An Optical Interferometer for the Measurement of Absolute Salinity

测量海洋盐度一直比测量温度更具挑战性，但它对海水密度同样重要。目前，它是通过测量海水的电导率以及温度和压力来推断的。另一种方法是使用光学折射率，但这需要非常高的灵敏度测量，这到目前为止是不切实际的。折射率特别有吸引力，因为它是对海水密度和盐度的更直接测量，并且可以提供绝对盐度的测量，而不是基于电导率的实际盐度，由于非导电营养物质浓度的变化，实际盐度存在系统误差。盐度已成为理解全球水循环的一个特别重要的变量，由于大多数雨水来自海洋的蒸发，因此它留下的盐度信号被证明对陆地降雨的季节性预测和确定水循环的长期趋势很有用。由于水的可用性是一个引起社会极大关注的问题，改进盐度测量已成为海洋学的一个优先事项。这里描述了一种使用多波长干涉仪的折射率测量盐度的方法。一种新的高速分析技术已经被发明（专利申请），它结合了单色干涉仪的灵敏度和广谱仪的绝对精度。广泛使用来自电信行业的光纤组件来实现非常低的噪声水平。本项目将构建并演示一种新型实用的海上干涉仪，以直接测量绝对盐度，并在测量海洋密度梯度方面达到新的精度水平。

Ocean salinity has always been more challenging to measure than temperature, yet is just as important to the density of seawater. At present it is inferred from measurements of the electrical conductivity of seawater, as well as temperature and pressure. An alternative approach is to use the optical refractive index, but this requires very high sensitivity measurements, which here-to-fore have been impractical. The refractive index is especially attractive because it is a more direct measurement of the seawater density and salinity, and would provide a measure of Absolute Salinity, instead of the conductivity-based Practical Salinity, which has systematic errors due to the variations in the concentrations of non-conductive nutrients. Salinity has emerged as an especially important variable for understanding the global water cycle, and since most rain originates by evaporation from the ocean, the salinity signals it leaves behind are proving useful for seasonal predictions of rainfall on land and for identifying long-term trends in the water cycle. Since water availability is an issue of great societal concern, improved salinity measurements have become an oceanographic priority.Here an approach to salinity measurements using the refractive index is described that uses a multi-wavelength interferometer. A new high-speed analysis technique has been invented (patent applied for) that combines the sensitivity of a monochromatic interferometer with the absolute accuracy of a broad spectrum instrument. Extensive use is made of fiber-optic components from the telecommunications industry to achieve very low noise levels. This project will construct and demonstrate a novel and practical sea-going interferometer to directly measure the Absolute Salinity and achieve new levels of accuracy in measuring the density gradients of the ocean.