During June and July of 1974, internal wave records totaling 21 days duration were made at a nominal depth of 350 m in a location 800 km offshore of San Diego, California. The measurements were made with a midwater capsule which profiles temperature while it drifts with the mean flow. The resulting vertical displacement spectra decrease generally as •o-: between the local inertial frequency •o• and the buoyancy frequency n with a pronounced peak just below n; outside these limits the spectra drop sharply. Vertical coherences are nearly frequency independent between •o• and n with the exception of a peak just below n corresponding to the peak in the displacement spectrum. A low-frequency (0 _< •o _< 0.5n) average of coherence (not squared) decreases linearly from 0.99 at l-m separation to 0.85 at 36-m separation. This result suggests that modal energy is distributed with mode numberj as (/': + j,:)-•, where j, -• 3. Phase spectra averaged over the same interval indicate little or no net vertical transport of energy. The wave spectra are consistent with those of a stationary Gaussian process for periods up to 12 hours.

The fluctuations in acoustic transmission between a broadband source and an autonomous redeiver moored somewhat below the sound channel axis at 23-kin range have been examined. The transmitted signal was centered at 2273 Hz. A variety of measures of the observed fluctuations (pulse and cw) for three well-resolved paths computed from 72 h of data are compared with theoretical predictions based on sound-speed perturbations due to internal wave vertical displacements. Measurement and theory are found to be consistent for some statistics and inconsistent for others. The theoretical predictions depend sensitively on the mean sound-speed profile. of ships' drift (since the source and receiver were suspended from ships). is In the experiment reported here the source and receiver were moored and 72 h of data were collected.Sections I and II describe the geometry of the experiment and the signal processing used. Section III describes the available environmental information, including the sound-speed field, the buoyancy frequency profile, and the internal wave energy level. Section IV gives the acoustic-fluctuation parameters computed from the environmental data, including a discussion of the limitations of the calculations. Sections V and VI are the main body of the paper, giving the detailed comparisons between measurements and theory for pulsed measurements and cw measurements, respectively. I. GEOMETRY The experiment was conducted approximately 90 km west of San Diego in San Clemente Basin, a 2000-m deep feature of the continental borderland (Fig. 1). The source and receiver were moored 23-km apart with estimated anchor locations 32ø37.10' N, 118 ø 08.40' W and 32 ø 24.85' N, 118 ø 06.45' W, respectively. The mooring tension was approximately 1000 lbs; subsurface flotation near 500-m depth was utilized. Pressure sensors at the transmitter and receiver gave mean depths of 1035 and 1057 m, respectively; the maximum observed depth excursion from the mean was 1.4 m.Ray calculations done for this geometry using a soundspeed profile and bottom topography measured at the time of the experiment give four refracted paths and one bottom-reflected path (Fig. 2). All other reflected paths arrive well after these paths. All paths except the two refracted paths with upper turning points near 300 m can be separated in the time domain.

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The fluctuations in acoustic transmission between a broadband source and an autonomous receiver moored somewhat below the sound channel axis at 23-km range have been examined. The transmitted signal was centered at 2273 Hz. A variety of measures of the observed fluctuations (pulse and cw) for three well-resolved paths computed from 72 h of data are compared with theoretical predictions based on sound-speed perturbations due to internal wave vertical displacements. Measurements and theory are found to be consistent for some statistics and inconsistent for others. The theoretical predictions depend sensitively on the mean sound-speed profile.