RAN CTD Profile Data - HMAS MELVILLE ProjectID: HI509MEL_M From: 2012-01-09 To: 2012-02-26

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 611 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise HI509MEL_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，数据由电导-温度-深度（Conductivity, Temperature and Depth, CTD）探头采集得到。
本数据集收录了RAN水文调查航次HI509MEL_M期间，于HMAS MELVILLE上完成的611组CTD剖面（casts）数据。
该CTD由Applied Microsystems Limited制造，型号为"Micro CTD"，作业中该型号被称为MVP200_CTD。
该CTD搭载四电极镀铂电导池、热敏电阻式温度传感器与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 Limited开展一次校准：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"标准完成校准，电导传感器则同时依托"Hart"温度标准与已知电导率的海水样本进行校准。
CTD传感器安装于鱼形探头上，该探头由MVP200型电动绞车控制。下放投放时，探头依靠自重以约2~3 m·s⁻¹的速度自由下落（绞车处于"空转轮"模式），随后通过绞车回收。数据在投放过程与回收过程中均有记录，采样率为25赫兹。
投放过程的数据质量更优，因此时传感器流经探头前端未受扰动的海水；回收过程中探头会以尾部先行翻转，前端传感器将遭遇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，其成因是温度与电导传感器的响应时间不匹配，需通过盐度去尖峰流程对数据进行校正，盐度去尖峰的具体细节可查阅历史元数据。
原始CTD压力数据并非单调序列，这源于绞车与船舶存在瞬态升降运动。因此需先对原始压力数据进行子集选取，得到单调递增序列，再以1分巴（decibar）为间隔开展线性插值。完成上述处理后，通过目视检查、与平均气候学数据及历史CTD剖面对比，为数据赋予质量控制标记。