## 1 Introduction
\begin{table}
\begin{tabular}{c c} \hline \hline
**Spectral Range (nm)** & **300–500 nm** \\ \hline
**Spectral resolution (nm)** & 0.6 (0.2 nm \(\times\) 3 samples) \\
**Spatial resolution** & 7 km NS \(\times\) 8 km EW @ Seoul \\  & 3.5 km NS \(\times\) 8 km EW for aerosol \\  & 5\({}^{\circ}\)S–45\({}^{\circ}\)N \\
**Spatial coverage** & 75\({}^{\circ}\)E–145\({}^{\circ}\)E \\
**Observation time** & 30 min \\
**Onboard calibration** & Solar, cal light source \\ \hline \hline \end{tabular}
\end{table} 
Table 1: GEMS specifications. Measurements in the UV range can be used to estimate the radiative absorptivity of aerosols [7], while those in the visible range provide optical depth and particle size information. The large contribution of Rayleigh scattering in the UV range increases sensitivity to aerosol absorptivity and the spectral features of backward radiance mainly vary with the amount, size and scattering properties of aerosols. Additionally, the surface tends to be darker in the UV range than in the visible over land pixels [8]. Based on these sensitivities, this study develops a UV-visible algorithm to retrieve aerosol optical depth (AOD), single scattering albedo (SSA) and aerosol layer height (ALH) from GEMS measurements. As aerosol extinction varies considerably with the chemical composition and physical properties of particles, an understanding of SSA, which represents the radiative absorptivity of particles, is required to evaluate aerosol effects on climate change. Additionally, estimations of ALH are important to estimating PM concentrations [9] and to retrieving gas concentrations for species such as NO\({}_{2}\) and HCHO. [PERSON] et al. [10] suggested that temporal variations of aerosols cannot be neglected for geostationary HCHO measurements, because the aerosol height in the boundary layer and scattering properties change the air mass factor (AMF). [PERSON] et al. [11] investigated effects of aerosol properties on NO\({}_{2}\) retrieval and found that the aerosol height relative to the NO\({}_{2}\) profile is the most significant factor in calculating AMF. They found that a 2 km error in aerosol height under high solar zenith angle (SZA) conditions leads to over 60% error in AMF and thus NO\({}_{2}\) vertical column density. The estimation of ALH is particularly important to AOD and SSA retrieval using UV-visible measurements because aerosol contributions to backward radiance in the shortwave region depend on the aerosol height, AOD and SSA, simultaneously. Accordingly, the Ozone Monitoring Instrument (OMI) near-UV aerosol algorithm [12; 13; 14] applied the backscatter coefficient of an active sensor, the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP; [PERSON] et al. [15]), to the retrieval of AOD and SSA from OMI measurements. [PERSON] et al. [14] reported that the use of the CALIOP climatology value as an input to the OMI near-UV algorithm improved the agreement between OMI and Aerosol Robotic Network (AERONET) AOD [16] at five AERONET sites as indicated by an increased correlation coefficient and decreased y-intercept. As an example, at the Banizombou site (13.5\({}^{\circ}\)N, 2.7\({}^{\circ}\)E), the correlation coefficient, y-intercept and root-mean square (RMS) error improved from 0.71, 0.21 and 0.19 to 0.75, 0.17 and 0.16, respectively. Their study mainly discussed the effects of the combined use of OMI, the Atmospheric Infrared Sounder (AIRS) and CALIOP on aerosol type classification and aerosol layer assumptions. With regard to AOP retrieval, the aerosol height has been estimated by adopting the multi-sensor measurements of the A-Train (Afternoon satellite constellation; NASA [17]). [PERSON] and [PERSON] [18] retrieved SSA and aerosol height for biomass-burning smoke using the MODerate resolution Imaging Spectrophotometer (MODIS) and the OMI and [PERSON] et al. [19] expanded the algorithm to retrieve smoke and dust aerosol height by synergistic use of the CALIOP, the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Ozone Mapping and Profiler Suite (OMPS).