TOPOGRAPHIC EFFECT ON SPECTRAL VEGETATION INDICES FROM LANDSAT TM DATA: IS TOPOGRAPHIC CORRECTION NECESSARY?

Eder Paulo Moreira*,Ieda Del Arco Sanches,Márcio De Morisson Valeriano,Antonio Roberto Formaggio

doi:10.1590/s1982-21702016000100006

Eder Paulo Moreira*, Ieda Del Arco Sanches + Show 2 more

Open Access

https://doi.org/10.1590/s1982-21702016000100006

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Abstract

The full potentiality of spectral vegetation indices (VIs) can only be evaluated after removing topographic, atmospheric and soil background effects from radiometric data. Concerning the former effect, the topographic effect was barely investigated in the context of VIs, despite the current availability correction methods and Digital elevation Model (DEM). In this study, we performed topographic correction on Landsat 5 TM spectral bands and evaluated the topographic effect on four VIs: NDVI, RVI, EVI and SAVI. The evaluation was based on analyses of mean and standard deviation of VIs and TM band 4 (near-infrared), and on linear regression analyses between these variables and the cosine of the solar incidence angle on terrain surface (cos i). The results indicated that VIs are less sensitive to topographic effect than the uncorrected spectral band. Among VIs, NDVI and RVI were less sensitive to topographic effect than EVI and SAVI. All VIs showed to be fully independent of topographic effect only after correction. It can be concluded that the topographic correction is required for a consistent reduction of the topographic effect on the VIs from rugged terrain.

Highlights

Remote sensing data have become an important source of information for studying vegetation on regional, continental and global scale
We evaluated the topographic effect on four vegetation indices from uncorrected and topography-corrected Landsat 5 TM data
The studied vegetation indices partially contributed to reduce the topographic effect on the spectral data

Summary

Introduction

Remote sensing data have become an important source of information for studying vegetation on regional, continental and global scale. In rugged mountainous areas the use of remote sensing data can be limited by the topographic effect (Horn, 1981). The topographic (or illumination) effect consists in variations of radiance levels of spectral data caused by differences in surface slope angle and aspect of the terrain, in combination with solar zenith and azimuth angles (Holben and Justice, 1980). It is assumed that topographic effect is considerably reduced in band ratio compared to single spectral bands (Holben and Justice, 1981) Based on this rationale, most studies consider that band ratio VIs (for example, the Normalized Difference Vegetation Index - NDVI) can overcome topographic effects on radiometric levels (Lee and Kaufman, 1986; Ekstrand, 1996; Huete at al., 1999). Low values of cos i indicate pixels under low illumination and high cos i are well-illuminated pixels (Dubayah and Rich, 1995)

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