Aronne Merrelli

Comparing Information Content of Upwelling Far-Infrared and Midinfrared Radiance Spectra for Clear Atmosphere Profiling

AbstractThe information content of high-spectral-resolution midinfrared (MIR; 650–2300 cm−1) and far-infrared (FIR; 200–685 cm−1) upwelling radiance spectra is calculated for clear-sky temperature and water vapor profiles. The wavenumber ranges of the two spectral bands overlap at the central absorption line in the CO2 ν2 absorption band, and each contains one side of the full absorption band. Each spectral band also includes a water vapor absorption band; the MIR contains the first vibrational–rotational absorption band, while the FIR contains the rotational absorption band. The upwelling spectral radiances are simulated with the line-by-line radiative transfer model (LBLRTM), and the retrievals and information content analysis are computed using standard optimal estimation techniques. Perturbations in the surface temperature and in the trace gases methane, ozone, and nitrous oxide (CH4, O3, and N2O) are introduced to represent forward-model errors. Each spectrum is observed by a simulated infrared spect...

Information content for cloud ice microphysics in the FIR radiance spectrum

Mid-infrared (MIR) radiance measurements in the atmospheric window (8 - 12 μm) have demonstrated sensitivity to ice particle microphysics, due to the spectral variation of the index of refraction of ice within the spectral range. The far infrared radiance (FIR) spectrum (17 - 50 μm) also contains a region of spectrally varying index of refraction. The longer wavelengths imply a smaller scattering size parameter, which in turn gives the ice particles different scattering properties in the FIR relative to the MIR. Generally, the FIR shows larger single scatter albedos and weaker forward scattering. Although the atmosphere has high opacity in the FIR due to the rotational absorption band of water vapor, high altitude ice clouds would be observable in the upwelling radiance spectrum even in moist tropical atmospheres. Thus, the FIR spectrum could be used for cloud property retrieval from satellite sensors. Using a modeling study, we investigate the information content for ice microphysical retrievals to chara...