Following the ZEN system design published by Almansa et al. (2017), conceived for dust aerosol optical depth monitoring, the capacity of the new ZEN-R52 radiometer to measure both column-integrated precipitable water vapor and AOD is presented in Almansa et al. (2020). This study presented PWV retrieved by the ZEN-R52 radiometer in IZO over a 10-month period (August 2017 to June 2018).

The ZEN-R52 has recent improvements in comparison with the old ZEN-R4: such as a smaller field of view; an increased signal-to-noise ratio; better stray light rejection and an additional channel at 940 nm for PWV retrieval. PWV and AOD are retrieved by using Zenith Sky Radiance (ZSR) measurements along with a lookup table (LUT) methodology. A comprehensive validation of ZEN PWV and AOD was performed using AERONET and FTIR spectrometer measurements as reference (Figure 1). The ZEN-R52 AOD uncertainty was calculated as 0.01 ± 0.13 AOD.

Figure 1.- PWV scatterplots between ZEN-R52, CE318-AERONET, CE318-IARC and FTIR at Izaña over a 10-month period (August 2017 to June 2018 a–f). The red line shows the linear fit equation, the broken grey line shows the diagonal and the colour bar indicates the density of data. Reprinted from Almansa et al. (2020).

Regarding the PWV analysis, a good agreement was found between the ZEN, AERONET and FTIR. The ZEN-R52 PWV uncertainty was calculated as ±0.089 cm or ±0.036 + 0.061 PWV for PWV < 1 cm.

The results published in this study confirm the suitability of the ZEN system to monitor aerosols and water vapour in remote regions. This new system can play can play an important role in increasing representativeness of ground based observing network which can be critical for constraining global and relatively coarse-resolution models and also for improving satellite validation and aerosol model evaluation and assimilation in remote regions.

Publications:

• Almansa, A. F., Cuevas, E., Torres, B., Barreto, Á., García, R. D., Cachorro, V. E., de Frutos, Á. M., López, C., and Ramos, R.: A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring, Atmos. Meas. Tech., 10, 565-579, doi:10.5194/amt-10-565-2017, 2017.

• Almansa, A.F.; Cuevas, E.; Barreto, Á.; Torres, B.; García, O.E.; Delia García, R.; Velasco-Merino, C.; Cachorro, V.E.; Berjón, A.; Mallorquín, M.; López, C.; Ramos, R.; Guirado-Fuentes, C.; Negrillo, R.; de Frutos, Á.M: Column Integrated Water Vapor and Aerosol Load Characterization with the New ZEN-R52 Radiometer, Remote Sens. 2020, 12, 1424, 2020