Can We Use the QA4ECV Black-sky Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) using AVHRR Surface Reflectance to Assess Terrestrial Global Change?

Gobron Gobron,Robustelli Robustelli,Marioni Marioni,Vermote Vermote

doi:10.3390/rs11243055

Abstract

NOAA platforms provide the longest period of terrestrial observation since the 1980s. The progress in calibration, atmospheric corrections and physically based land retrieval offers the opportunity to reprocess these data for extending terrestrial product time series. Within the Quality Assurance for Essential Climate Variables (QA4ECV) project, the black-sky Joint Research Centre (JRC)-fraction of absorbed photosynthetically active radiation (FAPAR) algorithm was developed for the AVHRR sensors on-board NOAA-07 to -16 using the Land Surface Reflectance Climate Data Record. The retrieval algorithm was based on the radiative transfer theory, and uncertainties were included in the products. We proposed a time and spatial composite for providing both 10-day and monthly products at 0.05º × 0.05º. Quality control and validation were achieved through benchmarking against third-party products, including Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) datasets produced with the same retrieval algorithm. Past ground-based measurements, providing a proxy of FAPAR, showed good agreement of seasonality values over short homogeneous canopies and mixed vegetation. The average difference between SeaWiFS and QA4ECV monthly products over 2002–2005 is about 0.075 with a standard deviation of 0.091. We proposed a monthly linear bias correction that reduced these statistics to 0.02 and 0.001. The complete harmonized long-term time series was then used to address its fitness for the purpose of analysis of global terrestrial change.

Highlights

The majority of solar radiation available to the Earth system is absorbed at or near the oceanic and continental surface
Few of these are directly observable from space, but they jointly determine the fraction of absorbed photosynthetically active radiation (FAPAR) that acts as an integrated indicator of the status and health of plant canopies and can be retrieved by space remote sensing techniques [2,3,4]
National Centers for Environmental Information (NCEI) values are slightly higher than the values of QA4ECV and Joint Research Centre (JRC)-Two-Stream Inversion Package (TIP) products, especially over the desert grassland

Summary

Introduction

The majority of solar radiation available to the Earth system is absorbed at or near the oceanic and continental surface. This energy is released to the atmosphere through fluxes of infrared radiation, as well as sensible and latent heat. The state and the evolution of terrestrial vegetation are characterized by a large number of physical, biochemical, and physiological variables Few of these are directly observable from space, but they jointly determine the fraction of absorbed photosynthetically active radiation (FAPAR) that acts as an integrated indicator of the status and health of plant canopies and can be retrieved by space remote sensing techniques [2,3,4]. FAPAR plays a critical role in the global carbon cycle and in the determination of the primary productivity of the biosphere [5,6,7]

Methods

Results

Conclusion