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New Digital Technical Note on Aerosol Optical Depth traceability obtained from photometers measurements of AERONET-CIMEL and GAW-PFR networks at the Izaña Observatory in the 2005-2015 period.

 

On September 25th, 2017, the Technical Digital Note No.23 of the State Meteorological Agency of Spain was published on its website. An analysis of the traceability of the optical aerosol depth (AOD) in the visible and near infrared bands from normal direct irradiance measurements comparison of the AERONET-CIMEL and GAW-PFR photometer networks at the Izaña Observatory is described.

The traceability between two different data series of the same variable is a way to measure the homogeneity between them, being able to qualify these series as equivalent or traceable provided they meet the established mathematical criteria even though they have been obtained by different equipments and methodologies. This Technical Note applies the concept of 95% traceability defined by WMO for high quality data of AOD and also analyzes the main factors cause non-traceability, when occurring, giving a quantitative estimation of such factors.

The AOD traceability study has been carried out on the four CIMEL channels closer to the PFR channels (870nm, 500nm, 440nm and 380nm). The traceability obtained is very high, above 91% and even exceeding 97% in the case of 870nm channel.

The main cause of non-traceability in the 870nm channel is associated with the calibration of one of the two instruments being compared, while for the other channels it is related to the AOD calculation itself.

For channels below 700nm, it is advisable to consider the absorption of NO2 when assessing AOD, especially in highly polluted areas with high tropospheric NO2 content.

The influence of cloudiness on non-traceability for the 870nm channel is just over 2.5%, while for the rest of the channels is somewhat higher than 32%.

 

The new Digital Technical Note can be downloaded at:

http://www.aemet.es/documentos/es/conocermas/recursos_en_linea/publicaciones_y_estudios/publicaciones/NT_23_AEMET/NT_23_AEMET.pdf