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A Half-Century Ago

August 18, 2018

Marvel Stalcup (with glasses) and Gus Day launch an early instrument to determine current speeds and directions from the research vessel Crawford circa 1965. Data were recorded on photographic film. Modern oceanographers use Acoustic Doppler Current Profilers (ADCPs). They transmit sound waves that ricochet off particles suspended in moving water and reflect back to the instrument. Due to the Doppler effect, sound waves bounced back from a particle moving away from the ACDP have a lower frequency when they return. Particles moving toward the instrument send back higher frequency waves. The instrument uses this Doppler shift to calculate how fast the particle and the water around it are moving.

(Photo courtesy of Woods Hole Oceanographic Institution Archives)