ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pUW22. A comparison of broadband and narrow-band transmission loss in shallow water.

Karen D. Frech

Bolt Beranek and Newman, 1300 North 17th St., Arlington, VA 22209

Calibrated acoustic measurements were made at the Hudson Canyon Experiment site [L. Maiocco and W. Carey, J. Acoust. Soc. Am. Suppl. 1 86, S8 (1989)] during area characterization test II(ACT II) conducted in September 1993. This site was chosen because it is a surveyed area with known geophysical and geoacoustic properties. Transmission loss was measured along the previously run radials from bore hole 6010 using calibrated small broadband explosive charge sources and a narrow-band continuous wave (cw) towed acoustic projector. These sources were, for the purposes considered here, co-located in range because of low test ship speed (under 5 kn). The receiving sensor was a 25 element stationary vertical line array spanning the majority of the water column (73 m), with 19 elements extending off the bottom (60 m) and 6 elements along the bottom (30 m). Using the principle of reciprocity, the hydrophone elements at each of the source depths enabled comparisons of the transmission loss measurements for broadband and cw sources to be made over a range interval from 4--22 km at two frequencies (200 and 900 Hz). The comparisons were performed by means of linear regression of the data from the two sources. The results of the comparison will be presented and will include a detailed discussion of the precision of the results and of possible sources of experimental error. Finally, the cw transmission loss from ACT II will be compared with the previous measurements of Maiocco and Carey.