Estimating site index from short term TanDEM-X canopy height models

The tree height growth from three vegetation seasons was fitted to height growth curves in order to estimate the site index, which is a variable related to forest site productivity. The tree height growth was evaluated for four different cases, in which remote sensing data from TanDEM-X and airborne laser scanning were used. The used method requires a digital terrain model and knowledge about the tree species. Furthermore, the remote sensing data were calibrated using Lorey'smean height heights or airborne laser scanning data. It was found that four annual acquisitions of calibrated TanDEM-X data covering three vegetation seasons could be used for estimating the site index on 27 0.5-ha field plots with 4.4-m (12.1%) RMSE. The site index could in a similarmanner be estimated from only two airborne laser scanning acquisitions, before and after four vegetation seasons, with 2.3-m (6.3%) RMSE.