RADTRAN With Spherical-Refractive Geometry.
ATMOSPHERIC AND ENVIRONMENTAL RESEARCH INC CAMBRIDGE MA
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RADTRAN is a model and computer program for computing atmospheric transmittance and radiance in the microwave region. The previous version of RADTRAN assumed a plane parallel non-refracting atmosphere for computing the amounts of absorbers and scatterers e.g. oxygen, water vapor, clouds, rain along the optical path. However, the plane-parallel assumption breaks down for zenith angles greater than about 80 degrees, leading to large errors in the calculated radiance and transmittance. The standard Phillips Lab atmospheric raytrace model FSCATM has been incorporated into RADTRAN as an option to calculate the absorber amounts. FSCATM uses spherical. refractive geometry to compute the layer-by-layer absorber amounts and density-weighted pressure and temperature for any slant path through the atmosphere. The atmospheric profiles from RADTRAN are retained. In the new program, called RADTRANS, the spherical-refractive geometry is available as an option, otherwise the program retains all the capabilities of the original version. However, the spherical geometry is incompatible with the multiple scattering model so the multiple scattering calculations must still be run using the plane-parallel geometry. Sample calculations are shown for the case of a satellite sensor scanning the nadir from 890 km. The radiance and the transmittance are calculated for 37, 90, and 150 GHz for both spherical and plane-parallel geometries. The results show differences of up to 70 K in brightness temperature at 37 GHz out near the horizon.... Microwave Radiation, Air mass, Atmospheric radiation, Transmittanceradiance models.
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