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ARS Home » Plains Area » El Reno, Oklahoma » Grazinglands Research Laboratory » Forage and Livestock Production Research » Research » Publications at this Location » Publication #369878

Research Project: Integrated Agroecosystem Research to Enhance Forage and Food Production in the Southern Great Plains

Location: Forage and Livestock Production Research

Title: Integrating eddy fluxes and remote sensing products in a rotational grazing native tallgrass prairie pasture

Author
item Wagle, Pradeep
item Gowda, Prasanna
item Neel, James - Jim
item Northup, Brian
item ZHOU, YUTING - Oklahoma State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2019
Publication Date: 1/7/2020
Citation: Wagle, P., Gowda, P.H., Neel, J.P., Northup, B.K., Zhou, Y. 2020. Integrating eddy fluxes and remote sensing products in a rotational grazing native tallgrass prairie pasture. Science of the Total Environment. 712:136407. https://doi.org/10.1016/j.scitotenv.2019.136407.
DOI: https://doi.org/10.1016/j.scitotenv.2019.136407

Interpretive Summary: Satellite-based remote sensing offers an efficient way to model or up-scale ground-measured eddy fluxes to larger spatial and longer temporal scales than the eddy covariance (EC) systems can monitor. However, the spatial resolution of satellite sensors vary widely, which may affect the up-scaling of fluxes to larger spatial domains. In this study, we examined the relationships between measured eddy fluxes and enhanced vegetation index (EVI) derived from MODIS at 500 and 250 m spatial resolutions, VIIRS at 500 m spatial resolution, and Landsat at 30 m spatial resolution but integrated at the paddock-scale. The experiment was conducted over a grazed native tallgrass prairie pasture, which was divided into nine paddocks for rotational grazing. The EVI data from all satellites showed consistency to detect vegetation phenology. Different timing and duration of grazing induced some heterogeneity among paddocks. The major contributing area for the measured eddy fluxes was mostly limited to one paddock containing the EC tower. As a result, Landsat-derived EVI that was integrated for the paddock containing the EC tower showed substantially stronger relationships with CO2 fluxes than did the MODIS-derived EVI at 500 and 250 m spatial resolutions and VIIRS-derived EVI at 500 m spatial resolution. The results highlight that spatial representativeness issues should not be neglected while calibrating or validating satellite-based models. Thus, it is crucial to integrate flux measurements and high-resolution remote sensing data depending on the heterogeneity of landscape surrounding the EC flux tower.

Technical Abstract: Eddy covariance (EC) systems provide integrated fluxes within their footprint areas. Spatial heterogeneity of up-scaled areas and spatio-temporal mismatches of the EC footprint and remote sensing pixels jeopardize the performance of most satellite-based models. To evaluate the impact of spatial resolution of satellite products on up-scaling of fluxes to larger spatial domains, we examined the relationships between measured eddy fluxes and the enhanced vegetation index (EVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) at 500 and 250 m spatial resolutions, Visible Infrared Imaging Radiometer Suite (VIIRS) at 500 m spatial resolution, and Landsat at 30 m spatial resolution but integrated at the paddock-scale. The experiment was conducted over a grazed native tallgrass prairie pasture, which was divided into nine paddocks for rotational grazing. The EVI data from all satellites showed consistency in detecting vegetation phenology. Seasonality of EC-measured fluxes corresponded well with remotely-sensed vegetation phenology. Daily magnitudes of net ecosystem CO2 exchange (NEE of ~-9 g C m-2) and evapotranspiration (ET of ~5.5 mm) were within the reported ranges for tallgrass prairie in the Southern Great Plains. Different timings and duration of grazing caused some heterogeneity among paddocks. Approximately 80% of contribution to eddy fluxes came from within 80 m upwind distance of the 2.7 m tall EC tower. The major contributing area for the measured fluxes was mostly limited to the paddock containing the EC tower. Although the EVI of different spatial scales showed strong relationships with CO2 fluxes, Landsat-derived EVI integrated for the paddock containing the EC tower showed substantially stronger relationships with CO2 fluxes, most likely due to due to similar spatial resolutions of remote sensing data and EC observations. The results illustrate that fine-scale spatial resolution satellite images that are suitable to EC footprints should be used for modeling or up-scaling of eddy fluxes to improve the performance of satellite-based models, especially in heterogeneous ecosystems.