REP - Red Edge Position

REP Red Edge Position

The point of maximum slope on the reflectance spectrum of a plant leaf between red and near‐infrared wavelengths is known as the red edge position (REP). 

Results are reported as the wavelength of the maximum derivative of reflectance in the vegetation red edge region of the spectrum in microns from 690 nm to 740 nm. The common range for green vegetation is 700 nm to 730 nm.

The REP is strongly correlated with foliar chlorophyll content, and hence it provides a very sensitive indicator for a variety of environmental factors affecting leaves such as stress, drought and senescence. The REP is also present in spectra for vegetation recorded by remote sensing methods. Due to its importance for the application of inversion procedures, a number of techniques have been developed for determining the REP for foliar spectral reflectance.

The red edge position index is sensitive to changes in chlorophyll concentrations, as higher chlorophyll concentrations absorb longer wavelengths. It is calculated as: 700+40*((670nm+780nm/2)-700nm/(740nm-700nm)

References:

Main, R., Cho, M. A., Mathieu, R., O’Kennedy, M. M., Ramoelo, A., & Koch, S. (2011). An investigation into robust spectral indices for leaf chlorophyll estimation. ISPRS Journal of Photogrammetry and Remote Sensing, 66(6), 751-761.