Assimilation of microwave backscatter to update modelled crop biomass and soil moisture: assessment and insights

We studied the potential of regional microwave backscatter data assimilation (DA) in AquaCrop, to improve surface soil moisture (SSM) and crop biomass estimates. The DA was performed in NASA’s Land information system, a software framework which allows for efficient model ensemble and DA runs. SSM and crop biomass simulations from AquaCrop were updated using Sentinel-1 synthetic aperture radar observations, over three regions in Europe in two separate DA experiments. The first experiment concerned updating SSM using VV-polarized backscatter, where the corrections were propagated via the model to the biomass. In the second experiment, the DA setup was extended by also updating the biomass with VH-polarized backscatter. Overall, the SSM evaluation showed that there is potential in using Sentinel-1 backscatter for assimilation in AquaCrop, but the present setup was not able to improve crop biomass estimates. Our study reveals how the complex interaction between SSM, crop biomass and backscatter affect the impact and performance of DA, offering insight into ways to optimize DA for crop growth estimation.