RAN CTD Profile Data - HMAS MELVILLE ProjectID: HI571MEL_M From: 2015-05-03 To: 2015-06-05

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 139 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise HI571MEL_M from HMAS MELVILLE.

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，这些数据由电导率-温度-深度（Conductivity, Temperature and Depth，简称CTD）探头采集得到。本数据集收录了RAN水文调查航次HI571MEL_M期间，于HMAS MELVILLE船上获取的139条CTD剖面（测站）数据。
该CTD探头由Applied Microsystems Limited公司制造，型号为“Micro CTD”，在业务应用中又被称为MVP200_CTD。该探头配备四电极镀铂电导率池、热敏电阻式温度传感器以及半导体应变片式压力传感器。
该CTD探头的传感器每12至18个月由制造商Applied Microsystems Limited进行一次校准：温度传感器采用‘Hart’温度标准进行校准，压力传感器采用‘Budenburg Deadweight’标准进行校准，电导率传感器则结合‘Hart’温度标准与已知电导率的海水样本完成校准。
CTD传感器安装于鱼形探头中，该探头由MVP200型电动绞车控制。在下行测量（downcast）阶段，探头依靠自身重量以约2~3 m/s的速度自由下落（绞车处于“自由轮”模式），完成测量后由绞车收回。数据会在下行阶段及通常在上行测量（upcast）阶段进行记录，采样率为25赫兹。下行采集的数据质量更高，因为此时传感器流经的是未受扰动的海水，水流从探头鼻部流过；而上行阶段时，探头会被翻转（尾部先行），鼻部传感器会遭遇来自探头尾部的扰动水流。
此类CTD探头易出现“盐度尖峰（salinity spiking）”现象，该现象由温度与电导率传感器的响应时间不匹配所导致。因此会对数据执行盐度去尖峰处理以校正该问题，关于盐度去尖峰流程的详细信息可查阅历史元数据。
原始CTD压力数据并非总是单调递增的，这是由于绞车与船舶存在瞬时的上下运动。原始压力数据会被筛选为单调递增序列，随后以1分巴（decibar）为间隔进行线性插值。之后会通过目视检查、与平均气候态数据及历史CTD剖面数据比对，为数据添加质量控制标记。