Resource information
Standard data products from NASA’s moderate resolution imaging spectroradiometer (MODIS) were available at launch (collection 3) and have undergone two revisions (collections 4 and 5) during the continuing Terra and Aqua missions. In 2000, a research project was conducted in large fields of corn and soybean to evaluate MODIS leaf area index (LAI) and land cover type (MOD15 and MOD12 data products, respectively) as input to crop yield models. Our objective was to compare collections 3, 4 and 5 with the ground data to determine data product improvement. Classification of land cover type for collections 3, 4 and 5 were similar to the USDA-NASS Cropland Data Layer. The collection 5 MOD15 LAI was considerably improved over earlier collections when the quality assurance flags indicated good LAI retrievals. Land surface reflectances (MOD09) of MODIS band 2 (near-infrared, 250-m) were used as inputs to an inversion of the scattering by arbitrarily inclined leaves (SAIL) model. Compared to the collection 5 MOD15 product, SAIL-derived LAI had approximately equal agreement with the field data and had less systematic bias in root mean square error (RMSE). MODIS data products were designed to address global scientific questions without reliance on ground data, whereas the SAIL model inversions required ground data for model inputs. The accuracy of MODIS observations was not limiting LAI accuracy for broadleaf crops; additional information from non-MODIS sources may be required for improved MOD15 LAI.
