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Table 2 Vegetation indices (VIs) used in the study and related source references

From: Estimation of vegetation water content using hyperspectral vegetation indices: a comparison of crop water indicators in response to water stress treatments for summer maize

Index

Formula

References

Indirect water-sensitive spectral VIs

 Normalized difference vegetation index (NDVI)

(Rnir − Rred)/(Rnir+ Rred)

[42]

 Red edge normalized ratio (NRred edge)

(R750 − R710)/(R750 + R710)

[43]

 Green chlorophyll index (CIgreen)

(R750/R550) − 1

[44]

 Red edge chlorophyll index (CIred edge)

(R750/R710) − 1

[44]

Direct water-sensitive spetral VIs

 Water index (WI)

R900/R970

[45]

 Moisture stress index (MSI)

R1600/R820

[46]

 Simple ratio water index (SRWI)

R860/R1240

[47]

 Normalized difference water index (NDWI)

(R860 − R1240)/(R860 + R1240)

[48]

 Normalized difference water index centered at 1640 nm (NDWI1640)

(R858 − R1640)/(R858 + R1640)

[49]

 Normalized difference water index centered at 2130 nm (NDWI2130)

(R858 − R2130)/(R858 + R2130)

[49]

  1. Rnir and Rred are the averaged reflectance among the waveband range to match MODIS data in the near-infrared (841–876 nm) and red (620–670 nm) wavelengths, respectively