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  • ItemArtigo
    GPSeq software for fast GPS ambiguities resolution on short baselines using kinematic relative positioning
    (2002-12-31) Machado, Wagner Carrupt [UNESP]; Monico, João Francisco Galera [UNESP]; Universidade Estadual Paulista (UNESP)
    Centimeter level GPS positioning is based on the very precise carrier beat phase measurements. However, this observable is ambiguous by a number of whole cycles between the satellite and receiver antenna at the first epoch of data collecting, which is called the ambiguity. GPS ambiguities are introduced as parameters to be estimated in the observation equations. However, since they are integer numbers there is no standard techniques for solve them. One of the ways is to apply sequential conditional least-squares estimation together with integer search techniques. The ambiguity resolution can be divided in two steps: estimation and validation. The estimation is concerned with the computation of the ambiguities values. The validation step is used to infer if the estimated value can be accepted or not. From the last decade until nowadays ambiguity resolution has been one of the most important research topic in geodetic positioning and a several methods have been proposed. Special attention has been made about the fast ambiguity resolution. The aim of this paper is to investigate the ambiguity resolution in the context of relative kinematic positioning and its implementation in the GPSeq software, which is a GPS data processing software developed in academic environment. In this paper some experiments about kinematic processing are presented, whose results shown that the GPSeq solution is compatible on the centimeter level with Reliance software. The results also shown an inefficiency of the ratio and the difference between the quadratic form of the residuals of the second best and best solution tests in validating the ambiguity resolution in time limits of solution of the baselines processed.
  • ItemArtigo
    GPS positioning in the Brazilian region during intense magnetic storm of the October, 29 2003
    (2008-07-01) Matsuoka, Marcelo Tomio; Camargo, PAULO DE OLIVEIRA [UNESP]; Batista, Inez Staciarini; Universidade Federal do Rio Grande do Sul; Universidade Estadual Paulista (UNESP); Instituto Nacional de Pesquisas Espaciais
    The error due to the ionosphere in the GPS observables depends on the Total Electron Content (TEC) in the ionospheric layer. The TEC varies regularly in time and space in relation to the sunspot number, the season, the local time, the geographic position, and others. However, the TEC can suffer abrupt modifications in its behavior due to the occurrence of intense magnetic storm. On 28 October 2003, at 1110 UT, a major solar flare took place from a sunspot directly in line with the Earth. A coronal mass ejection was observed to leave the Sun in the direction of the Earth, causing an intense magnetic storm that started at 0611 UT of the following day. In this paper, GPS data from RBMC and IGS network and Digisonde data were used, to analyze the influence of the intense magnetic storm that occurred on October 29, 2003 in the behavior of TEC and in the performance of the point positioning in the Brazilian region.
  • ItemArtigo
    An alternative to derive ionospheric and tropospheric SSR corrections for PPP-RTK using adaptive constraints
    (2023-01-01) de Oliveira, Paulo Sergio; Morel, Laurent; Galera Monico, João Francisco; Durand, Stéphane; Durand, Frédéric; Bezerra, Lucas dos Santos; Universidade Federal do Paraná (UFPR); Cnam/GeF; Universidade Estadual Paulista (UNESP)
    PPP-RTK (Precise Point Positioning–Real Time Kinematic) is a positioning method by GNSS (Global Navigation Satellite Systems), based on the SSR (State Space Representation) concept. One challenge for the fast convergence of PPP-RTK solutions in real-time applications is the mitigation of atmospheric effects (troposphere and ionosphere). Thus, using atmospheric models, PPP solutions can achieve accurate positions and shortened initialisation time. Such performance depends on the topology of permanent station networks and atmospheric conditions. The main objective of this contribution is to study the PPP-RTK and the optimised infrastructure in terms of costs and benefits to realise the method using atmospheric corrections.
