Abstract
Abstract. IASI measurements of spectral radiances made between the 1st April 2008 and the 15th April 2008 are compared with simulations performed using the RTTOV fast radiative transfer model utilizing regression coefficients based on different line-by-line models. The comparisons are performed within the framework of the European Centre for Medium-Range Weather Forecasts Integrated Forecast System using fields of temperature, water vapour and ozone obtained from short-range forecasts. Simulations are performed to assess the accuracy of the RTTOV computations and investigate relative differences between the line-by-line models and the quality of the spectroscopic databases on which the RTTOV coefficients are based.
Highlights
The exploitation of satellite radiance data for Numerical Weather Prediction (NWP) requires the use of an accurate and fast radiative transfer (RT) model to simulate radiances from an input atmospheric profile
Regression coefficients for Radiative Transfer Model for TOVS (RTTOV) are available based on the 43 profile training set described in Matricardi and Saunders (1999), the 52 profile training set described in Chevallier (2000) and, more recently, on the 83 profile training set described in Matricardi (2008)
Results in Infrared Atmospheric Sounding Interferometer (IASI) band 1 are plotted in Figs. 4, 5 and 6 where we show the mean value of the difference between observed and simulated radiances in units of equivalent black body brightness temperature for the Northern Hemisphere (30◦ N–90◦ N ), tropics (30◦ N–30◦ S) and Southern Hemisphere (30◦ S–90◦ S ) respectively
Summary
The exploitation of satellite radiance data for Numerical Weather Prediction (NWP) requires the use of an accurate and fast radiative transfer (RT) model to simulate radiances from an input atmospheric profile. In RTTOV the transmittances of the atmospheric gases are expressed as a function of profiledependent predictors This parameterization of the transmittances makes the model computationally efficient and fulfils the NWP requirement of near real-time monitoring and assimilation of satellite radiance data. Fast RT model errors are dominated by two main components: the parameterization used for the atmospheric transmittances and the errors associated with the spectroscopic parameters and the computational procedures adopted in the line-by-line (LBL) models on which fast RT models are generally based. LBL models are used to perform accurate radiance and atmospheric transmittance computations at very high spectral resolution but they are too computationally expensive to be used in an NWP operational environment. The assessment of the RTTOV accuracy has been carried out by running a number of ECMWF Integrated Forecast System (IFS) monitoring experiments where IASI spectra simulated by RTTOV have been compared to IASI spectra measured during the period 1st April 2008-15th April 2008 using short range operational forecasts of temperature, water vapour and ozone fields to specify the RTTOV input state vector
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