RAN CTD Profile Data - HMAS MERMAID ProjectID: HI544MER_M From: 2014-04-12 To: 2014-06-03

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 90 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise HI544MER_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.

本数据集包含由温盐深（Conductivity, Temperature and Depth，CTD）探头测量的压力、温度和盐度的质量控制垂直剖面。数据集包含90个CTD剖面（投测），这些剖面是在澳大利亚皇家海军（RAN）水文调查航次HI544MER_M期间，由HMAS MERMAID号舰船获取的。

该CTD由Applied Microsystems Limited公司制造，型号为“Micro CTD”。在实际操作中，该类型CTD被称为MVP200_CTD。它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Applied Microsystems Limited按12-18个月的周期进行校准。CTD温度传感器依据'Hart'温度标准校准；压力传感器采用'Budenburg Deadweight'标准校准；电导传感器则结合'Hart'温度标准与已知电导率的海水样本进行校准。

CTD传感器安装在鱼形探头上，探头由电动绞车（MVP200型）控制。下潜时，探头在自身重力作用下自由下落（绞车处于“自由轮”模式），速度约为2-3米/秒，随后被绞车回收。数据在下潜过程中记录，通常也在上浮过程中记录，采样率为25赫兹。下潜数据质量更高，因为传感器通过鱼头部分接触未受扰动的海水；而上浮时探头翻转（尾部朝前），鱼头处的传感器会遇到来自鱼尾的扰动水流。

该类型CTD易出现“盐度尖峰”现象，这是由温度传感器与电导传感器的响应时间不匹配导致的。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，请参阅历史元数据。

由于绞车或舰船的瞬时上下运动，原始CTD压力数据并非总是单调的。原始压力数据会被子集化以生成单调（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，并与平均气候学数据及历史CTD投测数据对比后，将被标记质量控制标识。