3 ACOUSTIC EFFECTS OF ENVIRONMENTAL VARIABILITY IN THE SWARM, PRIMER AND ASIAEX EXPERIMENTS J. LYNCH, A. FREDRICKS, J. COLOSI, G. GAWARKIEWICZ AND A. NEWHALL Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA 02543 E-mail: jlynch@whoi.edu C.S. CHIU Naval Postgraduate School (NPS), Monterey, CA 93943 E-mail: chiu@nps.navy.mil M. ORR Naval Research Laboratory (NRL), Washington, D.C. 20375 E-mail: orr@wave.nrl.navy.mil We present an overview of how the coastal oceanographic environment affected acoustic propagation and scattering in three recent major field experiments: SWARM (1995), PRIMER (1996–97), and ASIAEX (2000–01). In all three of these experiments, low frequency sound (50–600 Hz) was transmitted through strong coastal oceanographic features to array receivers. The differences and similarities of these experiments will be emphasized. In particular, we will focus on the effects of coastal oceanography, i.e. fronts, eddies, and internal waves. We begin with the SWARM experiment, which examined the effects of internal waves, particularly non-linear internal waves, on acoustic propagation and scattering. This experiment had excellent environmental support along a single across-shelf propagation path, and we were able to make good progress understanding the sound scattering within the context of this limited geometry. In the PRIMER experiment, we looked at oceanographic effects in a fully three-dimensional configuration, being supported by numerous environmental moorings and Sea Soar (undulating CTD) high-resolution hydrography. This experiment observed the effects of both the shelfbreak front, eddies and filaments, and nonlinear internal waves on the acoustic field. Finally, we examine the recent ASIAEX experiment, which again dealt with fully three-dimensional oceanography and along- and across-shelf acoustic propagation. ASIAEX had perhaps the best environmental support of the three experiments, including thirty environmental moorings, Sea Soar hydrography, satellite remote sensing, and acoustic flow visualization surveys. The acoustic monitoring included both a vertical and horizontal array, and moored and towed sources. Oceanographically, this experimental site featured some of the strongest non-linear internal waves we have seen to date. 1 Introduction The Yellow Sea experiments of Zhou et al. in the 1980’s, published in the Journal of the Acoustical Society of America in 1991 [1], created a major stir in the field of low frequency (50–1000 Hz) shallow water acoustics. Field data showed anomalous propagation loss N.G. Pace and F.B. Jensen (eds.), Impact of Littoral Environmental Variability on Acoustic Predictions and Sonar Performance, 3-10. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.