Event S59. In SWellEx-96 Experiment Acoustic Data

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”.

与S5事件（Event S5）类似，S59事件是SWellEx-96实验中沿等深线拖曳声源的观测任务。但与S5事件不同的是，S59事件中存在一个强干扰源。该事件尤其适用于研究强干扰源对弱目标探测与定位的影响。

研究船R/V Sproul于两个HLA阵列之间并略偏东侧的海域开始航行，以5节（2.5 m/s）的航速大致沿180米等深线向北行驶。在该事件的最后25分钟，拖曳船向左舷转向并完成一个环形航段。本次关注的干扰源初始位置位于所有阵列的西侧，随后向东南方向航行，途经两个HLA阵列之间，最终抵达阵列东侧海域。搭载于R/P FLIP浮动观测平台的雷达系统录制了视频，可获取干扰源与四个阵列之间的距离与方位信息。

### 声源系统
R/V Sproul同时拖曳了两个声源：分别为“深水声源”（J-15）与“浅水声源”（J-13），详细参数参见组件"S59 source frequencies"。
深水声源的拖曳深度约为54米，发射了多个声源级介于49 Hz至400 Hz之间的单频信号（tonals），该单频信号组被称为T-49-13。T-49-13单频信号组包含5组各13个单频信号，每组13个信号的频率覆盖范围均为49 Hz至400 Hz。第一组13个单频信号以最大声源级发射，被称为“高单频组”（High Tonal Set），其发射声源级约为158 dB。第二组单频信号的发射声源级约为132 dB，后续三组（第三、第四、第五组）的声源级均较前一组降低4 dB。
浅水声源的拖曳深度约为9米，发射了9个介于109 Hz至385 Hz之间的单频信号，该信号组被称为C-109-9S单频信号组（C-109-9S tonal set）。部分初始后处理工作采用了所谓的“噪声频率”，即能够表征噪声场的代表性频率，相关频率列表详见组件"S59 source frequencies"。

正如前文所述，可通过雷达数据与"geod"程序计算干扰源相对于各阵列的位置。补充说明：以HLA North阵列的中心为原点，R/P FLIP的距离为1.9 km，方位为真北偏东5度。结合雷达数据，可获取干扰源与R/P FLIP之间的距离与方位信息，详见组件"Range and bearing between interferer and R/P FLIP"。结合"geod"程序、上述信息以及R/P FLIP位置的先验知识，即可计算得到干扰源的经纬度坐标。同理，也可计算得到干扰源至HLA North阵列的距离与方位，详见组件"Range and bearing between interferer and HLA North"。

### 传感器系统
四个阵列（VLA、TLA、HLA North及HLA South）完整记录了此次时长65分钟的事件。S59事件的起始时间为格林尼治标准时间J134日11:45，结束时间为J134日12:50。注：J134日对应1996年5月13日。

### 环境参数
1996年5月13日（J134日），研究船R/V LaSalsa完成了4次温盐深仪（CTD, Conductivity-Temperature-Depth）观测。其中，CTD #20的观测位置（北纬32°40.60′，西经117°22.20′）与观测时间（格林尼治标准时间5月13日16:18）最接近S59事件的发生时段与海域。该声速剖面存在一层厚度约5米的弱混合层，其下为强负折射层，直至约40米深度；剖面剩余部分基本为等声速层，直至海底。声速数据经过盐度尖峰剔除处理，并以0.5米为间隔进行深度插值。地声参数源自测深与沉积物粒度数据库。如需了解波导参数的更多细节，请查看数据集条目"Environment data (1996-05-10 to 1996-05-18)"。

### 声源-接收阵距离
已针对S59事件的每一分钟计算得到拖曳声源至各接收阵列的距离数据，可在此处获取。如需下载包含声源位置、声源-接收阵距离以及用于计算此类数据的MATLAB M文件的压缩包，请选择组件"Source-to-receiver range data"。该数据的汇总图详见"Plot of source-to-receiver range data"。

### GPS数据
R/P FLIP（VLA阵列位置）与R/V Sproul（声源拖曳船）的原始GPS数据均已提供。R/P FLIP搭载的差分GPS（differential GPS）系统于格林尼治标准时间1996年5月8日16:52至1996年5月19日15:00期间记录了该平台的GPS信息。R/V Sproul搭载了两套GPS系统，用于记录声源拖曳船的GPS信息：其中MicroMariner系统的记录时段为1996年5月10日至5月15日（格林尼治标准时间），PCode系统的记录时段为1996年5月11日至5月15日（格林尼治标准时间）。如需下载包含所有GPS数据的压缩包，请选择组件"GPS data"。