Forward modeling of near-field optical processes in pure rotational Raman temperature lidar

In pure rotational Raman lidar (PRRL), near-field nonparaxial reception involves large off-axis return-ray angles that vary with height and alter the spectral responses of Raman-channel filters, causing channel ratio distortion and systematic temperature bias. Existing PRRL models assume height-independent channel spectral transmittance and therefore neglect this process. To quantify this process, we develop a forward simulation model that traces return rays through an interference-filter PRRL system and maps filter-surface incidence angle distributions to channel spectral responses, channel ratio, and temperature bias. Simulation results show height-dependent shifts in Raman-channel center wavelengths, while sensitivity analysis identifies the receiver field of view as the dominant parameter for the baseline configuration and prescribed scan ranges. Based on these results, we improve the receiver configuration and conduct numerical and experimental comparisons between the two configurations over 0.3-2.0 km. The improved configuration reduces the measured mean absolute error (MAE) by 37.5%, from 3.77 to 2.35 K, while the MAE between model predictions and measurements is below 0.9 K for each configuration, demonstrating that the model quantitatively describes near-field channel ratio distortion and temperature bias under the configurations and conditions examined here.