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Homogenized atmospheric water vapour data are an important prerequisite for climate analysis. Compared with other techniques, GPS has an inherent homogeneity advantage, but it still requires reprocessing and homogenization to eliminate impacts of applied strategy and observation environmental changes where a selection of proper processing strategies is critical. This paper comprehensively investigates the influence of the mapping function, the elevation cut-off angle and homogenization on long-term reprocessing results, in particular for zenith tropospheric delay (ZTD) products, using GPS observations at 44 IGS (International GNSS Service) stations during 1995 to 2014. In the analysis, for the first time, we included the mapping function (the latest Vienna mapping function, VMF3) and exploited homogenized radiosonde data as a reference for ZTD trend evaluations. Our analysis shows that both site position and ZTD solutions achieved the best accuracy when using VMF3 and the 3 ∘ elevation cut-off angle. Regarding the long-term ZTD trends, homogenization reduced the trend inconsistency among different elevation cut-off angles. ZTD trend results show that the impact of mapping functions is very small, with a maximum difference of 0.19 mm yr -1. On the other hand, the discrepancy can reach 0.60 mm yr -1 using different elevation cut-off angles. Low-elevation cut-off angles (3 ∘ or 7 ∘) are suggested for the best estimates of ZTD reprocessing time series when compared to homogenized radiosonde data or ERA5 reference time series. [ABSTRACT FROM AUTHOR]

Homogenized atmospheric water vapor is an important prerequisite for climate analysis. Compared with other techniques, GPS has inherent homogeneity advantage, but it still requires reprocessing and homogenization to eliminate impacts of applied strategy and observation environmental changes where a selection of proper processing strategies is critical. This paper comprehensively investigates an influence of the mapping function, the elevation cut-off angle and homogenization on long-term reprocessing results, in particular for Zenith Tropospheric Delays (ZTD) products, by using GPS observations at 46 IGS stations during 1995 to 2014. In the analysis, for the first time, we included the latest mapping function (VMF3) and exploited homogenized radiosonde data as a reference for ZTD trend evaluations. Our analysis shows that both site position and ZTD solutions achieved the best accuracy when using VMF3 and 3° elevation cut-off angle. Regarding the long-term ZTD trends, results show that the impact of mapping functions is very small, with a maximum difference of 0.3 mm/yr. On the other hand, the discrepancy can reach 2.5 mm/yr by using different elevation cut-off angles. Contrary to recommendations by previous studies, the low elevation cut-off angles (3° or 7°) are suggested for the best estimates of ZTD reprocessing time series when compared to homogenized radiosonde data or ERA5 reference time series. This conclusion has great significance by eliminating the conflict of different optimal elevation cut-off angles for climate analysis and other applications from GNSS data reprocessing. [ABSTRACT FROM AUTHOR]

The spatial and temporal variability distribution of atmospheric water vapour in Papua New Guinea region is investigated using three ground-based GNSS station datasets and are compared with radiosonde data and the ERA-Interim reanalysis to generate the atmospheric precipitable water vapour (PWV) products over PNG from 2000 to 2019. From this product, PWV variations on multiple timescales are studied, with the water vapour products of GNSS and ERA-Interim in good agreement with their large-scale changes, which is reflective of the large-scale water vapour transport. At daily periods, the diurnal amplitudes of GNSS is larger at the mainland station (3.5 mm) than the two island stations (1–1.8 mm). The ERA-Interim amplitudes are smaller than GNSS on a daily basis, and do not capture the diurnal phases correctly. The estimated long-term PWV linear trends are predominantly positive and statistically significant which is in agreement in sign to the increase in moisture expected by the Clausius-Clapeyron equation under the background of global temperature rise. In addition, the regional impact of PWV in PNG in response to the El Niño- Southern Oscillation events are analysed using a correlation analysis, focusing on the dynamic influence of the large-scale nature of the 2010–2012 Bimodal La Niña and 2015–2016 El Niño events. The sea surface temperature anomaly in the Niño 3.4 and Niño 4 regions are selected to describe these two events. Both events portray overall negative correlation characteristics at the three GNSS stations with stations PNGM and RVO_ showing the strongest correlation during the 2010–2011 La Niña event significant at a 99 % confidence level. [ABSTRACT FROM AUTHOR]

An amphiphilic graft copolymer (PVDF-g-PNIPAAm) with poly(vinylidene fluoride) (PVDF) main chains and poly(N-isopropylacrylamide) (PNIPAAm) side chains was synthesized via radical copolymerization, and flat sheet membranes of this copolymer were prepared by the phase inversion method. The process of membrane formation was investigated by ultrasonic time-domain reflectometry (UTDR). The structures and properties of the membrane, including its surface chemical structure, pore morphology, and water permeability, were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and a water permeation experiment, respectively. The relationship between the process of membrane formation and the properties of the membrane was studied. The results showed that the membrane displayed temperature sensitivity. Treating the PVDF for a longer period with alkali caused more PNIPAAm to graft onto the main chains, which influenced not only the microporous structure and formation process of the membrane but also the temperature sensitivity of the performance of the membrane. [ABSTRACT FROM AUTHOR]