Processed 2 minutes-averaged continuous VM-ADCP (vessel-mounted Acoustic Doppler Current Profiler) profiles during POLARSTERN cruise PS96

This data set was collected during the R. V. Polarstern cruise PS96. Outside territorial waters, current velocities were measured nearly continuously along the ship's track with a vessel-mounted TRD Instruments 153.6-kHz Ocean Surveyor ADCP. The transducers were located 11 meter below the water line and were protected against ice floes by an acoustically transparent plastic window. The current measurements used a pulse of 2 seconds and vertical bin length of 4 meters. The ship's velocity was calculated from position fixes obtained by the Global Positioning System (GPS). Heading, roll and pitch data from the ship's gyro platforms and the navigation data were used to convert the ADCP velocities into earth coordinates. The accuracy of the ADCP velocities mainly depends on the quality of the position fixes and the ship's heading data. Further errors stem from a misalignment of the transducer with the ship's centerline. The ADCP data were processed using the Ocean Surveyor Sputum Interpreter (OSSI) software developed by GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel. The reference layer was set to avoid near surface effects. The averaging interval was set to 120 seconds.
Sampling interval setting: 2s; Number of bins: 80; Bin length: 4m; Pulse length: 4m; Blank beyond transmit length: 4m.
Data processing setting: Upper depth of reference layer: 30m; Lower depth of reference layer: 80m; Time average: 120s; Misalignment angle: 0.900; amplitude: 1.0240.
The precision for single ping and 4m cell size reported by TRDI is 0.30m/s. Resulting from the single ping precision and the number of pings (most of the time 36) during 120seconds the velocity accuracy is nearly 0.05m/s.
(Velocity accuracy = single ping precision divided by square root of the number of pings)

本数据集采集于“极星号”（R. V. Polarstern）科考航次PS96期间。在领海以外海域，科考船沿航行轨迹采用船载TRD Instruments公司153.6kHz Ocean Surveyor型声学多普勒海流剖面仪（ADCP）近乎连续地测量海流流速。该仪器的换能器安装于吃水线以下11米处，并配有声学透明塑料护罩以抵御浮冰侵扰。本次海流测量采用2秒脉冲宽度，垂直分层长度为4米。科考船的航速通过全球定位系统（GPS）获取的定位数据解算得到。借助船载陀螺平台获取的航向、横滚及纵倾数据，结合导航信息，将ADCP测得的相对流速转换为地固坐标系下的绝对流速。ADCP测得流速的精度主要取决于定位数据与船载航向数据的质量。此外，换能器与船体中心线的安装偏差也会引入额外测量误差。ADCP数据采用基尔亥姆霍兹海洋研究中心（GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel）开发的Ocean Surveyor Sputum Interpreter（OSSI）软件进行处理。参考层设置用于规避近表层效应的影响，平均时长设置为120秒。
采样参数设置：采样间隔2s；分层总数80；分层长度4m；脉冲长度4m；发射后盲区长度4m。
数据处理参数设置：参考层上界深度30m；参考层下界深度80m；时间平均时长120s；安装偏角0.900；幅度系数1.0240。
TRDI官方公布的单ping且分层尺寸为4m时的测量精度为0.30m/s。结合单ping精度与120秒内的声脉冲次数（多数情况下为36次），最终流速精度可达约0.05m/s。（流速精度计算公式：流速精度=单ping精度 / 声脉冲次数的平方根）