  • ItemArtigo
    The urban climate of subtropical Atlantic costal cities: The conurbation of Florianopolis
    (2009-01-01) Mendonça, Magaly; Lombardo, Magda A.; Universidad Federal de Santa Catarina; Universidad Estadual de São Paulo
    This work demonstrates the simultaneous influence of geoecological and urban factors on the variation of temperature and other climatic elements of the Florianópolis conurbation. Data was obtained in various places, following synoptic time series, under different weather types, using a digital thermo hygrometer and visual information. The temperature gradients maps, compared with airport station, demonstrated a significant thermal conservation capacity in places occupied by buildings and dense and intense traffic. Urban heat archipelagos instead of a continuing urban heat island were recorded as a consequence of urban poly nucleus and site morphologic compartments. The most intense heat islands occurred in the central part of the region, when the polar air masses dominate or are under pre-frontal transition. These results are relevant for the evaluation of environmental quality, and should support urban planning diagnostics.
  • ItemArtigo
    Road extraction from low-cost GNSS-device dense trajectories
    (2023-01-01) de Moura Morceli, Bruno [UNESP]; Porfírio Dal Poz, Aluir [UNESP]; Universidade Estadual Paulista (UNESP)
    This paper proposes a method for road centerline extraction from dense Global Navigation Satellite System (GNSS) trajectories, collected by using low-cost GNSS-devices, i.e. smartphones. The proposed method basically consists in generating a frequency image by tracking the GNSS trajectories and then by applying the Steger line detector to the generated image to extract the road centerlines. The main motivation of using the Steger algorithm is its capability to detect lines with sub-pixel accuracy. To evaluate the obtained results, reference road centerlines are manually extracted from a georeferenced orthomosaic. The experiments performed demonstrate the high potential of applying the Steger line detector to frequency images, generated by using dense GPS (Global Positioning System) trajectories. The completeness and correctness values for the accomplished experiments were 98% and 99%, respectively. Additionally, the RMSE (Root Mean Square Error) ranged from 0.63 m to 2.39 m, or approximately 1/16 to 1/4 of the expected accuracy (about 10 m) of a point determined by the Single-Point Positioning (SPP) method, which is the GNSS positioning method usually employed by smartphones.
  • ItemArtigo
    Tree Species Classification in a Complex Brazilian Tropical Forest Using Hyperspectral and LiDAR Data
    (2023-05-01) Pereira Martins-Neto, Rorai [UNESP]; Garcia Tommaselli, Antonio Maria [UNESP]; Imai, Nilton Nobuhiro [UNESP]; Honkavaara, Eija; Miltiadou, Milto; Saito Moriya, Erika Akemi [UNESP]; David, Hassan Camil; Czech University of Life Sciences Prague (CULS); Universidade Estadual Paulista (UNESP); National Land Survey of Finland (NLS); University of Cambridge; Brazilian Forest Service (SFB)
    This study experiments with different combinations of UAV hyperspectral data and LiDAR metrics for classifying eight tree species found in a Brazilian Atlantic Forest remnant, the most degraded Brazilian biome with high fragmentation but with huge structural complexity. The selection of the species was done based on the number of tree samples, which exist in the plot data and in the fact the UAV imagery does not acquire information below the forest canopy. Due to the complexity of the forest, only species that exist in the upper canopy of the remnant were included in the classification. A combination of hyperspectral UAV images and LiDAR point clouds were in the experiment. The hyperspectral images were photogrammetric and radiometric processed to obtain orthomosaics with reflectance factor values. Raw spectra were extracted from the trees, and vegetation indices (VIs) were calculated. Regarding the LiDAR data, both the point cloud—referred to as Peak Returns (PR)—and the full-waveform (FWF) LiDAR were included in this study. The point clouds were processed to normalize the intensities and heights, and different metrics for each data type (PR and FWF) were extracted. Segmentation was preformed semi-automatically using the superpixel algorithm, followed with manual correction to ensure precise tree crown delineation before tree species classification. Thirteen different classification scenarios were tested. The scenarios included spectral features and LiDAR metrics either combined or not. The best result was obtained with all features transformed with principal component analysis with an accuracy of 76%, which did not differ significantly from the scenarios using the raw spectra or VIs with PR or FWF LiDAR metrics. The combination of spectral data with geometric information from LiDAR improved the classification of tree species in a complex tropical forest, and these results can serve to inform management and conservation practices of these forest remnants.
