ESTIMATION OF FUNCTIONAL AND STRUCTURAL TRAITS OF C3 AND C4 CROPS USING VENUS AND IN SITU REFLECTANCE DATA

VENμS was designed to provide multi-temporal (ever 2 days), multi-spectral reflectance data for monitoring and analyzing land surfaces over selected sites. Here, we report on the comparison between VENμS reflectances to ground-based measured reflectances (4-band SKYE radiometers) at three AmeriFlux agricultural sites (maize and soybean), NE USA, and estimating crop structural and functional traits. Reflectances from four spectral Venus bands, similar to the Skye radiometer bands (green, red, red edge and NIR) from the 2018 growing season were compared showing good correspondence. Two traits of both crops, structural - green LAI, and functional - fraction of PAR absorbed by photosynthetically active vegetation (fAPAR_green), were estimated using VENμS and SKYE reflectances; Normalized Vegetation Index (NDVI), green NDVI (NDVIgreen), red-edge NDVI (NDVIred edge), the Wide Dynamic Range Vegetation Index (WDRVI), and the Chlorophyll Index (CIred edge) were used. The relationships between the VIs and the crop biophysical properties differed slightly but with similar trends. NDVI, NDVIred edge and WDRVI were highly correlated to LAIgreen for both satellite- and ground-based systems while NDVI, NDVIgreen, NDVIrededge and WDRVI were moderately correlated to fAPARgreen. Algorithms using VENμS red edge spectral bands allowed estimation of green LAI in both crops with no re-parameterization. Comparisons between satellite-based and ground-based reflectances and VIs through the growing season indicate the potential of VENμS spectral data for monitoring and analyzing land surface functioning. Comparisons will continue for the 2019 growing season; VI relationships will be applied to estimate crop biophysical properties and phenology.