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Utilização da análise harmônica em séries temporais de dados EVI e ET de áreas canavieiras

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The objective of the study was to describe seasonal phenological profiles by means of the vegetation index and investigate the seasonal evapotranspiration cycle of sugarcane areas in the municipality of Barretos, São Paulo, by applying harmonic analysis to time series of EVI and evapotranspiration from products of the MODIS/Terra sensor. We used a 2-year time series of EVI data (16 days) and ET data (8 days) for the years 2010 and 2011. The vegetation presents seasonal and periodic behaviour; the harmonic analysis expresses the periodic phenomenon in a series of sinusoidal and cosinusoidal functions described in amplitude and phase values, from which we can extract the variance of each term in the data set. In the sugarcane area that presents annual seasonality, the majority of the variance was captured by the second harmonic, with vegetative vigour between the months of January and April. The additive term, the amplitude and the phase angles enable us to identify, respectively, the areas of lesser and greater vigour, the periodicity of events, and the period of maximum vegetative vigour. The study demonstrated the utility of the analysis for detecting areas of change in the vegetation, such as reform and expansion of sugarcane areas, showing potential for monitoring and analyzing landscape changes, with reduction in the data volume of temporal data series.