Retrieval of Water Vapor over Asia from Geostationary Environment Monitoring Spectrometer (GEMS) Measurements

Water vapor plays an important role in the energy budget since it is one of the main drivers of the greenhouse effect. Water vapor has absorption lines over wide wavelength ranges. Among them, retrieval of water vapor in the visible channels is advantageous for tropospheric water vapor observations. It is due to higher sensitivity in the planetary boundary layer regardless of land and ocean than in longer wavelengths. Therefore, we present a water vapor retrieval algorithm in the visible channels for the Geostationary Environment Monitoring Spectrometer (GEMS) onboard the GEO-KOMPSAT2B satellite. The algorithm utilizes the direct fitting method developed by Smithsonian Astrophysical Observatory (SAO). The retrieval process is composed of two steps: the spectral fitting is performed to optimize slant column (SCD) retrievals. Then, conversion of retrieved SCDs into vertical column densities (VCDs) is conducted hereafter. In this framework, the retrieval demonstrates that it represents the diurnal cycle of water vapor columns over Asia. It can also detect the water vapor transport patterns (e.g., Atmospheric River (AR)) over Asia. Since water vapor product is applicable not only for examining the climate patterns but also for improving the numerical weather model, GEMS H2O product is expected to be conducive to climate model studies.