## 3 Results
### Cloud Cover--Case Studies  
The advantages of using the proposed software, i.e., the RO approach, are demonstrated through four case studies. The first example (Figure 9) presents a situation with two cloud layers. The LO identified that the lower layer at the height of 6,000 ft was associated with cloud cover SCT (3-4 oktas, Table 4), whereas the second layer at the height of 12,000 ft covered the full sky, i.e., it was OVC (eight oktas). On the contrary, the standard AWOS detected only the second layer of clouds, as the lower layer (visible on Figure 9, as the dark area to the N and NW) was not directly above the ceilometer (located in the SE parts of the airport); thus, the lower layer was invisible to the standard AWOS. Overall, the RO was identical with the LO in terms of the cloud coverage, and they were also close in terms of the cloud base height (Table 4). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **AWOS** & **RO** & **LO** \\ \hline Maximum cloud cover & OVC & SCT & SCT \\ Minimum cloud base [ft] & 12,000 & 7000 & 6000 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Determination of the maximum cloud cover and the lowest cloud base height using three different approaches at LZTT, on 11 September 2018, at 09:20 UTC. AWOS—Automated Weather Observation System, RO—Remote observer, LO—Local observer, OVC—overcast, and SCT—scattered. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{5}{c}{**AWOS**} \\ \cline{3-6}  & & **FEW** & **SCT** & **BKN** & **OVC** \\ \hline \multirow{4}{*}{LO} & FEW & **3** & 5 & 10 & 8 \\  & SCT & 3 & **2** & 15 & 13 \\ \cline{1-1}  & BKN & - & - & **10** & 67 \\ \cline{1-1}  & OVC & - & - & 4 & **41** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: A comparison of the maximum cloud cover values determined by the AWOS and the local observers (LO). The exact matches along the diagonal are indicated in bold. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{5}{c}{**RO**} \\ \cline{3-6}  & FEW & **SCT** & **BKN** & **OVC** \\ \hline \multirow{4}{*}{LO} & FEW & **56** & 10 & - & - \\  & SCT & 2 & **21** & 10 & 1 \\ \cline{1-1}  & BKN & - & 2 & **68** & 7 \\ \cline{1-1}  & OVC & - & - & 13 & **35** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The same as in Table 2, but for the remote observers (RO) and the local observers (LO). The second example is associated with the presence of towering cumulus (TCU) up to 16 km from the airport. This type of cloud, together with cumulonimbus (CB), are significant cloud types in aviation; thus, their detection is of a general interest. Both the local and the remote observers identified TCU correctly (Figure 10), with no difference in the height of the minimum cloud base (Table 5). Conversely, the standard AWOS does not have an ability to recognize these types of clouds significant to the airport operation [1]. Nor did the standard AWOS detect the height of these clouds, because they are not in the sky above the ceilometer, but rather on the N-NW horizon. Arrows in Figure 10 also indicate further cloud types (altocumulus and cirrus); however, these are not significant in aeronautics, and they are not indicated in the METAR/SPEC messages. The third example demonstrates a special case, when, despite the sky being covered significantly, there is a 'hole' in the cloud cover (blue sky) right above the ceilometer. The all sky image in Figure 11 depicts cloud cover BKN (5-7 ktas), which was recognized by both the LO and the RO (Table 6). However, the standard AWOS failed to determine the cloud cover accurately due to a 'hole' in the cloud cover above the ceilometer, and indicated significantly underestimated cloud cover. \begin{table}
\begin{tabular}{c c c c} \hline  & **AWOS** & **RO** & **LO** \\ \hline Maximum cloud cover & -1  & FEW & FEW \\ Minimum cloud base [ft] & - & 4000 & 4000 \\ TCU or CB & - & TCU & TCU \\ \hline \end{tabular}
\end{table} 
Table 5: The same as Table 4, but for 14 September 2018, at 09:50 UTC. TCU—towering cumulus and CB—cumulonimbus.