Albert J. Williams 3rd
Woods Hole Oceanographic Institution

Personal exposure to oceanographic instrument developments in my career at Woods Hole Oceanographic Institution extending for 1969 to 2016 has brought me into contact with many of the important advances that have furthered our profession. The microstructure CTD in 1969 and 1970 employed precise digital technology in oceanographic measurements for the first time with Neil Brown’s use of ratio transformers as a digitizer of a 10 KHz signal. Sixteen binary ratios of turns (resolving one part in 65356) provided a measurement of temperature from -2 to 30 Celsius with a resolution of ½ millidegree C. The resolution of conductivity allowed salinity to be determined from 0 to 32 psu with a resolution of ½ milli psu. Pressure of 0-6400dBar was measured with a resolution of 0.1dBar (10cm of depth).

At nearly the same time, the VACM or Vector Averaging Current Meter was being adapted to log its current measurements on digital cassette tape in the SeaData recorder. This was the first modest scale dependable digital underwater recorder. This recorder was the start of removing the problem of logging underwater data digitally, facilitating autonomous underwater instrumentation. An example of a highly sensitive measurement from the deep sea was the Paros pressure sensor. This sensor used a crystal oscillator to convert a stress from a pressure-exposed bourdon tube to a change in frequency that was counted and the period determined with extreme precision such that a pressure change from several centimeters of depth change could be discriminated in 6000m of water. This was the sensor used in the DART buoys that were part of NOAA’s advanced warning system for tsunamis.
Meanwhile, current measurement was advanced by the development of the Acoustic Doppler Current Profiler. This Doppler sensor used some of the Texas Instrument multiply-and-add integrated circuits that facilitated real-time digital signal processing. These same technologies aided underwater acoustic communications. In this, oceanographic instrument advances depended on the technologies that cell phones and other commercial developments provided.

In the last dozen or so years we have developed instruments that give us global coverage: gliders, drifters, and profilers. But the development of AUVs with communications and navigation, in both shallow water and deep water, has provided us with presence even under ice shelves. For continuous coverage we have laid cables for observatories. Meanwhile, remote sensing has developed global surface coverage for geodesy, hydrography, temperature, and bio sensing. The in situ lab-on-chip has provided chemical and biological analyses on subsurface loggers and cabled observatories. Holographic images and in-situ flow cytometry have permitted continuous population monitoring. Finally, there are now expendable, “burner bots” that provide pH, fish tags, and possibly even an XBL or Expendable Benthic Lander to measure current in inaccessible places.