ALBERT

Description: The continental water storage is significantly in-fluenced by wetlands, which are highly affected by climate change and anthropogenic influences. The Pantanal, located in the Paraguay river basin, is one of the world’s largest and most important wetlands because of the environmental biodiversity that represents. The satellite gravity mission GRACE (Gravity Recovery And Climate Experiment) provided until 2017 time-variable Earth’s gravity field models that reflected the variations due to mass transport processes-like continental water storage changes-which allowed to study environments such as wetlands, at large spatial scales. The water storage variations for the period 2002-2016, by using monthly land water mass grids of Total Water Storage (TWS) derived from GRACE solutions, were evaluated in the Pantanal area. The capability of the GRACE mission for monitoring this particular environment is analyzed, and the comparison of the water mass changes with rainfall and hydrometric heights data at different stations distributed over the Pantanal region was carried out. Additionally, the correlation between the TWS and river gauge measurements, and the phase differences for these variables, were also evaluated. Results show two distinct zones: high correlations and low phase shifts at the north, and smaller correlation values and consequently significant phase differences towards the south. This situation is mainly related to the hydrogeological domains of the area.

Description: . Solid Earth tide is the periodic displacement due to the tidal force. This effect is present in all geodesic and geophysical observations and should be eliminated when high accuracy surveying is required. It is necessary to determine the amplitudes and phases of the harmonic constituents to estimate the terrestrial tide effect magnitude. This article presents a methodology for estimating and analyzing the amplitudes and phases of the solid Earth tide principal constituents from gravimetric/GNSS observations. The methodology was applied to data collected in the Manaus/AM and Brasília/DF stations, Brazil, to determine the amplitude and phase values for the long period, monthly, diurnal and semidiurnal constituents, besides determining the time required for the convergence of the estimated constituent values. The estimated amplitude and phase values, using gravimetric data, converged between the 2nd and 6th months of the time series. For the positioning observations, the constituents values converged between the 2nd and 17th month of the data series, except for the long period constituent, which requires a longer time series to obtain satisfactory values for both methods. The results show that the solid Earth tide constituents were better estimated by the gravimetric data compared to the positioning data considering the series analyzed.Keywords: gravimetry, GNSS, solid Earth tide, tidal constituents.RESUMO. Maré terrestre é o deslocamento periódico decorrente da força de maré. Este é um efeito que deve ser eliminado quando se deseja realizar levantamentos nos quais é necessária alta acurácia tanto em observações geodésicas quanto geofísicas. Para estimar o efeito de maré terrestre deve-se determinar as amplitudes e fases de suas componentes harmônicas. Este artigo apresenta uma metodologia para a estimativa das amplitudes e fases das principais componentes de maré terrestre, a partir de observações gravimétricas/GNSS. A metodologia foi aplicada a dados coletados em estações instaladas em Manaus/AM e Brasília/DF, Brasil, resultando na determinação dos valores de amplitude e fase para componentes de longo período, mensais, diurnas e semidiurnas, além da análise da convergência dos valores estimados para estas componentes. As amplitudes e fases calculadas, utilizando dados gravimétricos, convergiram entre o 2_ e o 6_ mês analisados, enquanto para os dados de posicionamento a convergência ocorreu entre o 2_ e o 17_ mês observado, com exceção da componente de longo período, que não pôde ser determinada em ambos os métodos. Para o período analisado, as componentes de maré terrestre foram melhor estimadas utilizando dados gravimétricos, se comparadas aos resultados obtidos com dados de posicionamento.Palavras-chave: gravimetria, GNSS, maré terrestre, componentes de maré.

Description: Para solicitação de resumo, entrar em contato com editor-chefe (editor@sbgf.org.br). 

Description: . Gravitydata coverage is quite complete in São Paulo state for a 5’ resolution. In addition, field works have been conducted to fill in gaps around the state. These efforts are the results of the Fundac¸˜ao de Amparo `a Pesquisa do Estado de S˜ao Paulo (FAPESP) Thematic Project that seeks to achieve the establishment of a geoid model, a height system, and the study of mean sea level. This paper presents a comparison between two geoidal height models; the first with information available up to 2008 (beginning of the project) and the second including all data collected. Both models have been derived using the modified Stokes integral through the FFT technique. The SHGEO package was used to derive the Helmert gravity anomalies, while the EGM2008 model was selected as a reference geopotential field restricted to degree and order 150, to obtain the long and medium wavelength components. The model was validated using the geoidal heights from 170 GPS observations on Bench Marks of the spirit leveling network. The corresponding height anomalies derived from recent geopotential models (GO CONS GCF 2 TIM R2, GOCO02S and EIGEN-6C) were also compared with the same quantities at the points of leveling, besides the official Brazilian model, MAPGEO2010. The findings showed that GEOIDSP2011 displayed better consistency with respect for the GPS/leveling than GEOIDSP2008 and the geopotential models.Keywords: geodesy, geoid, geopotential model. RESUMO. O estado de São Paulo possui uma cobertura bastante completa de dados gravimétricos para uma resolução de 5’. Além disso, trabalhos de campo estão sendo realizados com o objetivo de preencher os vazios no entorno do estado. Os recentes esforços nos levantamentos são devido ao Projeto Temático da FAPESP que tem, entre outras finalidades o estabelecimento de um modelo geoidal, além do estudo sobre sistemas de altitude e monitoramento do nível médio dos mares. Este artigo apresenta a comparação entre doismodelos de alturas geoidais; o primeiro cominformações disponíveis até 2008 (fase inicial do projeto) e o segundo incluindo os dados coletados até o momento. Ambos os modelos foram calculados utilizando a integral modificada de Stokes por meio da técnica FFT. O pacote computacional SHGEO foi empregado para determinar as anomalias de gravidade de Helmert, enquanto omodelo do geopotencial EGM2008 restrito até grau e ordem 150 foi selecionado para obter as componentes de longo e médio comprimento de onda. Osmodelos foramvalidados a partir da comparação das alturas geoidais em 170 marcos da rede de nivelamento onde observações GPS foram conduzidas. As anomalias de altura dos modelos mais recentes do geopotencial (GO CONS GCF 2 TIM R2, GOCO02S e EIGEN-6C) também foram comparadas com as mesmas grandezas nos pontos de nivelamento, além do modelo oficial brasileiro, o MAPGEO2010. Os resultados mostraram melhor consistência na comparação com os pontos GPS/nivelamento do modelo GEOIDSP2011 em relação ao GEOIDSP2008 e os modelos do geopotencial.Palavras-chave: geodésia, geoide, modelo do geopotencial.

