DOI: 10.6075/j0n014vk
title: Event S5. In SWellEx-96 Experiment Acoustic Data

description: Event S5 is a source tow along an isobath during the SWellEx-96 Experiment. During this event, there were no loud interferers present. The source ship (R/V Sproul) started its track south of all of the arrays and proceeded northward at a speed of 5 knots (2.5 m/s). Most of the source tow track occurred in water between 180 and 220 meters deep, with the second half of the tow along the 180 m isobath.

Sources
Two sources were simultaneously towed by the R/V Sproul: a "deep" source (J-15) and a "shallow" source (J-13), see component, “S5 source frequencies”. The deep source was towed at a depth of about 54 m. It transmitted numerous tonals of various source levels between 49 Hz and 400 Hz. This tonal set is known as T-49-13. The T-49-13 tonal pattern consists of 5 sets of 13 tones. Each set of 13 tones spans the frequencies between 49Hz and 400Hz. The first set of 13 tones is projected at maximum level and is referred to as the "High Tonal Set." These tones are projected with transmitted levels of approximately 158 dB. The second set of tones are projected with levels of approximately 132 dB. The subsequent sets (3rd, 4th, and 5th) are each projected 4 dB down from the previous set. Aside: At the beginning, midway point, and end of the track, the deep source stopped projecting CW tones and started projected FM chirps. The shallow source was towed at a depth of about 9m. It transmitted 9 frequencies between 109 Hz and 385 Hz, known as the C-109-9S tonal set. Some initial post-processing utilized so-called "noise frequencies." Those frequencies chosen to be representative of the noise field are listed in the component, “S5 source frequencies”.

Sensors
The vertical array (VLA) and tilted array (TLA) both recorded the full 75 minute event, while the two horizontal arrays (HLA North and South) recorded only the last 50 minutes. For the VLA and TLA, the start time of Event S5 is J131, 23:15 GMT. The HLA data begins at J131, 23:40 GMT. Note: Day J131 corresponds to 5/10/96.

Environment
A sound speed profile was generated from a local CTD cast, file "i9606.prn" located in the “CTD data” component of the collection item, “Environment data (1996-05-10 to 1996-05-18).” The downcast from Station 6 was obtained on 10 May 1996 from 21:05 to 21:21 PST, located at 117d22.11’W, between 32d39.12’N to 32d38.73’N. Alternatively, the CTD cast from Station 5, file "i9605.prn," would be an even more appropriate choice due to its temporal and spatial proximity to the source tow event. The sound speed data was salinity-despiked and depth-interpolated to every half meter. The geoacoustic parameters were derived from a database of soundings and grainsizes. For more details on waveguide parameters, view the collection item, “Environment data (1996-05-10 to 1996-05-18).”

Source-to-Receiver Range
Ranges from the towed source to the various receiving arrays have been calculated for each minute of the S5 Event and are available here. To download a tarball containing source position, source-to-receiver ranges, and a MATLAB M-file for calculating such, select the component, "Source-to-receiver range data". A figure summarizing that data is shown in “Plot of source-to-receiver range data”.

GPS
The raw GPS data is also available for both the R/P FLIP (VLA location) and the R/V Sproul (source location). Onboard the R/P FLIP, a differential GPS system recorded GPS information for FLIP from 5/8/96, 16:52 GMT to 5/19/96, 15:00 GMT. Onboard the R/V Sproul, two GPS systems recorded GPS information for the source tow ship: a MicroMariner system recorded from 5/10/96 to 5/15/96 GMT, and a PCode system recorded from 5/11/96 to 5/15/96. To download a tarball containing all of the GPS data, select the component, "GPS data".