The atmospheric informaton content of Earth's far infrared spectrum

A key component of the modern Earth observation system is the Mid-Infrared (MIR) hyperspectral sounder. Operational instruments on polar orbiting satellites are collecting a continuous record of highly accurate infrared spectra with a wide variety of applications in geoscience. Although some research instrumentation early in the development of the meteorological satellite used Far-Infrared (FIR) sensitive detectors, the primary focus of infrared instrumentation has been the MIR region. Recent developments in FIR instrumentation and a renewed interest in the FIR for climate applications has brought attention to this underexplored part of Earth's Infrared spectrum.;The information content of Earth's FIR spectrum is investigated within a modeling framework that simulates satellite observations of FIR and MIR spectra at hyperspectral resolution. The framework allows for direct comparison of the two spectral ranges, which can quantify the potential benefits of combining FIR spectral observations with the state of the art MIR observations. The framework is first applied to investigate the information content for retrieving the vertical temperature and water vapor profile in clear sky conditions. The FIR shows additional sensitivity to upper tropospheric and lower stratospheric water vapor, and a slight but consistent vertical resolution advantage relative to the MIR. By extending the simulation framework to include layer clouds composed of ice particles, the information content in cloudy sky profiles and cloud properties is investigated. In certain conditions, the FIR shows additional profiling information transmitted through the cloud layer and additional information above the cloud through the interaction between water vapor absorption and ice particle scattering and absorption. Finally, the including FIR spectra increases information content for cloud properties in cases where the MIR has poor sensitivity. These cases include high optical depth clouds and clouds with particle effective radius. Error propagation calculations are used to estimate the improvement on the resulting cloud Ice Water Path (IWP). These results suggest extending the spectral coverage of the hyperspectral sounder into the FIR would improve the retrieval of several important geophysical quantities.