Abstract in English:Abstract: Thermal reemission affects satellite orbits when a recoil force results from the emission of radiation from the satellite surface. In this study, the analysis of the thermal reemission force on the satellite is made separately, that is, when the satellite (CBERS 04A’s main body and the solar panels) are hit by the sunlight and when the satellite is into the shadow. Thus, it is presented an expression in an exponential form in order to explain the behavior of the perturbation due to thermal reemission on the panels when they are inside the Earth’s shadow. Both the time spent into the shadow and the relaxation time of the solar panels allowed an analysis of the behavior of the disturbing acceleration and of the orbital elements, during cooling and heating processes. The results presented in this study are promising in terms of practical applications.
Abstract in English:Abstract: This paper aimed to evaluate the use of Global Navigation Satellite System (GNSS) ellipsoidal heights in conjunction with height anomalies provided by Global Geopotential Model (GGM) XGM2019e, refined by Residual Terrain Modelling (RTM) technique, to obtain normal heights in Brazil, referred to the Imbituba Brazilian Vertical Datum (IBVD) and the International Height Reference System (IHRS). For this purpose, a local modelling approach has been analyzed in contrast to the national modeling one on the reference geopotential value. For this, a methodology based on geopotential space was adapted. In the local modeling, two study subregions were defined using the spatial clustering analysis of IBVD and GGM/RTM height anomalies differences outliers. The parameters have been estimated using three different configurations. In the parameters validation step, Root Mean Square Errors (RMSE) of the discrepancies between transformed and Brazilian official normal heights were calculated. In both subregions more accurate results have been obtained with the local modeling. In the SP1 subregion the accuracy increased tenfold (0.97m to 0.10m) and SP2 improved from 0.39m to 0.17m. For the linkage to the future realization of IHRS, the accuracy analysis was not possible. However, discrepancies between calculated normal heights and Brazilian official normal heights have been analyzed.
Abstract in English: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.