First evaluation of near-real-time photosynthetically active radiation from Himawari remote sensing observations under different aerosol, precipitable water, and cloud conditions in the tropical environment of Thailand

• This study presents the validation of PAR from the Himawari satellite in Thailand. • PAR from Himawari satellite was evaluated against EKO quantum sensors at 3 tropical sites. • PAR from Himawari satellite showed consistent overestimation. This study presents the first comprehensive assessment of near-real-time photosynthetically active radiation (PAR) derived from Himawari satellite products (PAR Himawari ) in the complex tropical environment of Thailand, which is characterized by variable aerosol concentration, precipitable water vapor, and cloud movement. Level 2.0 quality-assured PAR Himawari data were validated against ground-based EKO quantum sensor measurements (PAR EKO ) at three regions (Chiang Mai, Nakhon Pathom, and Songkhla) from 2018 to 2022. Results show strong linear correlations between PAR Himawari and PAR EKO (R² > 0.7). However, the magnitude of estimates remains uncertain. The Nash-Sutcliffe equation (NSE) was negative at Chiang Mai (-1.10), indicating poor estimation performance, while moderate NSE values of 0.29 and 0.50 were found at Nakhon Pathom and Songkhla, respectively. The relative root mean square error (rRMSE) ranged from 33.15 % to 64.32 %, and the relative mean bias error (rMBE) ranged from 23.82 % to 55.09 %, suggesting systematic overestimation by the satellite product. Further analysis confirmed that PAR Himawari residuals increase with aerosol optical depth (AOD) and precipitable water vapor. For cloud optical thickness (COT), residuals median values were positive under clear-sky conditions, approached zero under intermediate sky conditions, and shifted negative under overcast conditions. Overall, PAR Himawari shows higher errors when providing high PAR values, underscoring the need for improved aerosol and moisture corrections to enhance satellite PAR retrievals in tropical environments for ecological and agricultural applications.