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A wavelet-based technique for extracting the red edge position from vegetation reflectance spectra

The red edge position (REP) of a reflectance spectrum has been used as means to estimate the foliar chlorophyll content at leaf and canopy level. Most methods for extracting the REPs are based on the first derivative spectra and many studies have shown discontinuities in the REP data due to the existence of a double-peak feature in the first derivative spectra. This study proposes a new technique based on the continuous wavelet transform of foliar reflectance spectra, so that the double-peak problem could be avoided for extracting the REPs. The performance of the REPs extracted by the wavelet-based method was evaluated with data at leaf and canopy levels from a small-plot experiment of wheat crops. Our experimental results demonstrated that the wavelet-based method performed better than the two traditional methods. For the wavelet-based method, the best scale for extracting the REPs from canopy spectral data were higher than that from leaf spectral data. The findings are useful for us to understand the effect of canopy structure on REPs and the scale-dependent spectral contributions of foliar chemistry and canopy structure.