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1

Cross-comparison of meteorological parameters and ZTD observations supplied by microwave radiometers, radiosondes, and GNSS services

Trzcina Estera, Tondaś Damian, Rohm Witold

Geodesy and Cartography

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2021

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Vol. 70, no. 2

art. no. e08

EN

Water vapour radiometers (WVR) provide information about temperature and humidity in the troposphere, with high temporal resolution when compared to the radiosonde (RS) observations. This technique can provide an additional reference data source for the zenith tropospheric delay (ZTD) estimated with the use of the Global Navigation Satellite System (GNSS). In this work, the accuracy of two newly installed radiometers was examined by comparison with RS observations, in terms of temperature (T), absolute humidity (AH), and relative humidity (RH), as well as for the ZTD. The impact of cloud covering and heavy precipitation events on the quality of WVR measurements was investigated. Also, the WVR data were compared to the GNSS ZTD estimates. The experiment was performed for 17 months during 2020 and 2021. The results show agreement between RS and WVR data at the level of 2◦C in T and 1 gm-3 in AH, whereas for RH larger discrepancies were noticed (standard deviation equal to 21%). Heavy precipitation increases WVR measurement errors of all meteorological parameters. In terms of ZTD, the comparison of WVR and RS techniques results in bias equal to –0.4 m and a standard deviation of 7.4 mm. The largest discrepancies of ZTD were noticed during the summer period. The comparison between the GNSS and WVR gives similar results as the comparison between the GNSS and RS (standard deviation 7.0–9.0 mm).

2

An assessment of the quality of near-real time GNSS observations as a potential data source for meteorology

Dymarska N., Rohm W., Sierny J., Kapłon J., Kubik T., Kryza M., Jutarski J., Gierczak J., Kosierb R.

Meteorology Hydrology and Water Management. Research and Operational Applications

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2017

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Vol. 5, Iss. 1

3--13

EN

The Global Navigation Satellite System (GNSS) can be used to determine accurate and high-frequency atmospheric parameters, such as Zenith Total Delay (ZTD) or Precipitable Water Vapour (PW), in all-weather conditions. These parameters are often assimilated into Numerical Weather Prediction (NWP) models and used for nowcasting services and climate studies. The effective usage of the ZTDs obtained from a ground-based GNSS receiver’s network in a NWP could fill the gap of insufficient atmospheric water vapour state information. The supply of such information with a latency acceptable for NWP assimilation schemes requires special measures in the GNSS data processing, quality control and distribution. This study is a detailed description of the joint effort of three institutions – Wrocław University of Environmental and Life Sciences, Wrocław University, and the Institute of Meteorology and Water Management – to provide accurate and timely GNSS-based meteorological information. This paper presents accuracy analyses of near real-time GNSS ZTD validated against reference ZTD data: the International GNSS Service (IGS) from a precise GNSS solution, Weather Research and Forecasting (WRF) model, and radiosonde profiles. Data quality statistics were performed for five GNSS stations in Poland over a time span of almost a year (2015). The comparison of near real-time ZTD and IGS shows a mean ZTD station bias of less than 3 mm with a related standard deviation of less than 10 mm. The bias between near real-time ZTD and WRF ZTD is in the range of 5-11 mm and the overall standard deviation is slightly higher than 10 mm. Finally, the comparison of the investigated ZTD against radiosonde showed an average bias at a level of 10 mm, whereas the standard deviation does not exceed 14 mm. Considering the data quality, we assess that the NRT ZTD can be assimilated into NWP models.

3

Geodetic and geodynamic studies at Department of Geodesy and Geodetic Astronomy WUT

Brzeziński A., Barlik M., Andrasik E., Izdebski W., Kruczyk M., Liwosz T., Olszak T., Pachuta A., Pieniak M., Próchniewicz D., Rajner M., Szpunar R., Tercjak M., Walo J.

Reports on Geodesy and Geoinformatics

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2016

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Vol. 100

165--200

EN

The article presents current issues and research work conducted in the Department of Geodesy and Geodetic Astronomy at the Faculty of Geodesy and Cartography at Warsaw University of Technology. It contains the most important directions of research in the fields of physical geodesy, satellite measurement techniques, GNSS meteorology, geodynamic studies, electronic measurement techniques and terrain information systems.

4

Comparison of techniques for Integrated Precipitable Water measurement in the polar region

Kruczyk M.

