Ученые предложили использовать лидар как искусственное солнце для независимого измерения цвета океана

Newswise — Remote-sensing reflectance describes the proportion of incident light that exits the water and carries information about chlorophyll-a, particles, and colored dissolved organic matter. Existing in-water, above-water, and on-water measurements depend on sunlight and can be affected by variable skylight, sun glint, rough seas, low solar elevation, and darkness. Although lidar can actively illuminate the ocean and distinguish atmospheric returns from underwater signals, its observation geometry differs from passive ocean-color sensing. Whether lidar can reproduce conventional Rrs, and which system and water properties control accuracy, remain unresolved. Because of these challenges, deeper research is needed into active, illumination-independent Rrs measurement. Researchers from Xiamen University, the Fujian Ocean Innovation Center, Ocean University of China, and Stratospheres Inc. published (DOI: 10.34133/remotesensing.1066) the study in the Journal of Remote Sensing on June 25, 2026. They evaluated whether pulsed white-light lidar could act as a controllable “artificial sun” for direct Rrs measurement across the visible spectrum. The proposed approach addresses practical limitations of passive ocean-color observations, including dependence on daylight, skylight contamination, sun glint, low solar angles, and unstable sea-surface conditions that can restrict reliable measurements. The simulations identified the collection of multiple-scattered photons as the principal factor controlling measurement accuracy. When the receiving footprint was sufficiently large, reconstructed spectra achieved a mean absolute percentage error (MAPE) below 10% across chlorophyll-a concentrations of 0.01-5.00 mg/m3. A high-altitude airborne platform at 3,000 m met this criterion with a field of view (FOV) above 20 milliradians (mrad), while a representative spaceborne platform at 500 km also achieved MAPE below 10% with a 0.5 mrad FOV. Compared with passive approaches, white-light lidar supplies controllable broadband illumination and range-resolved measurements, allowing atmospheric returns and in-water signals to be separated before the depth-integrated spectrum is reconstructed. Platform altitude and receiver FOV jointly determined whether the telescope captured the spread of multiply scattered photons. At 10 m, representing a shipborne platform, MAPE remained above 40% because the footprint was too small. At 500 m, performance improved substantially, although very clear water remained difficult. At 3,000 m, MAPE fell below 10% across the tested chlorophyll-a range when FOV exceeded 20 mrad. Clear water and blue-green wavelengths required larger footprints because photons traveled farther and underwent more scattering. Representative scattering phase functions had relatively minor effects. To limit interference associated with sea-surface fluctuations, the researchers proposed removing lidar signals from the first 0.1 m below the surface before reconstructing Rrs. This preprocessing changed errors differently across wavelengths, reducing some red-band errors while potentially increasing blue-green relative errors. The conclusions are based on simulations of optically homogeneous Case 1 waters under calm-surface conditions and require field validation in practice. “These simulations indicate that white-light lidar could establish an active-source framework for measuring ocean color independently of ambient sunlight. Field comparisons with in situ observations, tests in optically complex waters, and improved treatment of inelastic scattering will be essential before the approach can support operational ocean monitoring and satellite calibration activities.” The team generated reference Rrs spectra with HydroLight and evaluated three Monte Carlo (MC) frameworks: passive backward standard MC (PB-SMC), active forward standard MC (AF-SMC), and active forward semi-analytical MC (AF-SAMC). Simulations used 2 × 109 photons per run and covered 65 bands from 400 to 720 nm at 5 nm intervals. The researchers tested four chlorophyll-a concentrations, four platform altitudes, multiple receiver FOVs, several scattering phase functions, Raman scattering, chlorophyll fluorescence, and calm sea-surface conditions, for an infinitely deep water column. Future work will compare lidar measurements with in situ radiometers, examine non-Case-1 waters, quantify the separate contributions of Raman scattering and chlorophyll fluorescence, and develop algorithms for retrieving inherent optical properties from reconstructed spectra. With successful field validation and engineering development, active Rrs measurement could support observations where passive methods are constrained by illumination, strengthen ocean-color satellite calibration and product validation, and improve monitoring of aquatic optical conditions across open-ocean, coastal, and inland-water environments under changing environmental and illumination conditions. ### References DOI Original Source URL https://doi.org/10.34133/remotesensing.1066 Funding information This work was supported in part by the National Natural Science Foundation of China under grant 42476184, and in part by the Xiamen Natural Science Foundation General Project under grant 3502Z202473033. About Journal of Remote Sensing The Journal of Remote Sensing, an online-only Open Access journal published in association with AIR-CAS, promotes the theory, science, and technology of remote sensing, as well as interdisciplinary research within earth and information science.