Environment Data (1996-05-10 to 1996-05-18). In SWellEx-96 Experiment Acoustic Data

Environment
The SWellEx test site has been extensively studied. An impressively detailed geoacoustic database and model exists for the region. In addition, a CTD survey was conducted during the SWellEx-96 Experiment to provide water column sound speed data.

Waveguide
For the waveguide (see component, "Waveguide plot"), the water depth is assumed to be the water depth at the array for range-independent processing. The seafloor is composed first of a 23.5 m thick sediment layer with a density of 1.76 g/cm^3 and a compressional attenuation of 0.2 dB/kmHz. The top of the sediment layer has a compressional sound speed of 1572.368 m/s while the bottom of the sediment layer has a compressional sound speed of 1593.016 m/s. Below the sediment lay an 800 m thick mudstone layer with a density of 2.06 g/cm^3 and an attenuation of 0.06 dB/kmHz. The top and bottom sound speeds of the mudstone layer are 1881 m/s and 3245 m/s, respectively. The geoacoustic model is completed by a halfspace with a density of 2.66 g/cm^3, an attenuation of 0.020 dB/kmHz, and a compressional sound speed of 5200 m/s.

Water Column Sound Speed
The CTD data from the SWellEx-96 Experiment was salinity-despiked and depth-interpolated every 0.5 m, yielding 51 final CTD casts. Each CTD data file contains five columns: (1) depth [m], (2) temperature [Deg C], (3) salinity (PSU), (4) sound speed (m/sec), and (5) sigma-t. Note: The times listed in the table component, "CTD locations" are local times (GMT - 7 hours). Add 7 hours to the listed time to convert to GMT. For a tarball containing ASCII versions of the CTD location information as well as the CTD data, select the component, "CTD data".

Bachman Database
Richard Bachman produced a seabed geologic model that is a gridded database containing water depth, sediment grain size, sediment thickness, and acoustic basement type. Grid cells are squares of side length equal to 2 arc seconds. The gridded database covers the area: 32 degrees 45 minutes to 32 degrees 33 minutes, and 117 degrees 26 minutes to 117 degrees 14 minutes.

Geographic data files are provided for: surface sediment grainsize (grainsiz.xyz), sediment thickness (sedthkms.xyz), basement rock type (basement.xyz), water depth (depth.xyz). Also needed is a sound speed profile, some are provided in the examples. Each data file has a companion README file explaining the units, derivation, and codes for land or null values (if any). The geographic data files ( *.xyz ) contain (X,Y,Z) triples, where X is the seconds west of 117 degrees 13 minutes west, and Y is seconds north of 32 degrees 32 minutes north. For example, if {x,y} = {-456,362}, the point is 456 seconds west of 117 degrees 13 minutes and 362 seconds north of 32 degrees 32 minutes.

Download the Bachman database by selecting component, "Bachman database". Note: The data herein was produced in September 1994, but represent the best information that was available for the period of Events S5 and S59.

The examples use a script call 'extract2.scr' that will take in a list of lat-long positions, will convert the positions into the corresponding arc second location in the database, and extract out the data corresponding to the lat-long position. There are three examples of extracting data from the bachman data base. All three examples call the script 'extract2.scr' to do the extraction. (Note: Matlab mapping toolbox required for range calculation.)

Example 1: The first example extracts the geo-acoustic data for the VLA location during SWellEx-96. The script to run this example is getVLA_GeoModel.scr. VLA location, 32 40.254 117 21.620, run through extract2.scr produces: 0.00, 219.73, 24.39, 5.05, 1.0 for columns 1-5, respectively, where: Column 1 = Range (m) from initial point, Column 2 = Water Depth (m), Column 3 = Two-way travel time in msec for sediment, Column 4 = Sediment Grain size, Column 5 = Basement Type (0-unknown, 1-Tertiary, 2-Cretaceous, 10-Land).

Example 2: The second example extracts a cut line along the longitude line 117 degrees 20 minutes (for NS track). This is a range independent track line. The script to run this example is plotBathyNS.scr.

Example 3: The third example extracts a cut line along the latitude line 32 degrees 39 minutes (for EW track). This is a range dependent track line. The script to run this example is plotBathyWE.scr.

bach2geo_MPL
Each of the Bachman database examples demonstrates how to extract data out of the Bachman geographic data base. But it does not produce a geoacoustic model. The document 'geo_modl.doc' explains how to construct a geoacoustic model from the output of the database. The program bach2geo_MPL implements the steps documented in 'geo_modl.doc'. There are two examples of how to use bach2geo_MPL.

Kraken Example: Using the results from Example 1, bach2geo_MPL is run to generate a kraken input. Kraken is then run 13 times (for 13 frequencies), with a MFP range-depth ambiguity surface computed from the average result of the 13 range-depth ambiguity surfaces.

RAM example: Using the results from Example 2, bach2geo_MPL is run to generate a RAM input file. The RAM input file is then used to produce a Transmission Loss plot at 201 Hz. Note that the computations to produce the geoacoustic model are dependent on the sound speed profile used as well as the results from the Bachman data base.

Download the bach2geo program and examples of how to run it by selecting component, "bach2geo program". Note this software is compiled for Red Hat Linux, but the source code is also present.

