Regiane Dalazoana

Review: Using an artificial neural network to improve the transformation of coordinates between classical geodetic reference frames

Advances in technology have allowed for the improvement of geodetic reference systems (GRSs). Relating different GRSs can be done by employing transformation parameters which may not, however, be satisfactory in certain applications due to the heterogeneous and local character of deformations caused by the procedures adopted in classical networks. Classical networks were established basically by procedures of triangulation and traverse survey, and the existence of these deformations justifies the search for new transformation methodologies. This study evaluated artificial neural networks (ANNs) as a tool for the transformation between GRSs. Frames points with known geodetic coordinates (latitude and longitude) in the South American Datum of 1969 (SAD69) system and in the older Corrego Alegre system, both still in use in Brazil, were chosen for this study. The SAD69 coordinates of the frame points were transformed into Corrego Alegre coordinates and then the computed coordinates were compared with known ones. Four tests were carried out in order to transform the coordinates. The first test involved the use of official transformation parameters and the formulas of Molodensky. In the second test, new transformation parameters were employed. In the third test new regional transformation parameters were determined, while the fourth test employed an ANN to predict the Corrego Alegre coordinates of the check points. Results indicated that the employment of an ANN transformed the coordinates most accurately, and indicated that they can be useful in modeling deformations in classical networks.

Local Effects in the Brazilian Vertical Datum

Nowadays, determining the topography of Mean Sea Level (Sea Surface Topography — SST) at the tide gauge station and its temporal variation is one of the most important aspects of defining a vertical Datum. Different approaches are used for this purpose: Oceanographic approach; Satellite altimetry associated with geostrophic levelling; Gravity associated with satellite positioning; Geodetic boundary-value problem approach (GBVP). In this sense, time series for observing tide gauge geocentric position permits to fix its geometric position and to detect local dynamic effects on the crust and in the SST. The main purpose of Work Group III in SIRGAS project (Geocentric System for the Americas) is to establish the link of all vertical reference systems in South America. In general, each national vertical network in that region was established under three particular conditions: local vertical datum; height system without physical meaning; and different spirit levelling standards. The unification of South American vertical datums, is a fundamental step to understand the observed off set among the networks in the region. The achieved results of two multiparametric on the brazilian vertical datum and their analysis are presented in this paper.

Brazilian Vertical Datum Monitoring - Vertical Land Movements and Sea Level Variations

UFPR’s Geodetic Instrumentation Laboratory carried out several geodetic campaigns at Brazilian Vertical Datum during the last nine years. The last campaign performed in the first semester of 2005 had as main goals: calibration of two sea level sensors of the tide gauge station; periodic GPS observations at one SIRGAS station, used to materialize the tide gauge geocentric position; and leveling of the benchmarks in the harbor area. In this work there are presented results obtained with this campaign and some comparisons to past campaigns. The main objective is to check the stability of the GPS station in order to estimate vertical land movements and sea level variations. GPS results indicate a tendency of subsidence of 0.2mm/a with a standard deviation of 0.1mm/a at the station.

Tests on Integrating Gravity and Leveling to Realize SIRGAS Vertical Reference System in Brazil

The integration of gravity data within the Brazilian leveling network is very difficult due to the historical dissociation between leveling and gravity surveys. This research was started, in the context of SIRGAS Project, to resolve this problem by evaluating different strategies and procedures with the aim of establishing some kind of gravity coverage over vertical reference stations. Data employed in this article comes from one of the few areas where the points of the Brazilian fundamental leveling network are entirely covered with gravity surveys and, in addition, connect three permanent GPS stations, two of which belong to the SIRGAS 2000 Reference Network. This will allow for several analyses regarding the Brazilian realization of SIRGAS Vertical System, including: an evaluation of the effects of adopting different types of heights; and the investigation of strategies and procedures to solve the absence of gravity values over benchmarks. Values of geopotential differences were computed and adjusted, for a 2300 km network consisting of six loops with perimeters ranging from 136 km to 690 km. Dynamic, Helmert, Normal and Normal-Orthometric reductions were generated and compared. The status of the development of a GIS designed for the tasks involved in geopotential numbers computation to be applied in the studies related to the SIRGAS Vertical Reference System is also presented.

Deformations Control for the Chilean Part of the SIRGAS 2000 Frame

With the adoption of the Geocentric Reference System for the Americas (SIRGAS), the determination of temporal variations and deformations in its frame are a necessary task. These tasks are fundamental in order to maintain the consistency of the frame with respect to the definition of SIRGAS, especially in the Chilean deformation area, where the variations are larger compared with the rest of the plate due to the convergence between the South American and Nazca plates. 21 permanent GPS stations was used. 14 of them are regional stations of the International GNSS Service (IGS), and 7 permanent GPS stations are from different regional networks. 10 of these 21 stations are located in the Chilean Andes were used to study the kinematic effects in this area. Some of them are also SIRGAS stations. Five years of GPS observations from 2000 to 2004 were selected in order to have a sufficient time period with enough coverage for the considered stations. Daily solutions were generated with the Bernese GPS Software 5.0 using IGS precise ephemeris, clocks and ERP. The normal equations were then accumulated and solved in a final combination where the coordinates and velocities of selected stations are weighted for the datum definition compatible with ITRF2000. The estimated velocities of the north Chilean Andes regions are ∼26–30 ± 2mm/yr, decreasing up to ∼16–25 ± 2mm/yr and for the south Chilean Andes the estimated velocities are ∼9–12 ± 2mm/yr. For the stable part of the continent the estimated velocities are ∼8–12 ± 2mm/yr. The final results are discussed and compared with the NUVEL-1A and SIRGAS velocity models (SIRGAS-VM).

Evaluating the Brazilian Vertical Datum Through Improved Coastal Satellite Altimetry Data

The integration of the Brazilian Fundamental Vertical Network (BFVN) with satellite altimetry data and multiple tide gauges (TG) is one way for an independent validation of the Brazilian Vertical System. Satellite altimetry (Sat-Alt) gives precise information on the sea surface topography (SSTop) over a great part of the oceans. However, SSTop is characterized by large differences at deep, open sea and at coastal or shallow waters. The evaluation/validation of the studies on BFVN could be achieved through the connection of the reference levels from TGs and Sat-Alt data, allowing SSTop “correction” at some selected TGs along the Brazilian coast. Initial tests were performed with SSTop estimates from the application of a 1D-filter to the EIGEN-GL04C geoid model and to the altimetric data from Jason-1 and TOPEX/Poseidon extended mission (T/P-EM). Tracks of these two satellites over deep, open oceans were taken as reference for connecting three selected TG reference levels. SSTop time series were obtained for Sat-Alt points near those TGs as well as for the crossing points between the reference tracks and those passing the TGs. These time series show good correlation along each TG-track but have low correlation to the ref-tracks. This points out the need for additional ref-tracks in order to improve that correlation

Evaluation of recent combined global geopotential models in Brazil

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.