Japan: Researchers in Japan are developing a novel Raman LiDAR technique which can provide efficient 3D monitoring for environmental surveys prior to seafloor exploration. Researchers say LiDAR is a promising technique for monitoring the seafloor. It offers a number of advantages over commonly used point sensors and is considered to be one of the best candidates for monitoring gases dissolved in water. Hydrothermal fluids emanating from seafloor vents contain gases such as hydrogen sulfide (H2S) and hydrogen (H2), whereas methane hydrate concentrates contain methane (CH4) and CCS stores CO2; thus, LiDAR is a suitable technique for monitoring undeveloped seafloor regions.
Carbon Dioxide is usually detected using IR absorption methods. However, water is a strong light absorber and has relatively high transmission in the short-wavelength spectral region (∼10–510nm) only. Thus, conventional IR absorption spectroscopy is not suitable for sensing gases dissolved in water. Therefore, the researchers propose using a Raman (inelastic scattering) LiDAR instrument with a green laser that has relatively high transmission in water. This technique involves irradiating the water with a 532nm laser beam and subsequently detecting the elastic (Mie and Rayleigh) scatterings at 532nm, as well as the Raman signals from the water.