NASA has posted an example of satellite and lidar observation of ash clouds for 16 May.
As NASA puts it
One reason for widespread closures was the challenge in knowing where the ash was. Many satellites can provide a bird’s-eye view (such as the top, nighttime image) that can identify thick plumes of ash, but few satellites can tell how high the ash is in the atmosphere. The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, however, records a vertical profile of the atmosphere, which reveals the altitude of ash clouds, shown in the lower image. These observations help modelers in volcanic ash advisory centers improve forecasting models and issue more accurate warnings to pilots and others with aviation interests.
Nighttime Ash Tracking with CALIPSO : Image of the Day