Comparison of different techniques for tropospheric wet delay retrieval over South America and surrounding oceans

Abstract

Water vapour (WV) plays a fundamental role in several weather processes that deeply influence human activities. Satellite based radiometers, Ground based Global Navigation Satellite Systems (GNSS) and Numerical Weather Models (NWM) permit to obtain either measurements or estimates or forecasts of WV. This work presents a 2 years systematic comparison to address the agreement on the tropospheric wet delay retrieved by the three mentioned independent techniques over permanent stations belonging to SIRGAS (Sistema de Referencia para las Américas) GNSS network. SIRGAS tropospheric total delay estimations are compared with the official International GNSS Service (IGS) ones, with the measurements from the Jason-1 satellite radiometer (JMR) in terms of Zenith Wet Delays (ZWD) and, finally, with the ZWD computed from ERA Interim, the last reanalysis dataset from the European Center for Medium-Range Weather Forecasts (ECMWF). All the differences between the techniques, which were considered in order to yield a reliable comparison, are discussed. The statistical results of mean (μ), standard deviation (σ) and correlation (ρ), show that the highest agreement is reached between SIRGAS and IGS products (μ = –0.5mm, σ = 5.6mm, ρ = 0.98), whereas slightly worse values are obtained in the comparisons with the JMR measurements (μ = –7.4mm, σ = 15.4mm, ρ = 0.91), and the ERA Interim data (μ = –1.5mm, σ = 16.6mm, ρ = 0.91).