Although the single threshold is still considered a suitable and easy-to-do technique to extract water features in spatiotemporal analysis, it leads to unavoidable errors. This paper uses an enumerative search to optimize thresholds over satellite-derived modified normalized difference water index (MNDWI). We employed a cross-validation approach and treated accuracy as a random variable in order to: (a) investigate uncertainty related to its application; (b) estimate non-optimistic errors involving single thresholding; (c) investigate the main factors that affect the accuracy’s model, and (d) compare satellite sensors performance. We also used a high-resolution digital elevation model to extract water elevations values, making it possible to remove topographic effects and estimate non-optimistic errors exclusively from orbital imagery. Our findings evidenced that there is a region where thresholds values can vary without causing accuracy loss. Moreover, by constraining thresholds variation between these limits, accuracy is dramatically improved and outperformed the Otsu method. Finally, the number of scenes employed to optimize a single threshold drastically affects the accuracy, being not appropriate using a single scene once it leads to overfitted threshold values. More than three scenes are recommended.

In this work, we aim to evaluate the feasibility and operational limitations of using Sentinel-1 synthetic aperture radar (SAR) data to monitor water levels in the Poço da Cruz reservoir from September 2016–September 2020, in the semi-arid region of northeast Brazil. To segment water/non-water features, SAR backscattering thresholding was carried out via the graphical interpretation of backscatter coefficient histograms. In addition, surrounding environmental effects on SAR polarization thresholds were investigated by applying wavelet analysis, and the Landsat-8 and Sentinel-2 normalized difference water index (NDWI) and modified normalized difference water index (MNDWI) were used to compare and discuss the SAR results. The assessment of the observed and estimated water levels showed that (i) SAR accuracy was equivalent to that of NDWI/Landsat-8; (ii) optical image accuracy outperformed SAR image accuracy in inlet branches, where the complexity of water features is higher; and (iii) VV polarization outperformed VH polarization. The results confirm that SAR images can be suitable for operational reservoir monitoring, offering a similar accuracy to that of multispectral indices. SAR threshold variations were strongly correlated to the normalized difference vegetation index (NDVI), the soil moisture variations in the reservoir depletion zone, and the prior precipitation quantities, which can be used as a proxy to predict cross-polarization (VH) and co-polarization (VV) thresholds. Our findings may improve the accuracy of the algorithms designed to automate the extraction of water levels using SAR data, either in isolation or combined with multispectral images.

The article addresses anthropogenic and geological conditions related to the development of soil subsidence in the western zone of Recife (Brazil). Over the past 50 years, human activity has intensified in areas previously affected by soft soils (clay, silt, and sandstone) resulting in subsidence due to additional loads (landfills and constructions). The duration of the settlement process can be significantly influenced by the specific characteristics of the soil composition and geological conditions of the location. This work presents, for the first time, accurate InSAR time series maps that describe the spatial pattern and temporal evolution of the settlement, as well as the correlation with the geological profile, and validation with Global Navigation Satellite System (GNSS) data. Persistent Scatterer Interferometry (PS-InSAR) was employed in the analysis of Single Look Complex (SLC) images generated by 100 ascending COSMO-SkyMed (CSK) and 65 PAZ (32 ascending, and 33 descending) from the X-band, along with 135 descending Sentinel-1 (S1) acquisitions from the C-band. These data were acquired over the period from 2011 to 2023. The occurrence of subsidence was identified in several locations within the western region, with the most significant displacement rates observed in the northern, central, and southern areas. In the northern region, the displacement rates were estimated to be approximately −20 mm/year, with the Várzea and Caxangá neighborhoods exhibiting the highest rates. In the central region, the displacement rates were estimated to be approximately −15 mm/year, with the Engenho do Meio, Cordeiro, Torrões, and San Martin neighborhoods exhibiting the highest rates. Finally, in the southern region, the displacement rates were estimated to be up to −25 mm/year, with the Caçote, Ibura, and Ipsep neighborhoods exhibiting the highest rates. Additionally, east–west movements were observed, with velocities reaching up to −7 mm/year toward the west. These movements are related to the lowering of the land. The study highlights that anthropogenic effects in the western zone of Recife contribute to the region’s vulnerability to soil subsidence.

