Using SAR-based products to calculate potato carbon uptake in a tropical Andean region

Gross primary productivity (GPP) is an essential parameter to estimate the efficiency of carbon transfer in terrestrial ecosystems. The daily GPP has been monitored in the past using mainly optical satellite imagery. However, GPP has never been monitored using satellite Synthetic Aperture Radar (SAR) imagery. We evaluate the possibility of using Sentinel-1 SAR data to estimate GPP and compare with field GPP measurements using eddy covariance (EC) systems in three commercial potato fields, located in the Andean region of Colombia, using three different water irrigation levels. Raw and processed radar data from Sentinel-1 were compared with the daily and accumulated GPP from the EC. Results indicate that SAR data has a high correlation with the accumulated GPP measured by the EC in the field. The normalized radar backscatter and radar brilliance coefficients with VH polarization show a good correlation with the EC accumulated GPP in irrigated potato fields (R-2: 0.77-0.81), while radar vegetation indices show a good correlation with the EC accumulated GPP in potato fields with no irrigation (R-2 approximate to 0.82). In particular, the accumulated GPP during the whole potato crop cycle was estimated with good accuracy (similar to 5% error with irrigation and similar to 10% error with no irrigation).