Percorrer por autor "Guiomar, Nuno"
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- Burned Areas Mapping Using Sentinel-2 Data and a Rao’s Q Index-Based Change Detection Approach: A Case Study in Three Mediterranean Islands’ Wildfires (2019–2022)Publication . Tiengo, Rafaela; Merino de Miguel, Silvia; Uchôa, Jéssica; Guiomar, Nuno; Freire Gil, Artur José; Sprintsin, Michael; Huang, WenjiangABSTRACT: This study explores the application of remote sensing-based land cover change detection techniques to identify and map areas affected by three distinct wildfire events that occurred in Mediterranean islands between 2019 and 2022, namely Sardinia (2019, Italy), Thassos (2022, Greece), and Pantelleria (2022, Italy). Applying Rao’s Q Index-based change detection approach to Sentinel-2 spectral data and derived indices, we evaluate their effectiveness and accuracy in identifying and mapping burned areas affected by wildfires. Our methodological approach implies the processing and analysis of pre- and post-fire Sentinel-2 imagery to extract relevant indices such as the Normalized Burn Ratio (NBR), Mid-infrared Burn Index (MIRBI), Normalized Difference Vegetation Index (NDVI), and Burned area Index for Sentinel-2 (BAIS2) and then use (the classic approach) or combine them (multidimensional approach) to detect and map burned areas by using a Rao’s Q Index-based change detection technique. The Copernicus Emergency Management System (CEMS) data were used to assess and validate all the results. The lowest overall accuracy (OA) in the classical mode was 52%, using the BAIS2 index, while in the multidimensional mode, it was 73%, combining NBR and NDVI. The highest result in the classical mode reached 72% with the MIRBI index, and in the multidimensional mode, 96%, combining MIRBI and NBR. The MIRBI and NBR combination consistently achieved the highest accuracy across all study areas, demonstrating its effectiveness in improving classification accuracy regardless of area characteristics.
- Using graph theory to analyse and assess changes in Mediterranean woodland connectivityPublication . Machado, Rui; Godinho, Sérgio; Guiomar, Nuno; Gil, Artur José Freire; Pirnat, JanezCONTEXT The Portuguese montado is an agro-silvopastoral system, similar to the Spanish dehesa, known for its cultural, economic and ecological value. Despite its importance, contrasting processes such as land abandonment and land use intensification, together with several other factors, have been responsible for montado degradation in the last decades. Biodiversitywise, assuring high levels of connectivity is vital for many species that, in turn, contribute to the natural processes on which a healthy and sustainable montado relies. OBJECTIVES To study the montado connectivity in the recent decades and infer what the changes represent to the short and medium dispersal species regarding habitat availability. METHODS The study was conducted in an area delimited by biogeographic boundaries in Southern Portugal where montado is abundant. We used a graph theory based approach and montado maps of 1984, 1999 and 2014 derived from remote sensing. RESULTS The results show a loss of montado associated to increasing fragmentation over time. This led to a global connectivity decrement likely to have negative implications for montado species. The most affected species are those more dependent on habitat characteristics, such as forest specialist birds, and those with low mobility that have lost great amounts of habitat not only due to montado loss but also due to the increasing fragmentation that makes suitable patches unreachable. CONCLUSIONS Given the montado environmental relevance, measures should be taken in order to stop its loss and preserve the core areas that have guaranteed the connectivity over time.