In 2008 we were fortunate enough to lead the maiden scientific voyages of the R/V Langseth, the new academic seismic research vessel in the U.S. Although the principal goal of the project was to image the deep structure of the volcanic arc in Costa Rica, we also devoted some effort to testing the efficacy of the Langseth as a platform for conducting research in seismic oceanography. The results were very successful -- we can say with confidence that the Langseth is wonderfully suited for imaging structure in the water column. (This work was funded by NSF-PO.)
We deployed 50 XBT's that measured ocean temperature, for comparison to our reflection data. To do the deployments, Captain Landow and Sci. Officer Ted Koczynski devised XBT "flumes" on the port and starboard sides, consisting of long PVC pipes angled downward from the paravane deck and supported by either the OBS deck crane or a vane boom. Here's a picture of the starboard XBT flume:
Although we were somewhat disappointed with the relatively monotonous temperature structure of this part of the Caribbean, we were quite surprised (and pleased) to see very clear reflections from even tiny temperature fluctuations, as the figures below show.
(click on the figure to enlarge):
Note that the temperature finestructure in the water column shown above is quite subtle -- there are just some very minor step-like fluctuations at the 10-m vertical scale, most likely due to internal wave strains. There are no temperature inversions. Yet even this weak finestructure creates very clear reflections in the data (
click on the figure to enlarge):
We believe these results will redefine the sensitivity of seismic reflection data in imaging ocean fine-structure. Certainly the powerful, broadband, well-tuned 36-gun array of the Langseth appears to be an ideal source for seismic oceanography.