Microwave radiometer, sun-photometer and GNSS multi-comparison of integrated water vapor in Southwestern Europe Vaquero Martínez, Javier Navas Guzmán, Francisco Alados Arboledas, Lucas Water vapor Sun-photometer GNSS Southwestern Europe Iberia This work presents a comparison of integrated water vapor (IWV) data recorded from microwave radiometer (MWR) and sun-photometer (SP) using global navigation satellite system (GNSS) IWV as reference in five midlatitude sites of Portugal and Spain (2003–2021). A very high correlation is obtained for both instruments (R2 between 0.94 and 0.98), although, while MWR shows a wet bias, SP exhibits a dry one. In addition, a dependence of mean bias error (MBE) and standard deviation (SD) on IWV has been observed, increasing (larger discrepancies) both indices as IWV increases. The solar zenith angle (SZA) dependence is also studied, finding slightly larger discrepancies for the MWR than for SP in comparison with GNSS for very high values of SZA. Finally, a marked seasonal dependence is observed for SP-GNSS differences, modulated by the IWV dependence explained above. In contrast, the seasonal dependence for MWR is quite weaker than it is for SP. Therefore, in spite of the excellent agreement found among the different instruments, it is recommended that: i) the dependence with IWV be studied and corrected to further increase the performance of the instruments, and ii) metadata be used to filter out situations in which the instrument cannot operate properly. 2023-05-15T11:01:45Z 2023-05-15T11:01:45Z 2023-03-08 journal article J. Vaquero-Martínez et al. Microwave radiometer, sun-photometer and GNSS multi-comparison of integrated water vapor in Southwestern Europe. Atmospheric Research 287 (2023) 106698[https://doi.org/10.1016/j.atmosres.2023.106698] https://hdl.handle.net/10481/81537 10.1016/j.atmosres.2023.106698 eng info:eu-repo/grantAgreement/EC/Horizonte2020/871115 http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional Elsevier