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Boletim de Ciências Geodésicas, Volume: 28, Issue: 3, Published: 2022
  • Assessment of tropospheric modeling on PPP-AR performances under brazilian atmospheric condition Original Article

    Theodoro, Lais Thuany Cardoso; Rodrigues, Tiago Lima; Oliveira Junior, Paulo Sérgio de; Vestena, Kauê de Moraes

    Abstract in English:

    Abstract: In the Global Navigation Satellite System (GNSS), ambiguity resolution (AR) can shorten observation time and increase the positioning quality. The correct tropospheric modeling is intrinsically related to the ability to perform AR. Here, we assessed the influence of different tropospheric correction alternatives on AR for static Precise Point Positioning (PPP) in Brazilian territory. Our goal was to provide directions to users when choosing a suitable tropospheric model for application in PPP-AR under Brazilian atmospheric conditions. Thus, this study was carried out using well-known models such as the Saastamoinen model and the Zenith Tropospheric Delay (ZTD) Estimation and Numerical Weather Prediction (NWP) model from CPTEC/INPE. Six GNSS stations from the Brazilian Network for Continuous Monitoring (RBMC) (BRAZ, UFPR, RNNA, POVE, SMAR, and SAGA) were selected. Different GNSS processing setups were considered for GNSS data registered at selected stations during summer and winter. The assessment was based on a statistical analysis of positioning accuracy during one-hour sessions. The results indicated that such as the ZTD Estimation, the NWP model provides an accuracy of a few centimeters. On the other hand, the Saastamoinen model provided decimeter level accuracy, thus it is not the recommended choice for PPP-AR in the experimental conditions.
  • Analysis of vertical reference levels in the brazilian coast: comparing local and global approaches Artigo Original

    Santana, Tulio Alves; Dalazoana, Regiane

    Abstract in English:

    Abstract: There is a historical search for the unification of different geodetic reference systems in order to better integrate geodetic investigations. In particular, coastal zones pose the challenge of connecting terrestrial and oceanic references when working with different vertical reference levels. This study aims to investigate the goodness-of-fit of ocean models to local observations, as well as to update and improve reference levels (RL) in two tide gauges (TGs) in Brazil (Imbituba and Fortaleza). Local RLs were connected to a global reference system (GRS80), which allowed absolute analyses using the mean sea surface (MSS) and lowest astronomical tide (LAT) models MSS_CNES_ CLS15, DTU_15_MSS, DTU_18_MSS and DTU_15_LAT. In the selected TGs, the MSS models showed a difference of centimeters in regards to the local mean sea level (MSL) defined by the Directorate of Hydrography and Navigation (DHN). Sea Surface Topography (SSTop) values were estimated from Global Geopotential Models and MSL data. The results indicated possible inconsistencies in the global model of LAT when compared to local observations, likely due to the difficulty of modeling coastal zones.
  • Analysis of quantitative methods for geodiversity in Chapada Diamantina, Bahia, Brazil Original Article

    Torlay, Roger; Nolasco, Marjorie Csekö; Castro, Paulo de Tarso Amorim de

    Abstract in English:

    Abstract: The concept of geodiversity has been developed by geoscientists since 1990 in different lines of research such as territorial and patrimonial planning, tourism and the dissemination of knowledge. However, little progress has been made in mapping and quantifying geodiversity. Thus, there are still gaps about the functionality of these graphics products. In order to contribute to these discussions, the aim of this research was to evaluate geodiversity quantification models in Chapada Diamantina National Park and municipality of Morro do Chapéu. The methods Serrano and Ruiz - Flaño and Pereira et al. were chosen for comparison. After choosing the criteria to compare as the choice of variables pertaining to each method, data processing was performed in a geographic information system. Maps with geodiversity indexes and frequency charts were generated. Finally, these products were analyzed using statistical methods and evaluated in the field. In both proposals for quantifying geodiversity, methodological limitations were found, which interfere with the purpose for which the index was created.
  • A new digital elevation model over South Africa based on ground and satellite data Original Article

