- 1Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, 00184 Rome, Italy (angelica.focardi@uniroma1.it)
- 2Istituto Nazionale di Geofisica e Vulcanologia, Rome 00143, Italy
- 3Ca' Foscari University of Venice Department of Environmental Sciences, Informatics and Statistics, Ca’ Foscari University of Venice, Venezia-Mestre 30172, Italy
- 4Laboratory for Models and Measurements for Air Quality, and Climate Observations SSPT-CLIMAR-AOC ENEA, 00123 Rome, Italy
- 5Department of Physics, Sapienza University of Rome, 00184 Rome, Italy
- 6Laboratory for Models and Measurements for Air Quality, and Climate Observations SSPT-CLIMAR-AOC ENEA, 00044 Frascati, Italy
A TriOS spectroradiometer (RAMSES-ARC) operating in the UV-Vis-NIR spectral range has been operating at the Thule High Arctic Atmospheric Observatory (THAAO, 76.5° N, 68.8° W, 225 m asl, https://www.thuleatmos-it.it/) in Pituffik, Greenland, since 2021. Its measurements are used to study Arctic cloud characteristics and the cloud optical thickness (COT) in particular. This effort will be extended with additional radiance measurements performed by means of a Zeiss PGS ShortWave InfraRed (SWIR) spectrometer which will be installed at the THAAO in March 2025 in order to further characterise cloud properties.
The RAMSES-ARC is used for in situ hyperspectral light field measurements, operating across a wavelength range of 320–950 nm with a field of view (FOV) of approximately 7° in air. The Zeiss spectrometer covers the 1000–2200 nm spectral range, is thermoelectrically cooled, and will be equipped with a custom-designed input optic to reduce the field of view of its standard fiber optic and with an in-house developed software for the data acquisition.
Ensuring long-term, high-quality measurements in extremely cold environments requires rigorous and repeated calibrations to maintain reliability across the entire spectral range. However, practical challenges, such as high costs and limited access to fully equipped calibration laboratories, often hinder the achievement of optimal calibrations. Furthermore, extended operations in low-temperature environments increase the risk of calibration drifts. This study presents a structured and repeatable calibration procedure that can be easily implemented in settings where advanced laboratory equipment is unavailable.
The calibration method employs a Gigahertz Optik GmbH 250 W halogen calibration lamp powered by a highly stabilised current source. The lamp’s optical axis is aligned perpendicularly to the centre of a Labsphere panel with a reflectance factor of about 0,99 for wavelengths shorter than 1800 nm and between 0,98 and 0,94 for wavelengths between 1800 nm and 2200 nm. The panel is positioned at a distance from the lamp optimised using ANSYS SPEOS software to ensure uniform irradiance distribution across the panel.
Additionally, this presentation will discuss the impact of the new calibration on COT estimates obtained by using the method described in Calì Quaglia et al. (2024).
The primary objective is to prove that the new calibration method maintains measurement integrity while guaranteeing repeatability and accuracy, particularly in scenarios requiring frequent recalibration.
Calì Quaglia, Filippo, et al. (2024), On the Retrieval of Cloud Optical Thickness from Spectral Radiances - A Sensitivity Study with High Albedo Surfaces, Journal of Quantitative Spectroscopy and Radiative Transfer, https://doi.org/10.1016/j.jqsrt.2024.109108.
How to cite: Focardi, A., Muscari, G., Calì Quaglia, F., Tosco, M., Meloni, D., Di Bernardino, A., Ciardini, V., Di Iorio, T., Pace, G., and di Sarra, A.: A calibration method for the UV-Vis-NIR and SWIR spectrometers installed at THAAO and its impact on the retrieval of cloud properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17572, https://doi.org/10.5194/egusphere-egu25-17572, 2025.
