canopies were combined. The accuracy of the complementary method of deriving the estimated AGB from the two sensors was assessed by obtaining the R2 and RMSE of the two sensors. The achieved R2 and RMSE is 0.98 and 188.35 kg respectively for the 16 plots.
The results in this study presented a potential method of addressing the need to provide accurate AGB/carbon assessment for a complex multi-layered tropical rain forest.
Keywords
Airborne LiDAR, Terrestrial laser scanner (TLS), Segment, AGB, allometric equation
Link to the Article