Spatial validation of the collection 4 MODIS LAI product in Eastern Amazonia

This paper reports on the validation of the Collection 4 MODIS leaf area index (LAI) product over the Tapajos region, eastern Amazonia. The validation site is enclosed in the h12v09 of the MODIS LAI product. The methodology to assess MODIS LAI accuracy included two main steps: 1) A multiple regression analysis for the generation of LAI surfaces, based on the relationships between field data and remote sensing information from the Enhanced Thematic Mapper Plus sensor, and between field data and topographic information from a digital elevation model; 2) the direct comparison of these LAI surfaces with the MODIS LAI surfaces. The analysis indicated that MODIS LAI is significantly overestimated for the Tapajos region by a factor of 1.18. No relationships between MODIS LAI and the validation surfaces were found. These results are indicative of a predominance of LAI retrievals by the backup algorithm, which is overcompensating LAI values at the saturation domain. The overgeneralization of the land cover layer (MOD12Q1) can be a source of uncertainties for the lookup table parameterization. Further validation efforts must be carried out over Amazonia for a quantitative quality assessment of the MODIS LAI surfaces in order to improve its accuracy.