A Model for Estimation of Fraction of Absorbed Photosynthetically Active Radiation from Multiple Satellite Data

The fraction of absorbed photosynthetically active radiation (FPAR) is a critical input parameter in many climate and ecological models. The accuracy of satellite FPAR products directly influences estimates of ecosystem productivity and carbon stocks. The targeted accuracy of FPAR products is approximately 10%, or 0.05, for many applications. Current FPAR products have an accuracy of 0.14 compared with total FPAR measurements, and 0.09 compared with green FPAR measurements. They are close to, but have not fulfilled, the accuracy requirement, and further improvements are needed.

This study combined a simplified radiative transfer based FPAR model and a refined surface reflectance database for estimation of FPAR from multiple satellite data, namely MODIS, MISR, and Landsat TM/ETM+. This new model improved the phenology curve of vegetation and the accuracy to 0.07 when validating with ground green FPAR measurements. Regional mapping of FPAR around the validation sites were demonstrated at multiple scales. The results showed that the retrieval rates were high and the FPAR distributions were consistent across the scales using this model. The FPAR derived from different satellite data had their distinct advantages. The FPAR retrieved from the multi-angular MISR data had the highest accuracy. The FPAR estimated from Landsat high spatial resolution data had detailed FPAR spatial distributions. The FPAR from MODIS had the highest temporal continuity. Further improvements of FPAR estimates could include the integration of FPAR across multiple scales.