Short communication Advantages of a two band EVI calculated from solar and photosynthetically active radiation fluxes Adrian V. Rocha *, Gaius R. Shaver The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA 1. Introduction The Normalized Difference Vegetation Index (NDVI) is commonly used to monitor the phenology, quantity, and activity of vegetation. NDVI can be measured remotely with satellites, calculated from ground-based measurements of surface reflec- tance, or calculated from measurements of incident and reflected solar and Photosynthetically Active Radiation (PAR) (Huete et al., 1994; Wilson and Meyers, 2007). Although NDVI provides researchers with a way to monitor vegetation, the sensitivity of NDVI to background reflectance and the tendency of NDVI to saturate at high leaf area may limit the use of this technique across a variety of vegetation types (Huete, 1988; Huete et al., 2002). The Enhanced Vegetation Index (EVI) is often employed as an alternative to NDVI because it is less sensitive to these limitations, but requires information on reflectance in the blue wavelengths, which is not available on some satellites and is difficult to extract from broadband radiation measurements. A two band EVI (EVI2) that does not require the blue band reflectance has been developed by taking advantage of the autocorrelative properties of surface reflectance spectra between the red and blue wavelengths (Jiang et al., 2008). However, the sensitivity of this autocorrelation to changes in background reflectance is not fully understood, and further testing is required before a universal relationship between reflectance in the red and blue wavelengths is established. We used leaf area harvests and three independent measures of surface reflectance from three sites located along a burn severity gradient (i.e. severe, moderate, unburned) to determine the sensitivity of NDVI and EVI2 to changes in background reflectance. Burn severity influenced background reflectance through differences in the amount of vegetation consumed in the fire, which in turn, resulted in albedo differences along the burn severity gradient. NDVI and EVI2 derived from incident and reflected solar and PAR measurements were validated against NDVI, EVI, and EVI2 derived from the MODerate resolution Imaging Spectrodiometer (MODIS) satellite and ground-based spectroradiometer measurements. The seasonal pattern and differences in magnitude of EVI and NDVI among the severe, moderate, and unburned sites were compared to determine the ability of the vegetation indices to resolve differences in surface greenness among sites. The ability of NDVI and EVI2 to capture differences in leaf area across the burn severity gradient was assessed with small plot based measurements of surface reflectance and Leaf Area Index (LAI) across burned and unburned tundra sites. Agricultural and Forest Meteorology xxx (2009) xxx–xxx ARTICLE INFO Article history: Received 23 January 2009 Received in revised form 20 March 2009 Accepted 26 March 2009 Keywords: Burn severity Vegetation phenology NDVI EVI2 Tundra ABSTRACT A two band Enhanced Vegetation Index (EVI2) without the blue band reflectance has recently been developed as a proxy for the phenology, quantity, and activity of vegetation. We compared the ability of EVI2 and the more commonly used Normalized Difference Vegetation Index (NDVI) to resolve differences in surface greenness and Leaf Area Index (LAI) among three sites located along a burn severity gradient in arctic tundra. We calculated vegetation indices from solar and photosynthetically active radiation fluxes, and validated these calculations against vegetation indices from the Terra MODerate resolution Imaging Spectroradiometer (MODIS) and ground-based spectroradiometer measurements. EVI2 performed slightly better than NDVI when comparing tower derived vegetation indices to MODIS and spectroradiometer derived vegetation indices. Burn severity decreased albedo and resulted in differences in soil background reflectance among sites. Soil darkening had no effect on EVI2, but artificially increased NDVI, resulting in separate relationships between NDVI and Leaf Area Index for burned and unburned tundra. Our results indicate that EVI2 has several advantages over NDVI including the ability to resolve LAI differences for vegetation with different background soil reflectance. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: arocha@mbl.edu (A.V. Rocha). G Model AGMET-4069; No of Pages 4 Please cite this article in press as: Rocha, A.V., Shaver, G.R., Advantages of a two band EVI calculated from solar and photosynthetically active radiation fluxes. Agric. Forest Meteorol. (2009), doi:10.1016/j.agrformet.2009.03.016 Contents lists available at ScienceDirect Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet 0168-1923/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2009.03.016