Mapping the height and above-ground biomass of a mixed forest using lidar and stereo Ikonos images

Our objective was to assess the accuracy of the forest height and biomass estimates derived from an Ikonos stereo pair and a lidar digital terrain model (DTM). After the Ikonos scenes were registered to the DTM with submetric accuracy, tree heights were measured individually by subtracting the photogrammetric elevation of the treetop from the lidar ground-level elevation of the tree base. The low residual error (1.66m) of the measurements confirmed the joint geometric accuracy of the combined models. Matched images of the stereo pair were then used to create a digital surface model. The latter was transformed to a canopy height model (CHM) by subtracting the lidar DTM. Plotwise height percentiles were extracted from the Ikonos-lidar CHM and used to predict the average dominant height and above-ground biomass. The coefficient of determination reached 0.91 and 0.79 for average height and biomass, respectively. In both cases, the accuracy of the Ikonos-lidar CHM predictions was slightly lower than that of the all-lidar reference CHM. Although the CHM heights did not saturate at moderate biomass levels, as do multispectrall or radar images, values above 300Mgha(-1) could not be predicted accurately by the Ikonos-lidar or by the all-lidar CHM.