An experiment to measure ocean surface waves with a high frequency radar that took place from Sept. 10, 1979 to Oct. 15, 1979. MARSEN was originally a ground truth campaign to provide and calibration and validation of SEASAT’s microwave instruments, although that focus was somewhat relaxed when SEASAT failed after gathering data for only 90 days. MARSEN included a collection of studies on wave dynamics, air–sea fluxes, and remote sensing via aircraft and ground–based systems, and was carried out in the North Sea. Key results included that drag coefficients depended on sea state and wave age, and that shallow water waves produce higher drag than deep water waves.