Table 3.

Summary of the selected spectral bands and regression coefficients for the lab-based spectral library using stepwise multiple linear regression. A dash denotes that the spectral band was not included in the model equation for the relevant heavy metal.

Spectral Bands	Coefficients of the Four Heavy Metals
	Pb	Zn	Cu	Cd
356 nm	90.729	-	-	-
358 nm	-	−4.369	-	-
359 nm	-	-	2.502	-
368 nm	-	5.055	-	-
376 nm	-	9.101	-	-
470 nm	-	−78.747	-	-
475 nm	-	127.870	-	-
484 nm	-	−53.910	-	-
618 nm	−25.105	-	-	-
651 nm	-	-	−0.628	-
1465 nm	-	-	-	−0.001
Constant	−0.057	−0.048	−0.016	0.002
R2	0.641	0.642	0.428	0.048