RAN CTD Profile Data - HMAS BENALLA ProjectID: HI568BEN_M From: 2015-02-26 To: 2015-04-14

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 231 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise HI568BEN_M from HMAS BENALLA.

The CTD was manufactured by Applied Microsystems Limited and is the "Micro CTD" model. This CTD type is referred to operationally as the MVP200_CTD. This CTD is fitted with a 4 electrode platinized conductivity cell, thermistor temperature sensor and a semiconductor strain gauge pressure sensor.

The CTD sensors are calibrated at the manufacturer Applied Microsystems Limited on a 12-18 month schedule. The CTD temperature sensor is calibrated against 'Hart' temperature standards. The pressure sensor is calibrated using 'Budenburg Deadweight' standards. The conductivity sensor is calibrated using 'Hart' temperature standards and seawater samples of known conductivity.

The CTD sensors are mounted to a fish-shape probe. The probe is controlled by an electric winch (MVP200 type). For downcasts the fish is allowed to free-fall (winch is in 'free-wheel' mode) under its own weight at about 2-3 ms-1 and then is winched back. Data is recorded in downcast and usually in upcast direction at a sampling rate of 25 Hz. The downcast data is of higher quality because sensors encounter undisturbed seawater that flows through the nose of the fish. On the upcast the fish is flipped around (tail first) and the sensors in the nose encounter disturbed flow from the fish tail.

This type of CTD is prone to a phenomenon called 'salinity spiking' caused by a mismatch between the response times of the temperature and conductivity sensor. Data undergoes a salinity de-spiking routine to correct for this. See the history metadata for further details on the salinity de-spiking process.

Raw CTD pressure data is not always monotonic due to transient up/down motion of winch/ship. Raw pressure data is subsetted to give a monotonic (increasing) sequence and then linearly interpolated to 1 decibar pressure intervals. Data is then flagged with quality control flags after visual inspection and comparison to average climatology and historical CTD casts.

本数据集包含经质量管控的压力、温度与盐度垂直剖面数据，由电导率、温度与深度（Conductivity, Temperature and Depth, CTD）探头采集所得。本数据集收录了231组CTD剖面（站位投放）数据，采自澳大利亚皇家海军（Royal Australian Navy, RAN）水文调查航次HI568BEN_M，搭载于HMAS BENALLA号舰艇之上。

该CTD由Applied Microsystems有限公司制造，型号为"Micro CTD"，在业务场景中被称为MVP200_CTD。该CTD配备了四电极镀铂电导池、热敏电阻式温度传感器以及半导体应变片式压力传感器。

CTD传感器每12至18个月由制造商Applied Microsystems有限公司进行一次校准。其中，CTD温度传感器采用哈特（Hart）温度标准进行校准；压力传感器采用布登伯格静重（Budenburg Deadweight）校准标准；电导传感器则结合哈特温度标准与已知电导率的海水样本完成校准。

CTD传感器被安装于鱼形探头上，该探头由MVP200型电动绞车操控。在下沉投放阶段，探头依靠自身重量以约2-3米每秒的速度自由下落（绞车处于"空转"模式），随后通过绞车回收。数据在下沉阶段与通常在上浮阶段均会被记录，采样率为25赫兹。下沉阶段采集的数据质量更高，因为此时传感器流经探头头部的海水未受扰动；而上浮阶段时，探头会被翻转（以尾部先行），探头头部的传感器会流经来自探头尾部的扰动水流。

该型号CTD易出现"盐度尖峰（salinity spiking）"现象，该现象由温度传感器与电导传感器的响应时间不匹配所引发。数据集已通过盐度去尖峰程序对该问题进行校正，有关盐度去尖峰流程的更多细节，请查阅历史元数据。

受绞车与舰艇的瞬时升降运动影响，原始CTD压力数据并非始终呈单调序列。原始压力数据会被筛选为单调递增序列，随后通过线性插值得到1分巴（decibar）的压力间隔数据。随后，经目视检查并与平均气候学数据及历史CTD站位数据比对后，会为数据赋予质量控制标记。