Ground-based canopy transmittance and satellite remotely sensed measurements for estimation of coniferous forest canopy structure

Ground-based measurements of forest canopy transmittance provide a ready means of estimating intercepted photosynthetically active radiation (IPAR) for use in calibrating satellite remotely sensed estimates of forest canopy structure. The relationship between canopy transmittance and Landsat Thematic Mapper (TM) near IR/red radiance ratio data was examined for a temperature coniferous forest study site in northwestern Montana. Semivariogram analysis showed that the canopy transmittance and the TM near IR/red ratio had a similar spatial autocorrelation structure. Due to the fine scale patchiness of the forest canopy, the canopy transmittance and TM data were averaged at the coarser scale of the hillslope terrain units for regression analysis. These hillslope averaged data sets showed a strong linear relationship ( R 2 = 0.66). The transmittance measurements were converted to leaf area index (LAI) but comparison with previous results obtained for coniferous forests in Oregon (Peterson et al., 1987) shows some differences in the relationship between LAI and TM near IR/red ratio.