Sensitivity test of GOCI dust aerosol index with aerosol absorptivity by using radiative transfer simulation and comparison with AERONET aerosol optical properties

For the monitoring of aerosol properties in East Asia using the Geostationary Ocean Color Imager (GOCI), the GOCI Yonsei aerosol retrieval (YAER) algorithm was developed and has been improved continuously since 2011. GOCI YAER algorithm contains several aerosol models consisted of various optical properties such as aerosol optical depth (AOD), fine-mode fraction (FMF), and single scattering albedo (SSA) for assuming every possible aerosol status. Then, AOD at 550 nm is retrieved from selected aerosol models which show least difference between observed top-of-atmosphere (TOA) reflectance and simulated TOA reflectance in terms of spectral AODs. Current inversion method is optimized for spectral AODs, especially AOD at 550 nm. Therefore, GOCI YAER AOD, FMF, and Angstrom exponent show reliable accuracy with ground-based AERONET and satellite-based MODIS and VIIRS products. However, SSA shows least accuracy (R = 0.2) with AERONET SSA, which is different from AOD, FMF, and AE. To improve accuracy of SSA retrieval, the inversion method should reflect a characteristic of aerosol absorptivity well, not only in the aerosol model construction as forward modeling. UV aerosol index from TOMS and OMI measurements, calculated by using 354 and 388 nm, provides the extent of aerosol absorptivity, which can be used for the improvement of aerosol model quality between absorbing and non-absorbing aerosol model. Instead of UV index, a dust aerosol index (DAI) can be calculated using two visible channels such as 412 and 443 (or 490) nm. Heavy dust plume, which is coarse and absorbing aerosol, in 47 April 2012 show DAI of 5, but heavy haze plume, which is fine and non-absorbing aerosol, in 6 May 2012 shows DAI close to 0. To find relationship between DAI and aerosol absorptivity properties, sensitivity is tested by using radiative transfer model (RTM), and retrieved GOCI DAI from observed TOA reflectance is compared with ground-based AERONET SSA and other optical properties. Both of simulation using RTM and comparison with ground-based measurement pursue understanding and finding relation between DAI and other optical properties as theoretically and empirically, and improving GOCI SSA retrieval accuracy, eventually.