Resumo em Inglês:

Abstract: GNSS integrity assessment has always been linked to the need for reliable positional information. Initially used in aviation, positional information gained even more relevance in terrestrial applications with the popularity of GNSS. However, the terrestrial environment has many influences over GNSS signals, which reduces the positional quality of tracking objects. Advances have been achieved in the use of integrity monitoring algorithms, but there are limitations to their use, especially those concerning positional accuracy in urban environments with low-cost devices. This paper aims to discuss a comparative method using two low-cost GNSS receivers designed for transportation applications and to verify whether this method can evaluate positional quality in pre-established locations, as well as the possibilities of using these devices for transportation applications, considering the positional error. Results show that, in the static experiment, the receiver assembled with a GPS antenna active embedded was more accurate than the receiver assembled with an external antenna, presenting better values in 5 out of 10 evaluated sites, while the external antenna performed better in only 2 sites. However, in a kinematic evaluation, the receiver assembled with an external antenna provided better results when considering positional error as assessment criterion, resulting in values less than or equal to 8 meters in 99.7% of the route evaluated, while the embedded antenna had 95.3%.

Resumo em Inglês:

Abstract: Technological advances in bathymetric equipment, positioning capacity, data processing, as well as the development of new ways of obtaining depth and other ways of exploring the submerged bottom, have been noticed in recent years. It is known that acoustic remote sensing is the most widely used technique for depth measurement. Survey systems can be embedded on various platforms and also provide different accuracies. Coupled to these systems are also Global Navigation Satellite System (GNSS), auxiliary sensors and speed profilers, improving the accuracy of the data obtained. Alternatively to the use of echo sounders, optical sensing (active and passive sensors) or satellite radar altimetry can be used to estimate depth. Thus, this study aims to present an overview of bathymetric survey methodologies, as well as the evolution of the use of sounding platforms, systems and sensors and various existing technologies. In addition, the main uncertainties involved and the advantages and disadvantages of the available solutions are also evidenced, providing the reader the ability to choose the most appropriate technique.

Resumo em Inglês:

Abstract: 3D Elevation Program (3DEP) aims to generate and disseminate high-resolution topographic elevation data from the source data products including lidar point clouds, original DEMs from which the 3DEP standard DEM datasets were produced, and additional data types produced from IfSAR collections. As such, the accuracy of 3DEP data varies due to the inconsistent quality of the source data. Hence, in order to test vertical accuracy of the current 3DEP data, two precise leveling data sets which are collected in the San Joaquin Experimental Range (SJER) in Fresno County and CalFire site in Davis, California are used as the baselines and the differences are computed. In the earlier studies, assessment of 3DEP data is accomplished using large-area elevation datasets. Nevertheless, these large-area elevation datasets are not as precise as differential (precise) leveling data sets. In this study, two relatively small sites (SJER and CalFire site) are surveyed utilizing precise leveling. These two project sites also differ from each other in terms of terrain relief and land cover. The results show that attainable precision is almost the same for 1/3 arc-second and 1 arc-second data sets. The data sets used for CalFire site are more precise than the data sets used for SJER site. CalFire site data sets are more accurate than SJER data sets. 1 arc-second data provides as good elevation information as 1/3 arc-second data. Terrain relief and land cover are important factors on vertical accuracy coming from 3DEP data.

Resumo em Inglês:

Abstract: The use of acoustic systems for mapping submerged areas is the most accurate way. However, echosounders are expensive and, in addition, the equipment requires a great deal of experience on the part of the specialist. From another perspective, orbital and aerial images (acquired by RPA’s- Remotely Piloted Aircraft) can offer bathymetric maps of larger locations that are difficult to access at a low operating cost. Therefore, the present study’s main objective was to evaluate the utility of RGB images obtained with RPA’s in water reservoirs. Thus, Artificial Neural Networks were used for depth training and prediction. Subsequently, it compared to the bathymetric data from the same pond in question, raised from acoustic sensors, quantifying the vertical uncertainty through three estimators. Regarding the statistical analysis, the RMSE and Ф estimators showed better reliability. The 300-point sample showed the best quality in processing. The results showed that the methodology could improve the management of water resources. The method allows reduced execution time and lowers cost, especially for using only the green, red and blue channels, easily found in most cameras coupled to RPA’s.

Resumo em Inglês:

Abstract: In recent years, the ability of GNSS systems to estimate high accuracy 3D positions has greatly contributed to the development of new monitoring techniques aimed at understanding the mechanisms by which the different Earth processes are generated. This paper presents the result of 9 GPS campaigns, between 2014 and 2019 for a group of 29 stations, held in the Guabirotuba urban area, Curitiba, Brazil, intending to estimate local crustal movements. The average magnitude and direction of horizontal velocities obtained for each site, allow demonstrating deformation of the southern zone of the area as a result of a local landslide process. The magnitude of the vectors varies between 1 and 16 mm/a horizontally. All sites had an absolute vertical movement, probably correlated with a local geological pattern or a physical site’s motion driven by environmental mass redistribution. The uncertainties in positions and velocities for a long-term survey (over 5 years), showed good consistency at most sites when compared with the coordinates and velocities precision of the latest SIRGAS solution. The typical precision for the station positions at the reference epoch was ±2 mm horizontally and ±5 mm vertically, and ±0.60 mm/a horizontally and ±1.37 mm/a vertically for the constant velocities.

Resumo em Inglês:

Abstract: The extensive use of GNSS positioning, combined with the importance of precise geoid heights for transformation between geodetic and orthometric heights, brings up the discussion of the influence of data uncertainties and the use of variable density values on these estimates. In this sense, we analyze the influence of the topographic masses density distribution and the data uncertainty on the computation of orthometric and geoid heights in stations of the High Precision Altimetric Network of Brazil, considering the Helmert and Mader methods. For this, we use 569 stations whose values of geodetic and normal heights, gravity, and geopotential numbers are known. The results indicate that orthometric heights are more sensitive to density values and to greater heights than to the Helmert and Mader methods applied. Also, we verify that the normal and orthometric heights present significant differences for the analyzed stations, considering the high correlation between the heights, which provide small values of uncertainty. However, our analyses show that the use of the Mader method, along with variable density values, provides either more rigorous or more reliable results.

Resumo em Inglês:

Abstract: Multiple regression equations (MREs) provide an empirical direct method of transforming coordinates between geodetic datums. Since they offer a means of modelling distortions, they are capable of a more accurate fit to datum-shift datasets than more basic direct methods. MRE models of datum shifts traditionally consist of polynomials based on relative latitude and longitude. However, the limited availability of low-power terms often leads to high-power terms being included, and these are a potential cause of instability. This paper introduces three variations based on simple partitions and 2 or 4 smoothly conjoined polynomials. The new types are North/South, East/West and Four-Quadrant. They increase the availability of low-order terms, enabling distortions to be modelled with fewer side effects. Case studies in Great Britain, Slovenia and Western Australia provide examples of partitioned MREs that are more accurate than conventional MREs with the same number of terms.