  • ItemArtigo
    Plasma bubble imaging by single-frequency GNSS measurements
    (2023-07-01) Christovam, Ana L. [UNESP]; Prol, Fabricio S.; Hernández-Pajares, Manuel; Camargo, Paulo O. [UNESP]; Universidade Estadual Paulista (UNESP); National Land Survey of Finland; Universitat Politècnica de Catalunya (UPC)
    Our investigation aims to answer if it is possible to detect plasma bubbles using single-frequency measurements of the Global Navigation Satellite System (GNSS). In this regard, we show a methodology based on a regional model to calibrate GNSS single-frequency measurements and derive ionospheric maps showing plasma bubbles in one of the most challenging conditions, the Brazilian region. Simultaneous observations of all-sky images at Cachoeira Paulista (22.7°S, 45.0°W), São João do Cariri (7.4°S, 36.5°W) and Boa Vista (2.8°N, 60.7°W) were used to compare the plasma bubbles structures. The results were validated by the comparison between airglow and total electron content (TEC) single-frequency maps in terms of keograms and drift velocities of the ionospheric plasma bubbles. Plasma bubbles were successfully observed by mapping TEC single-frequency. The rate of success in detecting the plasma bubbles with single-frequency TEC data was 65% when using keograms. In addition, in regions with good GNSS coverage, such as Cachoeira Paulista and São João do Cariri, it was easier to detect the plasma bubbles. The velocities of plasma bubbles were also obtained with good agreement in comparison with the velocities estimated using airglow data. For São João do Cariri, the mean drift velocities estimated with airglow data were 117.10 m/s whereas with TEC data were 117.94 m/s. Therefore, the results revealed the proposed method as an efficient tool for mapping the ionospheric plasma bubbles and computing their drift velocities. This technique provides new opportunities, in particular for ionospheric sounding, since the number of low-cost GNSS receivers continues growing.
  • ItemArtigo
    Using Geospatial Information to Map Yield Gain from the Use of Azospirillum brasilense in Furrow
    (2023-03-01) Martins, George Deroco; Xavier, Laura Cristina Moura; de Oliveira, Guilherme Pereira; de Lourdes Bueno Trindade Gallo, Maria [UNESP]; de Abreu Júnior, Carlos Alberto Matias; Vieira, Bruno Sérgio; Marques, Douglas José; da Silva, Filipe Vieira; Unversidade Federal de Uberlândia; Lallemand Soluções Biológicas LTDA; Universidade Estadual Paulista (UNESP)
    The application of biological products in agricultural crops has become increasingly prominent. The growth-promoting bacterium Azospirillum brasilense has been used as an alternative to promote greater yield in maize crops. In the context of precision agriculture, interpreting geospatial data has allowed for monitoring the effect of the application of products that increase the yield of corn crops. The objective of this work was to evaluate the potential of Kriging techniques and spectral models through images in estimating the gain in yield of maize crop after applying A. brasilense. Analyses were carried out in two commercial areas treated with A. brasilense. The results revealed that models of yield prediction by Kriging with a high volume of training data estimated the yield gain with a root-mean-square error deviation (RMSE%), mean absolute percentage error (MAPE%), and R2 to be 6.67, 5.42, and 0.88, respectively. For spectral models with a low volume of training data, yield gain was estimated with RMSE%, MAPE%, and R2 to be 9.3, 7.71, and 0.80, respectively. The results demonstrate the potential to map the spatial distribution of productivity gains in corn crops following the application of A. brasilense.
