Using GOES to estimate Sargassum aggregation drift velocity

Sargassum algae are proliferating at the surface of the Tropical Atlantic Ocean. Monitoring their drift and forecasting their future trajectories is key to facilitate disaster management and mitigate their impact at the coast. Successive satellite detections can be used to track Sargassum aggregations. The high temporal frequency (10 min) of the ABI sensor on board the GOES geostationary satellite strongly increases the probability to observe the ocean surface compared to low-orbiting sun-synchronous satellites. This data thus provides potentially rich information on Sargassum drift. In this study, GOES-ABI and MODIS data are used to automatically track Sargassum aggregations in the Western Tropical Atlantic (5-20°N, 50-70°W), over the period 2022-2024. GOES-retrieved velocity is consistent with MODIS for the same aggregations (complex correlation of 0.90-0.03i). GOES can retrieve twice as many velocity vectors as MODIS on average (~1300 yearly retrievals against ~600). Regressions of Sargassum drift against collocated SVP surface drifters drift and wind yielded a total wind effect of 0.036, consistent with recent study. When regressing Sargassum velocity against wind alone, wind effect is 0.032 vs 0.021 for undrogued drifters, indicating a larger contribution of wind in Sargassum drift. GOES velocities lead to lower regression fit than MODIS velocities, indicating lower accuracy. This study demonstrates the feasibility of the automatic tracking of Sargassum aggregations at daily scale using GOES, and provides useful data to calibrate Lagrangian forecast models of Sargassum drift.