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Accuracy assessment of high and ultra high-resolution combined GGMs, and recent satellite-only GGMs - Case studies of Poland and Ethiopia

Godah Walyeldeen, Szelachowska Małgorzata, Gedamu Andenet A.

Reports on Geodesy and Geoinformatics

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2024

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Vol. 117

38--44

EN

The launch of dedicated satellite gravity missions (CHAMP, GRACE, GOCE, and GRACE-FO), as well as the availability of gravity data from satellite altimetry and terrestrial/airborne gravity measurements have led to a growing number of Global Geopotential Models (GGMs) developed. Thus, the evaluation of GGMs is necessary to ensure their accuracy in recovering the Earth's gravity field on local, regional, and global scales. The main objective of this research is to assess the accuracy of recent GGMs over Poland in Central Europe and Ethiopia in East Africa. Combined GGMs of high (degree and order (d/o) 2190) and ultra high-resolution (d/o 5540) as well as five satellite-only GGMs were evaluated using gravity data from absolute gravity measurements and airborne gravity surveys over Poland and Ethiopia, respectively. Based on this evaluation, the estimated accuracy of the high-resolution combined GGM is at the level of 2 mGal. The estimated accuracy for the ultra-high-resolution combined GGM is ~2.5 times lower. The satellite-only GGMs investigated recover the gravity signal at an accuracy level of 10 mGal and 26 mGal, for the areas of Poland and Ethiopia, respectively. When compensating for the omitted gravity signal using a high-resolution combined GGM and the topography model, an accuracy of 2 mGal can be achieved.

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Research on gravity field modelling and gravimetry in Poland in 2019–2022

Krynski Jan, Dykowski Przemysław, Godah Walyeldeen, Szelachowska Małgorzata

Advances in Geodesy and Geoinformation

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2023

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Vol. 72, no. 2

art. no. e46, 2023

EN

The article presents the reviewed and summarised research activities of the Polish research groups on gravimetry and gravity field modelling in the period of 2019–2022. It contains the results of absolute gravity surveys for the maintenance of the international gravity reference level in Poland and Europe, and for geodynamic research with an emphasis on metrological aspects. It also contains relative gravimetry issues as well as the results of marine gravity surveys in the southern Baltic Sea. Non-tidal gravity changes were extensively investigated. Long-term gravity variations were monitored at the Borowa Gora Geodetic-Geophysical Observatory and in a few other locations in Poland. The contribution of gravimetric records to seismic studies was investigated. Temporal variations of the gravity field from GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (GRACE Follow-On) data, in particular, deformations of the Earth’s surface as well as temporal variations of heights, total water storage and groundwater storage were investigated. Moreover, GRACE-based products and the performance of monthly Global Geopotential Models (GGMs) were a subject of research. GGMs developed in last years were evaluated. The research on developing new approaches in geoid modelling and their validation was conducted. New regional and local geoid models were determined for Poland and Ethiopia. The use of different techniques for estimating the absolute sea level at sites of the selected network in the Baltic Sea was investigated.

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Research on Earth rotation and geodynamics in Poland in 2019–2022

Bogusz Janusz, Brzezinski Aleksander, Godah Walyeldeen, Nastula Jolanta

Advances in Geodesy and Geoinformation

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2023

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Vol. 72, no. 2

art. no. e41, 2023

EN

This paper summarizes the activity of the chosen Polish geodetic research teams in 2019–2022 in the fields of the Earth rotation and geodynamics. This publication has been prepared for the needs of the presentation of Polish scientists’ activities on the 28th International Union of Geodesy and Geodynamics General Assembly, Berlin, Germany. The part concerning Earth rotation is mostly focused on the estimation of the geophysical excitation of polar motion using data from Gravity Recovery and Climate Experiment (GRACE) and its follow-on (GRACE-FO) missions, and on the improvement of the determination of Earth rotation parameters based on the Satellite Laser Ranging (SLR), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and Global Navigation Satellite System (GNSS) satellite techniques. The part concerning geodynamics is focused on geodetic time series analysis for geodynamical purposes and monitoring of the vertical ground movements induced by mass transport within the Earth’s system, monitoring of the crustal movements using GNSS and newly applied Interferometric Synthetic Aperture Radar (InSAR), discussing the changes of the landslides and its monitoring using geodetic methods as well as investigations of seismic events and sea-level changes with geodetic methods. Finally, the recent research activities carried out by Polish scientists in the international projects is presented.