  • ItemArtigo
    A spatiotemporal classification approach to evaluate the impacts of land use and land cover changes before and after the Três Irmãos reservoir formation in the Tietê River, Brazil
    (2023-01-01) Lucchetta, Beatriz Cirino [UNESP]; Watanabe, Fernanda Sayuri Yoshino [UNESP]; do Carmo, Nariane Marselhe Ribeiro Bernardo; Universidade Estadual Paulista (UNESP); Inspectral–Innovative Tecnology Solutions
    Land use and land cover (LULC) maps are relevant tools to recognize deep changes in the natural landscape and direct strategies to minimize environmental impacts, being an important apparatus to obtain useful information in making decision by managers from watershed committees, political leaders and environmental agencies. Using Landsat multispectral images, this study aimed to investigate the changes in LULC of a watershed, influenced by the construction of the dam of the Três Irmãos hydroelectric plant, located in the low course of the Tietê River. The images were acquired in 1990, 2000, 2010 and 2018, which covers the periods before and after the flood caused by the dam build. For each date, LULC maps were generated using the supervised classification Maximum Likelihood (ML) algorithm. Those analysis has allowed identify possible influences of the reservoir formation over LULC in the watershed. A deep analysis showed a significant change of natural vegetation were flooded due to the damming, being partially recovered, in percentage terms, over time around the new watercourse. This study presents a reduction of 67% in the natural vegetation area from 1990 to 2000, while there was an increase of 35,36% between 2000 and 2018, when compared to the area occupied by natural vegetation existing in 1990. In addition, areas of natural vegetation also have been replaced by cultivated areas, which are predominant in the watershed.
  • ItemArtigo
    Pontos de Referência para Navegação por Motoristas com Deficiência na Visão de Cores
    (2019-01-01) Pugliesi, Edmur Azevedo [UNESP]; Moretti, Aline [UNESP]; Marques Ramos, Ana Paula; Tachibana, Vilma Mayumi [UNESP]; Universidade Estadual Paulista (UNESP); Universidade do Oeste Paulista
    The objective of this study is to identify potential landmarks for in-car navigation, considering drivers who present Color Vision Deficiency - CVD. In-Car Navigation Systems (RGNS) display traffic light and bridge over road, which are among the environment context elements more used by the drivers having Normal Color Vision – NCV. An empirical study investigated the demand for route guide information with a group of drivers who have CVD by using two techniques of information externalization, map sketch and verbal note. Data collected with drivers having CVD were compared between both techniques, and data collected from map sketch, originated from this study, were compared with data collected in a previous study, which used drivers having NCV. From the landmarks that presented the highest frequency of using among the participants, some are more important for route guidance than others. Verbal notes technique complemented the map sketch, suggesting that applicating just one would not be enough to find more conclusive results. Bridge over road and hospital were the most used, followed by park and traffic light. The attributes that defined the quality of landmarks are presented from the most valued. Traffic light, bridge over road and park should be included in maps of Car Navigation Systems to aid the task of route following for drivers having CVD. New landmarks may emerge according to the characteristics of each environment.
