Impact of RTIASI fast radiative transfer model error on IASI retrieval accuracy
SHERLOCK, Vanessa
This study quantifies the impact of specific forward model and Jacobian error characteristics on retrieval accuracy for RTIASI, a fast radiative transfer operator for IASI. In light of previous studies, improved estimates of forward model error covariance and fast model Jacobian errors have been made for two versions of RTIASI using three-case and single-case water vapour predictor schemes. Forward model errors present strong correlations within spectral bands and within the window regions. Error characteristics are comparable or the two versions with the exception of the H2O nu2 band instrumental noise and forward model error are comparable in magnitude and forward model errors govern long-range correlation structure. In this case, neglecting correlation structure can degrade retrieval of upper tropospheric temperature and humidity. In other spectral intervals instrumental noise makes the dominant contribution to the observation error covariance and the error incurred by a diagonal approximation to the forward model error covariance is small. In ...
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