Estimation of seasonal dynamics of understory NDVI in northern forests using MODIS BRDF data: Semi-empirical versus physically-based approach

The spatial and temporal patterns of the forest background reflectance are critically important for retrieving the biophysical parameters of the forest canopy (overstory) and for ecosystem modeling. In this short communication paper, we retrieved the seasonal courses of understory Normalized Difference Vegetation Index (NDVI) from MODIS BRDF data using the semi-empirical and physically-based approach. We compared the satellite-based understory NDVI series to seasonal courses of understory NDVI measured in the forests for three full growing seasons in boreal and hemiboreal sites in Northern Europe. Our results indicated both semi-empirical and physically-based approaches using MODIS BRDF data do have a potential to track seasonal changes in understory NDVI. Differences in the performance between of the two retrieval methods can be expected within the boreal zone depending on the level of forest fragmentation.