DOI: 10.6075/j0h993hk
title: Event S59. In SWellEx-96 Experiment Acoustic Data

description: Event S59, like Event S5, is a source tow along an isobath during the SWellEx-96 Experiment. However, unlike Event S5, Event S59 contains a loud interferer. This event is particularly useful for investigating the effects of a loud interferer on detecting/localizing a quiet target. The source ship (R/V Sproul) began its track between and slightly east of the two HLA's and traveled at a speed of 5 knots (2.5 m/s) roughly northward along the 180 m isobath. During the last 25 minutes of the event, the tow ship bears to port and completes a loop. The interferer of interest began west of the all of the arrays, proceeded southeast and between the two HLA's, and ended east of the arrays. A radar system aboard the R/P FLIP was videotaped, providing ranges and bearings between the interferer and the four arrays.

Sources
Two sources were simultaneously towed by the R/V Sproul: a "deep" source (J-15) and a "shallow" source (J-13); see component, “S59 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. 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, “S59 source frequencies”. As mentioned in the previous section, the interferer's position relative to the arrays can be determined using radar data and the program "geod." Aside: From the center of the HLA North array, the R/P FLIP is at a range of 1.9 km and at a bearing of 5 degs east of True North. Using the radar data, we can find the range and bearing between the interferer and the R/P FLIP (see component “Range and bearing between interferer and R/P FLIP”). Using the "geod" program, the above information, and the a priori knowledge of FLIP's position, the latitude and longitude of the interferer can then be calculated. Similarly, the range and bearing from the interferer to the HLA North array can be computed (see component “Range and bearing between interferer and HLA North”).

Sensors
All four arrays (VLA, TLA, HLA North, and HLA South) recorded the full 65-minute event. The start time of Event S59 is J134, 11:45 GMT and it ends at J134, 12:50 GMT. Note: Day J134 corresponds to 5/13/96.

Environment
On J134, four CTDs were taken on the R/V LaSalsa. Of these, CTD #20 was the closest spatially (32d40.60' N 117d22.20' W) and temporally (13 May, 16:18 GMT) to the S59 Event. This sound speed profile has a weak mixing layer (~5 m) over a strongly downward refracting layer to about 40 m. The remainder of the profile is essentially isovelocity to the seafloor. 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 S59 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”.