ABSTRACT Ensuring prompt and effective water quality monitoring is increasingly important. Remote sensing has been shown to be an effective tool for simplifying and speeding up this process. The aim of this study is to develop an empirical model to map the spatial and temporal dynamics of turbidity in Mirim Lagoon, located in southern Brazil. To achieve this, Sentinel-2A/B MSI sensor data were combined with turbidity data collected in situ. The model was applied to monthly images (with cloud cover ≤ 20%) in 2019 and 2020 using the Google Earth Engine (GEE) platform. Mean turbidity values in the lagoon did not vary significantly, remaining between 30 and 75 NTU overall. However, there were differences in turbidity levels between the northern and southern regions of the lagoon in some months of the investigated years. By applying this methodology and analyzing the results, we were able to better understand the behavior of turbidity throughout the lagoon and gain insights into the quality of this important freshwater source.

RESUMO Tem se tornado cada vez mais necessário garantir agilidade e eficácia no monitoramento da qualidade da água. Nesse sentido, o sensoriamento remoto tem se mostrado uma ferramenta eficaz, capaz de tornar esse processo mais rápido e simples. O objetivo do presente estudo é gerar um modelo empírico para mapear espacial e temporalmente a dinâmica da turbidez na Lagoa Mirim, sul do Brasil. Os dados do sensor MSI Sentinel-2A/B foram usados em combinação com os dados de turbidez coletados in situ. Os mapeamentos espaciais e temporais foram realizados na plataforma Google Earth Engine (GEE) aplicando o modelo em imagens mensais (cobertura de nuvens ≤ 20%), em 2019 e 2020. Os valores médios de turbidez observados na lagoa não apresentaram variações significativas; no geral, eles permaneceram entre 30 NTU e 75 NTU. Houve diferença nos níveis de turbidez entre as regiões Norte e Sul da lagoa em alguns meses dos anos investigados. A metodologia aqui aplicada e os resultados observados permitiram analisar o comportamento da turbidez em toda a extensão da Lagoa Mirim e conhecer melhor a qualidade da água nesta importante fonte de água doce.

Abstract Mirim lagoon is the second largest lacustrine water body in Southern Brazil, providing water for local communities. However, algae growth and water quality in the lagoon and in tributaries rivers is influenced by nutrient’s increase. In this context, this study performs the empirical and semi-empirical chlorophyll-a (Chl-a) modeling using remote sensing and in situ data for water quality assessment. Water quality data were collected at 15 sample locations in the lagoon on the date of Sentinel-2 satellite overpass. Surface reflectance data were derived from the Sen2Cor atmospheric correction method and correlated with Chl-a concentration. The best model presented a Pearson’s correlation coefficient = 0.81 and Mean Absolute Error = 0.13µg.L-1. Low Chl-a concentration is observed at the Northern lagoon, possibly due to suspended solids presence. The same occurs in the left margin, being associated with the influence of land use for agriculture. High Chl-a concentrations are associated with shallower and lentic areas. The mean Chl-a concentration predicted by the model was 17.34μg.L-1, similar to the observed value in situ (16.32μg.L-1). Overall, the empirical model developed can be applied as a tool to reduce costs and efforts in fieldwork measures and to understand eutrophication in this river-lake transition ecosystem.

Resumo A qualidade da educação no Brasil ainda avança lentamente, apesar dos esforços de políticas públicas. Embora a literatura internacional já aponta para a importância da gestão escolar e perfil do diretor no desempenho dos alunos, essa discussão é ainda recente no Brasil. Nesse estudo nós investigamos o efeito do processo de seleção de diretores no desempenho dos alunos de escolas públicas estaduais brasileiras. Os resultados mostram que que, embora o efeito do processo de seleção não seja claro, o efeito das características do diretor indica que processos mais técnicos e democráticos de escolha do diretor tendem a selecionar diretores mais qualificados em termos de liderança e habilidades gerenciais. O diretor experiente, que tem tempo para implementar mudanças e que adota práticas gerenciais para estimular os professores apresentam melhores resultados, em termos de desempenho dos alunos. Nesse sentido, é importante que o processo seletivo escolha profissionais com as características mencionadas.

Abstract Educational quality in Brazil has improved at a slow pace despite continued public policy efforts. The international literature has noted the importance of school management and the principal’s profile on students’ performance, but this discussion is recent in Brazil. In this study, we investigate the effects of the selection process of principals on students’ performance from public state schools in Brazil. We conclude that while the “selection process” channel is not clear, the “principal quality effect” indicates that the more democratic and technical selection methods tend to select most qualified principals in terms of leadership and managerial abilities. The principal who has time to implement changes, who adopts management practices to encourage teachers and has experience being the leader of the school present better results in terms of student’s performance. Therefore, it is important that the principal selection process choose professionals with the skills mentioned.