Trace gas retrieval including horizontal gradients Original Research Article

The development of a software package for the retrieval of vertical trace gas profiles from limb sounding measurements led to the analysis of the radiometric effects of inhomogeneous distributions of pressure, temperature and/or trace gases within simulated atmospheric layers as seen by a limb sounding instrument. These inhomogeneities called “horizontal gradients” affect the radiance measured by the instrument and — if unaccounted for - will degrade the retrieval quality of vertical pressure, temperature and/or trace gas profiles. On the other hand, if the retrieval of the vertical profiles is able to support the determination of horizontal gradients and if sufficient additional external knowledge about these gradients is available, then this offers an opportunity to retrieve vertical temperature and trace gas profiles with high accuracy. Several examples will demonstrate typical cases where the use of optimal estimation techniques including a priori knowledge of profiles and covariance data will deliver high quality results.