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 - 水深测量文件（Bathymetry Files）
本数据集为BROKE-WEST 2006科考项目相关数据。
1) 压缩包内含针对测线1至11的每一条声学回声文件（acoustics ev file）导出的.csv格式文件。
2) 各文件包含对应测线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01_02文件无有效数据：该区域海底深度超过5000米，超出了声呐测深仪的量程范围。
4) 每个文件包含11列数据，依次为：声脉冲（Ping）日期、声脉冲（Ping）时刻、声脉冲毫秒数、纬度、经度、位置状态、水深、测线状态、声脉冲（Ping）状态、海拔高度、GPS UTC时间。
5) 实际应用中，核心关注列应为声脉冲日期、声脉冲时刻、纬度、经度与水深。其余列为辅助声学信息，可忽略。测线状态应为1（代表数据有效），仅当海底特征可清晰辨识时才会标记有效水深。若海底无法通过声呐剖面图像（echogram）视觉辨识或判定不确定性过高，则不会标记有效水深，因此海底水深数据可能并非完全连续。
6) 仅在“沿测线”区域内才会记录海底水深：即满足声学调查要求的直线测线区域。偏离测线的操作（例如为探测锚泊设备、采集目标样本、开展常规拖网作业或考察疑似冰山）均被视为“偏离测线”，此类区域的数据将被排除在分析之外。
7) 本数据集记录的海底水深主要服务于声学分析中的噪声排除流程：文件中的水深值对应海底排除线，即设置在真实海底上方的阈值线，用于在声呐剖面图像中排除背景噪声。因此本数据集记录的海底水深可能低于真实海底深度，误差范围约为2至10米。
8) 另一项误差来源为：水深计算时采用的吸收系数与声速参数均为基于航前水文数据（hydrographic data）推导的默认值，且全数据集统一使用同一组参数。具体参数如下：120kHz频段吸收系数0.028 dB/m、38kHz频段0.010 dB/m、200kHz频段0.041 dB/m、12kHz频段（测深声呐，bathy sounder）吸收系数0.017 dB/m，声速统一采用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2006年5-6月的后续后处理（post-processing）流程中应用于本数据集。参数修订可能会导致计算水深产生小幅偏移，但整体偏移量较小。
10) 数据的重新处理还将提升海底探测的精度。更新后的数据集预计于2006年6月后发布，完成后将尽快向有需求的相关方提供。
11) 本数据集由Esmee van Wijk整理制作。