Abstract
We present the Moment Distance (MD) method to advance spectral analysis in vegetation studies. It was developed to take advantage of the information latent in the shape of the reflectance curve that is not available from other spectral indices. Being mathematically simple but powerful, the approach does not require any curve transformation, such as smoothing or derivatives. Here, we show the formulation of the MD index (MDI) and demonstrate its potential for vegetation studies. We simulated leaf and canopy reflectance samples derived from the combination of the PROSPECT and SAIL models to understand the sensitivity of the new method to leaf and canopy parameters. We observed reasonable agreements between vegetation parameters and the MDI when using the 600 to 750 nm wavelength range, and we saw stronger agreements in the narrow red-edge region 720 to 730 nm. Results suggest that the MDI is more sensitive to the Chl content, especially at higher amounts (Chl > 40 mg/cm2) compared to other indices such as NDVI, EVI, and WDRVI. Finally, we found an indirect relationship of MDI against the changes of the magnitude of the reflectance around the red trough with differing values of LAI.
Highlights
Over the past three decades, spectral indices have been devised to extract specific information for vegetation biophysical and biochemical properties
One example is the Wide Dynamic Range Vegetation Index (WDRVI) [6,28] that was initiated to enhance the dynamic range of the Normalized Difference Vegetation Index (NDVI) and later used for charactering vegetation dynamics [13,29,30] and estimating fractional vegetation cover [31]
Both show that at canopy level, small values of MD index (MDI) are associated with small values of Leaf Area Index (LAI)
Summary
Over the past three decades, spectral indices have been devised to extract specific information for vegetation biophysical and biochemical properties. The Normalized Difference Vegetation Index (NDVI) [4,16] exploits the strong differences in the red and NIR reflectances, where contrast in reflectance between vegetation and bare soil is maximal. Studies have shown the NDVI to asymptotically lose sensitivity under moderate to high biomass conditions and for certain ranges of LAI [24,25,26,27]. This shortcoming of the NDVI had led to the development of derivatives and alternative indices. One example is the Wide Dynamic Range Vegetation Index (WDRVI) [6,28] that was initiated to enhance the dynamic range of the NDVI and later used for charactering vegetation dynamics [13,29,30] and estimating fractional vegetation cover [31]
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