## 4 Results
### Cloud Top Height  
Collocated 4-km AGRI cloud top height products were compared with MODIS 1-km CTH retrievals. As discussed earlier (Section 3.2), the distance weighted averaged pixel-level MODIS CTH retrieval was compared to the AGRI products within the AGRI 4-km FOV.  
Based on this approach, CTH retrievals were collocated and compared for June, July, and August 2020. The statistical results of the comparison including mean absolute error, mean bias error, standard deviation, and correlation coefficient are presented in Table 3. The monthly comparison results were similar, with the CTH differences between AGRI and MODIS the smallest in June. For each month, the CTH difference was negative, and the average for these three months was \(-\)1.366 \(\pm\) 2.235 km. The negative mean cloud top height differences (AGRI-MODIS) suggest that on average, AGRI underestimated the CTH relative to MODIS by 1.366 \(\pm\) 2.235 km. The correlation coefficient value of each month was more than 0.74, indicating good correlation between the two datasets.  
Figure 3 shows the validations of CTH products of AGRI for the complete collocated samples. The color bar represents the total number of matched samples in every bin at an interval of 0.25 km. It can be seen that the collocated samples were basically concentrated on the 1:1 line. There were a large number of collocated samples in the height range of 7\(\sim\)10 km, where the AGRI CTHs was clearly lower than that of MODIS. Mean absolute error, mean bias error, standard deviation, correlation coefficient, and the number of collocated samples for the whole period was also marked, which was 1.776 km, \(-\)1.366 km, 2.235 km, and 0.759, respectively.  
To further investigate the CTH differences between AGRI and MODIS at different height, the layered MAE, MBE, and STD at an interval of 1 km for collocated samples are presented in Figure 4. It can be seen that the MAE, MBE, and STD of CTH between AGRI and MODIS showed an obvious trend of error increasing with height, and finally reached the maximum MAE and STD (MBE minimum) value at approximately 12 km. For clouds with a top height above 12 km, the MAE, MBE, and STD fluctuated slightly with height; and for clouds with a top height above about 14 km, the differences in CTH between AGRI and MODIS decreased rapidly. The large negative differences were associated with high clouds with CTH in the range of approximately 12 to 14 km. The positive differences were associated with low-level clouds (<4.5 km).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Month** & **Collocated Samples** & **MAE (km)** & **MBE (km)** & **STD (km)** & **CC** \\ \hline Jun. & 510,529 & \(1.501\) & \(-1.037\) & 2.006 & 0.773 \\ Jul. & 492,715 & \(1.902\) & \(-1.541\) & 2.266 & 0.760 \\ Aug. & 498,454 & \(1.933\) & \(-1.531\) & 2.383 & 0.748 \\ ALL & 1,501,698 & \(1.776\) & \(-1.366\) & 2.235 & 0.759 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Cloud top height over the Tibetan Plateau (TP) statistics of the mean absolute error (MAE), mean bias error (MBE), standard deviation (STD), and correlation coefficient (CC) between AGRI and MODIS during the periods June, July and August 2020. MODIS cloud top height retrievals are used as a benchmark.