Description: Despite present efforts to better understand glacier changes and their trends, the satellite gravimetry is a powerful tool still not applied in depth to study relatively large areas in the Andes of Argentina and Chile. In this work the mass variations of the Patagonian Icefield are analyzed together with the decrease trends of the ice layer in the region. The purpose of this study is to demonstrate the GRACE satellite mission (Gravity Recovery and Climate Experiment) ability to detect the water storage changes over the glaciers area. Furthermore, the variations of the hydrometric level of some Patagonian lakes were monitored by combining satellite altimetry data and in situ measurements with the observed water mass variations. Data from GRACE was used to estimate gravity trends, and high-resolution CSR GRACE RL05 mascon solutions were used to analyze the water storage change of the icefields in the region under study for the 2002-2017 period. Virtual stations from satellite altimetry obtained from a lake database and also hydrometric height data from in situ stations, located at Patagonian lakes in Argentina and Chile, were also used in order to compare the TWS from GRACE to the water level of the specific lakes. Additionally, correlation coefficients were determined at each station.  The results show a significant water storage decrease in the Icefield area, and they also demonstrate that the ice melt in southern Patagonia (of about 6 cm/year) tends to be more pronounced than in the northern region.

Description: Abstract

Description: The quasi-geoid model of São Paulo State was computed using the updated and filtered gravimetric data and the new system of the normal height of the 2018 Brazilian Vertical Reference Frame (BVRF). For the ocean area, gravity anomalies of the DTU13 model with a resolution of 1’ were used. To quantify the terrain effects through the Residual Terrain Model procedure, the SRTM15+ DTM was used. The computation of the quasi-geoid model was performed by numerical integration through the Fast Fourier Transform (FFT). The Molodensky gravity anomaly was determined in a 5’x5’ grid and reduced and restored using the Residual Terrain Model (RTM) technique and the XGM2019e global gravity model truncated at degree and order 720. The zero-order degree term was added in the final computation. The validation for the quasi-geoid model based on 291 GPS measurements in the leveling network has shown 18 cm RMS difference. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

Description: Other

Description: The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).

Description: Abstract

Description: The geoid model of São Paulo State was computed using the updated and filtered gravimetric data and the new system of the normal height of the 2018 Brazilian Vertical Reference Frame (BVRF). For the ocean area, gravity anomalies of the DTU13 model with a resolution of 1’ were used. To quantify the terrain effects through the Residual Terrain Model procedure, the SRTM15+ DTM was used. The computation of the quasi-geoid model was performed by numerical integration through the Fast Fourier Transform (FFT). The Molodensky gravity anomaly was determined in a 5’x5’ grid and reduced and restored using the Residual Terrain Model (RTM) technique and the XGM2019e global gravity model truncated at degree and order 250. The geoid model was derived from the Bouguer gravity anomalies. The zero-order degree term was added in the final computation. The validation for the quasi-geoid model based on 291 GPS measurements in the leveling network has shown 18 cm RMS difference. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

Description: Other

Description: The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).

Description: Abstract

Description: The quasi-geoid model of São Paulo State was computed using the updated and filtered gravimetric data and the new system of the normal height of the 2018 Brazilian Vertical Reference Frame (BVRF). For the ocean area, gravity anomalies of the DTU13 model with a resolution of 1’ were used. To quantify the terrain effects through the Residual Terrain Model procedure, the SRTM15+ DTM was used. The computation of the quasi-geoid model was performed by numerical integration through the Fast Fourier Transform (FFT). The Molodensky gravity anomaly was determined in a 5’x5’ grid and reduced and restored using the Residual Terrain Model (RTM) technique and the XGM2019e global gravity model truncated at degree and order 250. The zero-order degree term was added in the final computation. The validation for the quasi-geoid model based on 291 GPS measurements in the leveling network has shown 18 cm RMS difference. The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

Description: Other

Description: The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).