## 2 Materials and Methods
### DEM Validation
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Dataset** & **Shapiro-Wilk** & **Wilcoxon Signed-Rank Test** & **Pearson’s Correlation Test** \\  & **Normality Test** & _p-Value_ & _Correlation Coefficient_ \\ \hline D\_field & 8.49 \(\times 10^{-6}\) & 0.063 & 2.20 \(\times\) 10\({}^{-16}\) & 0.91 \\ D\_dem & 7.90 \(\times\) 10\({}^{-7}\) & 0.064 & 2.20 \(\times\) 10\({}^{-16}\) & 0.97 \\ \hline D\_field without outliers & 3.53 \(\times\) 10\({}^{-6}\) & 0.064 & 2.20 \(\times\) 10\({}^{-16}\) & 0.97 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the statistical tests of the population with and without outliers. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**TYPE** & **Doline** & **Depth\_Field** & **Z\_Min** & **Z\_Max** & **Z\_Mean** & **2D\_Surf.** & **Perimeter** & **Depth\_DEM** & **\(\Delta\)D** & **\(\mid\Delta\)D\(\mid\)** \\  & **ID** & **(m)** & **(m)** & **(m)** & **(m)** & **(m\({}^{2}\))** & **(m)** & **(m)** & **(m)** & **(m)** \\ \hline funnel & 201 & 17 & 1949 & 1963 & 1959 & 4608 & 172 & 14 & \(-\)3 & 3 \\ funnel & 217 & 20 & 1910 & 1928 & 1922 & 7661 & 241 & 18 & \(-\)2 & 2 \\ funnel & 227 & 26 & 1915 & 1940 & 1932 & 11,133 & 294 & 24 & \(-\)2 & 2 \\ funnel & 228 & 32 & 1910 & 1939 & 1929 & 12,446 & 305 & 29 & \(-\)3 & 3 \\ funnel & 220 & 25 & 1898 & 1919 & 1912 & 9029 & 261 & 21 & \(-\)4 & 4 \\ funnel & 184 & 26 & 1868 & 1891 & 1885 & 16,469 & 386 & 23 & \(-\)3 & 3 \\ funnel & 213 & 34 & 1860 & 1922 & 1900 & 61,677 & 869 & 62 & 28 & 28 \\ mixed & 322 & 11 & 1853 & 1864 & 1858 & 7505 & 249 & 11 & 0 & 0 \\ mixed & 6 & 15 & 1915 & 1929 & 1924 & 7672 & 254 & 13 & \(-\)2 & 2 \\ mixed & 199 & 26 & 1934 & 1957 & 1949 & 12,229 & 317 & 24 & \(-\)2 & 2 \\ mixed & 200 & 13 & 1948 & 1958 & 1955 & 8326 & 282 & 11 & \(-\)2 & 2 \\ mixed & 202 & 10 & 1963 & 1972 & 1968 & 7782 & 265 & 9 & \(-\)1 & 1 \\ mixed & 285 & 6 & 1885 & 1891 & 1888 & 5602 & 204 & 7 & 1 & 1 \\ mixed & 352 & 9 & 1921 & 1928 & 1925 & 5237 & 194 & 7 & \(-\)2 & 2 \\ mixed & 17 & 60 & 1882 & 1940 & 1917 & 50,258 & 569 & 58 & \(-\)1 & 1 \\ mixed & 248 & 8 & 1873 & 1891 & 1886 & 26,056 & 591 & 18 & 10 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._ \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Dataset** & **Shapiro-Wilk** & **Wilcoxon Signed-Rank Test** & **Pearson’s Correlation Test** \\  & **Normality Test** & _p-Value_ & _Correlation Coefficient_ \\ \hline D\_field & 8.49 \(\times\) 10\({}^{-6}\) & 0.063 & 2.20 \(\times\) 10\({}^{-16}\) & 0.91 \\ D\_dem & 7.90 \(\times\) 10\({}^{-7}\) & 0.064 & 2.20 \(\times\) 10\({}^{-16}\) & 0.97 \\ \hline D\_field without outliers & 3.53 \(\times\) 10\({}^{-6}\) & 0.064 & 2.20 \(\times\) 10\({}^{-16}\) & 0.97 \\ D\_dem without outliers & 1.06 \(\times\) 10\({}^{-5}\) & 0.064 & 2.20 \(\times\) 10\({}^{-16}\) & 0.97 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of the statistical tests of the population with and without outliers. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **D\_Field (m)** & **D\_Dem (m)** & **\(\Delta\)D (m)—All Measures** & **\(\Delta\)D (m)—No Outliers** \\ \hline minimum & 1 & 1 & 0 & 0 \\ first quartile & 6 & 5 & 1 & 1 \\ median & 11 & 11 & 2 & 2 \\ mean & 14 & 14 & 3 & 2 \\ third quartile & 20 & 18 & 3 & 3 \\ maximum & 67 & 62 & 28 & 7 \\ st. deviation & 11 & 12 & 4 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Basic statistics of the depth (D) and depth difference (\(\Delta\)D) of the investigated dolines. The boxplots in Figure 8 testify a good accuracy of the population without outliers (mean \(\Delta\)D value of 2 \(\pm\) 2 m). The dataset with outliers shows a mean \(\Delta\)D value of 3 \(\pm\) 4 m. The main differences represented by the 5 dolines identified as outliers range from 9 to 28 m, whereas the maximum error in the dataset without outliers is 7 m. As shown in the right boxplots of Figure 8, the main errors (both mean and median >2 m) are referred to funnel-shaped and bowl-shaped dolines.