Abstract
Abstract. This paper describes the first official release (v1.0) of RTTOV-gb. RTTOV-gb is a FORTRAN 90 code developed by adapting the atmospheric radiative transfer code RTTOV, focused on satellite-observing geometry, to the ground-based observing geometry. RTTOV-gb is designed to simulate ground-based upward-looking microwave radiometer (MWR) observations of atmospheric downwelling natural radiation in the frequency range from 22 to 150 GHz. Given an atmospheric profile of temperature, water vapor, and, optionally, cloud liquid water content, and together with a viewing geometry, RTTOV-gb computes downwelling radiances and brightness temperatures leaving the bottom of the atmosphere in each of the channels of the sensor being simulated. In addition, it provides the sensitivity of observations to the atmospheric thermodynamical state, i.e., the Jacobians. Therefore, RTTOV-gb represents the forward model needed to assimilate ground-based MWR data into numerical weather prediction models, which is currently pursued internationally by several weather services. RTTOV-gb is fully described in a previous paper (De Angelis et al., 2016), while several updates are described here. In particular, two new MWR types and a new parameterization for the atmospheric absorption model have been introduced since the first paper. In addition, estimates of the uncertainty associated with the absorption model and with the fast parameterization are given here. Brightness temperatures (TB) computed with RTTOV-gb v1.0 from radiosonde profiles have been compared with ground-based MWR observations in six channels (23.8, 31.4, 72.5, 82.5, 90.0, and 150.0 GHz). The comparison shows statistics within the expected accuracy. RTTOV-gb is now available to licensed users free of charge from the Numerical Weather Prediction Satellite Application Facility (NWP SAF) website, after registration. Coefficients for four MWR instrument types and two absorption model parameterizations are also freely available from the RTTOV-gb support website.
Highlights
RTTOV-gb is a fast radiative transfer code, designed to simulate ground-based upward-looking microwave radiometer (MWR) observations of atmospheric downwelling natural radiation
In order to assimilate groundbased radiometric observations, namely brightness temperatures (T B), a fast radiative transfer forward model is needed. This model allows rapid simulations of T B at selected radiometer channels based on the Numerical Weather Prediction (NWP) model state vector, i.e., atmospheric temperature and humidity profiles, similar to what RTTOV does for satellite sensors
RTTOVgb was trained using a later version of millimeter-wave propagation model (MPM), described by Rosenkranz (1998, hereafter R98), which is probably the most used among the ground-based microwave radiometry community
Summary
RTTOV-gb is a fast radiative transfer code, designed to simulate ground-based upward-looking microwave radiometer (MWR) observations of atmospheric downwelling natural radiation (i.e., radiances). RTTOV is widely used by many national and international meteorological services for assimilating down-looking observations from visible, infrared, and microwave radiometers, spectrometers, and interferometers aboard satellite platforms For this reason, RTTOV is maintained and continuously developed by the Numerical Weather Prediction (NWP) Satellite Application Facility (SAF) of the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). In order to assimilate groundbased radiometric observations, namely brightness temperatures (T B), a fast radiative transfer forward model is needed This model allows rapid simulations of T B at selected radiometer channels based on the NWP model state vector, i.e., atmospheric temperature and humidity profiles, similar to what RTTOV does for satellite sensors.
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