Comparative Analysis of MODIS Time-Series Classification Using Support Vector Machines and Methods Based upon Distance and Similarity Measures in the Brazilian Cerrado-Caatinga Boundary

Natanael Abade,Renato Guimarães,Sandro De Oliveira,Osmar Júnior

doi:10.3390/rs70912160

Abstract

We have mapped the primary native and exotic vegetation that occurs in the Cerrado-Caatinga transition zone in Central Brazil using MODIS-NDVI time series (product MOD09Q1) data over a two-year period (2011–2013). Our methodology consists of the following steps: (a) the development of a three-dimensional cube composed of the NDVI-MODIS time series; (b) the removal of noise; (c) the selection of reference temporal curves and classification using similarity and distance measures; and (d) classification using support vector machines (SVMs). We evaluated different temporal classifications using similarity and distance measures of land use and land cover considering several combinations of attributes. Among the classification using distance and similarity measures, the best result employed the Euclidean distance with the NDVI-MODIS data by considering more than one reference temporal curve per class and adopting six mapping classes. In the majority of tests, the SVM classifications yielded better results than other methods. The best result among all the tested methods was obtained using the SVM classifier with a fourth-degree polynomial kernel; an overall accuracy of 80.75% and a Kappa coefficient of 0.76 were obtained. Our results demonstrate the potential of vegetation studies in semiarid ecosystems using time-series data.

Highlights

Studies of the spatial distribution and the processes governing the Brazilian Cerrado-Caatinga transition can significantly inform the management of these biomes
We found that S-G with a window size of nine [84] refined the result obtained by the median filter and smoothed the temporal profile without interfering with the maximum and minimum values
We evaluated different support vector machines (SVMs) classifications considering main kernel functions, two input data types (NDVI-Moderate Resolution Imaging Spectroradiometer (MODIS) time series and MNF signal components), and the number of classes

Summary

Introduction

Studies of the spatial distribution and the processes governing the Brazilian Cerrado-Caatinga transition can significantly inform the management of these biomes. Ecotones are key indicators of local and global changes that facilitate an understanding of the landscape’s responses to changes in climate regimes and human influences. The Cerrado and Caatinga biomes have great biodiversity adapted to the seasonal stress that coexists in a complex mosaic [1,2,3]. The transition zone includes different vegetation types such as dry forest islands, gallery forests, and savannas that vary in their patch number and size. Anthropogenic alterations are increasing in this environment, which is causing landscape fragmentation and harm to ecological functioning. Semiarid ecosystems have been threatened worldwide, with a reduction in area of approximately 50%

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