Oceanographers commonly calculate large scale surface ocean circulation from satellite sea level information using a concept called “geostrophy,” which describes the relationship between oceanic surface flows and sea level gradient. Conversely, researchers rely on data from in-water current meters to measure smaller scale motion. New research led by University of Hawaiʻi at Mānoa oceanographer Bo Qiu has determined from observational data the length scale at which using sea level height no longer offers a reliable calculation of circulation.