Title: Comparison of dust layer heights from active and passive satellite sensors
Abstract: Abstract. Aerosol layer height is an essential parameter to understand the impact of aerosols on the climate system. As part of the European Space Agency Aerosol_cci project, aerosol layer height as derived from passive thermal and solar satellite sensors measurements, have been compared with aerosol layer heights estimated from CALIOP measurements. The Aerosol_cci project targeted dust type aerosol for this study. This ensures relatively unambiguous aerosol identification by the CALIOP processing chain. Dust layer height was estimated from thermal IASI measurements by four different algorithms (BIRA-IASB, DLR, LMD, LISA) and from solar GOME-2 (KNMI) and SCIAMACHY (IUP) measurements. Due to differences in overpass time of the various satellites, a trajectory model was used to move the CALIOP derived dust heights in space and time to the IASI, GOME-2 and SCIAMACHY dust height pixels. It is not possible to construct a unique dust layer height from the CALIOP data. Thus two CALIOP derived layer heights were used: the cumulative extinction height defined to be the height where the CALIOP extinction column is half of the total extinction column; and the geometric mean height which is defined as the geometrical mean of the top and bottom heights of the dust layer. In statistical average over all IASI data there is a general tendency to a positive bias of 0.5–0.8 km against CALIOP extinction-weighted height for three of the four algorithms assessed, while the fourth algorithm has almost no bias. When comparing to geometric mean height there is a shift by −0.5 km for all algorithms (getting close to zero for the three algorithms and turning negative for the fourth). The standard deviation of all algorithms is quite similar and ranges between 1.0 and 1.4 km. When looking at different conditions (day, night, land, ocean) there are is more detail in variabilities (e.g. all algorithms overestimate more at night than at day).