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Local modeling of weighted mean temperature in Iran and its impact on GNSS meteorology

Rahimi Hassan, Asgari Jamal, Nafsi Vahab

Acta Geophysica

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2022

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Vol. 70, no 3

1445--1454

EN

Weighted mean temperature (Tm) is used to determine water vapor content, precipitable water vapor, and integrated water vapor (IWV) in GNSS. This parameter is highly correlated with climate conditions as well as the type of the region. The case study is performed in Iran which has diverse climate. ERA5 reanalysis datasets were used at a compact grid of 0.125 ×0.125 between 2007 and the end of 2019 to model the Tm. The data obtained from 12 radiosonde stations along with an IGS station located in Tehran were employed in this research. Five models were examined for Tm. Bevis model, linear grouping model (LGM), and linear nearest grid point model (LNGPM) were considered as Tm linear models, and harmonic model (HM) and GPT2w model were used as nonlinear models. In LGM method the study region was divided into smaller areas with different linear model coefficients using spatial grouping method. The local model in each radiosonde station was considered as a reference. According to the results, the accuracy of linear models (Bevis and LGM model) was between 3 and 8 K (radiosonde data as reference); also 7 out of 12 stations in the LGM had higher accuracy than the Bevis model (based on RMSE). The accuracy of the two GPT2w models and the harmonic model was higher than the previous two models, and it was between 2 and 4 K. The IWV values were obtained using zenith total delay observations of IGS station located in Tehran using 5 models and were compared with the IWV values of the radiosonde station. The accuracy of the values in three linear models, Bevis, LGM, and LNGPM, was, respectively, 0.2, 0.17, and 0.14 kg m−2, and in the two nonlinear models, GPT2w and HM, was 0.13 kg m−2.

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Wyznaczenie parametrów opóźnienia troposferycznego dla stacji referencyjnej GNSS

Krasuski K.

Pomiary Automatyka Robotyka

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2016

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R. 20, nr 1

75--82

PL

W artykule przedstawiono rezultaty badań dotyczących wyznaczenia parametrów opóźnienia troposferycznego dla stacji referencyjnej Ryki. Parametry opóźnienia troposferycznego (ZHD, ZWD, ZTD, IPWV) zostały wyznaczone za pomocą modeli Hopfield, Simple, Saastamoinena i MOPS. W pracy wyznaczono również parametry meteorologiczne (temperaturę, ciśnienie i wilgotność względną) dla modelu standardowej atmosfery i MOPS. W pracy porównano również wartości parametrów opóźnienia troposferycznego dla modeli empirycznych z wynikami z programu GAPS.

EN

Article presents research results concerning to determination parameters of troposphere delay for Ryki reference station. The troposphere delay parameters (ZHD, ZWD, ZTD, IPWV) were estimated using Hopfield, Simple, Saastamoinena and MOPS models. In the paper, meteorological parameters (temperature, pressure, relative humidity) for standard atmosphere and MOPS model were also obtained. In the paper, the troposphere delay from empirical models were compared with results from GAPS software also.

3

Long series of GNSS Integrated Precipitable Water as a climate change indicator

Kruczyk M.

Reports on Geodesy and Geoinformatics

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2015

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Vol. 99

1--18

EN

This paper investigates information potential contained in tropospheric delay product for selected International GNSS Service (IGS) stations in climatologic research. Long time series of daily averaged Integrated Precipitable Water (IPW) can serve as climate indicator. The seasonal model of IPW change has been adjusted to the multi-year series (by the least square method). Author applied two modes: sinusoidal and composite (two or more oscillations). Even simple sinusoidal seasonal model (of daily IPW values series) clearly represents diversity of world climates. Residuals in periods from 10 up to 17 years are searched for some long-term IPW trend – self-evident climate change indicator. Results are ambiguous: for some stations or periods IPW trends are quite clear, the following years (or the other station) not visible. Method of fitting linear trend to IPW series does not influence considerably the value of linear trend. The results are mostly influenced by series length, completeness and data (e.g. meteorological) quality. The longer and more homogenous IPW series, the better chance to estimate the magnitude of climatologic IPW changes.

4

Integrated Precipitable Water Vapour measurements at Polish Polar Station Hornsund from GPS observations verified by aerological techniques

Kruczyk M., Liwosz T.

Reports on Geodesy and Geoinformatics

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2015

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Vol. 98

1--17

EN

We present results of the comparison of integrated precipitable water measurements from GPS solution and aerological techniques: CIMEL-318 sun-photometer and radiosoundings (RAOB). Integrated Precipitable Water (IPW) - important meteorological parameter is derived from GPS tropospheric solutions by known procedure for GPS station at Polish Polar Station, Hornsund (Svalbard). The relation between 2 m temperature and the mean temperature of atmosphere above, used to convert from wet part of tropospheric delay (ZWD) to IPW, has been derived using local radiosonde data at Ny Alesund. Sunphotometer data have been provided by AERONET. Quality of dedicated tropospheric solutions has been verified by comparison with EPN tropospheric combined product. Several IPW comparisons and analyses lead to determination of systematic difference between techniques: GPS IPW and sunphotometer data (not present in case of RAOBs). IPW measured by CIMEL is on average 5% bigger (0.5 mm) than IPW from GPS. This bias changes seasonally and is a function of atmospheric temperature what signals some systematic deficiencies in solar photometry as IPW retrieval technique. CIMEL IPW show some temperature dependent bias also in relation to radiosoundings.