A Brillouin-lidar for remote sensing of the temperature profile in the ocean: Progress towards the implementation

The knowledge of water temperature profiles of the upper-ocean mixed layer would provide valuable input to climate studies, weather forecasts and oceanography in general. Currently, their measurement is realized by in-situ techniques such as buoys, gliders and bathythermographs. In order to provide a more flexible and less cost-intensive method, a remote-sensing lidar technique is an attractive alternative. Guagliardo et al. proposed Brillouin scattering as a potential temperature tracer already in 1980. Due to recent progress in laser technology, the implementation is now possible. The Brillouin lidar we are developing consists of two main components: The light source is a pulsed, three stage Yb-doped fiber amplifier with subsequent frequency doubling. The measurement of the Brillouin shift is performed by a spectrally highly resolving atomic edge-filter in the form of an excited state Faraday anomalous dispersion optical filter (ESFADOF). Both components are intrinsically insensitive to vibrations and exhibit low power consumption, making them perfectly suited for the operation from a mobile platform. Combining the fiber amplifier with a scanning interferometer, we succeeded in performing first range resolved water temperature measurements in our laboratory setup. Concerning the ESFADOF detector, we recently improved the transmission characteristics considerably. It now provides steep transmission edges with a maximum transmission of 57%. In the near future, we plan to demonstrate the successful interplay of the ESFADOF with the fiber amplifier under laboratory conditions.