EVALUATION OF SPOT AND TM DATA FOR FOREST STRATIFICATION - A CASE-STUDY FOR SMALL-SIZE POPLAR STANDS

The value of SPOT and TM data for stratification of poplar stands prior to volume inventory is assessed. The stratification is based upon the poplar development stage, which is determined by canopy closure and tree height. The effect of development stage and type of understorey vegetation on the spectral radiance of poplar stands is analyzed throughout the vegetation period. The optimal acquisition date(s) and spectral range(s) and the most suited classification approach for discrimination of poplar development stages are determined. Satellite images recorded during the full growing season are to be preferred for poplar stand stratification according to development stage. In this period the interfering effect of the understory vegetation is minimal in proportion to the effect of the poplar stand development stage. Young poplar stands can accurately be classified as long as the appropriate spectral range of an image registered during the full growing period is selected. A multitemporal approach does not result in higher discrimination accuracies. Per field and per pixel approaches give similar classification accuracies. Although rather critical between old and middle-aged poplar stands, the discrimination between young and other poplar development stages is accurate enough for use in a stratification prior to volume inventory.