High-spectral-resolution LiDAR (HSRL) is essential for precise detection and retrieval of aerosol optical properties, making it a valuable tool in atmospheric aerosol studies. While the HSRL technique has seen rapid advancements in ultraviolet and visible wavelengths 355 nm/532 nm, development in the near-infrared HSRL domain is constrained by the limitations of spectral discriminators. In 2017, the National Center for Atmospheric Research (NCAR) has proposed a 780 nm near-infrared micro-pulse HSRL technique using rubidium (Rb) atom absorption lines and 780 nm semiconductor lasers. This approach provides a promising solution to the challenges facing near-infrared HSRL and has become a research focal point worldwide. However, the effect of various Rb absorption cell parameters on detection errors in the 780-nm HSRL system remains unexplored. In this paper, we address this gap by analyzing the influence of Rb cell parameters, system signal-to-noise ratio (SNR), and laser frequency stability on detection results, based on the absorption spectrum of rubidium isotope (⁸⁷Rb). This study offers theoretical guidance for designing 780-nm near-infrared HSRL systems, particularly in optimizing the temperature settings of the Rb cell spectral discriminator.

We employ the Monte Carlo method in this analysis. First, the HSRL error formula is derived, and the absorption spectrum is obtained based on the hyperfine structure of rubidium atoms. An error analysis model for the 780-nm HSRL system is then established. Subsequently, a simulated atmospheric model is developed (Fig. 6), incorporating the U.S. Standard Atmosphere Model for background aerosols, urban aerosols, and dust. Using this model, we evaluate the effects of system detection SNR, Rb cell temperature fluctuations, laser frequency stability, and the omission of Mie scattering signal transmittance T_a (T_a=0) on detection errors. The Monte Carlo method is applied to establish LiDAR equations under the conditions described, enabling backscattering coefficient retrieval based on theoretical derivation. Retrieval errors are then computed to demonstrate the integrated effect. Specifically, the retrieval error of the backscattering coefficient is calculated under the conditions where the Rb cell operates at 70 ℃ with a ±1 ℃ temperature fluctuation and laser output frequency fluctuation within 100 MHz.

HSRL system measurement accuracy is highly sensitive to the SNR, especially at elevated Rb cell temperatures, which can degrade the molecule channel signal. When the Rb cell temperature exceeds 65 ℃, SNR becomes the primary factor affecting measurement results, with retrieval errors reaching up to 20%. In addition, the retrieval error of the backscattering coefficient increases with higher Rb cell temperature due to decreased Rayleigh echo transmittance (Fig. 9). If the Rb cell temperature fluctuation is within ±1 ℃ when the temperature exceeds 65 ℃, the influence on backscattering coefficient retrieval error is relatively minor (Fig. 12). Higher Rb cell temperatures can also help reduce the measurement error from temperature fluctuations. With an Rb cell temperature above 65 ℃ and Mie scattering transmittance T_a set to zero, the backscattering coefficient retrieval error remains below 1%. Moreover, higher Rb cells correlate with reduced retrieval error at higher aerosol concentrations. Finally, fluctuations in laser source frequency significantly influence retrieval results. When frequency fluctuations reach 1 GHz, retrieval errors exceed 10%, even in the absence of other error factors. By contrast, at a 70 ℃ operating temperature with a 100 MHz frequency fluctuation range, the relative retrieval error reduces to 0.1% (Fig. 14).

The operational temperature of the ⁸⁷Rb absorption cell critically influences HSRL system retrieval accuracy. With an absorption cell length of 63 mm, the recommended temperature range is 65 ℃ to 75 ℃. Within this range, system SNR, laser frequency stability, and Rb cell temperature stability are vital factors influencing detection accuracy. The simulation results demonstrate that when the ⁸⁷Rb absorption cell is 63 mm in length, operating at 70 ℃ with laser frequency stability within 100 MHz, the comprehensive retrieval deviation of the backscattering coefficient remains below 10% (Fig. 15).