A Shipborne Observation Study of Sea Surface-Layer Chlorophyll-a Concentration Using Marine Lidar

Abstract

The seawater chlorophyll-a concentration is a core parameter for characterizing the biomass of marine phytoplankton. Marine lidar provides a viable active remote sensing method for detecting seawater chlorophyll-a concentration. To detect optical parameters and chlorophyll-a concentration of the sea surface layer, a dual-field-of-view marine lidar system was designed and developed. This system uses a 532 nm laser as the emission light source, features a dual-field-of-view receiving structure, and includes four independent signal acquisition channels: parallel and perpendicular polarization signals at 532 nm, fluorescence signal at 685 nm, and Raman signal at 650 nm. The marine lidar system primarily consists of an optical subsystem and a signal acquisition and control subsystem. This paper introduces its structural design and signal data processing methods. For chlorophyll-a concentration retrieval, the fluorescence-Raman normalization method is primarily utilized to obtain the profile of sea surface-layer chlorophyll-a concentration. In September 2025, an observation was conducted in the South Yellow Sea aboard the research vessel “Chuangxin 2” of the Institute of Oceanology, Chinese Academy of Sciences. The data are compared with in-situ chlorophyll-a concentration obtained from 18 fixed observation stations along the route using a chlorophyll/turbidity sensor. The results show that the goodness of fit R2 between the fluorescence-Raman signal ratio of the marine lidar and the in-situ chlorophyll-a concentration is 0.8798. Subsequently, using the calibrated retrieval method, chlorophyll-a concentration data from both underway and fixed-point observations of the marine lidar are analysed, validating the effectiveness of this system for quantitative detection of seawater chlorophyll-a.