The ionosphere may not only degrade the accuracy of the GNSS positioning but also reduce its availability because there is a high dependence between signal losses and ionospheric irregularities. Irregularities in the Earth's ionosphere may produce rapid fluctuations in phase and amplitude. These rapid fluctuations are called ionospheric scintillation. Thus, loss of signal can occur due to the effects of diffraction and refraction, which cause a weakening in the signal received by the GNSS receivers. In this way, this paper aims to evaluate the magnitude of ionospheric scintillation in Brazil and the performance of the positioning under its influence in the period of high solar activity in the current cycle (24), through the Spearman correlation analysis and the Wavelet periodogram. For that, three-year time series (2012 to 2014) of the S4 index and 3D MSE (Mean Squared Error) of three Brazilian stations with different ionospheric conditions were considered, PALM (near the Geomagnetic Equator) PRU2 (Equatorial region and Anomalies) and POAL (Mid-latitude region). Thus, it was possible to evaluate the correlation between the accuracy of the precise point positioning using only the C/A code of the GPS satellite and the S4 index. As a result, there was a correlation of 53% and 51%, using the Spearman method, for the PALM and PRU2 series, respectively. In addition, considering the analysis of space-frequency in relation to time by the Wavelet coherence method, a correlation of more than 70% is noted in the period of greatest 3D MSE concerning the spring and autumn equinox months.

No levantamento topográfico planialtimétrico, os meios mais difundidos de aquisição de dados são através da Estação Total e do posicionamento GNSS (Global Navigation Satellite System). Com a evolução tecnológica ocorrida na área de aquisição de dados planialtimétricos surge o VANT (Veículo Aéreo Não Tripulado), sobretudo pela redução do custo de equipamentos e a rapidez na obtenção dos dados, diante da topografia. Deste modo, o presente trabalho busca comparar os dados de levantamento planialtimétrico, cálculo de área, perímetro e vetorização das edificações geradas por dois métodos de aquisição de dados (topografia e aerofotogrametria por meio de VANT), utilizando as instalações da Comissão Regional de Obras do Exército Brasileiro localizado em Belém-PA. Cabe ressaltar, que os métodos utilizados alcançaram as precisões preconizadas, quais sejam,  poligonal Classe II PAC (NBR 13133/1994) para a utilização da Estação Total e PEC (Precisão de Exatidão Cartográfica) classe A no caso da utilização do VANT. Os resultados apresentados na aquisição de dados utilizados na forma comparativa, evidencia que não existe uma técnica perfeita. Assim, pode-se utilizar um ou outro método para situações diferentes e apresentar as vantagens e desvantagens associadas em cada método para elaboração do plano diretor e mapeamento da área em questão.

Elevation mapping at ground level is challenging in forested areas like the Amazon region, which is mostly covered by dense rainforest. The most common techniques, i.e. photogrammetry and short wavelength radar, provide elevations at canopy level at best, while most applications require ground elevations. Even lidar and P-band radar, which can penetrate foliage and measure elevations at ground level, have some limitations which are analyzed in here. We address three research questions: To what extent can a terrain model be replaced by a more easily available canopy-level surface model for topography-based applications? How can the elevation be obtained at ground level through forest? Can a priori knowledge of general continental relief properties be used to compensate for the limits of measurement methods in the presence of forest?

Perform change detection of Earth's surface features is important to understand both the dynamics of the phenomena and for the prediction of impacts and to support decision-making. During the last decades were developed several change detection techniques from images, among them those based on remote sensing images. In general, the change detection involves the use of a set of multi-temporal data, which permits quantitative analysis of the phenomenon of interest. An application of great interest of these techniques is the automatic detection of changes in the vicinity of reservoirs, which can be used as auxiliary data in a monitoring system of the areas of interest. In such a system it is expected that the changes resulting from human activity are detected even if there are factors that cause differences between scenes, such as atmospheric conditions, scene lighting, sensor view point, soil moisture, among other factors. Considering this context, this paper presents the evaluation results of a change detection approach based on a modification applied to the RCEN (Radiometric Rotation Controlled by Non change axis) technique. The method was implemented and applied to a set of orthorectified images obtained by orbital system SPOT 6, taken at two different times on the Canoas I reservoir, under concession from Duke Energy (currently CTG Brasil). The results showed that the algorithm based on modified RCEN technique was efficient to detect automatically changes.