Three of the main technological developments in our profession during the last two decades have been satellite positioning, multi-beam echo sounding and current profiling while under way. Using the doppler principle to measure frequency shifting as an indication of relative speed was effectively applied underwater. The 3D current vector was made visible by combining simultaneous measurements in 3 or 4 directions. Furthermore, this was done at many different levels during one transmission/reception cycle, so that a profile of current vectors could be registered at high repetition rates.

Rob van Ree, contributing editor, Hydro International 

Hydro international keeps an eye on developments by conducting product surveys at regular intervals. The previous ADCP survey was published in December 2007. In 2010, four manufacturers returned our questionnaire, giving details on a total of 15 different systems. The full comparison can be found on the Hydro international website. The table shown on these pages only compares four systems, one from each manufacturer, their selection being based on a similar frequency of approximately 300kHz, which leads to a range of 100 - 150m. Comparison, however, remains cumbersome.

Although Teledyne RD Instruments have their Workhorse Mariner on offer, they did not provide details for this system on the questionnaire. Instead, they answered our queries for the Workhorse Horizontal 300 kHz, which has 3 rather than 4 beams.

As to be expected, the four systems show many similarities, and their differences are small. Reported (horizontal) accuracy varies somewhat: FlowQuest300 and Workhorse Horizontal measure a 2 knot current with accuracy up to 0.5cm/sec, while Continental and ADP measure the same current with accuracy of up to 1.5cm/sec. As usual, the accuracy figures should be used with care, as different people may use it to describe incomparable quantities.

Compared with the 2007 product survey, no major changes were visible in the systems on which the submitting companies reported. At least for the time being, the revolutionary introduction of these current profilers has changed into the phase of gradual improvements, to the benefit of the hydrographic community.