Table 3.

Summary of the most used spectral indices for monitoring of crop stress. ρRED, ρGREEN and ρBLUE, represent the spectral reflectance of red band, green band and blue band respectively. ρNIR: reflectance of the near-infrared band. ρSWIR: reflectance of the shortwave-infrared band. ρMIDIR: reflectance of the mid-infrared band.

name	abbreviation	formula	description with related traits and challenges	references
difference vegetation index	DVI	NIR – Red	sensitive to the amount of vegetation; simplest ratio; does not deal with the difference between reflectance and radiance caused by the atmosphere or shadows	Jordan [136]
simple ratio	SR	ρNIR/ρRED	ratio of NIR scattering to chlorophyll and light absorption used for simple vegetation distinction	Jordan [136]
modified simple ratio	MSR	(ρ800 − ρ445)/(ρ680−ρ445)	a combination of renormalized NDVI and SR to improve sensitivity to vegetation characteristics	Chen [137]
modified red-edge simple ratio index	MRESR	(ρ750 – ρ445)/(ρ705 nm – ρ445)	vegetation for low nitrogen stress	Datt [138]
normalized difference vegetation index	NDVI	(ρNIR – ρRED)/(ρNIR + ρRED)	measuring green vegetation through normalized ration ranging from −1 to 1	Rouse et al. [135]
green normalized difference vegetation index	GNDVI	(ρNIR − ρGREEN)/(ρNIR + ρGREEN)	modification of NDVI, more sensitive to chlorophyll content	Agapiou et al. [139]
red-edge normalized difference vegetation index	RENDVI	(ρNIR − ρRedEdge)/(ρNIR + ρRedEdge)	modification to NDVI, using red-edge information to probe for changes in vegetation health	Gitelson & Merzlyak [140]
green optimized soil adjusted vegetation index	GOSAVI	(ρNIR − ρGREEN)/(ρNIR + ρGREEN + 0.16)	variation of NDVI to reduce the soil effect	Sripada et al. [141]
optimized soil adjusted vegetation index	OSAVI	(ρNIR − ρRED)/(ρNIR + ρRED + 0.16)	provides greater soil variation than SAVI for low vegetation cover	Sripada et al. [141]
green ratio vegetation index	GRVI	ρNIR/ρGREEN	related with leaf production and stress	Sripada et al. [141]
red, green ratio index	RGRI	ρRED/ρGREEN	relative expression of leaf redness caused by anthocyanin to that of chlorophyll	Gamon & Surfus [142]
nonlinear index	NLI	(ρNIR2 − ρRED)/(ρNIR2 + ρRED)	modification of NDVI used to emphasize linear relations with vegetation parameters	Goel & Qin [143]
leaf water content index	LWCI	log(1 − (ρNIR − ρMIDIR))/ −log(1 − (ρNIR − ρMIDIR))	moisture content of the leaf canopy	Ceccato et al. [144]
enhanced vegetation index	EVI	2.5[(ρNIR – ρRED)/(ρNIR + 6 * ρRED – 7.5 * ρBLUE + 1)]	optimize the vegetation signal with improved sensitivity in high biomass regions	Huete et al. [145]
photochemical reflectance index	PRI	(ρ531 − ρ570)/(ρ531 + ρ570)	indicator of leaf and plant canopy photosynthetic efficiency	Gamon et al. [146]
structure insensitive pigment index	SIPI	(ρ800 − ρ445)/(ρ800 + ρ680)	Indicator of increased canopy stress (carotenoid pigment)	Pen̄Uelas et al. [147]
modified red edge NDVI	mRENDVI	(ρ750 − ρ705)/(ρ750 + ρ705 −2 * ρ445)	capitalizes on the sensitivity of the vegetation red-edge to small changes in canopy foliage content, gap fraction and senescence	Sims & Gamon [35]
normalized difference water index	NDWI	(ρNIR − ρSWIR)/(ρNIR + ρSWIR)	measures the change in the water content of leaves by using the NIR and SWIR bands	Gao [148]
moisture stress index	MSI	(ρ1599)/(ρ819)	sensitive to increasing leaf water content; used in canopy stress analysis and productivity prediction	Behmann et al. [69]
normalized difference infrared index	NDII	(ρ819 − ρ1649)/(ρ819 + ρ1649)	sensitive to changes in water content of plant canopies; used in crop agricultural management, forest canopy monitoring, and vegetation stress detection	Hardisky et al. [149]
plant senescence reflectance index	PSRI	(ρ680 − ρ500)/ρ750	an increase in PSRI indicates increased canopy stress (carotenoid pigment), the onset of canopy senescence, and plant fruit ripening; vegetation health monitoring, plant physiological stress detection, and crop production and yield analysis	Merzlyak et al. [150]