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A cloud identification and profiling algorithm is being developed for the Multi-Spectral Imager (MSI), which is one of the four instruments that the Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) spacecraft will feature. During recent work, we noticed that the MSI response function could shift substantially among some wavelengths (0.67 and 1.65 µm bands) owing to the smile effect, that is an effect in which a shift in the center wavelength appears as a distortion in the spectral image. We evaluated how the smile effect affects the cloud retrieval product qualitatively and quantitatively. We chose four detector pixels from bands 1 and 3 with the nadir pixel as the reference to elucidate how the smile effect error affects the cloud optical thickness (τ) and effective cloud droplet radius (re) by simulating the MSI forward radiation with Comprehensive Analysis Program for Cloud Optical Measurement (CAPCOM). We also evaluated the error in simulated scenes from a global cloud system resolving model and a satellite simulator to measure the effect on actual observation scenes. For typical shallow warm clouds (τ = 8, re = 8 μm), the smile effect on the cloud retrieval was not significant in most cases (up to 6 % error). For typical deep convective clouds (τ = 8, re = 40 μm), the smile effect on the cloud retrieval was even less significant in most cases (up to 4 % error). Moreover, our results from two oceanic scenes using the synthetic MSI data agreed well with the forward radiation simulation, indicating that the error from the smile effect was generally within 10 %. [ABSTRACT FROM AUTHOR]

We estimated the average dust single scattering albedo ([[omega].sub.0]) over the Sahara using four years of moderate resolution imaging spectroradiometer data. The method employed is based on the theory that the critical surface reflectance ([[rho].sub.c]) for which the reflectance at the top-of-the-atmosphere is not influenced by the variability of dust optical thickness depends on [[omega].sub.0]. The average dust absorption over the Sahara was estimated to be smaller than that previously reported in the literature, and this may be causing the cooling of the climate system. Our method enables one to estimate [[omega].sub.0] from data with a variety of aerosol optical thickness values using samples in the vicinity of [[rho].sub.c]. Use of satellite data over large areas and for long periods enables quantification of the average dust absorption over the entire Sahara. OCIS codes: 010.0280, 010.1110, 010.5620, 280.1100.

We conducted vicarious calibration of the Global Imager (GLI) in visible to near-infrared channels over different targets. For calibration over the ocean, we used the normalized water-leaving radiance derived from the Marine Optical Buoy (MOBY) and the aerosol optical properties (aerosol optical depth, size distribution, and refractive index) obtained through the Aerosol Robotic Network (AERONET). For calibration over land, we used the ground-based measurement data at Railroad Valley Playa. The following GLI characteristics are recognized from the calibration results. First, GLI underestimates the radiance in channels 1, 2, 4, and 5. Next, in the near-infrared channels, there is good agreement between the observed and simulated radiance over bright targets. On thee other hand, it is suggested that the GLI overestimates the radiance over dark targets (e.g., on the order of 15% at 4.0 W/[m.sup.2]/[micro]/sr in channels 18 and 19). Furthermore, we evaluated these calibration results over different targets taking into account the difference in the target radiance and in the accuracy between the two results. This combined evaluation of vicarious calibration results suggests the possibility that the GLI-observed radiance has offset radiance versus the simulated radiance. Index Terms--Global Imager (GLI), Marine Optical Buoy (MOBY), radiative transfer, vicarious calibration.

We have developed a global vicarious calibration scheme for spaceborne ocean-color sensors, simulating top-of-atmosphere radiance globally using a radiative transfer model, SeaWiFS Level 3 eight-day mean products, and an in-water optical model. This is a relative calibration against two channels used to detect aerosol properties; however, it enables us to determine the spatial and temporal characteristics of the vicarious calibration coefficients (Kvc) without in situ observations. We applied this scheme to the NASDA Global Imager (GLI), which operated from January 25, 2003 to October 24, 2003. Kvc exhibited the following properties: 1) channel characteristics of 1.0-1.1 (GLI was lower than the simulation) in channels 1-9 (380-565 nm), nearly 1.0 in channels 10-19 (625-865 nm), and 0.91-0.98 in channels 24-29 (1050-2210 nm); 2) scan-angle dependency and its temporal changes in channels 1-3; and 3) scan-mirror side differences and temporal changes. Applying Kvc to GLI ocean-color processing produced outputs consistent with the ground observation data. This scheme is also useful for generating consistent products from different ocean-color sensors in orbit. Index Terms--Atmospheric correction, Vicarious calibration, Global Imager (GLI), Sea-viewing Wide Field-of-view Sensor (SeaWiFS).

Surface downward radiation (SDR), including shortwave downward radiation (SWDR) and longwave downward radiation (LWDR), is of great importance to energy and climate studies. Considering the lack of reliable SDR data with a high spatiotemporal resolution in the East Asia–Pacific (EAP) region, we derived SWDR and LWDR at 10-min and 0.05° resolutions for this region from 2016 to 2020 based on the next-generation geostationary satellite Himawari-8 (H-8). The SDR product is unique in terms of its all-sky features, high accuracy, and high-resolution levels. The cloud effect is fully considered in the SDR product, and the influence of high aerosol loadings and topography on the SWDR are considered. Compared to benchmark products of the radiation, such as Clouds and the Earth's Radiant Energy System (CERES) and the European Centre for Medium-Range Weather Forecasts (ECMWF) next-generation reanalysis (ERA5), and the Global Land Surface Satellite (GLASS), not only is the resolution of the new SDR product notably much higher, but the product accuracy is also higher than that of those products. In particular, hourly and daily root-mean-square errors of the new SWDR are 104.9 and 31.5 W m−2, respectively, which are much smaller than those of CERES (at 121.6 and 38.6 W m−2, respectively), ERA5 (at 176.6 and 39.5 W m−2, respectively), and GLASS (daily of 36.5 W m−2). Meanwhile, RMSEs of hourly and daily values of the new LWDR are 19.6 and 14.4 W m−2, respectively, which are comparable to that of CERES and ERA5, and even better over high-altitude regions. [ABSTRACT FROM AUTHOR]