Abstract: Satellite altimetry missions and tide gauges allow the monitoring of sea level variations over time. While tide gauges monitor sea level relative to a local reference, satellite altimetry missions do so in relation to the Earth’s geocenter. From the comparison between time series generated by these two methods, we observed differences that may be related to possible vertical land movement (VLM). Our objective in this study is to determine the linear trends of VLMs from the difference between the sea level trend found by the satellite altimetry missions TOPEX/Poseidon, JASON 1, 2 and 3 (v SA ) and the sea level trend found by the tide gauge of Imbituba in Santa Catarina (SC), Brazil (v TG ). For this, we demarcated cells along the satellite tracks at a radius of up to 500 km over the ocean from the location of the tide gauge station. The mean values for v SA (1992-2017) and v TG (2002-2015) were 2.5 mm/a ±1.2 mm/a and 5.4 mm/a ±1.9 mm/a, while the mean values for v SA (2007-2015) and v TG (2007-2015) were 7.1 mm/a ±4.6 mm/a and 13.0 mm/a ±4.2 mm/a, respectively. The comparison of VLM obtained between the combination of v SA and v TG and GNSS showed results with better consistency over longer time series.

Abstract: There is a historical search for the unification of different geodetic reference systems in order to better integrate geodetic investigations. In particular, coastal zones pose the challenge of connecting terrestrial and oceanic references when working with different vertical reference levels. This study aims to investigate the goodness-of-fit of ocean models to local observations, as well as to update and improve reference levels (RL) in two tide gauges (TGs) in Brazil (Imbituba and Fortaleza). Local RLs were connected to a global reference system (GRS80), which allowed absolute analyses using the mean sea surface (MSS) and lowest astronomical tide (LAT) models MSS_CNES_ CLS15, DTU_15_MSS, DTU_18_MSS and DTU_15_LAT. In the selected TGs, the MSS models showed a difference of centimeters in regards to the local mean sea level (MSL) defined by the Directorate of Hydrography and Navigation (DHN). Sea Surface Topography (SSTop) values were estimated from Global Geopotential Models and MSL data. The results indicated possible inconsistencies in the global model of LAT when compared to local observations, likely due to the difficulty of modeling coastal zones.

Resumo O propósito deste trabalho é apresentar uma nova estimativa para o afastamento vertical entre ambos os data verticais brasileiros: DVB-I, em Imbituba-SC, e DVB-S, em Santana-AP. A Rede Altimétrica Fundamental Brasileira (RAFB) atualmente conta com mais de 69000 estações com altitudes normais-ortométricas conhecidas; 472 destas estações estão conectadas ao marégrafo localizado em Santana-AP, na porção Norte do Brasil, e as demais estão conectadas ao marégrafo localizado em Imbituba-SC, na região Sul do Brasil e principal referência vertical brasileira. A estimativa do afastamento é baseada em comparações entre altitudes normais-ortométricas de referência e calculadas por valores obtidos através de observações GNSS discretas em referências de nível da RAFB, altitudes normais-geoidais calculadas do MGG XGM2016, o qual comprovadamente melhor modela esta variável na região, e através de uma abordagem relativa para determinações altimétricas, a qual também é, comprovadamente, a melhor forma para manipular as variáveis cabíveis. Como resultado, um afastamento vertical de 1.32 m ± 0.07 m foi obtido, o qual é coerente com estudos anteriores realizados com mesmo intuito. Este estudo surge como uma nova validação da metodologia empregada em si, alcançando resultados satisfatórios através de manipulação independente mesmo com a baixa qualidade dos dados de entrada na região.

Abstract This paper aims to present a new estimate for the vertical offset between both Brazilian vertical data: DVB-I, in Imbituba-SC, and DVB-S, in Santana-AP. Brazilian Fundamental Altimetric Network (BFAN) currently has over 69000 stations with known normal-orthometric heights; 472 of these stations are connected to a tide gauge located in Santana-AP, at the North portion of Brazil, and the other ones are connected to a tide gauge located in Imbituba-SC, at the South portion of Brazil and considered Brazilian's main vertical reference. The vertical offset estimate is based on comparisons between reference and calculated normal-orthometric heights from values obtained arising of discrete GNSS observations on BFAN benchmarks, normal-geoid heights calculated from GGM XGM2016, which has proven to better model this variable in the region, and through a relative approach for heights determination, which has also proven to be the best way to handling the appropriate variables. As a result, a vertical offset of 1.32 m ± 0.07 m was obtained, which is coherent to previous studies performed in the same intent. This study up-comes as a new validation of the employed methodology itself, by achieving satisfactory results through independent manipulation even with low quality of input data for the region.