A realidade aumentada (RA) é uma tecnologia com novo paradigma de interface com os usuários que vem crescendo em importância na apresentação de produtos cartográficos. A visualização de elementos naturais é incorporada à representação estática terrestre em um ambiente digital interativo. Essa transformação provoca mudanças na forma como os usuários percebem os produtos cartográficos que antes eram apresentados em meios analógicos. O uso da realidade aumentada potencializa a apresentação de produtos cartográficos tridimensionais dinâmicos, e permite ampliar o aspecto cognitivo de usuários não especialistas em contato com documentos cartográficos. A tecnologia remonta a década de 1960, e nos dias atuais tem se expandido em diversas funcionalidades em vários setores. O artigo discute a incorporação da realidade aumentada na construção do modelo 3D do campus da Universidade Federal de Pernambuco. Tal modelo foi utilizado em experimento aplicado a usuários não especialistas, tendo-se como eixos de avaliação: aspecto territorial, interpretação de elementos, e aspecto comunicativo. Os resultados do experimento mostram que o processo de ensino-aprendizagem na área da cartografia é um campo fértil para atuação da RA, tornando-se um ponto de partida para a elaboração de uma base cartográfica aumentada.

As Ciências Geodésicas por meio de seus métodos e equipamentos de medição fornecem informações geoespaciais de uso corrente aos projetos de engenharia e gestão territorial que exigem a crescente demanda pela densificação da Rede Altimétrica de Alta Precisão do Sistema Geodésico Brasileiro. A materialização da coordenada altimétrica na superfície terrestre é representada pelas Referências de Nível - RRNN, cujas coordenadas são determinadas a partir das redes altimétricas existentes. Considerando a única referência de nível (RN1660P) homologada pelo Instituto Brasileiro de Geografia e Estatística no campus da UFPI em Teresina, em 2017, foi implantada uma rede geodésica altimétrica com dezenove marcos de concreto, do tipo tronco de pirâmide e chapa incrustada no seu topo. Atualmente, a rede geodésica altimétrica da UFPI possui 57,9% dos marcos em bom estado de conservação e disponíveis para uso, sendo que oito marcos se encontram destruídos ou vandalizados que evidencia a necessidade de manutenção da mencionada rede. Neste sentido, considerando a relevância das referências de nível para a continuidade das diversas atividades desenvolvidas na UFPI e seu entorno, este artigo tem como objetivo propor a manutenção da rede geodésica altimétrica, atendendo os requisitos de padronização, distribuição territorial, materialização, segurança, acessibilidade, estabilidade e visibilidade de satélites, bem como proceder a integração da referida rede ao Sistema Geodésico Brasileiro, a partir de estações de referência da RAAP e da RBMC, a fim de homologar as RRNN junto ao IBGE.

One of the main causes of land subsidence in the world is the exploitation of groundwater above the regeneration capacity of the aquifer systems. However, the rapid urban growth in estuarine areas can also contribute to the development of this phenomenon. An example of this occurs in the city of Recife, northeastern Brazil. The municipality is built on an estuarine plain composed of several rivers (Capibaribe, Beberibe, Tejipió), which formation results from the occupation of humid areas and mangroves. In recent decades, the excessive removal of water resources from the subsoil has caused the reduction of more than 100 meters of the deep aquifer piezometric level in some places. The presence of these factors in Recife may contribute to land subsidence. To detect this phenomenon, the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique was used. The dataset consisted of 135 Sentinel-1A Interferometric Wide (IW) Single Look Complex (SLC) images from September 2016 to April 2021. The images were acquired in descending orbits and VV polarization. The results of the PSInSAR analysis reveal that in Recife there are several areas of land subsidence with a rate close to -15 mm/year. The main occurrence of soil settlement is observed in large recently built areas in the west zone, and small areas in the north zone. Minor cases occur in the southern zone due to the exploitation of groundwater. The identification of these land subsidence areas can help in the study of urban drainage to avoid flooding sites and in the adoption of mitigating measures for the suitable use of underground water resources.