Evaluation of six satellite-derived Fraction of Absorbed Photosynthetic Active Radiation (FAPAR) products across the Australian continent

The satellite FAPAR products are compared to ~ 800 observation-based estimates of fractional vegetation cover at field sites across Australia. After accounting for offsets in FAPAR, relatively high agreement occurs at sites classified as grasslands, shrublands and managed land (agriculture). Significant disagreement occurs at sites correctly classified as forests. Consequently, some products show significant differences in FAPAR between regions of similar vegetation cover but different biome classification. We find that all products show a much lower sensitivity to fractional vegetation cover (range in coefficient of linear regression: 0.28-0.61) than is predicted theoretically (0.96-1.18) using a canopy radiative transfer model. Reasons for this discrepancy are discussed.