Table 4.

Determination accuracies of Ni concentrations based on Vis–NIR spectral bands.

Preprocessing	PLSR		PCR		SVMR
	RMSE	R2	RMSE	R2	RMSE	R2
SG + CR	1.82	0.34	1.81	0.35	1.53	0.61
SG + CR + NOR	1.71	0.42	1.78	0.37	1.69	0.49
SG + CR + MSC	1.82	0.34	2.24	0.008	1.53	0.61
SG + CR + SNV	1.82	0.34	2.02	0.2	1.53	0.61
SG + CR + FD	0.27	0.99	1.88	0.3	1.39	0.7
SG + CR + NOR + FD	0.21	0.99	1.89	0.29	1.46	0.65
SG + CR + MSC + FD	1.29	0.67	1.86	0.32	1.28	0.75
SG + CR + SNV + FD	0.4	0.97	1.87	0.31	2.27	0.8
SG + CR + SD	0.25	0.99	1.82	0.34	1.17	0.8
SG + CR + NOR + SD	1.59	0.5	1.82	0.34	1.31	0.74
SG + CR + MSC + SD	0.19	0.99	1.78	0.37	1.12	0.8
SG + CR + SNV + SD	0.07	0.99	1.87	0.31	1.14	0.83
SG + CR + LOG	1.82	0.34	1.81	0.35	1.54	0.61
SG + CR + NOR + LOG	1.98	0.22	2.23	0.01	1.64	0.56
SG + CR + MSC + LOG	1.82	0.34	2	0.2	1.53	0.61
SG + CR + SNV + LOG	1.48	0.57	2.24	0.006	1.47	0.76