  • ItemArtigo
    Two-Way Assessment of Ionospheric Maps Performance Over the Brazilian Region: Global Versus Regional Products
    (2023-02-01) Jerez, Gabriel O. [UNESP]; Hernández-Pajares, Manuel; Goss, Andreas; Prol, Fabricio S.; Alves, Daniele B. M. [UNESP]; Monico, João F. G. [UNESP]; Schmidt, Michael; Universidade Estadual Paulista (UNESP); Research Groups; Deutsches Geodätisches Forschungsinstitut der Technischen Universität München; Finnish Geospatial Research Institute (FGI)
    Vertical total electron content (VTEC) has great importance in describing the ionosphere. VTEC values are commonly distributed in regular grids by means of so-called global ionospheric maps (GIMs) and regional ionospheric maps (RIMs). Although considerable research has been conducted to develop regional and global models, there is no clear understanding of the benefits of using RIMs over GIMs. Aiming to contribute to this discussion, our investigation presents a comparison between seven global and regional ionospheric maps considering two approaches: (a) ionosonde data-based assessment and (b) global navigation satellite systems (GNSS) positioning assessment. A challenging low latitude ionosphere scenario, the Brazilian region, was selected during a week with an active geomagnetic storm. The assessment results with ionosonde data have shown better performance of the RIM products named OTHR and OTRG. Among the global products, CODG and UQRG have shown the best performances. The worst results were obtained with the RIM named Instituto Nacional de Pesquisas Espaciais. The assessment with GNSS positioning led to larger and noisier errors close to the equatorial anomaly. Two of the analyzed RIMs presented expected large errors in stations at the edges of the coverage area. To overcome this issue, a hybrid product was proposed to extend the RIM covered region. The proposed hybrid product (OTRG) presented the best results in the GNSS positioning domain.
  • ItemResenha
    A Retrospective of Global Navigation Satellite System Ionospheric Irregularities Monitoring Networks in Brazil
    (2023-01-01) de Paula, Eurico Rodrigues; Monico, João Francisco Galera [UNESP]; Tsuchiya, Ítalo Hirokazu [UNESP]; Valladares, Cesar Enrique; Costa, Sônia Maria Alves; Marini-Pereira, Leonardo; Vani, Bruno César; Moraes, Alison de Oliveira; Ciências Planetárias e Aeronomia – Ciências Espaciais e Atmosféricas; Universidade Estadual Paulista (UNESP); W.B. Hanson Center for Space Sciences; Instituto Brasileiro de Geografia e Estatística Diretoria de Geociências Coordenação de Geodésia; Divisão de Pesquisa; Ciência e Tecnologia de São Paulo; Divisão de Eletrônica
    The use of Global Navigation Satellite System (GNSS) for air and terrestrial navigation and for many applications is increasing in the last decades. However, the Earth’s ionosphere causes GNSS signal delay due to the total electron content (TEC) and scintillation in the signal phase and amplitude. This scintillation can give rise to deleterious effects in the GNSS positioning. So, it is important to assess the effects of the ionosphere over the GNSS signal. To achieve this goal, it is necessary to have a large spatial and temporal coverage of data from many different sounders, being the GNSS receivers of great importance due to their global coverage and availability. In this work, we present a retrospective of the scintillation monitoring networks in Brazil and their characteristics. As the RBMC network managed by the IBGE provides TEC and as rate of TEC index (ROTI) is well correlated with ionospheric irregularities, we present also the RBMC network description. These RBMC GNSS receivers provide data in regions with scarcity of scintillation monitors. The description of the Ionospheric Scintillation Monitoring Receivers (ISMR) Query Tool, that is a web software that has been supporting research on the ISMR data, is also presented.
  • ItemArtigo
    GNSS Radio Occultation: a Review of the Theory, Missions, and Products
    (2022-10-01) Jerez, Gabriel Oliveira [UNESP]; Alves, Daniele Barroca Marra [UNESP]; Nespolo, Raphael Silva [UNESP]; Monico, João Francisco Galera [UNESP]; Hernández-Pajares, Manuel; Universidade Estadual Paulista (UNESP); Universitat Politècnica de Catalunya
    Radio occultation (RO) have been used for probing the atmosphere of other planets since the 1960s. With the development of Global Navigation Satellite System (GNSS) and missions with Low Earth Orbit (LEO) satellites emerged the possibility of investigations of the Earth's atmosphere with the application of RO-GNSS. From the GNSS satellites to the receivers onboard LEO satellites, the propagated signals are influenced by the atmosphere in different ways. The transmitted signal is refracted, so it can be collected by the onboard receiver in spite of the superposition made by the Earth. This geometry makes it possible to calculate refractive indices, which contain information about the composition of the Earth's atmosphere. Several profiles can be obtained from the refractive index, for instance temperature, pressure, and electron density. In this paper a theoretical review of the GNSS-RO technique is carried out, aiming to present the technique and its potential to researchers from various areas who have the possibility of using it. First, a brief history of the development of the technique is presented, as well as the main missions related to this topic, including the status of missions currently operational and some future perspectives. In addition, the main elements involved in the occultation geometry are presented, as well as the main concepts and formulations for obtaining the profiles. Finally, some products from RO-GNSS missions are presented and analyzed.
