Harmonizing solar photometry calibration methods: A Cross-Network Calibration Study at Izaña Observatory

Aerosols are a significant factor in the radiative forcing of the Earth, influencing both climate and air quality. Accurate monitoring and measurement of aerosol properties are therefore essential. The spatial and temporal extent of these measurements is critical for analyzing the global distribution of aerosols and detecting shifts in global trends. The World Meteorological Organization’s Global Atmosphere Watch (GAW) program highlights the importance of Aerosol Optical Depth (AOD) as a key metric in studying atmospheric aerosols. To facilitate these studies, several networks of sun-sky-lunar photometers have been established over the years. Prominent among these are the AErosols RObotic NETwork (AERONET), Sky Measurements Network (SKYNET), and the Global Atmosphere Watch - Precision Filter Radiometer (GAW/PFR). Each network employs distinct instruments, calibration techniques, and data retrieval methods, leading to variations in the AOD measurements obtained.

The Izaña Observatory, located at 2,373 meters above sea level on the island of Tenerife, Spain (28.3ºN; 16.5ºW), is managed by the Izaña Atmospheric Research Center which is part of the Spanish Meteorological Agency (AEMET). Its elevated position in the free troposphere provides ideal conditions for employing the Langley plot calibration method. This technique benefits from minimal atmospheric interference, which significantly enhances the accuracy of solar and atmospheric measurements. In November 2019, the observatory launched a year-long intercomparison campaign, employing a diverse array of sun-sky-lunar photometers including a Prede POM unit from SKYNET and a Cimel CE318-T model from AERONET, to systematically compare and validate their data.

The objective of this study is to leverage the concurrent measurements obtained from both instruments to conduct simultaneous Langley plot calibrations. By doing so, we aim to elucidate and identify the primary differences between the photometers. This analysis will not only highlight discrepancies but also contribute to enhancing the calibration accuracy of both networks. This approach will provide insights into the consistency and reliability of the AOD measurements, facilitating improvements in measurement techniques and data comparability across different networks.