Remote sensing of salt concentration in rivers using VIPA-based Brillouin spectrometers on unmanned aerial vehicles

A significant fraction of North American rivers and streams are becoming salter and this has a variety of negative environmental and socio-economic consequences. Improving our ability to monitor water quality remotely is highly desirable. Combining Brillouin spectroscopy and LIDAR was been suggested to be a promising avenue for airborne or spaceborne temperature profiling of oceans, but much work remains to be done. We propose to employ VIPA-based Brillouin spectrometers to monitor salt concentration in rivers, streams, and pounds remotely from unmanned aerial vehicles. We present preliminary remote sensing measurements from 2 m away in which we measure the concentration of sodium chloride with a precision on the order 1 g/L. We also present simulations of a depth-resolving confocal scheme, demonstrating <0.5 m axial resolution from 50 m altitude. Finally, we demonstrate the ability to measure Brillouin spectra on a vibrating platform.