The Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) is an Essential Climate Variable that can be monitored from space and provides information on the state of and changes in the photosynthetic activity of vegetation. It allows for the quantification of terrestrial vegetation productivity and carbon cycling. The detection of trends and anomalies in vegetation activity can also help to improve the characterisation of extreme climate events and support environmental policies.
Optical remote sensing is the most appropriate tool for monitoring FAPAR over vegetated surfaces from space. However, the limited lifetime of satellite instruments does not permit the assembling of a long time series on the basis of a single sensor; observations from multiple sensors, which differ in spatial resolution and time of acquisition, need to be merged into a continuous time series. The JRC created such an extensive dataset of FAPAR (recorded every 10 days, at about 1 km resolution, from September 1997 to April 2012), combining information from two sensors: the NASA/Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the European Space Agency (ESA)/Medium Resolution Imaging Spectrometer Instrument (MERIS).
This paper describes the JRC methodology used to combine the two sensors’ observations. Tested over Europe and the Horn of Africa, this methodology was also able to reduce the noise, fill the gaps and correct trends in the data, providing a time-consistent coverage of FAPAR.
Further applications of this methodology could include the study of the impact of land use changes and drought on vegetation, carbon budgets and climatic changes.