A Brillouin lidar for remote sensing of the temperature profile in the ocean — Towards a simultaneous measurement of temperature and salinity

The knowledge of water temperature profiles of the upper-ocean mixed layer provides valuable input to climate studies, weather forecasts and oceanography in general. A remote-sensing lidar is an attractive method for real-time measurements of these data. The principle idea of our approach is a lidar using the time-of-flight information to measure the depth and relying on spontaneous Brillouin scattering as the temperature indicator. Recently, we demonstrated the feasibility of our approach in a laboratory test with water of 0
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/
₀₀
salinity. The test demonstrated spatial resolution under near real-time conditions, i.e. averaging 1000 laser shots (1s measurement duration) and an accuracy of 0.5 °C. By averaging up to 100,000 laser shots, an accuracy up to 0.07 °C was possible. A first field test in the Mediterranean gave us the opportunity to study the systematic behavior under real-life conditions and showed the principal functionality of the system. A drawback of the approach is that one has to rely on historical salinity data. However, the linewidth of the Brillouin scattered spectral contributions is also dependent on temperature T and salinity S. Here, we present data of the Brillouin linewidth as a function of S and T and derive a model describing their dependencies.