Ocean currents from lowered acoustic Doppler current profilers (LADCP) of the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) starting 2015 assembled at the University of Hawaii and Lamont-Doherty Earth Observatory, Columbia University

This collection holds the Lowered Acoustic Doppler Current Profile (LADCP) estimates of ocean currents collected for the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP). GO-SHIP brings together scientists with interests in physical oceanography, the carbon cycle, marine biogeochemistry and ecosystems, and other users and collectors of ocean interior data, and coordinates a network of globally sustained hydrographic sections as part of the global ocean/climate observing system including physical oceanography, the carbon cycle, marine biogeochemistry and ecosystems.

To understand the ocean currents through the water column, LADCPs are employed. LADCPs estimate deep ocean absolute currents and shear. LADCP specialists of the University of Hawaii (UH) and the Lamont-Doherty Earth Observatory (LDEO) serve as the conduit to integrate LADCP data from international sources into a common database in support of GO-SHIP. LADCP data in this collection begin in 2015 with 1-2 cruises per year, which revisit World Ocean Circulation Experiment (WOCE) transect lines across the major ocean basins. Files within each granule of the collection consist of either ASCII text or NetCDF formats for the science-ready data, though there are some proprietary formats for the raw data directories, which are included to give advanced users the opportunity to reprocess the set.

ADCPs use the Doppler shift of an outgoing frequency along a beam to return measured velocity along that beam. ADCPs typically have 4 beams, allowing measurement of velocity in 3 dimensions, in bins of varying distances from the transducer head. In this application, the ADCP is mounted on a Conductivity-Temperature-Depth (CTD) rosette frame and lowered along with the rest of the package, hence called Lowered ADCP ("LADCP"). The goal is to determine water velocities to the full depth of the ocean for each LADCP deployment. Ocean velocities are very small (few cm/s), especially in the deep water. The package is typically lowered or raised at 1m/s for much of the water column, creating a challenging data processing situation. Lowered ADCP data requires ancillary information to calculate ocean velocities and turbulence parameters. Ancillary measurements included in the submission package include Conductivity, Temperature, Depth, at 24Hz, with 1Hz position, and shipboard ADCP data.

For the NCEI archive of GO-SHIP LADCP, three levels are defined: 1) Level-0, raw LADCP and ancillary data streams of the down- and up-cast, 2) Level-1, processed LADCP and ancillary data streams for the down-, up-, and averaged cast, and 3) Level-2 science-ready subset of select parameters. Presently only Levels 0 and 1 will be archived since work continues for defining error associated with Level 3. There is one processed file per station cast. The ancillary streams of Level-1 are the basic oceanographic variables of interest, and may also include a variety of additional fields associated with the processing.