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Investigation of background noise in the GNSS position time series using spectral analysis – A case study of Nepal Himalaya

Ray Jagat Dwipendra, Vijayan M. Sithartha Muthu, Godah Walyeldeen, Kumar Ashok

Geodesy and Cartography

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2019

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Vol. 68, no. 2

375--388

EN

Position time series from permanent Global Navigation Satellite System (GNSS) stations are commonly used for estimating secular velocities of discrete points on the Earth’s surface. An understanding of background noise in the GNSS position time series is essential to obtain realistic estimates of velocity uncertainties. The current study focuses on the investigation of background noise in position time series obtained from thirteen permanent GNSS stations located in Nepal Himalaya using the spectral analysis method. The power spectrum of the GNSS position time series has been estimated using the Lomb–Scargle method. The iterative nonlinear Levenberg–Marquardt (LM) algorithm has been applied to estimate the spectral index of the power spectrum. The power spectrum can be described by white noise in the high frequency zone and power law noise in the lower frequency zone. The mean and the standard deviation of the estimated spectral indices are […] for north, east and vertical components, respectively. On average, the power law noise extends up to a period of ca. 21 days. For a shorter period, i.e. less than ca. 21 days, the spectra are white. The spectral index corresponding to random walk noise (ca. –2) is obtained for a site located above the base of a seismogenic zone which can be due to the combined effect of tectonic and nontectonic factors rather than a spurious monumental motion. Overall, the usefulness of investigating the background noise in the GNSS position time series is discussed.

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On the contribution of dedicated gravity satellite missions to the modelling of the Earth gravity field ‒ A case study of Ethiopia and Uganda in East Africa

Godah Walyeldeen, Gedamu Andenet A., Bedada Tulu B.

Geoinformation Issues

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2018

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Vol. 10, no. 1(10)

5--15

EN

Since the first decade of this millennium, the three dedicated gravity satellite missions (DGSMs): CHAMP (Challenging Minisatellite Payload), GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity field and steady-state Ocean Circulation Explorer) had remarkably contributed to the modelling of the Earth’s gravity field and its temporal variations. Moreover, in 22 May 2018, the GRACE-FO (GRACE Follow-On) has been launched to continue the measurements of GRACE satellite mission. On the basis of data from those DGSMs, Global Geopotential Models (GGMs) are continuously developed. The main aim of this research is to evaluate the recent GGMs and assess the contribution of DGSMs to the modelling of the Earth’s gravity field over East Africa. Gravity functionals, e.g. quasigeoid height and gravity disturbance, obtained from recent GGMs developed with the use of data from DGSMs were evaluated using terrestrial gravity data available in Ethiopia and GNSS/levelling data in Uganda. The results obtained were analysed and discussed. The main findings reveal an improvement of ca. 40–50% on the modelled gravity field from GGMs that include data from GOCE satellite mission.

PL

Od pierwszej dekady obecnego tysiąclecia do poprawy modelowania pola siły ciężkości Ziemi oraz jego zmian w czasie przyczyniły się ogromnie trzy grawimetryczne misje satelitarne: CHAMP (Challenging Minisatellite Payload), GRACE (Gravity Recovery and Climate Experiment) oraz GOCE (Gravity field and steady-state Ocean Circulation Explorer). Ponadto w maju 2018 roku zostały wystrzelone satelity misji GRACE-FO (GRACE Follow-On) kontynuującej dostarczanie danych pomiarowych otrzymywanych z misji GRACE. Na podstawie tych danych są stale opracowywane globalne modele geopotencjału. Głównym celem podjętych w niniejszej pracy badań jest ocena wygenerowanych w ostatnich kilku latach globalnych modeli geopotencjału oraz oszacowanie wpływu grawimetrycznych misji satelitarnych na modelowanie pola siły ciężkości Ziemi dla obszaru Etiopii i Ugandy w Afryce Wschodniej. Z globalnych modeli geopotencjału opracowanych na podstawie danych z grawimetrycznych misji satelitarnych, wyznaczono funkcjonały pola siły ciężkości, tj. zakłócenie grawimetryczne i wysokość quasigeoidy, a następnie porównano je z dostępnymi lotniczymi/naziemnymi danymi grawimetrycznymi dla obszaru Etiopii oraz danymi satelitarno-niwelacyjnymi dla obszaru Ugandy. Uzyskane wyniki poddano analizie i dyskusji. Zaobserwowano poprawę dokładności modelowanego ziemskiego pola siły ciężkości o ok. 40–50% w przypadku wykorzystania globalnych modeli geopotencjału opracowanych z użyciem danych z misji satelitarnej GOCE.