Abstract
Mapping of terrestrial chlorophyll fluorescence from space has shown potential for providing global measurements related to gross primary productivity (GPP). In particular, space-based fluorescence may provide information on the length of the carbon uptake period. Here, for the first time we test the ability of satellite fluorescence retrievals to track seasonal cycle of photosynthesis as estimated from a diverse set of tower gas exchange measurements from around the world. The satellite fluorescence retrievals are obtained using new observations near the 740nm emission feature from the Global Ozone Monitoring Experiment 2 (GOME-2) instrument offering the highest temporal and spatial resolution of available global measurements. Because GOME-2 has a large ground footprint (~40×80km2) as compared with that of the flux towers and the GOME-2 data require averaging to reduce random errors, we additionally compare with seasonal cycles of upscaled GPP estimated from a machine learning approach averaged over the same temporal and spatial domain as the satellite data surrounding the tower locations. We also examine the seasonality of absorbed photosynthetically-active radiation (APAR) estimated from satellite measurements. Finally, to assess whether global vegetation models may benefit from the satellite fluorescence retrievals through validation or additional constraints, we examine seasonal cycles of GPP as produced from an ensemble of vegetation models. Several of the data-driven models rely on satellite reflectance-based vegetation parameters to derive estimates of APAR that are used to compute GPP. For forested (especially deciduous broadleaf and mixed forests) and cropland sites, the GOME-2 fluorescence data track the spring onset and autumn shutoff of photosynthesis as delineated by the upscaled GPP estimates. In contrast, the reflectance-based indicators and many of the models, particularly those driven by data, tend to overestimate the length of the photosynthetically-active period for these biomes. Satellite fluorescence measurements therefore show potential for improving the seasonal dependence of photosynthesis simulated by global models at similar spatial scales.
| Original language | English |
|---|---|
| Pages (from-to) | 375-391 |
| Number of pages | 17 |
| Journal | Remote Sensing of Environment |
| Volume | 152 |
| DOIs | |
| State | Published - Sep 2014 |
Funding
Funding for this work was provided in part by the NASA Carbon Cycle Science program ( NNH10DA001N ). The authors gratefully acknowledge EUMETSAT and the MODIS data processing team for making available the GOME-2 and MODIS data sets, respectively, used here as well as the algorithm development teams. We also thank James Collatz, Randy Kawa, William Cook, Yen-Ben Cheng, Larry Corp, Petya Campbell, Qingyuan Zhang, and Arlindo da Silva for helpful discussions. We are indebted to Philip Durbin for assistance with the GOME-2 satellite data set. We also thank Joshua Fisher and an anonymous reviewer for helpful comments that helped to improve the paper. This study uses eddy covariance data acquired by the FLUXNET community and in particular by the following networks: AmeriFlux ( U.S. Department of Energy, Biological and Environmental Research, Terrestrial Carbon Program ( DEFG0204ER63917 and DEFG0204ER63911 )) AfriFlux, CarboAfrica, CarboEuropeIP, CarboItaly, CarboMont, FluxnetCanada (supported by the CFCAS , NSERC , BIOCAP , Environment Canada , and NRCan ), GreenGrass, KoFlux, LBA, NECC, OzFlux, and USCCC. We acknowledge the financial support to the eddy covariance data harmonization provided by the CarboEuropeIP , FAOGTOSTCO , iLEAPS , Max Planck Institute for Biogeochemistry , National Science Foundation , University of Tuscia , Wageningen University CALM Group (Climate change and Adaptive Land and Water Management) , Universit Laval and Environment Canada and U.S. Department of Energy and the database development and technical support from the Berkeley Water Center, Lawrence Berkeley National Laboratory, Microsoft Research eScience, Oak Ridge National Laboratory, University of California Berkeley, University of Virginia, and South Dakota State University. Sites in the U.S. also acknowledge support from the National Science Foundation (NSF) , U.S. Department of Agriculture (USDA) , and the U.S. Department of Energy (DOE) . Funding for this research was also provided by the Biological and Environmental Research Program (BER), U.S. DOE , through the Midwestern Center of the National Institute for Global Environmental Change (NIGEC) under Cooperative Agreements DE-FC03-90ER61010 , and from the BER under Cooperative Agreements DE FG02-03ER63624 and DE-FG03-01ER63278 , NOAA grant NA09OAR4310063 , and NASA grants NNX10AR63G and NNX11A008A . Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the DOE. Access to the MMSF AmeriFlux site is provided by the Indiana Department of Natural Resources, Division of Forestry. The ZA-Kru site was supported by the NASA Terrestrial Ecology Program (Grant # NNX08AI77G ) and NSF Biocomplexity Program (Grant # EAR-0120630 ) through grants to NPH. The OzFlux sites (AU-Wac, AU-Fog, AI-How) were provided by Jason Beringer who was funded under an Australian Research Council FT ( FT1110602 ) and project support from DP130101566. Support for collection and archiving was provided through the Australia Terrestrial Ecosystem Research Network (TERN) ( http://www.tern.org.au ).
Keywords
- Carbon uptake period
- Chlorophyll
- Fluorescence
- Flux tower
- GOME-2
- Gross primary productivity
- Growing season
- Light-use efficiency
- Phenology
- Vegetation