Determination of needle area indices of coniferous forest canopies in the NOPEX region by ground-based optical measurements and satellite images

Eight coniferous 'ground truth' stands were studied in the NOPEX region. Ne edle area indices (LAI) of the stands were estimated via regressions on the tree parameters and stand density measured on the respective sample plots. Reflectances of the ground truth stands were simulated by a forest reflect ance model and related to the canopy LAI. In all short-wave spectral bands of Landsat TM and SPOT, decreasing non-linear trends of stand reflectance a long with an increase in LAI were observed. The trends were confirmed by an analysis of satellite images. With the logarithmic regression of stand LAI on Landsat TM or SPOT DNs, the ground truth information can be extended to the rest of coniferous forests in the NOPEX region with approximate relati ve error in LAI 30-40%. The best spectral bands appeared to be TM5, SPOT XS 2, SPOT XS1, TM7 and TM3. Canopy LAI can be successfully estimated from the coefficients of penetration of direct and diffuse radiation to the forest Boor. This has been demonstrated by an analysis of the results of ground-ba sed measurements of canopy transmission of the ground truth stands by means of a four-channel field radiometer. (C) 1999 Elsevier Science B.V. All rig hts reserved.