This document outlines the tools and processes involved in calibrating a RAMSES-ARC spectrometer manufactured by TriOS GmbH and used for measuring the atmospheric radiance in the Ultraviolet (UV), Visible (Vis) and Near Infrared (NIR) spectral ranges. Although calibration is essential for accurate measurements, it often involves high costs and specialized equipment. This document proposes a relatively simple, repeatable calibration procedure aimed at maintaining high accuracy while minimising costs. This work is particularly relevant for long term atmospheric monitoring in remote and harsh environments where consistency in calibration procedures are crucial. This document also shows how the instrument’s data are processed and the impact of the different calibration results on the acquired data. The spectrometer’s fundamental characteristics, such as the background signal, have remained stable over the last 6 years. However, the correction function measured in this work and used to calibrate observed spectra produces spectral radiances that differ by 3%, on average, from those obtained by using the correction function measured 3 years ago with a different calibration setup. Additionally, both corrections (2025 and 2022) produce radiances that differ from those calculated by using the calibration function provided by the manufacturer in 2019 (by 9% and 6%, respectively). We studied the robustness of the calibration setup employed in this work and our findings show that the spectrometer’s orientation relative to the main optical axis of the setup is the most significant factor influencing calibration accuracy. Small variations of a few centimetres in the distances of the reflectance panel from the spectrometer and from the baffles do not significantly affect acquisitions
Focardi et al. (Wed,) studied this question.