Yong Yang

In this paper, a Fe Boltzmann temperature-measuring lidar featuring narrow-linewidth solid-state lasers and daytime detection capability is presented. The system adopts seed-injected optical parametric oscillator and amplifier technology, effectively compressing the laser linewidth to below 200 MHz. Moreover, a frequency stabilization scheme based on potassium saturated absorption spectroscopy locks the laser wavelength to the center of the iron resonance lines. In addition, the system is equipped with dual-wavelength etalons at 372 nm and 374 nm, with filter bandwidths of 8.3 GHz and 9.8 GHz, respectively. Together with high-precision coordinated temperature–pressure control and a large-aperture receiving telescope, the system effectively suppresses intense daytime background light and enables daytime observations. The demonstrated daytime-capable Fe lidar provides an effective scheme for precise probing of atmospheric dynamics in the mesosphere and lower thermosphere.

The 589 nm three-frequency lidar systems are widely employed for detecting atmospheric parameters in the mesosphere and lower thermosphere (MLT). Recently, the single-peak atomic frequency discriminator (SPAFD) has enabled 589 nm three-frequency lidars to measure wind fields in the stratosphere and mesosphere. However, research on their application for near-surface aerosol measurements remains limited. This paper proposes a method for diurnal aerosol detection using the 589 nm three-frequency lidar integrated with SPAFD. The specific configuration of the lidar system is described in detail, along with the retrieval algorithm for aerosol optical parameters derived from the three-frequency backscatter signals. Continuous 69-h observation results of the aerosol backscatter ratio are provided, followed by an analysis of the diurnal evolution of the planetary boundary layer (PBL) height. This approach enables existing 589 nm lidar systems to acquire aerosol diurnal detection capabilities without additional hardware costs or operational expenses. At present, the retrieval of aerosol extinction coefficients is constrained to altitudes above 10 km due to geometric overlap factor limitations. To overcome this, a dedicated low-altitude detection channel will be integrated in future iterations to enable full-altitude measurements. This advancement will establish the 589 nm lidar as a highly efficient tool for full-altitude, diurnal atmospheric detection.

A single-peak atomic frequency discriminator (SPAFD) specifically designed for 589 nm Doppler lidar systems has been developed, which integrates both narrowband filtering and high-precision frequency discrimination capabilities at 589 nm. The SPAFD exhibits a peak transmittance of 70% and a full width at half maximum (FWHM) of 2 GHz. The detection sensitivity has been validated through theoretical simulations and experimental verification. By integrating the SPAFD into a 589 nm three-frequency Doppler lidar system, the system retains its capability for daytime wind field detection in the mesopause region while enabling daytime wind profiling from the troposphere to the stratosphere. Continuous 5-hour daytime wind observations are demonstrated, achieving a temporal resolution of 1 hour and a spatial resolution of 1 km, with a wind speed uncertainty of ±5 m/s at 40 km altitude in daytime. With future improvements of the 589 nm laser power and repetition rate, the SPAFD will enable the lidar system to achieve daytime wind measurements across the full-altitude atmosphere.

Understanding the thermodynamic horizontal structure of the mesopause is essential for studying atmospheric wave dynamics and energy transport. However, conventional models like MSISE-00 exhibit some discrepancies from lidar observations in the mesopause. To obtain a more reliable horizontal temperature structure, this study integrates coordinated lidar observations from Urumqi, Yuzhong, and Yangbajing with models using a three-dimensional variational (3DVAR) data assimilation method to construct a high-resolution temperature field over northwestern China. The assimilated temperature profiles closely match lidar observations, with the RMSE (root mean square error) of residual reductions of 67.35% at Urumqi, 60.69% at Yuzhong, and 34.80% at Yangbajing. Independent validation at Korla showed a RMSE of residual reductions of 40.14%, confirming the model’s effectiveness. The thermodynamical horizontal structures of the mesopause obtained from this model were also analyzed. The lidar-based model for the mesopause extends the observation results from disparate lidar stations to the area between lidar stations and will contribute to a deeper understanding of upper atmospheric dynamics.

