Retrieval of Aerosol Properties from Combined Sun-Lunar Photometer and Ceilometer Observations Using the GRASP Algorithm at L’Aquila site (Italy)

Accurate characterization of aerosol optical and microphysical properties is crucial for understanding their role in atmospheric processes and climate. Remote sensing instruments, such as photometers and ceilometers, offer complementary information: photometers provide column-integrated aerosol observations, while ceilometers give vertically-resolved backscatter profiles. The synergy between these instruments can be enhanced through advanced inversion algorithms. In this study, we investigate the retrieval of aerosol properties using the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm, as shown in Roman et al. (2018), focusing particularly on the integration of lunar photometer observations.

While solar photometry is well-established for daytime aerosol characterization, nighttime retrievals remain challenging due to the absence of sunlight. The last decade developments in lunar photometry (e.g. Barreto et al. 2016), allow for aerosol measurements using the moon as a light source. This opens new possibilities for continuous, 24-hour aerosol monitoring, especially when complemented with ceilometer measurements.

In our work, we apply the GRASP algorithm to combined datasets consisting of daytime/nighttime photometer AOD and radiances, and ceilometer backscatter profiles, collected at ACTRIS L’Aquila station in Italy. GRASP is used for the retrievals, leveraging the synergy between photometric and lidar-like observations to constrain aerosol properties such as size distribution, refractive index, volume concentration and vertical profile.

We present case studies that demonstrate the added value of incorporating lunar photometer data, especially during nighttime long-range transport episodes. Preliminary results show that the inclusion of lunar observations significantly improves the temporal coverage and consistency of aerosol retrievals, allowing for better constraints on nighttime aerosol dynamics.

This study highlights the potential of integrating lunar photometry into routine aerosol monitoring networks, as recently done in the AERONET network, particularly when used in combination with ceilometers and advanced inversion tools like GRASP. The approach supports continuous observation capabilities, improving our ability to monitor aerosol variability and support atmospheric and climate research.

• BARRETO, África, et al. The new sun-sky-lunar Cimel CE318-T multiband photometer–a comprehensive performance evaluation. Atmospheric Measurement Techniques, 2016, 9.2: 631-654.
• ROMÁN, Roberto, et al. Retrieval of aerosol profiles combining sunphotometer and ceilometer measurements in GRASP code. Atmospheric Research, 2018, 204: 161-177.