A Refractometer for Measuring Thermohaline Density Microstructure in the Ocean

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Here we report an optical sensor for measuring millimeter-scale thermohaline density variations in the ocean. The instrument is based on a fiber Fabry-Perot white light interferometer which can resolve the refractive index of water to better than 2 x 10-8 within a sample volume smaller than 1 mm3 at a sample rate of 500 Hz. This equates to detectable absolute salinity variations of 0.0001 g/kg, temperature variations smaller than 0.0007°C, and density variations of 0.00007 kg/m3. Data collected from laboratory characterization and a field deployment suggest the sensor could be useful as a gradiometer for measuring diapycnal mixing down to sub-millimeter scales. While obtaining high absolute accuracy in refractive index and density was not a primary consideration, the sensor was designed with such an eventual goal in mind, and various aspects of achieving it are discussed.
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These csv files correspond to the raw data that was used to generate Figures 4, and 6-13.
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