  • ItemArtigo
    Distinguishing ionospheric scintillation from multipath in GNSS signals using geodetic receivers
    (2022-10-01) Li, Chendong; Hancock, Craig M.; Vadakke Veettil, Sreeja; Zhao, Dongsheng; Galera Monico, João F. [UNESP]; Hamm, Nicholas A. S.; University of Nottingham; Loughborough University; China University of Mining and Technology; Universidade Estadual Paulista (UNESP)
    Ionospheric scintillation is an important phenomenon affecting GNSS positioning accuracy. Scintillation parameters, S4 and σφ, are usually used to characterize scintillation in amplitude and phase, respectively. S4 and σφ can be contaminated by multipath effects in certain circumstances. Similarly, the multipath parameter (MP) can also be affected by scintillation. Therefore, it is difficult to distinguish whether an increase in the scintillation parameters and MP is caused by scintillation or multipath. However, it is important to know the type of interference to apply appropriate mitigation measures. It is known that the multipath effect is periodic as compared to scintillation if the receiver location is fixed. Based on this peculiar feature, this article proposes to use parameters MP, S4, σφ and the rate of change of total electron content index (ROTI) characterize the receiver station surroundings so that multipath and scintillation effects can be distinguished. The Global Positioning System (GPS) data for two one-month records at two pairs of low-latitude stations, namely SAO0P-SJCU and SJCU-SJCE, located in Sao Paulo, Brazil, were used to generate elevation layered plots and parameter values against elevation and azimuth (PEA) plots for each satellite on each day. The second station was used as a reference for validating the conclusion. The results provide evidence that the proposed methodology can identify all multipath, scintillation and hybrid (of multipath and scintillation) events using scintillation indices and identify some multipath, scintillation and hybrid events using MP and ROTI. For hybrid events below 30° elevation, this methodology is not effective.
  • ItemArtigo
    Automatic Building Boundary Extraction from Airborne LiDAR Data
    (2019-07-01) Carrilho, André Caceres [UNESP]; dos Santos, Renato César [UNESP]; Pessoa, Guilherme Gomes [UNESP]; Galo, Mauricio [UNESP]; Universidade Estadual Paulista (UNESP)
    This paper aims to evaluate the quality of the automatic extraction of building contours from airborne LiDAR data in order to verify if the errors obtained in the building roof areas are compatible with the criteria established by the Brazilian Law n° 10.406, January 10th, 2002. Two approaches were compared: one present in LAStools software (lasboundary) and the other being a variant of the α-shape algorithm, whose parameter α is estimated adaptively for each building. In addition, both approaches were applied to two datasets, one with an average point density of 5.8 pts/m2 and the other with 12.5 pts/m2. In this work three quality parameters were computed: F-score, relative error in area, and PoLiS metric. The assessment of the results indicates that most of the results met the criteria established by the above-mentioned law. The variant of α-shape algorithm seems to be better than the lasboundary, indicating that the dynamic approach to determine the parameter α contributes to the quality, especially on complex buildings. Finally, the use of the point cloud with higher average point density results in higher accuracy in the building boundary extraction.