Geoinformation Issues

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2015

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Vol. 7, no. 1(7)

15--27

EN

Tropospheric delay estimates (tropospheric product) for selected International GNSS Service (IGS) and EUREF Permanent Network (EPN) stations made it possible to asses two areological techniques in the polar region (mainly in Greenland). Integrated Precipitable Water (IPW) – important meteorological parameter is derived from GPS tropospheric solutions by a known procedure for GPS stations. To convert from the wet part of tropospheric delay (ZWD) to IPW, the relation between 2 m temperature and the so-called mean temperature of the atmosphere above was derived using local radiosonde data for nearby GPS stations. Sunphotometer data were provided by AERONET (NASA AErosol RObotic NETwork). IPW comparisons lead to the determination of a systematic difference between the techniques of GPS IPW and sunphotometer data (not present in the case of RAOBs). IPW measured by sunphotometer CIMEL (Cimel Electronique) is several percent smaller than IPW from GPS (both IGS and EPN solution). The bias changes seasonally and is a function of atmospheric temperature. It signals some systematic deficiencies in solar photometry as the IPW retrieval technique. CIMEL IPW shows some temperature dependent bias also in relation to radiosoundings.

PL

Rozwiązania troposferyczne IGS i EPN zostały wykorzystane do przetestowania dwu technik pomiarów aerologicznych dla stacji GNSS w regionie polarnym (Grenlandia). Parametr meteorologiczny jakim jest scałkowana zawartość pary wodnej (IPW) został pozyskany za pomocą standardowej procedury opisanej w literaturze. Do przeliczania IPW z wilgotnej części opóźnienia opracowano lokalny model temperatury średniej (zależność linowa względem temperatury na wysokości 2 metrów nad powierzchnią ziemi) wyznaczony z radiosondowań prowadzonych w sąsiedztwie stacji GNSS. Pomiary fotometryczne udostępnia sieć pomiarów aerozoli AERONET działająca pod egidą NASA. Porównania kilkuletnich szeregów IPW wykazują systematyczne różnice między IPW z GNSS a fotometrem słonecznym (ale nie radiosondażem). IPW z fotometru jest nie tylko średnio kilka procent mniejsza niż z GNSS ale różnica ta zmienia się wraz z porami roku i temperaturą (co jest szczególnie widoczne w warunkach polarnych). To wykazuje pewien istotny problem z fotometrią słoneczną jako techniką pomiarów kolumnowej pary wodnej. Fotometr wykazuje systematyczną różnicę IPW (zależną od temperatury atmosferycznej) także w stosunku do wyników radiosondażu.

5

Integrated precipitable water from GNSS as a climate parameter

Kruczyk M.

Geoinformation Issues

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2014

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Vol. 6, no. 1(6)

21--35

EN

Tropospheric delay estimates (tropospheric product) on selected International GNSS Service (IGS) and EUREF Permanent Network (EPN) stations exhibit large information potential for meteorology and climate research. Long time series of integrated precipitable water (IPW) averaged hourly, daily and monthly can serve as climate indicators. As IPW is mostly influenced by global circulation, not surface processes, correlations of IPW with basic meteorological surface parameters have been analysed. Even more revealing are changes in correlation coefficients calculated for montly periods for different regions. Simple charts of IPW/temperature which can be treated as climatologic diagrams were investigated. Some of these charts have been analysed with some climatologic insight. This form of presenting IPW statistics reveals the variability of sensonal IPW values. IPW clearly represents the diversity of world climates and is a valuable meteorological and climatologic parameter.

PL

Obliczane opóźnienia troposferyczne (czyli tak zwany produkt troposferyczny) są standardowym efektem działalności międzynarodowych służb: Międzynarodowej Służby GNSS (IGS) i Permanentnej Sieci EUREF (EPN) dostarczają cennych informacji wykorzystywanych w meteorologii i klimatologii. Długie serie rozwiązań scałkowanej (kolumnowej) zawartości pary wodnej (IPW) po odpowiednim uśrednieniu w przedziałach godzinnym, dobowym i miesięcznym mogą służyć jako indykatory lokalnego klimatu. Zmienność IPW jest zdeterminowana w pierwszym rzędzie przez cyrkulację globalną atmosfery, co potwierdzają wyniki analiz korelacji IPW z podstawowymi parametrami meteorologicznymi rejestrowanymi na stacjach GNSS. Szczególnie interesujące są zmiany współczynnika korelacji obliczanego w okresach miesięcznych. Ujawniają one charakterystyczne cechy lokalnej cyrkulacji w różnych regionach. W pracy zaproponowano użycie pewnego rodzaju diagramu klimatologicznego (IPW/temperatura w odcinkach miesięcznych, uśrednione w okresie wieloletnim). Wybrane wykresy tego typu zostały przeanalizowane pod kątem cech klimatu. Poza mniej lub bardziej wyrazistą zmiennością sezonową średnie wartości IPW pozwalają wyodrębnić tak różne strefy klimatyczne, jak i szczególne cechy klimatu lokalnego.