RAN CTD Profile Data - HMAS SHEPPARTON ProjectID: HI558SHE_M From: 2014-10-17 To: 2014-11-28

This dataset contains quality controlled vertical profiles of pressure, temperature and salinity measured by a Conductivity, Temperature and Depth (CTD) probe. The dataset contains 224 CTD profiles (casts) obtained during RAN Hydrographic Survey cruise HI558SHE_M from HMAS SHEPPARTON.

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）探针采集的、经过质量控制的压力、温度与盐度垂直剖面数据。本数据集包含224条CTD剖面（测次）数据，采集自RAN水文勘测航次HI558SHE_M，搭载平台为HMAS SHEPPARTON。

该CTD探针由Applied Microsystems有限公司制造，型号为"Micro CTD"。该型号CTD在业务中被称为MVP200_CTD。该CTD搭载四电极镀铂电导池、热敏电阻温度传感器以及半导体应变片式压力传感器。

该CTD传感器由制造商Applied Microsystems有限公司按照12至18个月的周期进行校准。其中，温度传感器以哈特（Hart）温度标准进行校准，压力传感器采用布登伯格活塞压力（Budenburg Deadweight）标准进行校准，电导传感器则以哈特温度标准与已知电导率的海水样本进行校准。

CTD传感器搭载于鱼形探头上，该探头由MVP200型电动绞车控制。在下投测次时，探头依靠自身重量以约2~3米每秒的速度自由下落（绞车处于自由轮模式），随后通过绞车回收。数据将在下投阶段与通常的上浮阶段采集，采样率为25赫兹。下投阶段的数据质量更高，因为传感器流经的是探头前端未受扰动的海水；而上浮阶段时，探头会被翻转（以尾部先行），此时前端传感器会受到来自探头尾部的扰动水流影响。

该型号CTD易出现“盐度尖峰”现象，该现象由温度传感器与电导传感器的响应时间不匹配所引发。为此，数据集会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时升降运动，原始CTD压力数据并非始终单调递增。为此，原始压力数据会被截取为单调递增序列，随后通过线性插值得到1分巴间隔的压力数据。之后，研究人员会通过目视检查，并与海洋气候平均数据及历史CTD测次剖面进行比对，为数据添加质量控制标记。