Spatial distribution analysis of the OMI aerosol layer height: a pixel-by-pixel comparison to CALIOP observations

Short summary

Aerosol layer height (ALH) was retrieved from the OMI 477 nm O₂–O₂ band and its spatial pattern evaluated over selected cloud-free scenes. We used a neural network approach previously trained and developed. Comparison with CALIOP aerosol level 2 products over urban and industrial pollution in east China shows consistent spatial patterns. In addition, we show the possibility to determine the height of thick aerosol layers released by intensive biomass burning events in South America and Russia.

Key figures

Maps of Aqua MODIS τ (550 nm) from the combined DT and DB Collection 6 (see Sect. 2.3) and collocated OMI aerosol index from near-UV (UVAI) values (see Sect. 3) over cloud-free scenes for the urban and industrialized cases in eastern China. The dark thick lines represent the track of CALIPSO space-borne sensor over the selected case studies: (a, d) 2 October 2006, (b, e) 6 October 2006, and (c, f)1 November 2006.

Retrieved OMI ALH compared with vertical profile of aerosol total backscatter coefficient (532nm) from the CALIOP L2 product. Maximal distance between OMI pixels and CALIOP ground track is 50 km. Only cloud-free OMI pixels, collocated with Aqua MODIS Collection 6 aerosol cells, τ (550 nm) ≥ 0.55 (from the MODIS DT and DB algorithms), are selected: (a) 2 October 2006, (b) 6 October 2006, and (c) 1 November 2006.

Maps of Aqua MODIS τ (550 nm) from the combined DT and DB Collection 6 (see Sect. 2.4) and collocated OMI aerosol index from near-UV (UVAI) values (see Sect. 3) over cloud-free scenes and intensive biomass burning episodes. The dark thick lines represent the track of CALIPSO space-borne sensor over the selected case studies: (a, e) South America on 24 August 2006, (b, f) South America on 30 September 2007, (c, g) eastern Russia on 8 October 2010, and (d, h) eastern Russia on 23 June 2012.

Retrieved OMI ALH compared with CALIOP along-track vertical profile observations for biomass burning case over South America: (a) CALIOP L2 aerosol total backscattering (532 nm), (b) CALIOP L2 aerosol backscattering (1064 nm), (c) CALIOP L1 attenuated backscattering (532 nm), and (d) CALIOP L1 attenuated backscattering (1064 nm).

Retrieved OMI ALH compared with CALIOP L1 along-track vertical profile observations (532 and 1064 nm) for biomass burning cases: (a, b) 30 September 2007 in South America, (c, d) 8 August 2010 in eastern Russia, and (e, f) 23 June 2012 in eastern Russia.

Abstract

A global picture of atmospheric aerosol vertical distribution with a high temporal resolution is of key importance not only for climate, cloud formation, and air quality research studies but also for correcting scattered radiation induced by aerosols in absorbing trace gas retrievals from passive satellite sensors. Aerosol layer height (ALH) was retrieved from the OMI 477 nm O₂ − O₂ band and its spatial pattern evaluated over selected cloud-free scenes. Such retrievals benefit from a synergy with MODIS data to provide complementary information on aerosols and cloudy pixels. We used a neural network approach previously trained and developed. Comparison with CALIOP aerosol level 2 products over urban and industrial pollution in eastern China shows consistent spatial patterns with an uncertainty in the range of 462–648 m. In addition, we show the possibility to determine the height of thick aerosol layers released by intensive biomass burning events in South America and Russia from OMI visible measurements. A Saharan dust outbreak over sea is finally discussed. Complementary detailed analyses show that the assumed aerosol properties in the forward modelling are the key factors affecting the accuracy of the results, together with potential cloud residuals in the observation pixels. Furthermore, we demonstrate that the physical meaning of the retrieved ALH scalar corresponds to the weighted average of the vertical aerosol extinction profile. These encouraging findings strongly suggest the potential of the OMI ALH product, and in more general the use of the 477 nm O₂ − O₂ band from present and future similar satellite sensors, for climate studies as well as for future aerosol correction in air quality trace gas retrievals.