Investigating relationships between Landsat ETM plus sensor data and leaf area index in a boreal conifer forest

The aim of this paper is to investigate the feasibility of using Landsat ET M+ data for the determination of leaf area index (LAI). The investigation i s prompted by the need for obtaining spatially distributed data on LAI to b e used as input for carbon modelling of northern boreal forests. Detailed f ield data have been collected in a coniferous forest area in Uppland, centr al Sweden, dominated by Norway spruce and Scots pine. A forest canopy refle ctance model (Kuusk and Nilson, 2000) has been used to simulate stand refle ctances in the Landsat ETM+ wavelength bands as a means of investigating th e theoretical reflectance response to LAI changes. The analysis shows that the response to changes in LAI is strongest in the visible wavelength bands , particularly Channel 3, whereas only weak response is noted in the NIR ba nd and for some vegetation indices [simple ratio (SR) and NDVI]. Modelled r eflectances are influenced by various other factors, particularly ground re flectance and leaf biochemical properties. Observed reflectances from the L andsat ETM+ sensor have been compared with reflectance modelling results an d with field-based LAI estimates. The results indicate that LAI estimation using inverse canopy reflectance modelling may be difficult, given the larg e number of input parameters required and the current level of uncertainty in these parameters. Statistical relationships between LAI and observed ETM + reflectances are strongest in ETM+ Channel 7. (C) 2001 Elsevier Science I nc. All rights reserved.