Shipborne single-photon fluorescence oceanic lidar: instrumentation and inversion

Laser-induced fluorescence (LIF) technology has been widely applied in remote sensing of aquatic phytoplankton. However, due to the weak fluorescence signal induced by laser excitation and the significant attenuation of laser in water, profiling detection becomes challenging. Moreover, it remains difficult to simultaneously retrieve the attenuation coefficient (K l i d a r m f) and the fluorescence volume scattering function at 180° (βf) through a single fluorescence lidar. To address these issues, a novel all-fiber fluorescence oceanic lidar is proposed, characterized by: 1) obtaining subsurface fluorescence profiles using single-photon detection technology, and 2) introducing the Klett inversion method for fluorescence lidar to simultaneously retrieve K l i d a r m f and βf. According to theoretical analysis, the maximum relative error of βf for the chlorophyll concentration ranging from 0.01 mg/m³ to 10 mg/m³ within a water depth of 10 m is less than 20%, while the maximum relative error of K l i d a r m f is less than 10%. Finally, the shipborne single-photon fluorescence lidar was deployed on the experimental vessel for continuous experiments of over 9 hours at fixed stations in the offshore area, validating its profiling detection capability. These results demonstrate the potential of lidar in profiling detection of aquatic phytoplankton, providing support for studying the dynamic changes and environmental responses of subsurface phytoplankton.