Table 2.

The statistical results of yield estimation obtained using the optimal SIs—that is, the plant biochemical index (PBI)—the ground-measured winter-wheat plant height (H), and the winter-wheat plant height extracted from UAV-based hyperspectral images (H_CSM), respectively, for different growth stages.

Growth Stage	Parameter	Linear Regression
		R2	RMSE (kg/ha)	NRMSE (%)
Jointing	PBI	0.21	1253.69	21.51
	H	0.01	1404.43	24.09
	HCSM	0.05	1380.85	23.69
Flagging	PBI	0.44	1056.38	18.12
	H	0.09	1344.59	23.07
	HCSM	0.22	1250.78	21.46
Flowering	PBI	0.63	856.61	14.70
	H	0.13	1319.21	22.63
	HCSM	0.23	1247.67	21.41

Note: R²: coefficient of determination; RMSE: root-mean-square error; NRMSE: normalized root-mean-square error.