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, 5 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 10 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, 15 ocean) there is more detail in variabilities (e.g. all algorithms overestimate more at night than at day).

Contribution of IASI to the Observation of Dust Aerosol Emissions (Morning and Nighttime) Over the Sahara Desert

“…In the same study, spatial distributions of AOD have also been compared to MODIS/TERRA and Spinning Enhanced Visible and Infrared Imager (SEVIRI), showing a strong consistency. Still at daily scale, IASI altitudes have been compared with CALIOP mean altitudes (Kylling et al, 2018). Comparisons with CALIOP are not easy to interpret, given the different characteristics of the two instruments: much higher vertical resolution of CALIOP (IASI provides information on the atmospheric vertical structure with a resolution of ~1 km in the lower troposphere to 2 km in the free troposphere, Chalon et al, 2001; see also the iasi.cnes.fr/en and https://www.eumetsat.int websites), observation times differing by about 4 hr, difference in the altitude definition, difference in the spatial resolution, low CALIOP repeat cycle of 16 days, lower CALIOP daytime signal‐to‐noise ratio.…”

Reducing Aerosol Forcing Uncertainty by Combining Models With Satellite and Within‐The‐Atmosphere Observations: A Three‐Way Street

“…Although coverage by these measurements is currently limited, their precision has demonstrated value in constraining and/or validating models aimed at simulating downwind wildfire smoke and volcanic ash dispersion (e.g., Zhu et al, 2018a;Vernon et al, 2018). A number of satellite-based, passive-imager spectral techniques, at wavelengths ranging from the ultraviolet (UV) to the infrared, offer greater aerosol layer-height coverage, at the cost of additional assumptions that increase uncertainty (e.g., Jeong & Hsu, 2008, Griffin et al, 2020Go et al, 2020;Kylling et al, 2018;Lu et al, 2021;Lyapustin et al, 2020). Passive-imager techniques, especially in UV channels, have also been effective in constraining aerosol occurrence, and even amount, over cloudy scenes (e.g., Torres et al, 2012;Meyer et al, 2015;Sayer et al, 2019).…”

Estimates of the vertical distribution of desert dust and conden-sation nuclei over the Mediterranean, with the synergistic use of active and passive remote sensing techniques

“…Beyond its climatological value, our CALIPSO dust product has been utilized to study the physics of the dust cycle in the atmosphere (Georgoulias et al 2016;Solomos et al 2017;Kosmopoulos et al 2017;Amiri-Farahani et al 2017;Kylling et al 2017).…”