Abstract
The ability to monitor sugarcane expansion in Brazil, the world’s largest producer and exporter of sugar and second largest producer of ethanol, is important due to its agricultural, economic, strategic and environmental relevance. With the advent of flex fuel cars in 2003 the sugarcane area almost doubled over the last decade in the South-Central region of Brazil. Using remote sensing images, the sugarcane cultivation area was annually monitored and mapped between 2003 and 2012, a period of major sugarcane expansion. The objective of this work was to assess the thematic mapping accuracy of sugarcane, in the crop year 2010/2011, with the novel approach of developing a web platform that integrates different spatial and temporal image resolutions to assist interpreters in classifying a large number of points selected by stratified random sampling. A field campaign confirmed the suitability of the web platform to generate the reference data set. An overall accuracy of 98% with an area estimation error of −0.5% was achieved for the sugarcane map of 2010/11. The accuracy assessment indicated that the map is of excellent quality, offering very accurate sugarcane area estimation for the purpose of agricultural statistics. Moreover, the web platform showed to be very effective in the construction of the reference dataset.
Highlights
Due to its agricultural [1], economic [2], strategic [3,4] and environmental [5,6,7] relevance, sugarcane cultivation in the South-Central region of Brazil has been annually monitored and mapped using Landsat-like images and visual interpretation since 2003 through the Canasat Project [8]
The following remote sensing images and ancillary data were used in the present work: (i) 396 images acquired by Landsat-5 and Landsat-7 from January 2009 through to September 2010; (ii) MODIS-EVI2 time series (February 2000–December 2011) of the MOD09 product for the entire South-Central region
South-Central region of Brazil produced by the Canasat Project
Summary
Due to its agricultural [1], economic [2], strategic [3,4] and environmental [5,6,7] relevance, sugarcane cultivation in the South-Central region of Brazil has been annually monitored and mapped using Landsat-like images and visual interpretation since 2003 through the Canasat Project (www.dsr.inpe.br/laf/canasat/en) [8]. The annual thematic maps have been used to estimate the cultivated sugarcane area and as reference for monitoring sugarcane harvesting practices [9], for assessing land use change in response to sugarcane expansion [10,11], and for analyzing crop yield [12]. These maps were carefully created using images acquired during specific periods of the sugarcane crop calendar, they have not yet been evaluated with an objective method of quality assessment to determine their utility and applicability [13,14,15,16]. Difficult access to extensive geographic regions and frequent land use changes can hinder the process of accuracy assessment but should not reduce the credibility of these assessments [21]
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