SO174 raw data of EM120 multibeam echosounder (bathymetry & beam time series)

Between 01.10.2003 and 12.11.2003, bathymetric data was acquired in the Gulf of Mexico during the R/V SONNE cruise SO174. The expedition was dedicated to the types and structures of near-surface marine methane hydrates and the environmental conditions required for their formation. Furthermore, the cruise aimed at the assessment of microbiological turnover and deployments of long-term observatories for examination of the mechanisms controlling the formation and dissociation of gas hydrate. Bathymetric mapping with the multibeam echosounder (MBES) SIMRAD EM120 was utilized to conduct high-quality seafloor maps in water depths between 500 and 1000 m, covering an area of 350 km² and notably improving the resolution of existing bathymetry. Sub-bottom profiling and plume imaging, visual seafloor observation, lander deployments, sediment coring, CT scanning and biological sampling complemented the research programme.

CI Citation: Paul Wintersteller ([e-mail]) as responsible party for bathymetry raw data ingest and approval.

Description of the data source:
During the SO174 cruise, the hull-mounted multibeam echosounder (MBES) SIMRAD EM120 was utilized to perform bathymetric mapping. It allows to conduct surveys in water depths of up to 11,000 m. Two transducer arrays transmit frequency coded acoustic signals (11.25 to 12.6 kHz). Data acquisition is based on successive emission-reception cycles of the signal. While the emission beam has a dimension of 150° across and 2° along track, the reception is obtained from 191 overlapping beams with widths of 2° across and 20° along track. The beam footprint has a dimension of 2° by 2°. The beam spacing can be set to equidistant or equiangular. For further information on the system, consult: https://www.km.kongsberg.com/
Depth is estimated from each beam by using the two-way travel time and the beam angle known from each beam, and taking into account the ray bending due to refraction in the water column by sound speed variations. Combining phase and amplitude is used to provide measurement accuracy practically independent of the beam pointing angle. A sound velocity for the calibration of the SIMRAD EM120 profile was obtained through a CTD cast.

Responsible persons during this cruise / PI: Gerhard Bohrmann ([e-mail]) & Florian Meier ([e-mail])

Chief Scientist: Gerhard Bohrmann ([e-mail])
CR: http://oceanrep.geomar.de/13539/1/GEOMAR_Rep_117_SO174.pdf
CSR: https://www2.bsh.de/aktdat/dod/fahrtergebnis/2003/20040025.htm

2003年10月1日至2003年11月12日期间，R/V SONNE号科考船执行SO174航次期间在墨西哥湾海域获取了水深测量数据。本次科考航次旨在研究近海底海洋甲烷水合物的类型与结构，以及其形成所需的环境条件；此外，本航次还致力于评估微生物周转过程，并布设长期观测站，以探究调控天然气水合物形成与分解的机制。

研究团队使用多波束测深声呐（multibeam echosounder, MBES）SIMRAD EM120开展水深测绘工作，在500至1000米的水深范围内完成了350平方千米海域的高质量海底地形图绘制，显著提升了现有水深地形数据的空间分辨率。亚底质剖面探测、羽流成像、海底视觉观测、着陆器布放、沉积物岩芯取样、CT扫描及生物样本采集等手段，对本研究计划进行了补充完善。

CI引用：保罗·温特斯特勒（[e-mail]）为水深原始数据的录入与审核负责人。

数据源描述：
SO174航次期间，船体搭载的多波束测深声呐SIMRAD EM120被用于开展水深测绘。该系统可在最大11000米的水深环境中实施勘测。其配备两组换能器阵列，可发射频率编码的声学信号（频率范围11.25至12.6 kHz）。数据采集基于信号的连续发射-接收循环流程：发射波束的横向张角为150°，沿航迹方向张角为2°；接收则通过191个重叠波束完成，每个接收波束的横向张角为2°、沿航迹方向张角为20°，波束脚印尺寸为2°×2°。波束间距可设置为等距或等角模式。如需了解该系统的更多信息，请参考：https://www.km.kongsberg.com/

水深值通过各波束对应的声波双向传播时间与已知波束角进行估算，并考虑因水体声速变化引发的声波在水柱中的折射效应所导致的射线弯曲。系统结合相位与振幅信息进行解算，使测量精度几乎不受波束指向角的影响。SIMRAD EM120剖面校准所需的声速数据，通过CTD剖面测量获取。

本航次负责人/项目负责人：格哈德·博尔曼（[e-mail]）与弗洛里安·迈尔（[e-mail]）

首席科学家：格哈德·博尔曼（[e-mail]）
CR：http://oceanrep.geomar.de/13539/1/GEOMAR_Rep_117_SO174.pdf
CSR：https://www2.bsh.de/aktdat/dod/fahrtergebnis/2003/20040025.htm