Comparison of In Situ Current Measurement Methods, the Accuracy Achieved in the Field and Recommendations for Engineering Design Applications

Abstract

Here we present a wealth of comparison data from acoustic backscatter current meters against current meters that use an active acoustic path (the RPS CM04). The data cover a wide range of environmental conditions. Very poor agreement between current meters frequently occurs, presenting as both bias and noise. The causes of the differences remain unproven, although for acoustic profilers deployed in deep water, failure of the assumption of the same flow in all beams is a possible source of significant error. As a result of decade’s worth of comparisons plagued with unexplained differences, we have reduced confidence in the accuracy of current data collected by acoustic backscatter sensors. We therefore avoid (where practical) using these instruments when the application of the current data is for engineering design, where uncertainty in accuracy can have significant cost or risk consequences.