Articles | Volume 10, issue 11
Research article
22 Nov 2017
Research article |  | 22 Nov 2017

Quality assessment of integrated water vapour measurements at the St. Petersburg site, Russia: FTIR vs. MW and GPS techniques

Yana A. Virolainen, Yury M. Timofeyev, Vladimir S. Kostsov, Dmitry V. Ionov, Vladislav V. Kalinnikov, Maria V. Makarova, Anatoly V. Poberovsky, Nikita A. Zaitsev, Hamud H. Imhasin, Alexander V. Polyakov, Matthias Schneider, Frank Hase, Sabine Barthlott, and Thomas Blumenstock

Abstract. The cross-comparison of different techniques for atmospheric integrated water vapour (IWV) measurements is the essential part of their quality assessment protocol. We inter-compare the synchronised data sets of IWV values measured by the Bruker 125 HR Fourier-transform infrared spectrometer (FTIR), RPG-HATPRO microwave radiometer (MW), and Novatel ProPak-V3 global navigation satellite system receiver (GPS) at the St. Petersburg site between August 2014 and October 2016. As the result of accurate spatial and temporal matching of different IWV measurements, all three techniques agree well with each other except for small IWV values. We show that GPS and MW data quality depends on the atmospheric conditions; in dry atmosphere (IWV smaller than 6 mm), these techniques are less reliable at the St. Petersburg site than the FTIR method. We evaluate the upper bound of statistical measurement errors for clear-sky conditions as 0.29 ± 0.02 mm (1.6 ± 0.3 %), 0.55 ± 0.02 mm (4.7 ± 0.4 %), and 0.76 ± 0.04 mm (6.3 ± 0.8 %) for FTIR, GPS, and MW methods, respectively. We propose the use of FTIR as a reference method under clear-sky conditions since it is reliable on all scales of IWV variability.

Short summary
Water vapour is one of the most important gases in the Earth’s atmosphere and plays a unique role in climate and weather forming. Cross-comparison of different systems for monitoring the atmospheric integrated water vapour (IWV) measurements is an essential part of their testing and validation protocol. We compare coincident measurements of IWV by different techniques over Saint Petersburg (Russia), assess their quality in various atmospheric conditions, and give recommendation for data users.