Considering the efforts to establish Global Reference Systems linked to the geopotential space, new alternatives are sought to address the problems found in the classic national vertical networks. The Brazilian Vertical Reference Frame (BVRF) was materialized in two different segments with independent datums (Imbituba and Santana tide gauges) due to the terrain difficulties for conventional leveling. The 2018 BVRF realization, in the geopotential space, still remains without interoperability between its segments. We analyze alternatives for physical connection based on the new precepts of the International Association of Geodesy (IAG) involving the geopotential space. Some proposed solutions for physical connection based on GPS leveling associated with gravimetry are presented. These solutions were developed with the aim of evidencing the discrepancy between the two BVRF segments, now carried out in terms of geopotential numbers and normal heights. The results indicate differences ranging from about 45 cm to 140 cm between the two segments depending on the strategy employed. Comparisons with previous determinations based on indirect strategies and involving previous BVRF realizations are made.

/pdf/physical-connection-between-bvrf-segments-based-on-leveling-1igh3kgn2k.pdf

Physical connection between bvrf segments based on leveling associated with gravimetry

Comparação entre abordagens absoluta e relativa em determinações altimétricas baseadas em observações GNSS e Modelos Globais do Geopotencial

The present paper intends to develop an alternative methodology for prediction of normal-orthometric heights through Brazilian Legal Amazon Rain Forest, a region that imposes logistical-operational difficulties for fieldwork and in which there is considerable precariousness in the Brazilian Fundamental Altimetric Network (BFAN), evidencing the need to improve the network in question to fully align with the current recommendations for the achievement of the International Height Reference Frame. An alternative strategy is based on GNSS observations and the use of global geopotential models (GGMs); alternatively, it uses the national geoid model MAPGEO2015 to evaluate employability. To do so, an approach in three different variants is performed: a) use of absolute and relative approaches for altimetric determination; b) use of GGM extracts obtained in different degrees of development and MAPGEO2015; and c) the use of geoid height and height anomaly for normal-geoid height modeling. Data regarding GNSS observations are extracted from the stations of the SAT-GPS network, coinciding with BFAN stations, with information of both ellipsoidal and normal-orthometric heights; GGMs extracts are obtained pointwisely for the main current combined MGGs. Given the low mean accuracy of data in the study area and its low linkage with BFAN, it is chosen to adopt a test area —the state of Parana— best suited for elaboration and solidification of the strategy for a later application in the area of study. From the studies conducted in the test area, there is an unquestionable advantage of using the relative approach over the absolute one allied to GGMs, with an average of 72% better results for extracts developed up to  degrees 2190 and 720; MAPGEO2015 was an exception to such results, presenting no adequacy to the relative approach.

/pdf/alternativa-para-determinacao-de-altitudes-normais-40pqvgx2c2.pdf

Alternativa para determinação de altitudes normais-ortométricas na Amazônia legal brasileira

The study and understanding of the geodynamic aspects on the planet require global geodetic references with an order of accuracy better than the magnitude of the effects and with consistency and reliability. In this sense, this paper aims to present the new gravimetric infrastructure in the Brazilian southeast. A set of 22 absolute gravity stations were measured and materialized in the region. Additionally, gravity densification was carried out throughout the region aiming at a quasigeoid model. In the last decade, almost 3,000 points were collected. The model was computed by the least-squares collocation methodology using a recent geopotential model in the long- wavelength component and recent digital terrain model to compute the terrain correction. The quasigeoid model was validated with 136 global navigation satellite system (GNSS)/leveling stations and the RMS is 0.25 m. Furthermore, GNSS/leveling stations were compared with five recent geopotential models and the mean RMS difference was 0.28 m. Absolute and relative gravity stations will improve the national geodetic infrastructure, especially concerning the International Height Reference Frame and the International Gravity Reference Frame. 

New Gravimetric Infrastructure in Southeast Brazil: From Absolute Gravity Network to a Geoid Model

: 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.

/pdf/use-of-gnss-and-a-refined-ggm-xgm2019e-for-determining-29j7rvwj.pdf

Use of GNSS and a refined GGM (XGM2019e) for determining normal heights in the Imbituba Brazilian Vertical Datum and in the International Height Reference System

Abstract The aim of this paper is to present a quantitative analysis of the adequacy of the main currently existing combined Global Geopotential Models (GGMs) for modeling normal-geoid heights throughout Brazil. As major advances have been reached since mid-2016 in the combined GGMs elaboration and development, the main objective of this analysis is to verify if, in fact, the most recent models present superior or equivalent performance to the most performant previous models. The analysis was based on comparisons between normal-geoid height values obtained fromGNSS/leveling solutions and values calculated from GGMs XGM2016, GOCO05C, EIGEN-6C4 and EGM2008, according to different geopotential functionals - geoid height and height anomaly - and in different degrees of development, always through the relative method. This procedure was applied to 997 stations which carry information of both ellipsoidal and normal-orthometric heights, located all over Brazil. As a main result, it was observed the superior performance of the recent combined GGMs, GOCO05C and XGM2016, when compared to the older models, EIGEN-6C4 and EGM2008, when all of them are developed up to degree 720, the maximum degree of the recent models; and a approximate equality of results when all of the models are used in their individual maximum degrees.

Evaluation of recent combined global geopotential models in Brazil

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Evaluation of recent combined global geopotential models in Brazil