Bathymetry Data from the 12KHZ sounder on the BROKE-West voyage of the Aurora Australis, 2006

Readme - Bathymetry Files Data for BROKE-WEST 20061) Zipped folder contains .csv files created from each acoustics ev file for Transects 1 to 11.2) These files contain subsections of each transect of variable length (usually between 50 and 100 km).3) No data exists for files; Transect01_01 and 01_02 as the sea floor was greater than 5000m deep in these areas and was below the range set for the sounder.4) Each file contains 11 columns of data; Ping_date, Ping_time, Ping_milliseconds, Latitude, Longitude, Position_status, Depth, Line_Status, Ping_status, Altitude, GPS_UTC time.5) For practical purposes, the columns of interest will be Ping_date, Ping_time, Latitude, Longitude and Depth. Other columns are ancillary acoustics information and can be ignored. Line status should be 1 (meaning good) as sea floor was only picked when it could be easily defined. If the sea floor could not be visually defined or was deemed to uncertain, it was not picked in the echogram. Hence sea floor may not be totally contiguous.6) Depth of the sea floor was only defined for those areas deemed to be 'on transect', i.e. straight transects for acoustics survey purposes. Deviations from the transect, i.e. to pick up moorings, conduct target or routine trawls or visit nice looking bergs were deemed 'off transect' and were excluded from the analysis.7) Sea floor depth was primarly defined for the purposes of the acoustics analysis, i.e. exclusion from the echograms. Hence the values in the files are for the 'sea floor exclusion line' that is set above the true sea floor in order to exclude noise from the analysis. This means the sea floor depths in these files are likely to be an underestimate of the true depth. The uncertainty is likely to be of the order of 2 to 10m.8) Another source of error is that depth was calculated with values of absorption coefficient and sound speed set to default values derived from pre-cruise hydrographic data. One value for each parameter was applied to the whole data set. These values were; 0.028 dB/m (120 KhZ), 0.010 dB/m (38kHz), 0.041 dB/m (200 kHz), 0.0017 dB/m (12kHz - bathy sounder) for absorption coefficient and 1456 m/s for sound speed.9) These values will be recalculated from the oceanographic data derived during the voyage and applied to the data set during post-processing (forthcoming analyses for May-June 2006). Revision of these parameters may cause a slight shift in the calculated depths, although this is likely to be small. 10) Reprocessing of the data may also result in more accurate bottom detection. This data should be available post June 2006 and will be sent to interested parties as soon as it is completed. 11) Dataset was created by Esmee van Wijk.

说明文档：测深文件 BROKE-WEST 2006科考数据集
1. 压缩包内包含针对断面1至11的每条声学EV文件转换生成的.csv格式数据文件。
2. 各文件包含对应断面的可变长度子段数据，通常长度介于50至100千米之间。
3. Transect01_01与Transect01_02两个文件无有效数据：该区域海底水深超过5000米，超出了测深仪的探测量程。
4. 每个文件包含11列数据，分别为：ping日期（Ping_date）、ping时间（Ping_time）、ping毫秒数（Ping_milliseconds）、纬度（Latitude）、经度（Longitude）、位置状态（Position_status）、水深（Depth）、断面状态（Line_Status）、ping状态（Ping_status）、高度（Altitude）、GPS UTC时间（GPS_UTC time）。
5. 实际应用中，所需关注的列应为ping日期、ping时间、纬度、经度与水深。其余列均为辅助声学信息，可忽略。断面状态应取值为1（代表数据有效），因为仅当海底可被清晰识别时才会记录该数据。若海底无法通过目视识别或识别结果存在不确定性，则不会在声呐图（echogram）中标注海底位置，因此海底数据可能并非完全连续。
6. 仅在被认定为“沿断面区域”内，即声学调查所需的直线断面区域，才会记录海底水深数据。偏离断面的作业（例如投放/回收锚泊设备、开展目标采样或常规拖网、考察外观异常的冰山）均被视为“脱离断面”，相关数据将被排除在分析之外。
7. 海底水深数据的记录初衷是用于声学分析，即从声呐图中排除海底噪声。因此文件中的水深值对应“海底排除线”——该线设置于真实海底上方，用于在分析中滤除噪声。这意味着文件中的海底水深数据可能低于真实水深，误差范围约为2至10米。
8. 另一处误差来源为：水深计算时采用的吸收系数与声速参数均取自航前水文数据的默认值，且全数据集统一使用这一组参数。所用参数如下：吸收系数分别为0.028 dB/m（120 kHz）、0.010 dB/m（38 kHz）、0.041 dB/m（200 kHz）、0.0017 dB/m（12 kHz——测深声呐），声速为1456 m/s。
9. 后续将基于科考过程中获取的海洋学数据重新计算上述参数，并在后处理阶段应用至数据集（相关分析预计于2006年5-6月完成）。调整这些参数可能会使计算得到的水深产生小幅偏移，不过偏移量通常较小。
10. 数据的重新处理也可提升海底探测的精度。重新处理后的数据集预计将于2006年6月后发布，完成后将尽快发送给有需求的相关方。
11. 本数据集由Esmee van Wijk整理制作。