Eight coniferous ‘ground truth’ stands were studied in the NOPEX region. Needle 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 reflectance 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 along 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 relative error in LAI 30–40%. The best spectral bands appeared to be TM5, SPOT XS2, SPOT XS1, TM7 and TM3. Canopy LAI can be successfully estimated from the coefficients of penetration of direct and diffuse radiation to the forest floor. This has been demonstrated by an analysis of the results of ground-based measurements of canopy transmission of the ground truth stands by means of a four-channel field radiometer.
Agricultural and Forest Meteorology – Elsevier
Published: Dec 31, 1999
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