Parameterization of surface brightness temperature to retrieve trace gases from radiance spectra measured with a nadir view

Any inversion algorithm that ignores the wavenumber dependence of the surface emissivity could cause systematic errors in the retrieval of atmospheric trace gas concentrations from high-resolution nadir radiances. The error can become serious when the emissivity is significantly dependent on wavenumber within the measurement wavenumber region, while in many cases the emissivity spectrum is not known a priori. The authors developed a method to retrieve trace gas concentrations and the wavenumber-dependent surface brightness temperature simultaneously, based on the fact that the emissivity spectrum is much smoother than the absorption cross sections of gaseous molecules. The feasibility of applying the method to the interferometric monitor for greenhouse gases data was tested using numerical simulations, and the method proved to be helpful in avoiding the retrieval errors due to the wavenumber dependence of emissivity. The method will be applicable also to the remote soundings of the atmospheres on other planets or satellites whose surface materials are not known.