Use of middle infrared radiation to estimate the leaf area index of a boreal forest

The leaf area index (LAI) of boreal forest can. be estimated using reflecte d radiation recorded by satellite sensors. Measurements of visible and near infrared radiation are commonly used in the normalized difference vegetati on index (NDVI) to estimate LAI. However, research, mainly in tropical fore st, has demonstrated that LAI is related more closely to radiation of middl e infrared wavelengths than of visible wavelengths. This paper derives a ve getation index, VI3, based on radiation from vegetation recorded at near an d middle infrared wavelengths. For a boreal forest canopy, the relationship between VI3 and LAI was observed to be much stronger than that between NDV I and LAI. In addition, the LAI estimated using VI3 accounted for about 76% of the variation in field estimates of LAI, compared with about 46% when u sing the NDVI. We conclude that information provided by middle infrared rad iation should be considered when estimating the leaf area index of boreal f orest.