“Aerosol retrievals derived from a low-cost Calitoo sun-photometer taken on board a research vessel” paper published in Atmospheric Environment
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As part of the activities within the World Meteorological Organization (WMO) Measurement Lead Centre (MLC) program on the potential use of low-cost handheld sun photometers for operational activities, and in collaboration the Spanish Institute of Oceanography (IEO), the study Aerosol Retrievals Derived from a Low-Cost Calitoo Sun-Photometer Taken on Board a Research Vessel has been published in Atmospheric Environment.
This study presents a comprehensive 5-year period assessment of aerosol optical depth (AOD) and Ångströn Exponent (AE) data from a hand-held Calitoo sun photometer on board the Ángeles Alvariño research vessel (Figure 1 a,b,c). Observations spanned March 2018 to September 2023, focusing on key maritime regions such as the Canary Islands, coasts of North Africa, the Mediterranean, Portugal, the Cantabrian, and the Bay of Biscay (Figure 1d). The Calitoo device measures solar irradiance at three wavelengths (465, 540, and 619 nm).
Figure 1.- (a,b) Pictures of the Ángeles Alvariño vessel belonging to the Spanish Institute of Oceanography (IEO-CSIC). (c) Calitoo sun photometer. (d) Map of localization of available Calitoo measurements on board the oceanographic vessel Ángeles Alvariño between March 2018 and September 2023. The AOD value at a wavelength of 540 nm is indicated by the color of the dots.
Uncertainty analysis for Calitoo cimel retrievals was performed using the Monte Carlo method, yielding an expanded uncertainty ranging between 0.008 and 0.050 with a mean and standard deviation of 0.032±0.008 for the three wavelengths. Our results also highlight the remarkable calibration stability of the Calitoo (<2.6%) over this 5-year period. Calitoo AOD values were assessed using reference AOD data from Santa Cruz de Tenerife (the Canary Islands), El Arenosillo (Huelva), and Palma de Mallorca (the Balearic Islands) Aerosol Robotic Network (AERONET) stations. The comparison revealed a good agreement with correlation coefficients ranging from 0.727 to 0.917and mean bias ranging from -0.030 to -0.001 (Figure 2).
Figure 2.- Map of localization of available Calitoo measurements on board the oceano-graphic vessel Ángeles Alvariño: (a) Canary Islands (26°-32°N, 20°-12°W), (b) Balearic Islands (37°-42°N, 0°-5°E), (c) Huelva (36°-37°N, 8°-6°W). The yellow dots indicate the location of the AERONET stations (Santa Cruz de Tenerife, Palma de Mallorca, and El Arenosillo). The AOD value at a wavelength of 540 nm is indicated by the color of the dot. Scatterplot of Calitoo AOD versus AERONET-AOD between March 2018 and September 2023 at 465 nm (black color), 540 nm (blue color), and 619 nm (red color) at (d) Canary Islands, (e) Balearic Islands, (f) Huelva. The dotted lines are the least-squares fits. The small figures represent the occurrence distributions of the AOD differences (Calitoo AOD – AERONET-AOD).
These findings underscore Calitoo’s reliability for aerosol studies in regions where AERONET instruments or other aerosol networks are unavailable. Likewise, given the low cost of Calitoo photometers, they could be deployed on board a large number of merchant and passenger ships or in other remote or under monitored areas, providing near real-time AOD/AE data to enhance our understanding of aerosols processes or for model or satellite assimilation/validation.
For more details about this work please refer to: García, R. D., Barreto, Á., Rey, C. Fraile-Nuez, E., González-Vega, A., González-Vega, A., León-Luis, S.F., Alcantara, A., Almansa, A. F., Guirado-Fuentes, C., González-Sicilia, P., Cachorro, V.E., and and Bouchar, F.: Aerosol retrievals derived from a low-cost Calitoo sun-photometer taken on board a research vessel. Atmospheric Environment, Volume 341, 15, https://doi.org/10.1016/j.atmosenv.2024.120888, 2024.
