Dushaw, Brian (6/3/98)

I would like to second Jim Lynch's comments concerning acoustic tomography. In order to inject some reality into discussions concerning tomography, I am appending a list of selected publications that employed tomography with an oceanographic focus. It seems to me that people with strong negative opinions of tomography are often not aware of the recent publications (I am sure this phenomena is not limited to tomography). People employing tomography have certainly become a small (frequently oppressed, if I might whine a little) minority in the PO community.

The frequent complaint about tomography appears to be the cost, expressed by that age-old, broken-record, demonstrably-false opinion (see the refereed publications): "why should we support tomography when current meter moorings will do the same thing?" Peter Worcester is of the opinion that tomographic moorings are not significantly more expensive than current meter moorings. Dan Rudnick, on the other hand is adamant, that current meter moorings are far cheaper. This would seem to be an issue that could easily be resolved, but in any case when tomography gains more widespread use, it is obvious that the both the cost and complexity of these instruments will decrease. Perhaps one issue that NSF might address is how to transition such quality instrumentation - tomographic or otherwise - beyond the development stage to something that is cheaper, simpler and may be more widely applied. The catch-22 situation is that some equipment is too expensive for many people to use, but this equipment would be cheaper if many people used them.

Although some people may have the impression that acoustic tomography is unusual in having such an extended period of development, almost every technology now widely used at sea has undergone a similar 15-20 year gestation period (Wunsch, C., "Comments on oceanographic instrumentation development," J. Oceanogr. Soc., 2 26-7, 64, 1989.)

I am all in favor of ocean observations by a multitude of cheap instruments. It seems to me, however, that sacrificing quality time series from current meters, tomography or other means to exclusively fund these cheap instruments is foolish. At some level if oceanographers get to be too cheapskate, they begin to shoot themselves in the foot in terms of research dollars as well as observation quality. There has been much said about the terrific accomplishments of and potential of satellite observations - I point out that if any other observation program spent money in the billions of dollars, be it floats, current meters or tomography, that program would no doubt also have terrific accomplishment. You do sometimes get what you pay for, and cheap (or expensive for that matter) observations made at a single point will always be noisy. For this reason I do not agree that "150 ALACE type floats are better than 5 acoustic sound sources for tomography to describe the ocean's circulation (C. Erickson)" (if for no other reason than it is a vague statement).

I get the frightening impression that somewhere at the bottom of this debate are people who have already made up their minds that there is nothing new to observe in the ocean. Therefore, the thinking goes, the only instruments we need are those to observe known phenomena.... This would be surprising if it were true.

B. Dushaw dushaw@apl.washington.edu

Selected References on Acoustic Tomography

The AMODE-MST Group, "Moving ship tomography in the North Atlantic," EOS, Trans. Am. Geophys. Union, 75, pp. 17, 21, 23, 1994.

The ATOC Group, "The general circulation and heat budget of the North Pacific ocean from acoustc tomography, satellite altimetry, and a general circulation model," Science, submitted 1998.

Chester, D., P. Malanotte-Rizzoli, J. Lynch, and C. Wunsch, "The eddy radiation field of the Gulf Stream as measured by acoustic tomography," Geophys. Res. Lett., 21, 181-184, 1994.

Cornuelle, B. D. and P. F. Worcester, "Ocean Acoustic Tomography: Integral data and ocean models, in: Modern Approaches to data Assimilation in Ocean Modeling, P. Malanotte-Rizzoli, ed., Elsevier, 97-115, 1996.

Dushaw, B. D., and P. F. Worcester, "Resonant diurnal internal tides in the North Atlantic," Geophys. Res. Lett., in press, to appear June 1998.

Dushaw, B. D., G. D. Egbert, P. F. Worcester, B. D. Cornuelle, B. M. Howe, K. Metzger, "A TOPEX/POSEIDON global tidal model (TPXO.2) and barotropic tidal currents determined from long-range acoustic transmissions," Prog. in Oceanogr., in press, to appear May 1998.

Dushaw, B. D., P. F. Worcester, B. D. Cornuelle, and B. M. Howe, "Barotropic and baroclinic tides in the central north Pacific Ocean determined from long-range reciprocal acoustic transmissions," J. Phys. Oceanogr., 25, 631-647, 1995.

Dushaw, B. D., D. B. Chester, and P. F. Worcester, "A review of ocean current and vorticity measurements using long-range reciprocal acoustic transmissions," IEEE Oceans '93 Conf. Rec., October, pp. I-298-I-305, 1993.

Dushaw, B. D., P. F. Worcester, B. D. Cornuelle, and B. M. Howe, "Variability of heat content in the central North Pacific in summer 1987 determined from long-range acoustic transmissions," J. Phys. Oceanogr., 23, 2650-2666, 1993.

Menemenlis, D., D. Stammer, C. Wunsch, B. D. Dushaw, and the ATOC group, "Preliminary estimates of North Pacific circulation from combined altimetry, acoustic tomography, and a general circulation model," International WOCE Newsletter, 25, February 1997.

Menemenlis, D., A. T. Webb, C. Wunsch, U. Send, and C. Hill, Basin-scale ocean circulation from combined altimetric, tomographic, and model data, Nature, 385, 618-621, 1996.

Mikhalevsky, P. N., A. B. Baggeroer, A. Gavrilov, and M. Slavinsky, "Experiment Tests Use of Acoustics to Monitor Temperature and Ice in Arctic Ocean," EOS, Trans. Am. Geophys. Union, 76 (July 4, 1995), p. 269, 1995.

Morawitz, W. M. L., P. J. Sutton, P. F. Worcester, and B. D. Cornuelle, "Three-Dimensional Observations of a Deep Convective Chimney in the Greenland Sea during Winter 1988/89," J. Phys. Oceanogr., 26, 2316-2343, 1996.

Munk, W., P. Worcester, and C. Wunsch, Ocean Acoustic Tomography. Cambridge University Press, New York, 1995, 433 pp.

Pawlowicz, R., J. F. Lynch, W. B. Owens, P. F. Worcester, W. M. L. Morawitz, and P. J. Sutton, "Thermal evolution of the Greenland Sea Gyre in 1988-89, J. Geophys. Res., 100(NC3), 4727-4750, 1995.

Send, U., F. Schott, F. Gaillard, and Y. Desaubies, "Observation of a deep convection regime with acoustic tomography, J. Geophys. Res., 100, 6927-6941, 1995.

Spiesberger, J. L., P. J. Bushong, K. Metzger, Jr., and T. G. Birdsall, "Basin scale tomography: synoptic measurements of a 4000-km length section in the Pacific, J. Phys. Oceanogr., 19, 1073-90, 1989.

Worcester, P. F., J. F. Lynch, W. M. L. Morawitz, R. Pawlowicz, P. J. Sutton, B. D. Cornuelle, O. M. Johannessen, W. H. Munk, W. B. Owens, R. Shuchman, and R. C. Spindel, "Evolution of the large-scale temperature field in the Greenland Sea during 1988-1989 from tomographic measurements," Geophys. Res. Lett., 20, 2211-14, 1993.