Table 3.

The validation results of PLSR models in the three time periods.

Time since deposition	Cross-validation		External validation			Expanding test
	RMSECV	R2	RMSEP	R2	RPD	RMSEP	R2	RPD
Indoor model
0.25–7 d	1.20	0.72	1.18	0.72	1.90	1.53	0.53	1.19
7–85 d	5.88	0.94	5.83	0.94	4.08	12.93	0.71	1.73
0.25–107 d	7.51	0.94	7.24	0.94	4.20	13.34	0.80	2.24
Outdoor model
0.25–7 d	0.91	0.84	1.10	0.76	2.09	2.15	0.08	0.99
7–85 d	6.35	0.93	4.77	0.96	5.14	19.99	0.31	0.70
0.25–107 d	6.31	0.96	6.43	0.95	4.42	23.61	0.38	0.77