Feasibility of retrieving upper tropospheric water vapor from observations of far-infrared radiation

摘要

Since the early 1970's, infrared remote sensing of water vapor has been based exclusively on observations of mid-infrared (mid-ir) emission from the strong 6.3μm vibration-rotation band. However, the outgoing longwave radiation from Earth is dominated by emission in the far-infrared (far-ir) at wavelengths greater than 15μm. The source of this far-ir radiation is upper tropospheric water vapor. Furthermore, there are a growing number of novel instrument concepts that propose measuring the thermal far-ir spectrum for the purpose of radiation budget sensing and climate fingerprinting. As a result, we investigate the feasibility of retrieving upper tropospheric water vapor from nadir-viewing observations of far-ir spectral emission. We find that it is possible to retrieve upper tropospheric water vapor from measurements of the far-ir spectral radiation, and that the vertical resolution can be significantly improved by combining measurements from the far-ir and mid-ir spectrum.