Comparison of the cloud top heights retrieved from MODIS and AHI satellite data with ground-based Ka-band radar

To better understand the accuracy of cloud top heights (CTHs) derived from passive satellite data, ground-based Ka-band radar measurements from 2016 and 2017 in Beijing are compared with CTH data inferred from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Himawari Imager (AHI). Relative to the radar CTHs, the MODIS CTHs are found to be underestimated by -1.10 +/- 2.53 km on average and 49% of CTH differences are within 1.0 km. The AHI CTHs are underestimated by -1.10 +/- 2.27 km and 42% are within 1.0 km. Both the MODIS and AHI CTH retrieval accuracy depends strongly on the cloud depth (CD). Large differences are mainly due to the retrieval of thin clouds of CD < 1 km, especially when the cloud base height is higher than 4 km. For clouds with CD > 1 km, the mean CTH difference decreases to -0.48 +/- 1.70 km for MODIS and to -0.76 +/- 1.63 km for AHI. It is found that MODIS CTHs with higher values (i.e. > 6 km) show smaller discrepancy with radar CTH than those MODIS CTHs with lower values (i.e. < 4 km). Statistical analysis illustrate that the CTH difference between the two satellite instruments is lower than the difference between the satellite instrument and the ground-based Ka-band radar. The monthly accuracy of both CTH retrieval algorithms is investigated and it is found that summer has the smallest retrieval difference.