Remote sensing of particulate organic carbon in the South China Sea using airborne high-spectral-resolution LiDAR.

The vertical profiles of particulate organic carbon (POC) in the South China Sea (SCS) observed during an airborne high-spectral-resolution light detection and ranging (LiDAR) (HSRL) flight experiment conducted on May 24, 2024, were examined. We developed a robust inversion model to estimate the vertical profile distribution of the POC along the airborne HSRL flight track by integrating the airborne HSRL-measured particulate backscattering coefficient, chlorophyll-a concentration (Chla), and in-situ measurements. The vertical profile distribution of the POC for a total flight track of 24 km fluctuated in the range of 0.86 to 93.89 mg m^-3. The results revealed significant vertical and horizontal heterogeneity in the POC profiles, with elevated concentrations observed in the surface and subsurface layers where phytoplankton biomass dominated. The airborne HSRL-measured POC was subjected to correlation analysis with satellite observations and in-situ measurements, yielding a determination coefficient (R²) of 0.8436 and a root mean square error (RMSE) of 5.0862 mg m^-3. The vertical distribution of the ratio of Chla to POC (Chla/POC) provided key insights into the balance between living phytoplankton biomass and nonliving organic detritus. Stratification and physical processes, such as upwelling, mixing, and turbulence, have been shown to influence POC dynamics, particularly in regions of localized productivity. This research underscores the importance of HSRL technology as a tool for high-resolution oceanic carbon monitoring, contributing to improved biogeochemical models for assessing carbon sequestration efficiency.