Abstract
Remote Sensing techniques are useful to determine planted areas, especially of commodities like maize and soybeans (summer cultures). The vegetation indexes as NDVI (Normalized Difference Vegetation Index) has been used to map agricultural areas due to its low cost and accessibility. Therefore the objective of this study was to develop a new methodology to generate masks of summer crops based on fitting second order polynomial equations to temporal NDVI profiles. The results showed that selecting polynomial equations with r 2 fitting above 0.75, a Kappa index of 0.86 and a global accuracy of 93% is obtained. This is slightly higher than the results obtained when using the maximum-minimum NDVI technique, with a Kappa index of 0.82 and a global accuracy of 91%. However, while quantifying the areas under study, one verified that the mask used by the proposed methodology, was closer to the official IBGE data, with a difference of -10.25%, followed by the vector technique with 23% and by the maximum-minimum NDVI, with a difference of 42.8%.
Highlights
Information on the dynamics of crops in Brazil are extremely important because the space occupied by them changes constantly due to market, environment, migration and public policy, to mention only a few factors
The methodology proposed for the generation of a summer crop mask by second order polynomial equations adjusted to temporal NDVI profiles, was based on the behavior of both crops in the field, because they have unique patterns of temporal profiles, according to a graphic representation (Figure 5)
One verifies here that the Kappa values of 0.82 and global accuracy of 91% are slightly below those obtained by the polynomial methodology, but the omission error of 0.04% for the summer crops demonstrates that the maximum-minimum NDVI mask was excellent for the identification of summer crops
Summary
Information on the dynamics of crops in Brazil are extremely important because the space occupied by them changes constantly due to market, environment, migration and public policy, to mention only a few factors. The governmental bodies responsible for the estimation of cultivated areas in Brazil are IBGE (Brazilian Institute for Geography and Statistics) and CONAB (National Company for Provision/Ministry for Agriculture, Livestock and Provision) and at regional level, there are several organizations connected to State governments such as DERAL/SEAB (Department of Rural Economy from the Paraná State, Secretary for Agriculture). These institutions perform field surveys and data analysis for the estimation of areas, which are expensive and time consuming. CONAB took the initiative to aggregate to its analysis tools, information derived from remote sensing and geo-processing, to subsidize decisions for the estimation of areas and harvest from cultures (CONAB 2012)
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