Abstract

NICACIO JUNIOR, Eurico Lourenço. Alternativa para determinação de altitudes normais-ortométricas na Amazônia Legal Brasileira. Rev. cartogr. [online]. 2019, n.98, pp.179-199.  Epub Mar 14, 2022. ISSN 2663-3981.  https://doi.org/10.35424/rcarto.i98.146.

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 Paraná- 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 todegrees 2190 and 720; MAPGEO2015 was an exception to such results, presenting no adequacy to the relative approach. For the other analyzed variables -different functional and GGMs- expected non-standardized behavior is achieved, with only MGG and functional signaling for best modeling the normal-geoid height in the area called optimal configuration. It is discussed a strategy for validating results and treating outliers. A consolidated strategy is then elaborated, which is applied to the study area. With this application, normal-orthometric heights of 602 points are calculated in the Brazilian Legal Amazon Rain Forest, based on the relative method and the optimal configuration for the region. After treatment of outliers, it is verified that this procedure produces an average discrepancy of 13.87 cm in a controllable area, unlike the one with the absolute method and the national geoid model, which produces average discrepancy of 36.28 cm for the same stations. As an additional contribution, an estimate is made for the offset between the Brazilian vertical Data based on the methodology elaborated, resulting in a vertical distance of approximately 1.32 ± 0.07 m, a consistent result regarding other determinations already carried out.

Keywords : normal-orthometric heights; Brazilian Legal Amazon Rain Forest; alternative methodology; GGMs; relative method.

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