Southern Ocean Current Observations from the U. S. Antarctic Research Vessels

Introduction

This website documents our USAP project of Southern Ocean current observations on the RVIB Nathaniel B. Palmer and ARSV Laurence M. Gould (PIs Teresa Chereskin, SIO and Eric Firing, UH). The program began in 1999 with the following goals:

• to establish a program of routine shipboard acoustic Doppler current profiler (ADCP) data collection, processing, and dissemination on the Antarctic research vessels;

• to provide improved monitoring of, and access to, the ADCP data for individual science missions;

• to improve public access to the data via the National Oceanographic Data Center (NODC), Joint Archive for Shipboard ADCP Data (JASADCP) at the University of Hawaii, and through our websites;

• to use the data to examine the structure and statistics of upper ocean currents in the Southern Ocean;

• to augment the ongoing high resolution XBT time series in Drake Passage with a time series of direct velocity observations.

Additional goals under our renewal project (2004) are

• to add new velocity profiling capability through the addition of an Ocean Surveyor 38 kHz phased array Doppler sonar (to improve range) while maintaining the old RDI narrowband 150 kHz ADCP (for resolution);

• to develop and implement a new Unix-based data acquisition program that can handle multiple sonars and single ping data acquisition (to improve the data recovery under sub-optimal conditions such as heavy seas and ice).

As of November 2004, the new suite of programs, UHDAS, is in use for ADCP data logging. New algorithms for automated processing and plotting have also been implemented. Although a final processing of the ADCP data set will be needed after the cruise, we hope that the differences between the final version and the automated processed version will be small. The biggest differences will likely be found under adverse conditions: shallow water, heavy seas, lack of scatterers, and bad weather.

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L. M. Gould ADCPs and Gentoo

The L. M. Gould has two RDI Doppler sonars. The newest is a 38 kHz Ocean Surveyor ADCP (OS38) which can reach to 1200 m in good weather in its deep-profiling mode. In bad weather, low scattering conditions, or some speed/heading/sea state conditions that entrain bubbles under the transducer, the range is less. There is also an RDI 150 kHz narrowband instrument (NB150) that profiles at higher resolution to as deep as 300 m. Data acquisition for both sonars and the requisite ancillary navigation streams occurs via the UHDAS software, written by Eric Firing and Jules Hummon, University of Hawaii. Ocean Surveyors are capable of running in either broadband mode (higher resolution at the expense of penetration) or narrowband mode (slightly deeper profiling but lower resolution). It is also capable of interleaving these pings, which is what we prefer. We have defaults set up for bottom track ON, 12 m bins in OS broadband mode (os38bb), and 24 m bins in OS narrowband mode (os38nb). Our processing treats these data streams as if they came from separate instruments, though work is underway to combine them into a single high-resolution, deep-profiling product. The NB 150 default setup is bottom track ON and 8 m bins.

**IMPORTANT** ONLY the ET should make changes to the UHDAS configuration. There are only a few configurable parameters. Should you want to make changes, please make the request to the ET and help us to maintain the integrity of our program.

Data acquisition for both sonars, automated processing, web serving and diskserving is done by our ADCP Linux pc, Gentoo. Gentoo belongs to the ship; Gentoo is NOT available for general use. Please respect this restriction and help us to maintain the integrity of this computer for acquisition and processing. Access to raw data, preliminary processed data, and plots is through NFS mount, SAMBA share, and this website.

This website provides access to preliminary processed matlab data files and data plots. You can look at the plots and download both plots and data using any browser and the links on the sidebar. Quick Links are plots that you might want to keep open as a UHDAS display, since we prefer that Gentoo be kept in the Monitor tab during data acquisition. (They are the same plots that can be viewed using the PLOT tab of UHDAS on Gentoo). The profile plots show the most recent 5 min of data, with profiles of averaged currents, percent good, and a color contour of the amplitude for each sonar data type. The vector and contour links point to plots that give an overview, with vector showing the currents from a single depth layer on a map with topography and contour showing the time evolution. In addition, there is a suite of standard plots produced for each sonar data type, and to examine these, follow the sidebar link under web access and choose the sonar and plot or data type. The data available through the website are averaged data in Matlab files. Raw data are available via NFS (Unix) and Samba (Windows) as described in the NFS and Samba link.

**IMPORTANT** The figures should be updating regularly. If for some reason the figures quit updating (either OS38 or NB150), check the UHDAS logging panels on Gentoo under the Monitor tab and make sure everything is green. If they are, DON'T ADJUST ANYTHING: the raw data are good, but the processing software hit a glitch for some reason. There's not much anyone on the ship can do about it but wait, and hope it recovers. There is a good chance plotting will recover at the next even 2-hour interval, when a new data file is started.

OS38 Photos links to a web page of photos (courtesy of RPSC) that document the OS38 installation on the LMG during the August 2004 shipyard period in Fourchon, LA.

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Acknowledgements

We depend on the hard work and high competence of the Raytheon personnel on the Palmer and the Gould; we are grateful for their assistance, without which this project would be impossible. This program is funded by the National Science Foundation Office of Polar Programs.

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