Ancestry of ADCPs

Fifty years ago, an incredibly creative period of work by William S. Richardson ushered in the modern era of ocean instrumentation for measuring currents. Although an ADCP uses sonar-based technology, quite different from Richardson's devices, the functional capabilities of an ADCP can be traced to his pioneering work. ADCPs measure time series of vertical profiles of water currents. This approach merged two instrumentation streams -- current metering and vertical profiling-- both of which were founded in Richardson's work. In this paper, we review connecting threads from ADCPs to Richardson's pioneering inventions. For the most part, time variability of currents has been studied by using self-recording current meters deployed on a mooring line for an extended period. Typically their data sets described the history of concurrent motions at a few depths. Conversely, the vertical structure of currents has been studied by using free-falling velocity profilers that provided, for a time limited by cruise duration, well resolved snapshots of ocean currents throughout the water column yet separated by hours. While at Woods Hole Oceanographic Institution, Bill Richardson developed a self-recording current meter and methods for deploying several of them on a deep-sea mooring line. Later, at the University of Miami, he developed a free-falling device -- dropsonde -- for measuring water volume transport. Though distinct developments, both were motivated by the same goal: measuring the Gulf Stream.