Combining solar and lunar photometry for aerosol optical depth retrievals at the free troposphere of the
Subtropical North Atlantic

Trainer: Africa Barreto

Introduction: Since the 1990s, solar photometry has provided reliable, long-term information about key aerosol
properties to better understand the role of aerosols in Earth’s climate. However, this technique alone has been
unable to capture day-to-night variations, introducing a bias in climatological studies and a critical lack of information
to understand aerosol processes. Lunar photometry is an emerging technique capable of filling the gaps in aerosol
monitoring at nighttime. This is particularly crucial in high latitudes and polar regions due to the prolonged absence
of solar illumination.

Idea: In this project, we will learn the principal technique for retrieving Aerosol Optical Depth (AOD) at nighttime
using data from the Cimel CE318-TS instrument located at Roque de Los Muchachos (La Palma, Canary Islands, Spain).
This high-altitude observatory (2396 m above sea level) is an excellent location for astronomy and atmospheric
observations. A long series of AOD observations since 2018 is available to conduct aerosol climatology analyses
during both day and nighttime (only since 2023).

1. Learn about the different techniques available in lunar photometry, their different pros/cons and the inherent
problems in lunar photometry.
2. Install the different modules (in Python or Matlab) necessary to compute the RIMO lunar exo-atmospheric
irradiance model.
3. Perform the photometric calibration during daytime using the Langley-Plot technique.
4. Perform the photometric calibration at night by means of the day-to-night calibration transfer using the RIMO
extraterrestrial lunar irradiance model.
5. Retrieve the AOD series for day and night, including for nighttime the AOD calculated by means of the RIMO
Correction Factor (RCF) technique.
6. Solar and lunar products can be compared with the operational products of the NASA-AERONET network (routine
AOD at day and the provisional lunar data).

Goal: The main goal of this project is to develop the necessary skills to retrieve AOD at nighttime using various
techniques, comparing their respective results, and proceeding with the characterization of aerosols during both day
and nighttime in the free troposphere of the Subtropical North Atlantic. An abstract can be submitted to the
EMS2024 Harmonia session, and depending on the results, a paper can be submitted to a peer-reviewed journal.