## 5 Conclusions  
In order to increase the measurement accuracy of quantitative and qualitative analyses in coal, estimations using the LIBS, the PLS, SNR, and CA methods were performed to validate the measurement accuracy of each method. Based on the estimated concentrations using the CA, PLS, and SNR methods, the calibration curves for each of the elements (C, H, O, and S) were obtained. The calorific values were estimated based on the elemental concentrations of the coal samples acquired from three different analysis methods. The CA method showed an improved accuracy with the \(R^{2}\) of 0.971 compared to PLS and SNR with \(R^{2}\)s of 0.914 and 0.777, respectively. The calculated calorific values of coal using [PERSON]'s equation were compared to those of the chemical analysis. The error between the calculated value and the chemical analysis was a minimum of 0.16% to a maximum of 6.99% for the CA method, and those of the PLS and SNR methods ranged from 8.72 to 17.71% and from 10.7 to 22.9%, respectively. The determination of the calorific value using the CAwas in good agreement with the value obtained by conventional chemical analysis. Conceptualization, S.-M.K. and S.-J.M. ; methodology, K.-H.P. ; software, K.-H.P. ; validation, K.-H.P. ; formal analysis, S.-M.K. ; investigation, K.-H.P. ; data curation, K.-H.P. ; funding--acquisition, S.-J.M. ; writing--original draft preparation, S.-M.K. and K.-H.P. ; writing --review and editing, [PERSON]-H.C. and [PERSON]-[PERSON]; visualization, C.-M.R. ; supervision, S.-J.M. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Coal Name** & \multicolumn{3}{c}{**Concentration (\%)**} & \multicolumn{3}{c}{**Calorific Value**} & **Chemical Analysis** & \multirow{2}{*}{**Error**} \\  & **C** & **H** & **O** & **S** & **(kcal/kg)** & **(kcal/kg)** & \\ \hline GUNVOR & 73.3 & 3.77 & 15.54 & 0.89 & 6572.42 & 7360 & 10.70 \\ MSI-1 & 65.44 & 3.85 & 17.98 & 0.68 & 5855.07 & 6915 & 15.33 \\ MSJ-2 & 68.75 & 3.48 & 20.35 & 0.79 & 5895.41 & 6852 & 13.96 \\ LANNA HARITA & 68.08 & 3.18 & 18.18 & 0.61 & 5827.31 & 6619 & 11.96 \\ MACQUARIE & 67.2 & 2.48 & 19.46 & 0.86 & 5465.48 & 6705 & 18.49 \\ PEABODY & 63.49 & 2.18 & 18.21 & 0.65 & 5111.45 & 6630 & 22.90 \\ KPU & 62.94 & 2.14 & 11.12 & 0.57 & 5356.83 & 6619 & 19.07 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Predicted calorific value of various coal samples by signal-to-noise ratio method. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Coal Name** & \multicolumn{3}{c}{**Concentration (\%)**} & \multicolumn{3}{c}{**Calorific Value**} & **Chemical Analysis** & \multirow{2}{*}{**Error**} \\  & **C** & **H** & **O** & **S** & **(kcal/kg)** & **(kcal/kg)** & \\ \hline GUNVOR & 74.01 & 4.27 & 17.31 & 0.54 & 6717.97 & 7360 & 8.72 \\ MSI-1 & 67.23 & 4.42 & 15.96 & 0.47 & 6278.41 & 6915 & 9.21 \\ MSI-2 & 66.42 & 4.23 & 19.79 & 0.75 & 5988.81 & 6852 & 12.60 \\ LANNA HARITA & 69.01 & 3.24 & 18.13 & 0.76 & 5928.66 & 6619 & 10.43 \\ MACQUARIE & 67.8 & 3.71 & 18.94 & 0.69 & 5956.39 & 6705 & 11.16 \\ PEABODY & 65.9 & 2.77 & 17.65 & 0.6 & 5532.49 & 6630 & 16.55 \\ KPU & 63.59 & 2.02 & 9.32 & 0.62 & 5446.66 & 6619 & 17.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Predicted calorific value of various coal samples by partial least squares. **Funding:** This work was supported by the Technology Innovation Program (or Industrial Strategic Technology Development Program--Development of technical support platform for welding material and process) (20017251, Development of laser welding automation system for electric coil joining system to manufacture electrical vehicle motors) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). **Data Availability Statement:** Not applicable. **Acknowledgments:** This work was supported by the National Research Foundation of Korea (NRF) entitled \"Development of Coal Analyzing System Using Laser Induced Breakdown Spectroscopy for Clean Coal Power Plant\" (No. NRF-2016R1D1A1B03935556).