## 6 Conclusions  
This paper compared the FY-4A/AGRI and Terra/MODIS Collection 6 pixel-level cloud mask and cloud top height results over the Tibetan Plateau to better understand the cloud products' performance and characteristics of the new generation GEO satellite imager FY-4A/AGRI. Additionally, MODIS cloud retrievals were used as benchmarks. To facilitate the comparison, an accurate and computationally efficient collocation algorithm was developed. The comparison was conducted for the period of June, July, and August 2020. The comparison results showed that in general, the AGRI cloud mask over the TP is reliable for cloudy conditions. On average, AGRI underestimates the cloud top heights. For cloud detection, the two approaches (AGRI and MODIS) showed a fractional agreement of 0.93 for cloudy conditions, and 0.73 for clear-sky scenes when the MODIS cloud mask retrievals were used as a benchmark. However, there were distinct differences for \"probably clear\" and \"probably cloudy\" scenes, mainly due to the two totally different theoretical methodologies used by AGRI and MODIS. The agreement was generally better for cloudy conditions than for clear scenes. Significant disagreement found in the southern part of the TP for clear-sky conditions can be partially attributed to only a few clear pixels during the summer monsoon season over that region. The largest disagreement for cloudy-sky scenes occurred in some small regions located in the southern, southwestern, and northeastern part of the TP. AGRI and MODIS can obtain good agreement for detecting clouds with higher CTH, and AGRI tends to miss lower CTH clouds due to the lack of thermal contrast between the clouds and the surface of the TP. For cloud top height products, the comparison shows that the mean cloud top height differences (AGRI-MODIS) were negative (\(-1.366\pm 2.235\) km), suggesting that on average, AGRI underestimates the CTH relative to MODIS. The CTH differences between AGRI and MODIS showed an obvious trend of increasing error with height, and reached the largest difference at approximately 12 km. In general, there were few CTH differences, especially over the eastern part of the TP. The largest differences due to significant underestimation by AGRI occurred over small areas located in the southern, southwestern, and northern part of the TP. For the southern and southwestern part of the TP, the obvious CTH differences can be partially attributed to the CTH underestimation of clouds with high CTH (>12 km). Figure 7: A 0.5\({}^{\circ}\) grid of the **(a)** mean cloud top height absolute error (MAE) and **(b)** mean cloud top height bias error (MBE) are presented. For each 0.5\({}^{\circ}\) grid box, the mean of all the collocated differences (AGRI-MODIS) within the box was calculated based on the same dataset with Table 3. In **(a)**, the deep blue value shows that AGRI and MODIS have the same cloud top height results, while the red values represent that there are large CTH differences between these two systems; in **(b)**, a negative difference (blue) results when the mean AGRI cloud top height was lower than MODIS, while the deep red values represent AGRI overestimating the cloud top height relative to MODIS (the maximum bias value was 0.564 km). Blank space means that there were no matched pixels under the corresponding conditions. **Author Contributions:** Conceptualization, W.X. and D.L. ; Methodology, W.X. ; Software, W.X. ; Validation, W.X. ; Formal analysis, W.X. ; Investigation, W.X. ; Resources, D.L. ; Data curation, W.X. ; Writing--original draft preparation, W.X. ; Writing--review and editing, W.X. ; Visualization, W.X. ; Supervision, D.L. ; Project administration, D.L. ; Funding acquisition, D.L. Both authors have read and agreed to the published version of the manuscript.