    Malindi, Mihlali; Odera, Patroba Achola

    Abstract in English:

    Abstract: This study makes contributions toward development of accurate DEM from ground and satellite data over South Africa. This is achieved by preparing recent satellite-based DEMs (AW3D30, SRTM, ASTER, TanDEM-X, and MERIT), assessing their vertical accuracy, selecting candidate DEMs, modelling errors for the candidate DEMs and fusing candidate DEMs. Following removal of outliers from each DEM, a different number of ground levelling data are used in the assessment of the DEMs (AW3D30 - 26,364 points, SRTM - 25,727, ASTER - 23,773, TanDEM-X - 25,964 and MERIT- 24,485). The standard deviations of the differences between ground levelling and DEMs heights are ±5.09, ±7.03, ±9.20, ±4.99 and ±8.36 m for AW3D30, SRTM, ASTER, TanDEM-X and MERIT, respectively. AW3D30 and TanDEM-X are therefore selected for fusion. The two candidate DEMs are improved by applying a combination of linear regression, multiple regression, and adaptive terrain-dependent methods using 17,307 model data points. A fused DEM is developed from improved candidate DEMs using a combination of different fusion methods and assessed using 8,657 data points (distinct from the model points). The standard deviation of the height differences between ground levelling and the fused DEM is ±4.290 m, and it is more accurate than all satellite based DEMs considered in this study.
  • Using terrestrial laser scanner and RPA-based-photogrammetry for surface analysis of a landslide: a comparison Original Article

    Garcia, Guilherme Pereira Bento; Grohmann, Carlos Henrique; Viana, Camila Duelis; Gomes, Elton Barbosa

    Abstract in English:

    Abstract: Gravitational mass movements are natural destructive processes that can cause enormous losses. New technologies such as laser scanning and remotely piloted aircrafts (RPA) along with Structure-from-Motion-Multi-View Stereo (SfM-MVS) photogrammetry technique provides an alternative to conventional mapping methods. A hill with a landslide located in the city of Cunha - SP was surveyed by terrestrial laser scanner (TLS) and RPA-based SfM-MVS. SfM-MVS point cloud covers a larger area and point distribution is more homogeneous while TLS points have an uneven distribution. Small distances between point clouds were predominant in the vicinity of the landslide and greater differences only occurred on the scene edges. DEMs (Digital Elevation Model) were generated from both point clouds. The volume of material displaced from the upper part (scarp) of the landslide was 70.05 m3 for the TLS DEM and 77.15 m3 for the SfM-MVS while the volume of material accumulated in the lower part (body) of the landslide was 66.85 m3 and 62.68 m3 respectively. Slope and roughness were calculated and showed very similar results for TLS and SfM-MVS.
  • Cartographic Accuracy Standard (CAS) of the digital terrain model of the digital and continuous cartographic base of the state of Amapá: case study in the city of Macapá Original Article

    Santos Filho, Herondino dos; Cornero, Cecilia; Pereira, Ayelen; Nero, Marcelo

    Abstract in English:

    Abstract: The Cartographic Accuracy Standard (CAS) is a quality parameter used by the Brazilian standard to estimate the positional quality of cartographic products in their degree of precision, also including altimetry. The Digital and Continuous Cartographic Base of Amapá - BCDCA has a large amount of freely available spatial information, for the study of its territory within the state of Amapá. This project, a partnership between the Government of the State of Amapá and the Directorate of Geographical Services of the Brazilian Army (DSG), obtained a large amount of SAR data by interferometry. Among the resulting products, the Digital Terrain Model - DTM has a wide range of applications: watershed analysis, infrastructure program, diagnosis of environmental risks and so many others. Therefore, the present work aims to evaluate the altimetric data (DTM) provided by the BCDCA through 2172 orthometric points calculated from the Brazilian Network for Continuous Monitoring - RBMC measured in the field in the city of Macapá, capital of the State of Amapá. For the level curves, the results presented class A for the 1: 10 000 scale, at an equidistance of 5 m, showing that the DTM product is highly reliable for urban applications.
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