Estimation of nitrate nitrogen content in cotton petioles under drip irrigation based on wavelet neural network approach using spectral indices

Table 2 Calculation methods and reflectance of spectral indices

Spectral index		Abbreviation	Formula	References
Trilateral parameters	Red edge amplitude	Dr	Maximum first derivative within 680–760	[38]
	Red edge area	SDr	Sum of first derivative values in red edge	[38]
	Yellow edge amplitude	Dy	Maximum first derivative within 560–640	[39]
	Yellow edge area	SDy	Sum of first derivative values in yellow edge	[39]
	Blue edge amplitude	Db	Maximum first derivative within 490–530	[39]
	Blue edge area	SDb	Sum of first derivative values in blue edge	[39]
Vegetation index	Red edge ratio spectral index	RD	R₇₄₀/R₇₂₀	[40]
	Red edge model index	CI_red-edge	(R₇₈₀/R₇₁₀) − 1	[41]
	Normalized difference red edge index	NDRE	(R₇₉₀R₇₂₀)/(R₇₉₀ + R₇₂₀)	[42]
	Normalized difference spectral index	ND705	(R₇₅₀ − R₇₀₅)/(R₇₅₀ + R₇₀₅)	[43]
	Near infrared ratio spectral index	NIR	R₇₈₀/R₇₄₀	[44]
	Red edge ratio spectral index	RI-1 dB	R₇₃₅/R₇₂₀	[45]

ISSN: 1746-4811