Table 2.

Parameters of frequency domain characteristic indexes.

$p_{16}=\frac{{{\displaystyle \sum }}_{k=1}^{K}s\left(k\right)}{K}$	$p_{17}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(s\left(k\right)-p_{16}\right)}^2}{K-1}$
$p_{18}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(s\left(k\right)-p_{16}\right)}^3}{K{\left(\sqrt{p_{17}}\right)}^3}$	$p_{19}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(s\left(k\right)-p_{16}\right)}^4}{K{p_{17}}^2}$
$p_{20}=\frac{{{\displaystyle \sum }}_{k=1}^K{f}_{k}s\left(k\right)}{{{\displaystyle \sum }}_{k=1}^{K}s\left(k\right)}$	$p_{21}=\sqrt{\frac{{{\displaystyle \sum }}_{k=1}^K{\left(f_k-p_{20}\right)}^{2}s\left(k\right)}{K}}$
$p_{22}=\sqrt{\frac{{{\displaystyle \sum }}_{k=1}^K{f_k}^{2}s\left(k\right)}{{{\displaystyle \sum }}_{k=1}^{K}s\left(k\right)}}$	$p_{23}=\sqrt{\frac{{{\displaystyle \sum }}_{k=1}^K{f_k}^{4}s\left(k\right)}{{{\displaystyle \sum }}_{k=1}^K{f_k}^{2}s\left(k\right)}}$
$p_{24}=\sqrt{\frac{{{\displaystyle \sum }}_{k=1}^K{f_k}^{2}s\left(k\right)}{{{\displaystyle \sum }}_{k=1}^{K}s\left(k\right){{\displaystyle \sum }}_{k=1}^K{f_k}^{4}s\left(k\right)}}$	$p_{25}=\frac{p_{21}}{p_{20}}$
$p_{26}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(f_k-p_{20}\right)}^{3}s\left(k\right)}{K{p_{21}}^3}$	$p_{27}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(f_k-p_{20}\right)}^{4}s\left(k\right)}{K{p_{21}}^4}$
$p_{28}=\frac{{{\displaystyle \sum }}_{k=1}^K{\left(s\left(k\right)-p_{20}\right)}^{\frac{1}{2}}s\left(k\right)}{K\sqrt{p_{17}}}$

$s\left(k\right)$ is the spectrum, $k=1,2,\dots ,K$. $K$ is the number of spectral lines, and $f_k$ is the frequency value of the $K$th spectral line.