The transmission spectrum of a narrow-band interference filter is crucial and highly influenced by factors such as the temperature and angle, thus requiring precise and online measurements. The traditional method of measuring the transmission spectrum of an interference filter involves the use of a spectrometer, but the accuracy of this method is limited. Moreover, placing a narrow-band interference filter inside a spectrometer hinders real-time online measurements. To address this issue, there is demand for high-precision online spectral testing methods. In response to this demand, we propose and experimentally validate a fine spectral characterization method for narrow-band interference filters. This method uses a narrow-linewidth tunable laser, achieving a spectral resolution in the MHz range for online testing. Two types of narrow-band interference filters were tested using the constructed laser spectroscopy experimental system, obtaining a transmission spectrum with a spectral resolution of 318 MHz. In comparison to spectrometer-based methods, our proposed method demonstrates higher spectral accuracy, enables online measurements, and provides more accurate measurements for special spectral interference filters. This approach has significant application value and promising development prospects.

Based on the resonance fluorescence scattering mechanism, a narrowband sodium (Na) lidar can measure temperature and wind in the mesosphere and lower thermosphere (MLT) region. By using a narrowband spectral filter, background light noise during the day can be suppressed, allowing for continuous observations. To obtain full-diurnal-cycle temperature and wind measurement results, a complex and precise retrieval process is required, along with necessary corrections to minimize measurement errors. This paper introduces the design of a data acquisition unit for three frequencies in three directions of the Na lidar system in the Chinese Meridian Project (Phase II) and investigates the calibration and retrieval methods for obtaining diurnal temperature and horizontal wind in the MLT region, using a Na Doppler lidar with Faraday anomalous dispersion optical filter (FADOF). Furthermore, these methods are applied to observations conducted by a Na lidar in Beijing, China. The wind and temperature results over full diurnal cycles obtained from the all-solid-state Na Doppler lidar are reported for the first time and compared with temperature measurements from satellite, as well as wind observations from a meteor radar. The comparison demonstrates a reasonable agreement between the results, indicating the rationality of the lidar-retrieved results and the feasibility and effectiveness of the data correction and retrieval method.

Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer.

A dual-wavelength tunable lidar system that simultaneously detects the Ca and C a + layers has been established in Yanqing Station (40.41°N, 116.01°E). The lidar system implements a pulsed Nd:YAG laser that simultaneously pumps two dye lasers, which reduces the hardware configuration of the lidar system. The two dye lasers use infrared laser dyes with high conversion efficiency suitable for long-term observation. The resonance wavelengths of Ca and C a + are generated by frequency doubling of the two infrared laser beams. We compared the dual-wavelength tunable lidar system to previous dye-based systems and performed experiments to determine resonance frequencies to within 0.4 pm and to test the dual optical fiber receiving system and found it does not cause cross talk. Three nights of preliminary simultaneous observations of Ca and C a + layers are reported; the diversity of these observations begs for more systematic observations and challenging interpretations in terms of Ca processes in the ionosphere and illustrates the effectiveness of this system for aeronomy and space physics studies.

Due to the severe interference from strong solar background light on the received signal, daytime ground-based lidar observation of the sodium (Na) layer is challenging. In this paper, a Na lidar permitting full-diurnal-cycle observation of the metal Na layer over Beijing, China (40.5°N, 116°E) was reported. In order to suppress the skylight background during daytime effectively with less signal losses, a dual-channel Faraday filtering unit was implemented in the lidar receiver. Based on the diurnal Na lidar system, a good number of continuous observational results that lasted more than 120 h with good signal-to-noise ratio were obtained, demonstrating its reliability. Considerable variations within the Na layer during the day were revealed, especially on the layer top and bottom side. In particular, strong sporadic Na layer (Nas) events that occurred during the daytime of 3 consecutive days were also captured with complete evolution process. These observational results showed the advantages of the diurnal Na lidar for investigating the metal layer photochemistry and dynamics in the mesosphere and lower thermosphere region. Na layer observations over the whole diurnal cycle not only benefit the improvements of current theoretical models, but also can allow for a specialized analysis of Nas that occur in the daytime and provide valuable observational support for investigating the rapid production and disappearance mechanisms of Na atoms.