Estimation of sunflower planted areas in Ukraine during full-scale Russian invasion: Insights from Sentinel-1 SAR data

Data limitations and attributability issues due to the full-scale Russian invasion of Ukraine in February 2022 presents continuing challenges in assessing production of major commodity crops in Ukraine. Up-to-date satellite imagery provides evidence of rapid changes in cropland within temporary occupied territories (TOT) by Russia within Ukraine. Ukraine is the world's top producer and exporter of sunflower and, therefore, monitoring, and quantifying changes in areas and production of sunflower is extremely important. We used Sentinel-1 (S1) synthetic aperture radar (SAR) images to quantify changes in sunflower planted areas in Ukraine during 2021-2022. We developed an operational workflow and produced the first available 20-m resolution sunflower maps over Ukraine. We developed a SAR-based generalized approach for sunflower mapping using a previously developed phenological metric and estimated sunflower planted areas and corresponding changes in 2021 and 2022 using a sample-based approach. Sunflower area was estimated at 7.10 +/- 0.45 million hectares (Mha) in 2021 which was reduced to 6.75 +/- 0.45 Mha in 2022, reflecting a 5% decrease compared to the preceding year. The reduction was mainly observed in the Russian-occupied regions while we did not find significant changes in sunflower areas in Ukrainian-controlled areas. In addition to traditional sunflower producing regions in the south and south-east of Ukraine we found new sunflower emerging hotspots along the south-central and north-eastern regions. Overall, the decrease in sunflower planted area was less severe than previously expected and reported in media for the entire Ukraine. This study demonstrates the utility of Earth observation data, namely Sentinel-1/ SAR, for monitoring sunflower cultivation areas in regions where ground access is not possible or feasible due to armed conflict.