RAN CTD Profile Data - HMAS MERMAID ProjectID: SRATD-0030MER_M From: 2011-11-25 To: 2011-12-01

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 2 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise SRATD-0030MER_M from HMAS MERMAID.

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控制的压力、温度和盐度垂直剖面数据，由温盐深（Conductivity, Temperature and Depth，CTD）探头测量所得。数据集包含2条CTD剖面（cast），采集于澳大利亚皇家海军水文调查航次SRATD-0030MER_M期间，搭载平台为澳大利亚皇家海军舰艇美人鱼号（HMAS MERMAID）。

该CTD由应用微系统有限公司（Applied Microsystems Limited）制造，型号为“Micro CTD”。在实际操作中，此类型CTD被称为MVP200_CTD。该CTD配备了四电极镀铂电导池、热敏电阻温度传感器和半导体应变片压力传感器。

CTD传感器由制造商应用微系统有限公司按12-18个月的周期进行校准。CTD温度传感器依据“哈特温度标准”校准；压力传感器采用“布登堡静重标准”校准；电导传感器则结合“哈特温度标准”与已知电导的海水样本进行校准。

CTD传感器安装于鱼形探头上，探头由MVP200型电动绞车控制。下潜段时，探头在自身重力作用下以约2-3米/秒的速度自由下落（绞车处于“空转模式”），随后被绞车收回。数据在下降段记录，通常也在上升段记录，采样率为25赫兹。下潜段数据质量更高，因传感器接触的是流经探头前端的未受扰动海水；上升段时探头翻转（尾部朝前），前端传感器会遭遇来自探头尾部的扰动水流。

此类CTD易出现“盐度尖峰”现象，其成因是温度与电导传感器的响应时间不匹配。数据需经过盐度去尖峰处理以修正此问题。有关盐度去尖峰过程的更多细节，请参见历史元数据。

由于绞车或船舶的瞬时上下运动，原始CTD压力数据并非始终单调。原始压力数据需经过子集化处理以获得单调（递增）序列，随后线性插值至1分巴的压力间隔。数据经目视检查，并与平均气候态及历史CTD剖面数据对比后，将被标记质量控制标识。