Infl uence of Atmospheric Correction in the Conversion of Radiance to Refl ectance Data on EVI Calculation in RapidEye Image
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Abstract
The aim of this study was to compare the eff ects of the reduction of radiance to scaled surface refl ectance by means of
atmosphere correction using the radiative transfer model (FLAASH) and the refl ectance at the top of the atmosphere
(TOA), band to band, to Ortho - Level 3A scene of RapidEye, on Enhanced Vegetation Index (EVI). We considering
six targets: water, urban, bare soil, gallery forest, fi eld vegetation and savanna vegetation. For comparison, we used the
method quick_diff _stats, whose results are one image with the diff erence between digital numbers of worked images
and a text fi le containing the frequency of distribution (single and cumulative) for each pixel diff erence value of digital
numbers and their corresponding percentage. We adjusted a linear regression on EVI’s data and applied the D’Agostino-Pearson normality test. For normal data, we calculated the Pearson correlation coeffi cient and for non-parametric
data, we used the Kendall correlation coeffi cient. To evaluate the atmospheric correction, positive values indicate
predominance of FLAASH atmospheric correction and negative values, the TOA method. In bands 1, 2 and 3 the TOA
refl ectance overlapping FLAASH method, while in bands 4 and 5 was the reverse (FLAASH predominance). To evaluate EVI, we compared four pars: EVI from FLAASH and EVI from TOA, using red band; EVI from FLAASH and
EVI from TOA, using red-edge band; EVI from FLAASH, using red band, and EVI from FLAASH, using red-edge
band; and EVI from TOA, using red band, and EVI from TOA, using red-edge band. All comparisons indicated high
correlation, despite of normality. Results showed that atmospheric correction is unnecessary to calculate EVI, and the
red band was better than red-edge band to use EVI.
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