The ash cloud heights retrieved using the GOES-R methodology (IR method) are compared to CALIPSO cloud boundaries inferred from the total attenuated backscatter. Ash clouds were identified by matching the CALIOP lidar data to SEVIRI infrared measurements. These are cases where the ash cloud was obvious in the SEVIRI infrared data (but not necessarily in the CALIOP data alone). Nearly all of the ash clouds observed by CALIPSO were optically thin. As such, the GOES-R approach, which accounts for transmission of radiation through the cloud, performs much better than the opaque cloud assumption.