Measuring Coastal Currents Using ADCPs on AUVs



The invention of the ADCP revolutionized studies of coastal circulation worldwide. Working from moving vessels, ADCP operators measure continuous transects of full-depth current profiles, often around consecutive circuits throughout a tidal cycle. If each circuit is treated as a snapshot, then it should be completed before the current field changes significantly due to tidal variation. 

Coastal waters receive discharge and runoff from land—both directly and through estuaries and inlets. This input has come under scrutiny due to deteriorating marine ecosystems, worsened by pollutants and excessive nutrient loading. Quantifying how effluent and water properties are transported and spread will help advance understanding of their impact on coastal waters. 

To address these goals, small autonomous underwater vehicles (AUVs) can replace boats in coastal surveys, observing both flow fields and water properties continuously and concurrently—for instance, while tracking effluent plumes or river discharge. 

Vehicles fitted with Teledyne RDI DVLs carry an embedded ADCP, which can measure coastal currents at many depths simultaneously—above and below the vehicle if a dual head is installed—while the AUV flies at a constant depth. 

The DVL’s pinpoint positioning improves not just the vehicle’s trajectory but the quality of data and images gathered at high sampling rates. Transects of ADCP profiles collected during spatial surveys enable end-users to be better informed in order to describe local circulation patterns and to assess the mechanisms driving ocean processes. As well, maps of ADCP-based velocity fields permit detailed comparison with output from coastal circulation models, allowing for validation, calibration, and even refinement of the models. ​