Wyniki wyszukiwania - BazTech

1

On the analysis of temporal geoid height variations obtained from GRACE-based GGMs over the area of Poland

Godah W., Szelachowska M., Kryński J.

Acta Geophysica

|

2017

|

Vol. 65, no. 4

713--725

EN

Temporal mass variations in the Earth system, which can be detected from the Gravity Recovery and Climate Experiment (GRACE) mission data, cause temporal variations of geoid heights. The main objective of this contribution is to analyze temporal variations of geoid heights over the area of Poland using global geopotential models (GGMs) developed on the basis of GRACE mission data. Time series of geoid height variations were calculated for the chosen subareas of the aforementioned area using those GGMs. Thereafter, these variations were analyzed using two different methods. On the basis of the analysis results, models of temporal geoid height variations were developed and discussed. The possibility of prediction of geoid height variations using GRACE mission data over the area of Poland was also investigated. The main findings reveal that the geoid height over the area of Poland vary within 1.1 cm which should be considered when defining the geoid model of 1 cm accuracy for this area.

2

On the selection of GRACE-based GGMs and a filtering method for estimating mass variations in the Earth system over Poland

Godah W., Szelachowska M., Krynski J.

Geoinformation Issues

|

2015

|

Vol. 7, no. 1(7)

5--14

EN

Since the launch of the GRACE (Gravity Recovery And Climate Experiment) satellite mission in 2002, significant progress in the knowledge regarding the temporal variations of the Earth’s gravity field has been achieved. The main objectives of this contribution are to define a suitable filter to reduce the noise contained in the latest release, i.e. RL05, of GRACE-based GGMs as well as to select the most suitable GRACE-based GGM time series for estimating mass variations in the Earth system over Poland. The performance of the Gaussian filter with different radii and the de-correlation filters (DDK1–DDK5) applied to reduce the noise contained in those GGMs was examined. First, they were investigated globally. Then, they were examined over the area of Poland, in particular, over two basins, i.e. the Vistula river basin and the Odra river basin. Moreover, both the internal and external accuracy of RL05 GRACE-based GGMs were assessed. Error degree variances of geoid heights were calculated on the basis of these models. Equivalent water thickness variations obtained from GRACE-based GGMs were compared with the corresponding ones obtained from the hydrology model. The obtained results were analysed and discussed. Finally the filtering method and the GGM time series most suitable for estimating mass variations in the Earth system over Poland were selected.

PL

Satelitarna misja GRACE (Gravity Recovery And Climate Experiment zapoczątkowana w 2002 roku znacząco przyczyniła się do rozwoju wiedzy o zmianach w czasie pola siły ciężkości Ziemi. Głównym celem niniejszego opracowania jest zdefiniowanie odpowiedniego filtru do redukcji szumu zawartego w ostatniej wersji, tj. wersji 5. globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE, jak również wybór najbardziej odpowiedniego szeregu czasowego globalnych modeli geopotencjału wyznaczonych na podstawie danych z misji GRACE, do określenia zmian rozkładu mas w systemie Ziemia dla obszaru Polski. W szczególności badano wpływ filtrów Gaussa o różnych promieniach oraz filtrów dekorelacyjnych (DDK1–DDK5) na redukcję szumu zawartego w globalnych modelach geopotencjału. Na początku wpływ użycia filtru był badany w ujęciu globalnym. Następnie wpływ ten został zbadany dla obszaru Polski – oddzielnie dla dorzeczy Wisły i Odry. Ponadto, została oszacowana zarówno wewnętrzna, jak i zewnętrzna dokładność wersji 5. globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE. Obliczono wariancje błędów wysokości geoidy dla poszczególnych stopni badanych modeli. Zmiany ekwiwalentnej warstwy wody wyznaczone z globalnych modeli geopotencjału opracowanych na podstawie danych z misji GRACE zostały porównane z odpowiednimi zmianami otrzymanymi z modelu hydrologicznego. Wyniki poddano analizie i dyskusji. Ostatecznie wybrano metodę filtracji oraz szereg czasowy globalnych modeli geopotencjału najbardziej odpowiednie do oszacowania zmian rozkładu mas w systemie Ziemia dla obszaru Polski.

3

On accuracy of current geopotential models estimated through comparison of quasi-geoid models and GPS/levelling data

Novak P., Kostelecky J., Klokocnik J.

Reports on Geodesy

|

2006

|

z. 1/76

245-251

EN

Gravity-dedicated satellite missions CHAMP and GRACE provide accurate data that can be inverted into geopotential coefficients forming global geopotential models (GGM). Through an estimation process, mean square errors of these coefficients can be elvaluated. In most cases, even the entire variance-covariance matrices are computed. However, these errors are only formaI and do not represent weIl the actual accuracy of estimated coefficients, thus also of various gravity field parameters synthesized from these coefficients. For this reason validation procedures for the new GGMs are being sought since the classical validation methocts reached their limits. This article discusses the validation procedure of the GGM through its comparison with idependent data estimated at selected GPS/leveIling stations over the area of Central Europe. Due to a different spectral content of height anomalies synthesized from the GGM and of those derived from combination of ellipsoidal and normal heights at selected points of the European Vertical Reference Network, the GGM-based low-frequency height anomaly is completed for a missing higth-frequency component based on high resolution and high accuracy ground gravity and elevation data. The methodology is also applied on a set of GPS/leveIling stations in the Czech Republic. In accordance with previous validation tests of GGMs based on data of crossover altimetry, obtained results indicate that the current GGMs estimated from single/dual-sateIlite data seem to have significant problems namely with low-order and degree coefficients.