  • ItemArtigo
    Two-Way Assessment of Ionospheric Maps Performance Over the Brazilian Region: Global Versus Regional Products
    (Amer Geophysical Union, 2023-02-01) Jerez, Gabriel O. [UNESP]; Hernandez-Pajares, Manuel; Goss, Andreas; Prol, Fabricio S.; Alves, Daniele B. M. [UNESP]; Monico, Joao F. G. [UNESP]; Schmidt, Michael; Universidade Estadual Paulista (UNESP); Univ Politecn Catalunya UPC; Tech Univ Munich; Finnish Geospatial Res Inst FGI
    Vertical total electron content (VTEC) has great importance in describing the ionosphere. VTEC values are commonly distributed in regular grids by means of so-called global ionospheric maps (GIMs) and regional ionospheric maps (RIMs). Although considerable research has been conducted to develop regional and global models, there is no clear understanding of the benefits of using RIMs over GIMs. Aiming to contribute to this discussion, our investigation presents a comparison between seven global and regional ionospheric maps considering two approaches: (a) ionosonde data-based assessment and (b) global navigation satellite systems (GNSS) positioning assessment. A challenging low latitude ionosphere scenario, the Brazilian region, was selected during a week with an active geomagnetic storm. The assessment results with ionosonde data have shown better performance of the RIM products named OTHR and OTRG. Among the global products, CODG and UQRG have shown the best performances. The worst results were obtained with the RIM named Instituto Nacional de Pesquisas Espaciais. The assessment with GNSS positioning led to larger and noisier errors close to the equatorial anomaly. Two of the analyzed RIMs presented expected large errors in stations at the edges of the coverage area. To overcome this issue, a hybrid product was proposed to extend the RIM covered region. The proposed hybrid product (OTRG) presented the best results in the GNSS positioning domain.
  • ItemArtigo
    Assessment of GPS positioning performance using different signals in the context of ionospheric scintillation: a month-long case study on Sao Jose dos Campos, Brazil
    (Univ Federal Parana, Centro Politecnico, 2022-01-01) Christovam de Souza, Ana Lucia [UNESP]; Jerez, Gabriel Oliveira [UNESP]; Camargo, Paulo de Oliveira [UNESP]; Marra Alves, Daniele Barroca [UNESP]; Universidade Estadual Paulista (UNESP)
    The ionospheric scintillation associated to small-scale irregularities in the ionospheric layer can lead to performance degradation of Global Navigation Satellite Systems (GNSS) signals, and the reduction of positioning accuracy. The influence of the ionospheric layer on the GNSS systems is expected to be different for each signal since it is transmitted on different carrier frequencies. This paper presents the results of a quantitative analysis of the scintillation amplitude of GPS (Global Positioning System) signals at L1, L2 and L5 frequencies, aiming to evaluate the impact of the ionospheric scintillation effects on the GPS frequencies. As the ionospheric scintillation may impact positioning accuracy, we also present an assessment of GPS point positioning using those frequencies. The GPS sample data were collected for 30 days between November and December 2014 at SJCE station located in Sao Jose dos Campos (SP), Brazil. Such a region is subjected to the equatorial anomaly effects being characterized by the occurrence of strong ionosphere scintillation. Considering the quantitative analysis, during the different levels of ionospheric scintillation presented a similar behavior, the magnitude of scintillations is small for the L1 signal and larger for L5. In general, the results confirmed that lower frequencies (L2 and L5) suffer more impact from intense scintillation than L1. Regarding the positioning assessment, the multi-frequency positioning was more accurate than single frequency. Considering dual-frequency positioning, results with L1-L2 were more accurate than those with L1-L5 signals. With single-frequency positioning, the L1 signal was more accurate compared to the L2 frequency.
