DRI Update: 12 November 1999

We are now essentially to the end of SAX99, and I am pleased to report that the experimental work has gone exceptionally well right up to the end. At the present time, the R/V Seward Johnson has returned to CSS for offloading on Nov. 12 after the main recovery effort. Part of the APL group will be joined by Rob Wheatcroft and Maziet Cheseby (OSU) for a trip back to the experimental site for the final recovery effort. The present schedule is for the Seward Johnson to return to CSS on Sunday the 14th for final offloading on Monday the 15th.

Much of the experimental activity since the last DRI Update on Oct. 26 involved continuation of work mentioned in that update. Penetration and backscattering efforts have been pursued almost continuously by the APL and ARL groups, and additional laser line scanner measurements of sediment temporal change were made by SIO (Jaffe/Moore/Ochoa). The Tracor group (Holliday/Greenlaw/McGehee) continued monitoring zooplankton and nekton migration through the lunar cycle with high frequency acoustics, NRL continued a wide range of sediment characterization measurements, and Jumars/Self/Schmidt continued their studies of acoustic effects of macrofauna and microbiology. A roughly chronological description of activities follows, but only activities which differed significantly from those described previously are included.

During the R/V Pelican's final leg (Leg 8; Oct. 25-29) with Pete Jumars Chief Scientist, Paul Johnson and Mike Hutnak (UW) used a tripod to make in situ permeability measurements versus depth. During three days of operation (Oct. 26-28) measurements were made along 3 track lines: 7 stations on a N-S track just to the east of our main experimental area, 7 stations on an E-W track just to the south of the CSS (Lopes) experimental area, and 5 stations on a W-E track through the low frequency area (used by Bob Stoll and later by Dale Bibee). The second track extended far enough west of the main experimental site to reach a trough with mud at the sediment surface.

During Leg 8 Jumars conducted a series of 20 benthic grabs (2 mm sieve) in a region surrounding the SAX99 site which showed substantial variability in the types of animals recovered. The Pelican transited to CSS on Oct 28 for unloading to complete its part of SAX99, with Jumars, Self, and Schmidt transferring to the Seward Johnson to continue their work.

On Oct. 28 CSS carried out SAS operations aboard Mr. Offshore to the south of the main experimental site passing by the CSS target field set up by Joe Lopes. All diving operations were suspended due to the SAS work, allowing a number of divers to spend the day on shore.

The remaining work described below occurred on the Seward Johnson. Joe Lopes and his group (Ed Kloess, Iris Paustian, and John Stroud) collected backscatter and bistatic data from the region of the CSS target field during the week of Oct. 25, concluding on Oct. 30. Results from the SIO laser line scanner showed two distinct times scales for roughness change using high precision single line scans. Small-scale changes were noted on characteristic times of roughly an hour that likely are related to the rapid decorrelation observed in BAMS 40 kHz scans. Larger scale roughness changes were also observed with longer characteristic times (e.g.,order of one day); these changes appear to be related to particular events such as weather driven swell events. [These comments should be considered very preliminary.]

On Oct. 31 we experienced a 20 kt SE wind and 4-6 ft seas with the prospect of higher wind and waves. The decision was made to drop all cables over the side and bring the Seward Johnson out of the 4-pt moor before any damage had been done to the cables or moorings. This was done without incident and we transited to CSS arriving at about 2000. Nov. 1 was spent dockside at CSS with heavy rain in the morning and one wind gust to 35 kts. Dale Bibee (NRL) came on board at this point to continue work started earlier on the Pelican. We returned to the experiment site on Nov. 2, arriving in the afternoon, and by the next morning wind and sea conditions had returned to excellent. While still out of the 4-pt moor the CSS tower was recovered on the morning of the 3rd and by noon the Seward Johnson was back in its 4-pt moor. Cables were recovered that afternoon, and APL, ARL, and Tracor systems came back on line without incident. However, the SIO laser line scanner cables were damaged by this event, which signaled the end of laser line scanner operations.

Peter Jackson and David Gunn of the British Geological Survey arrived at SAX99 on Oct. 29 with their high precision resistivity array to measure porosity variability. To bring out their equipment, which included several heavy boxes requiring crane transfer, we were able to send the Seward Johnson Boston Whaler to the Destin Coast Guard Station (whose help was greatly appreciated) for the shore tranfer. Our standard Boston Whaler runs to Destin, about 7 miles away, were to a marina without crane facilities; these were often used when conditions were too rough for direct shuttles to the beach or if a lot of gear was being transported. By far the most common mode of transport to shore was by zodiac to the beach in front of the Sandman Motel, and we typically had 2-3 runs a day. The Jackson/Gunn resistivity measurements were made during the Nov. 3- Nov. 8 period, leaving on the 9th again via the Destin Coast Guard Station.

Nov. 3 was also the day that David Thistle and Keith Suderman (FSU) returned to SAX99 to continue their work on fine scale emergence trapping. Their work continued daily through Nov. 8.

A typical day during this period included 10-15 activities, several occurring simultaneously. Acoustic penetration work moved into a phase with surface modifications, for example, flattening the surface or making small scale ripples with uniform wavelength. DJ Tang (APL) made deployments of his tomography system. Kevin Briggs made deployments of Tony Lyons's digital stereocamera. A time series of photos made after a uniform ripple had been made in the sediment showed dramatic change with time due to biologics. Liko Self deployed and monitored emergence traps. Dale Bibee did further low frequency sediment propagation measurements employing both an airgun and a hammerplate. Tracor extended their work to include low frequency backscatter from the bottom including a buried or proud sphere. NRL continued to make a multitude of sediment characterization studies too numerous to itemize in detail. Backscattering studies were made with surface modifications such as ripples of uniform wavelength, or the addition of shells or marbles. The construction of "Bragg rakes" for making ripple fields nearly became cottage industry on the Seward Johnson.

In recent days attention has turned to recovery, which has proceeded as smoothly as the initial deployment and experimental execution. As of Oct. 12, all equipment has been recovered except the moorings used for the Seward Johnson 4-pt moor and Wheatcroft's tripod.

During the course of the experiment we have attempted to keep a lookout for marine mammals and turtles. A system was developed at APL to listen for dolphins during SAX99. Sound measured with a hydrophone gives a direct audio output and is also processed to give a continuous time- frequency display. With this listening aid as well as visual observations, it was possible to keep track of nearby dolphins. It became clear early on that dolphins were rarely nearby during the day, but were often in the area at night, sometimes within tens of meters of the ship. Thus, night work with high sound levels was avoided. When high sound level work was to be done, the period 1130-1330 was set aside for such work. During this period no diving was permitted and an extra effort was made to monitor for the presence of dolphins. High sound level operations were not begun until no dolphins were detectable in the vicinity. With these precautions, no other restrictions were required in our experimental work due to the presence of dolphins. One large turtle was sighted moving away from the ship one day just before the beginning of one of the high sound level sessions. A short delay was called to allow the turtle to pass out of range. Only one other small turtle was seen (by divers) during the entire experiment.

I would like to thank all those involved in SAX99 for their efforts in making it a success. The spirit of cooperation was truly outstanding.