A new paper on adapting the RTTOV radiative transfer model for the purpose of assimilating ground-based microwave radiometer data and is available from GMD [1]
Links[1] http://www.geosci-model-dev.net/9/2721/2016/ [2] http://www.gaia-clim.eu/system/files/article_documents/gmd-9-2721-2016.pdf