Generating Pseudo-Realistic Infrared Observations for Observing System Simulation Experiments

Observing System Simulation Experiments (OSSEs) are essential for evaluating and designing remote sensing systems using synthetic observations. A key aspect of OSSEs is tuning observation errors, typically by comparing data assimilation (DA) statistics from real and synthetic observations. However, during instrument design, only limited specifications, such as spectral response functions, are available. This paper presents a method for generating pseudo-realistic infrared observations for proposed instruments using high-resolution IASI measurements as a reference. The approach involves converting Infrared Atmospheric Sounding Interferometer (IASI) measurements into infrared spectra using the Fast Fourier Transform (FFT) and inverse FFT (iFFT), then deriving channel-specific radiances for new instruments by convolving sensor response functions. Validation using IASI and AIRS simulations shows a mean difference below 0.1 K and a standard deviation under 0.5 K when comparing Fourier-derived AIRS brightness temperatures with those from a radiative transfer model. The accuracy of these conversions is confirmed by reconstructing IASI brightness temperatures via FFT, yielding negligible differences. An example of how these pseudo-observations can be used in OSSE experiments is presented, and the results are discussed.