1 RTTOV-gb v1.0 - Updates on sensors, absorption models, 1 uncertainty, and availability 2 Domenico Cimini 1,2 , James Hocking 3 , Francesco De Angelis 2 , Angela Cersosimo 1 , Francesco 3 Di Paola 1 , Donatello Gallucci 1 , Sabrina Gentile 1 , Edoardo Geraldi 1 , Salvatore Larosa 1 , 4 Saverio Nilo 1 , Filomena Romano 1 , Elisabetta Ricciardelli 1 , Ermann Ripepi 1 , Mariassunta 5 Viggiano 1 , Lorenzo Luini 4 , Carlo Riva 4 , Frank S. Marzano 5,2 , Pauline Martinet 6 , YunYoung 6 Song 7 , Myoung Hwan Ahn 7 , and Philip W. Rosenkranz 8 . 7 1 National Research Council of Italy, Institute of Methodologies for Environmental Analysis, Potenza, 85050, 8 Italy 9 2 Center of Excellence CETEMPS, University of L’Aquila, L’Aquila, 67100, Italy 10 3 MET OFFICE, Exeter, United Kingdom 11 4 DEIB - Politecnico di Milano, IEIIT – CNR, Milano, Italy 12 5 University of Rome La Sapienza, Rome, Italy 13 6 CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France 14 7 School of Engineering, Ewha Womans University, Seoul, South Korea 15 8 Massachusetts Institute of Technology, Cambridge, MA, 02139, USA 16 Correspondence to: D. Cimini (domenico.cimini@imaa.cnr.it) 17 Abstract. This paper describes the first official release (v1.0) of RTTOV-gb. RTTOV-gb is a FORTRAN 90 18 code developed by adapting the atmospheric radiative transfer code RTTOV, focused on satellite observing 19 geometry, to the ground-based observing geometry. RTTOV-gb is designed to simulate ground-based upward- 20 looking microwave radiometer (MWR) observations of atmospheric downwelling natural radiation in the 21 frequency range from 22 to 150 GHz. Given an atmospheric profile of temperature, water vapour and, 22 optionally, cloud liquid water content, and together with a viewing geometry, RTTOV-gb computes the bottom 23 of atmosphere radiances and brightness temperatures in each of the channels of the sensor being simulated. In 24 addition, it provides the sensitivity of observations to the atmospheric thermodynamical state, i.e. the Jacobians. 25 Therefeore, RTTOV-gb represents the forward model needed to assimilate ground-based MWR data into 26 numerical weather prediction models, which is currently pursued internationally by several weather services. 27 RTTOV-gb is fully described in a previous paper (De Angelis et al., 2016), while several updates are described 28 here. In particular, two new MWR types and a new parameterization for atmospheric absorption model have 29 been introduced since the first paper. In addition, estimates of the uncertainty associated with the absorption 30 model and with the fast parameterization are given here. Brightness temperatures (T B ) computed with RTTOV- 31 gb v1.0 from radiosonde profiles have been compared with ground-based MWR observations at six channels 32 (23.8, 31.4, 72.5, 83.5, 90.0, and 150.0 GHz). The comparison shows statistics within the expected accuracy. 33 RTTOV-gb is now available to licensed users free of charge from the Numerical Weather Prediction Satellite 34 Application Facility (NWP SAF) website, after registration. Coefficients for four MWR instrument types and 35 two absorption model flavors are also freely available from the RTTOV-gb support website. 36 37 Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-285 Manuscript under review for journal Geosci. Model Dev. Discussion started: 21 January 2019 c  Author(s) 2019. CC BY 4.0 License.