Abstract
Remote sensing of the fraction of absorbed Photosynthetically Active Radiation (fPAR) has become a timely option to monitor forest productivity. However, only a few studies have had ground reference fPAR datasets containing both forest canopy and understory fPAR from boreal forests for the validation of satellite products. The aim of this paper was to assess the performance of two currently available satellite-based fPAR products: MODIS fPAR (MOD15A2, C5) and GEOV1 fPAR (g2_BIOPAR_FAPAR), as well as an NDVI-fPAR relationship applied to the MODIS surface reflectance product and a Landsat 8 image, in a boreal forest site in Finland. Our study area covered 16 km2 and field data were collected from 307 forest plots. For all plots, we obtained both forest canopy fPAR and understory fPAR. The ground reference total fPAR agreed better with GEOV1 fPAR than with MODIS fPAR, which showed much more temporal variation during the peak-season than GEOV1 fPAR. At the chosen intercomparison date in peak growing season, MODIS NDVI based fPAR estimates were similar to GEOV1 fPAR, and produced on average 0.01 fPAR units smaller fPAR estimates than ground reference total fPAR. MODIS fPAR and Landsat 8 NDVI based fPAR estimates were similar to forest canopy fPAR.
Highlights
The fraction of absorbed Photosynthetically Active Radiation by green vegetation is a determinant of energy flows between the soil and atmosphere, and is one of the Essential ClimateVariables (ECVs) according to international Global Climate Observing Systems-network (GCOS) [1].fPAR has a central role in global environmental monitoring because it is directly linked with ecosystem functioning, and is retrievable from space
Concept introduced by Monteith [2], if Light Use Efficiency (LUE) is assumed to be relatively invariable within species, the net primary productivity of terrestrial ecosystems can be estimated from fPAR when the amount of incident
We show data from Terra instead of the combined product because GEOV1 fPAR is acquired at the same time and its development has partly been based on data from the MODIS Terra sensor
Summary
FPAR has a central role in global environmental monitoring because it is directly linked with ecosystem functioning, and is retrievable from space. Concept introduced by Monteith [2], if LUE is assumed to be relatively invariable within species, the net primary productivity of terrestrial ecosystems can be estimated from fPAR when the amount of incident. Empirical methods for the retrieval of fPAR from space are commonly based on combinations of the reflectance of vegetation in the red and Near Infrared (NIR) spectral bands. Several satellite-based fPAR products have been developed during the past decade. These products are crucial for estimating the seasonal and long-term courses of fPAR of forest areas. Recent studies have concentrated on the intercomparison and evaluation of different fPAR products over large areas, e.g., over
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