【试验环境】SWellEx试验场已得到广泛研究，该区域拥有一套极为详尽的地声数据库（geoacoustic database）与地声模型。此外，在SWellEx-96试验期间开展了CTD（Conductivity Temperature Depth，温盐深测量）勘测，以获取水柱声速数据。

【波导模型】对于波导（详见组件“波导绘图”），在距离无关处理中，水深取试验阵列所在位置的实际水深。海底结构依次为：一层厚度23.5m的沉积层，密度为1.76 g/cm³，压缩衰减系数为0.2 dB/kmHz；该沉积层顶部的压缩声速为1572.368 m/s，底部压缩声速为1593.016 m/s。沉积层下方为厚度800m的泥岩层，密度为2.06 g/cm³，衰减系数为0.06 dB/kmHz，其顶部与底部声速分别为1881 m/s与3245 m/s。地声模型的底层为半无限空间介质，密度为2.66 g/cm³，衰减系数为0.020 dB/kmHz，压缩声速为5200 m/s。

【水柱声速数据】SWellEx-96试验获取的CTD数据已完成盐度野值剔除与每0.5m步长的深度插值处理，最终得到51组有效CTD剖面。每份CTD数据文件包含5列数据：(1) 水深[m]，(2) 温度[℃]，(3) 盐度(PSU)，(4) 声速(m/s)，(5) 密度西格玛（sigma-t）。注意：组件“CTD位置”表格中所列时间为当地时间（比格林尼治标准时间晚7小时，即GMT-7），需将所列时间加7小时方可转换为格林尼治标准时间。如需获取包含CTD位置信息与CTD原始数据的ASCII格式压缩包，请选择组件“CTD数据”。

【巴赫曼数据库】Richard Bachman构建了一套海底地质模型，该模型为网格化数据库，包含水深、沉积物粒度、沉积物厚度与声学基底类型四类数据。网格单元为边长2角秒的正方形。该网格化数据库覆盖区域为：北纬32°45′至32°33′，西经117°26′至117°14′。

本次提供的地理数据文件包括：表层沉积物粒度数据（grainsiz.xyz）、沉积物厚度数据（sedthkms.xyz）、基底岩性数据（basement.xyz）与水深数据（depth.xyz）。此外还需声速剖面数据，部分示例中已提供相关数据。每份数据文件均附带README文档，用于说明数据单位、推导过程以及陆地或空值的编码规则（若存在）。所有*.xyz格式的地理数据文件均采用(X,Y,Z)三元组形式存储，其中X为相对于西经117°13′的西向角秒数，Y为相对于北纬32°32′的北向角秒数。例如，若{x,y} = {-456,362}，则该点位于西经117°13′以西456角秒，北纬32°32′以北362角秒。

如需下载巴赫曼数据库，请选择组件“巴赫曼数据库”。注意：本数据集生成于1994年9月，但为S5与S59试验时段可获取的最优数据。

本次示例采用`extract2.scr`脚本，该脚本可接收经纬度坐标列表，将其转换为数据库中对应的角秒坐标，并提取对应经纬度位置的相关数据。本次共提供3组从巴赫曼数据库中提取数据的示例，所有示例均调用`extract2.scr`脚本完成数据提取。（注：距离计算需使用Matlab地图工具箱）

【示例1】首个示例用于提取SWellEx-96试验期间甚长基线阵列（VLA，Very Long Baseline Array）位置的地声数据，运行脚本为`getVLA_GeoModel.scr`。将VLA位置坐标32°40.254′N，117°21.620′W输入`extract2.scr`后，得到的5列输出结果依次为：0.00、219.73、24.39、5.05、1.0，各列含义如下：第1列为距初始点的距离(m)，第2列为水深(m)，第3列为沉积物往返传播时间(ms)，第4列为沉积物粒度，第5列为基底类型（0-未知，1-第三纪，2-白垩纪，10-陆地）。

【示例2】第二个示例用于提取沿西经117°20′的剖面数据（适用于南北向测线），该测线为距离无关测线，运行脚本为`plotBathyNS.scr`。

【示例3】第三个示例用于提取沿北纬32°39′的剖面数据（适用于东西向测线），该测线为距离相关测线，运行脚本为`plotBathyWE.scr`。

【bach2geo_MPL工具】前述巴赫曼数据库的示例仅展示了如何从地理数据库中提取数据，无法直接生成地声模型。文档`geo_modl.doc`详细说明了如何基于数据库输出结果构建地声模型，而`bach2geo_MPL`程序则实现了`geo_modl.doc`中描述的全部步骤。本次提供了2组`bach2geo_MPL`的使用示例。

【Kraken示例】基于示例1的输出结果，运行`bach2geo_MPL`以生成Kraken输入文件。随后将Kraken程序运行13次（对应13个频率），并基于13次距离-深度模糊度曲面的平均结果计算匹配场处理（MFP，Matched Field Processing）的距离-深度模糊度曲面。

【RAM示例】基于示例2的输出结果，运行`bach2geo_MPL`以生成RAM输入文件，随后利用该输入文件绘制201Hz频率下的传播损耗（Transmission Loss）曲线。需注意，地声模型的构建结果依赖于所选用的声速剖面以及巴赫曼数据库的输出数据。

如需下载`bach2geo_MPL`程序及其运行示例，请选择组件“bach2geo程序”。注意：本软件已编译为Red Hat Linux可执行版本，同时附带完整源代码。