DSB system-noise temperature near 0.7 GHz) [9]. e project is led by Kyoto University and involves NICT, JAXA, and several other universities. NICT contributes to the mission concept denition, instrument design, and simulation studies. e realization of the mission is still under consideration. A Model describing the propagation of the radiation through the atmosphere, such as AMATERASU, is essential for analyzing remote measurements. e model provides the relationship between the radiances measured with the instrument and the atmospheric state. AMATERASU is called the forward model (FM) and retrieving atmo-spheric information from the radiance is done by the in-verse model. e quality of the retrievals depends on that of the measured radiances and on the FM accuracy. In addition, the FM must be fast enough to allow the process-ing of the large amount of data acquired with a satellite mission.2.2Simulation studiesSimulation studies are a prerequisite when dening a new instrument. ey provide quantitative information to atmospheric and instrumental scientists helping them to converge toward the best compromise between scientic requirements and technological feasibility. e forward model is the core of the simulator. It computes the outgoing radiation from line-of-sights pass-ing through the limb at dierent altitudes (Fig. 4). e ray-path is divided in small segments (length <5 km) in which the atmosphere is assumed homogenous. e algo-rithms for unpolarized radiation are described in [1][12] and the polarized one in [13]. In short, the radiance exiting a small segment with length ds is:()()()()() , Equation 1where I(s)=[i(s), q(s), u(s), v(s)]T is the Stokes vector describing the 4 polarization states of the radiation at the position s, B is the Stokes vector of the unpolarized black-body radiation at the temperature T, is the 4x4 absorp-FiF2Limb sounding representation for SIW and SMILES-2. On the right-side, a representative view of SIW with its two antennas (30 cm diameter) is shown (Omnisys Instruments).FiF3Left panel: Simulated DSB Spectra for SIW. The frequency is that of the lower sideband (local oscillator 638.075 GHz, 1 MHz resolution, 1200 K DSB system-noise temperature). Right panel: Retrieval of LOS wind, O3, H2O and temperature (red lines). The true solution is shown in green and the blue lines show the profiles used to initialize the calculation. The horizontal lines show the 2- error bars. Figure taken from [8].1094-5 AMATERASU（テラヘルツ大気放射伝達モデル）の新機能 : SIWとSMILES-2ミッションのためのGPUによる多偏波放射伝達計算の高速化
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