Browsing by Author "Xavier, Antonio"
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- A minimum cross entropy approach to disaggregate agricultural data at the field levelPublication . Xavier, Antonio; Fragoso, Rui; Costa Freitas, M. B.; Rosario, Maria do Socorro; Valente, FlorentinoAgricultural policies have impacts on land use, the economy, and the environment and their analysis requires disaggregated data at the local level with geographical references. Thus, this study proposes a model for disaggregating agricultural data, which develops a supervised classification of satellite images by using a survey and empirical knowledge. To ensure the consistency with multiple sources of information, a minimum cross-entropy process was used. The proposed model was applied using two supervised classification algorithms and a more informative set of biophysical information. The results were validated and analyzed by considering various sources of information, showing that an entropy approach combined with supervised classifications may provide a reliable data disaggregation.
- An approach using entropy and supervised classifications to disaggregate agricultural data at a local levelPublication . Xavier, Antonio; Fragoso, Rui; Costa Freitas, M. B.; Rosario, Maria do SocorroChanges in the Common Agricultural Policy (CAP) had several consequences on land-use and on the environment. This calls for detailed disaggregated agricultural data with precise geographical references. To tackle such problems data disaggregation processes are needed and a series of studies are being carried out at international level, which still have not taken the utmost advantage of remote sensing technologies by combining them with mathematical programming methods, namely entropy. Therefore, the objective of this article was to provide an approach to disaggregate agricultural data at the local level, taking advantage of the existent up-to-date satellite imagery and an entropy approach for manage different sets of data. The results were compared with other approaches and showed to be coherent, and may be improved further with the inclusion of other information.
- Integration of fire risk in a sustainable forest management modelPublication . Costa Freitas, Maria de Belem; Xavier, Antonio; Fragoso, RuiIn Mediterranean areas, forest fires are a considerable risk most years. The seasonality of the climate with a dry summer, high temperatures and low rainfall (which implies increased flammability of materials) is one of the main factors in the ignition and progression of fires. This factor conjugated with more favourable biophysical conditions (e.g., high slopes, aspect) leads to easy propagation and the increasingly destructive power of such phenomena. To prevent and reduce the consequences of forest fires, it is necessary to simulate and forecast the territory use and management, not only focused on forest areas, but also on all land uses and agricultural activities that may coexist there, considering the probability of fire occurrence. The objective of this paper is to present a methodological approach to address the integration of fire risk in integrated Mediterranean forest management models. The methodological approach considers simultaneously the climatic conditions through different times of the year (more or less favourable to forest fire damage) and structural conditions addressed to land uses, aspect, slope, roads and demographic density. The methodological approach was implemented in a management area located in the Algarve, in southern Portugal. The results for the Algarve region showed that the proposed approach is very useful for managers, since it allowed the calculation of fire susceptibility, vulnerability and fire damage, according to several climatic scenarios. It also allowed the incorporation of different paths regarding different fire risk conditions and the minimization of risk due to fire damage through different management responses.