  • ItemArtigo
    Weighted Iterative CD-Spline for Mitigating Occlusion Effects on Building Boundary Regularization Using Airborne LiDAR Data
    (2022-08-26) Dos Santos, Renato César [UNESP]; Habib, Ayman F.; Galo, Mauricio [UNESP]; Universidade Estadual Paulista (UNESP); Purdue University
    Building occlusions usually decreases the accuracy of boundary regularization. Thus, it is essential that modeling methods address this problem, aiming to minimize its effects. In this context, we propose a weighted iterative changeable degree spline (WICDS) approach. The idea is to use a weight function for initial building boundary points, assigning a lower weight to the points in the occlusion region. As a contribution, the proposed method allows the minimization of errors caused by the occlusions, resulting in a more accurate contour modeling. The conducted experiments are performed using both simulated and real data. In general, the results indicate the potential of the WICDS approach to model a building boundary with occlusions, including curved boundary segments. In terms of Fscore and PoLiS, the proposed approach presents values around 99% and 0.19 m, respectively. Compared with the previous iterative changeable degree spline (ICDS), the WICDS resulted in an improvement of around 6.5% for completeness, 4% for Fscore, and 0.24 m for the PoLiS metric.
  • ItemArtigo
    Comparative Evaluation of a Newly Developed Trunk-Based Tree Detection/Localization Strategy on Leaf-Off LiDAR Point Clouds with Varying Characteristics
    (2022-08-01) Zhou, Tian; dos Santos, Renato César [UNESP]; Liu, Jidong; Lin, Yi-Chun; Fei, William Changhao; Fei, Songlin; Habib, Ayman; Purdue University; Universidade Estadual Paulista (UNESP)
    LiDAR data acquired by various platforms provide unprecedented data for forest inventory and management. Among its applications, individual tree detection and segmentation are critical and prerequisite steps for deriving forest structural metrics, especially at the stand level. Although there are various tree detection and localization approaches, a comparative analysis of their performance on LiDAR data with different characteristics remains to be explored. In this study, a new trunk-based tree detection and localization approach (namely, height-difference-based) is proposed and compared to two state-of-the-art strategies—DBSCAN-based and height/density-based approaches. Leaf-off LiDAR data from two unmanned aerial vehicles (UAVs) and Geiger mode system with different point densities, geometric accuracies, and environmental complexities were used to evaluate the performance of these approaches in a forest plantation. The results from the UAV datasets suggest that DBSCAN-based and height/density-based approaches perform well in tree detection (F1 score > 0.99) and localization (with an accuracy of 0.1 m for point clouds with high geometric accuracy) after fine-tuning the model thresholds; however, the processing time of the latter is much shorter. Even though our new height-difference-based approach introduces more false positives, it obtains a high tree detection rate from UAV datasets without fine-tuning model thresholds. However, due to the limitations of the algorithm, the tree localization accuracy is worse than that of the other two approaches. On the other hand, the results from the Geiger mode dataset with low point density show that the performance of all approaches dramatically deteriorates. Among them, the proposed height-difference-based approach results in the greatest number of true positives and highest F1 score, making it the most suitable approach for low-density point clouds without the need for parameter/threshold fine-tuning.
  • ItemResenha
    GBAS: Fundamentals and availability analysis according to σvig
    (2022-01-01) Silva, Weverton Da Costa [UNESP]; Monico, João Francisco Galera [UNESP]; Universidade Estadual Paulista (UNESP)
    Ground-based augmentation system (GBAS) was developed to guide aircraft precision approach and landing, aiming to replace the instrument landing system (ILS), which is currently used in most airports worldwide. GBAS based on differential positioning with reference stations that provide differential corrections to the aircraft to improve its positioning accuracy and ensure other performance parameters such as integrity, continuity, and availability. However, using GBAS in low latitude regions such as Brazil, the occurrence of ionospheric irregularities can affect global navigation satellite system (GNSS) performance so that it does not meet the requirements for aviation. This article evaluates five vertical ionospheric gradient variability scenarios for a GNSS data set of four reference stations, one station simulating an aircraft with GBAS in a static model based on performance requirements for Category Approach Type - CAT I. The results showed that the increase in the variability of the ionosphere and the geometry of satellites used in positioning could affect the integrity and availability of GBAS. In the scenario of more significant variability of the ionosphere evaluated, there was a loss of 38.4% of the availability of GBAS for the CAT I approach.