The uncertainty of the atmospheric integrated water vapour estimated from GNSS observations

Abstract

Abstract. Within the Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) there is a need for an assessment of the uncertainty in the integrated water vapour (IWV) in the atmosphere estimated from ground-based global navigation satellite system (GNSS) observations. All relevant error sources in GNSS-derived IWV are therefore essential to be investigated. We present two approaches, a statistical and a theoretical analysis, for the assessment of the uncertainty of the IWV. The method is valuable for all applications of GNSS IWV data in atmospheric research and weather forecast. It will be implemented to the GNSS IWV data stream for GRUAN in order to assign a specific uncertainty to each data point. In addition, specific recommendations are made to GRUAN on hardware, software, and data processing practices to minimise the IWV uncertainty. By combining the uncertainties associated with the input variables in the estimations of the IWV, we calculated the IWV uncertainties for several GRUAN sites with different weather conditions. The results show a similar relative importance of all uncertainty contributions where the uncertainties in the zenith total delay (ZTD) dominate the error budget of the IWV, contributing over 75 % of the total IWV uncertainty. The impact of the uncertainty associated with the conversion factor between the IWV and the zenith wet delay (ZWD) is proportional to the amount of water vapour and increases slightly for moist weather conditions. The GRUAN GNSS IWV uncertainty data will provide a quantified confidence to be used for the validation of other measurement techniques.

A review of sources of systematic errors and uncertainties in observations and simulations at 183 GHz

“…The GNSS-estimated PW has an uncertainty of ∼ 2 % in the mean (< 1.0 mm) (Ning et al, 2016). However, a recent analysis of the upper-air sounding network deployed during the CINDY/DYNAMO/AMIE field campaign has revealed a statistically significant dry bias, of unclear origin, in the GNSS values (∼ 2.0 mm in PW) in moist conditions at some sites (Ciesielski et al, 2014).…”

EPN-Repro2: A reference GNSS tropospheric data set over Europe

“…As a rule of thumb, 9 mm repeatability in the up component (i.e. 3 mm in ZTD as explained in Santerre, 1991) are needed to fulfil the requirement of retrieving IWV at an accuracy level of 0.5 kg m −2 (Bevis et al, 1994;Ning et al, 2016b). As shown in Fig.…”

Development of time-varying global gridded Ts-Tm model for precise GPS-PWV retrieval

“…GPS-PWV has different error sources with different properties, including GPS ZWD error, surface temperature and 305 pressure measurement errors, and Tm estimation error (Ning et al, 2016), etc. It is complicated to evaluate GPS-PWV uncertainty due to the lack of collaborated additional independent techniques to monitor water vapor at GPS site.…”