RAN CTD Profile Data - HMAS LEEUWIN ProjectID: SRATA-0252LEE_M From: 2014-08-18 To: 2014-09-15

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 322 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise SRATA-0252LEE_M from HMAS LEEUWIN.

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.

本数据集包含由电导率-温度-深度（Conductivity, Temperature and Depth，简称CTD）探头采集的、经过质量控制的压力、温度与盐度垂直剖面数据。

本数据集共包含322条CTD剖面（测站站位）数据，采集自澳大利亚皇家海军水文调查航次SRATA-0252LEE_M，搭载平台为HMAS LEEUWIN舰。

该CTD探头由应用微系统有限公司（Applied Microsystems Limited）制造，型号为"Micro CTD"，业务场景中常称其为MVP200_CTD。该探头配备四电极镀铂电导池、热敏电阻温度传感器以及半导体应变片式压力传感器。

CTD传感器的校准周期为12至18个月，由制造商应用微系统有限公司执行。其中，温度传感器采用哈特（Hart）温度标准进行校准，压力传感器采用巴登伯格静重式（Budenburg Deadweight）压力标准进行校准，电导率传感器则同时采用哈特温度标准与已知电导率的海水样本完成校准。

CTD传感器安装于鱼形探头之上，该探头由MVP200型电动绞车控制。在下放测站剖面（downcast）时，探头依靠自身重量以约2至3米每秒的速度自由下落（绞车处于自由轮模式），完成下放后再通过绞车回收。数据将在下放过程及通常伴随的上浮过程中采集，采样率为25赫兹。下放过程采集的数据质量更高，因为传感器流经探头前端的未受扰动海水；而上浮过程中探头会翻转（尾先出水），前端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，该现象由温度传感器与电导率传感器的响应时间不匹配所导致。为此，数据集已通过盐度去尖峰校正流程对数据进行修正，有关盐度去尖峰处理的详细信息，请参阅历史元数据。

由于绞车与船舶的瞬态升降运动，原始CTD压力数据并非始终单调递增。为此，首先会对原始压力数据进行筛选，得到单调递增的序列，随后通过线性插值将数据重采样至1分巴（decibar）的压力间隔。之后，研究人员将通过目视检查，并与平均气候态数据及历史CTD测站数据进行比对，为数据添加质量控制标记。