This is the Lamont page relating to the acquisition and processing of data from Lowered Acoustic Doppler Current Profiler (LADCP) instruments. It is maintained by Andreas M. Thurnherr.
In addition to the more common profiles of horizontal ocean velocity, data from LADCP/CTD systems can also be processed for vertical velocity. This can be accomplished with a simple method that consists in subtracting vertical package velocity, derived from CTD pressure time series, from the LADCP relative velocity measurements and binning the results in depth space. Away from boundaries, vertical velocity in the ocean is dominated by high-frequency (near-N) internal gravity waves, which are associated with vertical velocities ranging between a few mm/s in open-ocean background conditions and a few 10s of cm/s in Luzon Strait. LADCP-derived vertical velocities are particularly useful in the context of turbulence and mixing studies, because there is a simple and close relationship between vertical kinetic energy (VKE) and turbulent dissipation. I maintain an implementation, including a manual, of the LADCP_w software package, which allows calculation of vertical-velocity, VKE and parameterized dissipation profiles from standard LADCP/CTD data. The software is available from this server.
In order to remove the effects of horizontal instrument motion from the velocity measurements obtained by LADCP systems, elaborate data processing is required. There are two fundamentally different methods used for this purpose: The shear method described by Firing and Gordon (1990) and by Fischer and Visbeck [J. Tech. 1993], and the velocity inversion method described by Visbeck [J. Tech. 2002]. I maintain implementations of both methods, available from this server:
Velocity Inversion Version IX. This software, which is the official LADCP data processing software used for US GO-SHIP cruises, was originally written by M. Visbeck. I re-designed the user interface, wrote a manual, and I have been maintaining the software and providing user support since 2004.
Re-Implementation of the UH Shear Method. One of the main reasons why use of LADCP systems became widespread during the WOCE was the pioneering processing software written and maintained by E. Firing and his group at the University of Hawai'i. Because the UH implementation is somewhat cumbersome to set up and use, and because it is no longer supported, I re-implemented a slightly simplified version of this software. The new implementation of the shear method is intended, in particular, for use in shear-based finestructure parameterizations and for processing tow-yo and yo-yo casts. In 2015 the software was adapted to allow processing of 600kHz RDI ADCP data collected on Webb Slocum gliders [Thurnherr et al., IEEE 2015].
Most instruments used for LADCP work are manufactured by Teledyne/RDI, who provide DOS and Windows software for communicating with the instruments (for setup and data downloading). In order to avoid having to use a Microsoft operating system, I implemented a portable data acquisition system for RDI ADCPs based entirely on popular public-domain tools. Data acquisition is controlled by a set of expect scripts, which use a perl-based program (called bbabble) to communicate with one or two RDI ADCPs. The LDEO LADCP data acquisitions software is available from this server.
Over the years I wrote a set of user manuals for the acquisiton and processing of LADCP data:
GO-SHIP Manual for Acquiring Lowered Doppler Current Profiler Data [A.M. Thurnherr, M. Visbeck, E. Firing, B. King, J. Hummon, G. Krahman and B. Huber, 2009]
How to Process LADCP Data with LDEO Software Version IX [A.M. Thurnherr, 2004]
How to Process LADCP/CTD Data for Vertical Velocity and VKE [A.M. Thurnherr, 2015]
Additional information on processing LADCP data for both horizontal and vertical velocity is available in a collection of methods papers, which includes all papers referenced on this page. Assessing the quality of LADCP data is often not trivial. Examples can be found in a set of LADCP data reports and post-cruise qualilty-control reports.
|© 2012 A.M. Thurnherr (e-mail)||created: Tue Sep 11 11:35:39 2012||modified: Wed Jan 17 12:01:44 2018|