Impact of flux footprint heterogeneity of agricultural site on surface-atmosphere exchange

Vegetation dynamics and characteristics in the changing area of footprints of eddy covariance sensors influence the measurements. The objective of the study is twofold: 1/ estimation of flux footprints variation and heterogeneity during the vegetation development using high spatial resolution satellite data; 2/evaluation the impact of land cover heterogeneity on the evapotranspiration (ET) and gross primary productivity (GPP) in the course of vegetation season of two crops. The study started in 2018 at field (cca 45 ha) seeded with cover crop of legume-cereals and clover (Trifolium pratense) - stable crop in 2019 season. The flux footprints of eddy covariance (EC) tower have been predicted using simple parametrization method (Kljun 2004) and calculation of the ET and GPP using standard ICOS protocols. We used the VNIR bands of the Venus and Sentinel-2. Moreover, we acquired airborne hyperspectral data (CASI, 1 m, 10 nm) at date of the satellite overpasses, resampled it to spatial and spectral resolution of each satellite data and estimated variation in satellite pixels. . Preliminary results display significant differences in footprint variability calculated from different data sources when using several vegetation indices (NDVI, EVI, RER) as a proxy of crop cover. This indicates an importance of precise information about the changes of footprint shape and size and their relation to changes in surface properties. More study is still needed in testing the procedure with other crops and focus should be paid to data preprocessing (atmospheric correction).