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 GNSS observations. All relevant error sources in GNSS-derived IWV is therefore essential to be investigated. We present two approaches, a statistical and a theoretical analysis, for the assessment of the uncertainty of the IWV. It will be implemented to the GNSS IWV data stream for GRUAN in order to obtain a specific uncertainty for each data point. In addition, specific recommendations are made to GRUAN on hardware, software, and data processing practices to minimize 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 with over 75 % to 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, taking the uncertainty into account from diurnal to decadal time scales.

Corrections of Radiosonde‐Based Precipitable Water Using Ground‐Based GPS and Applications on Historical Radiosonde Data Over China

“…Since 1990s, ground‐based GPS has been proved to be a powerful tool in measuring water vapor content with advantages of high accuracy, high temporal resolution, long‐term stability, and all‐weather operations (Bevis et al, ). All of these advantages make ground‐based GPS very appealing to quantify systematic errors in other humidity observations (e.g., Vey et al, ; Wang & Zhang, ; Zhang et al, ), to correct biases in radiosondes (e.g., Liang et al, ), to validate humidity correction models (Dai et al, ; Zhao et al, ), and to derive long‐term water vapor trends in different regions (e.g., Gradinarsky et al, ; Nilsson & Elgered, ; Ning et al, ). Considering these advantages, the ground‐based GPS has been identified as a priority 1 measurement for PW in the Global Climate Observation System Reference Upper‐Air Network which aims to provide long‐term, high‐quality records of variables for climate applications (Seidel et al, ).…”

Progress in managing the transition from the RS92 to the Vaisala RS41 as the operational radiosonde within the GCOS Reference Upper-Air Network

“…CC BY 4.0 License. measurements, although some like the GNSS-based total water vapor column product is likely to be certified in the near future (Ning et al, 2016). Protocols for the development and the delivery of geophysical profiles from the various remote sensing techniques are being finalized.…”

Validating the water vapour content from a reanalysis product and a regional climate model over Europe based on GNSS observations

“…Over time, the computation carried out by the different EUREF analysis centres experiences sometimes inconsistencies due to e.g. the updates of the reference frame and applied models, the use of difference elevation cut-off angles, different mapping functions (Ning et al, 2016a). A homogeneous reprocessing of the whole dataset is thus mandatory to overcome such problems prior using this dataset for any climate application.…”