Table 4. Calibration and validation results for SMC estimation based on different modeling strategies.

Model	R2cal	RMSEC	R2val	RMSEP	RPD	Abbreviations
PI_RF	0.896	1.768	0.907	1.477	3.396	PIR
NDI_RF	0.856	2.104	0.872	1.479	3.245	NDIR
DI_RF	0.832	2.310	0.852	1.665	2.908	DIR
RI_RF	0.828	2.367	0.847	1.606	2.867	RIR
RI_ELM	0.823	2.301	0.820	1.984	2.322	RIE
PI_ELM	0.823	2.351	0.817	2.196	2.435	PIE
NDI_ELM	0.824	2.302	0.815	2.277	2.389	NDIE
DI_ELM	0.781	2.566	0.774	2.087	2.220	DIE