Cruise Report, RV ATAIR, Cruise 067I033-1, Bremerhaven – Thybor?n – Aberdeen, 23 Jul – 15 Aug 2024 23 Figure 5.8. Distribution of stations carried out during cruise 067I033-1 with water sampling and subse- quent filtration for chlorophyll-a determination (red dots). The chlorophyll-a concentrations measured in the laboratory serve 1) as a rough measure of phytoplankton biomass and 2) are used for comparison with the chlorophyll-a concentrations determined by remote sensing for ground truthing. Phytoplankton Sampling Understanding the distribution and behaviour of plankton is key to deciphering the complex dynamics of marine ecosystems. The assimilation of satellite data bridges the gap between observation and theory. The EnsAD project aims to improve real-time forecasting capabilities for potentially problematic phytoplankton groups by integrating hyperspectral remote sensing data from the EnMAP and PACE satellites into biogeochemical models for the North Sea and Baltic Sea. In order to adapt the algorithms, the composition of the phytoplankton must be known during the satellites' flyover. For this purpose, the phytoplankton was collected and its taxonomic composition determined in the home laboratory for ground truthing.