Research On The Spatial Decorrelation Effects Of Synthetic Aperture Imaging Radiometers

It is now well established that Synthetic Aperture Imaging Radiometers(SAIR) promise to be powerful sensors for high-resolution observations of the Earth at low microwave frequencies. However, large aperture synthesis radiometers confront severe spatial decorrelation or so-called fringe-washing effects due to wide field of view requirement. As a result, the correlator output signal incurs a loss of brightness scene information at high spatial frequencies. What's more, the calibration is a crucial issue since most techniques inherited from radio astronomy cannot be directly applied. Within this context, the present work aims to study the fringe-washing errors attributable to the spatial decorrelation effects onto the reconstructed brightness temperature map in large aperture synthesis radiometers with wide field of view, and introduce two methods for calibration of the fringe-washing errors.Firstly, the basic imaging theory of SAIR is presented, the spatial resolution and the radiometric sensitivity are computed. Then, the causes, the mathematical model and the constraints of spatial decorrelation effects are analyzed in detail, and the impact of it on reconstructed brightness temperature map is simulated and estimated using Fourier transform and G-Matrix inversion algorithms. Finally, this paper describes two methods used to calibrate fringe-washing effects with respect to bandwidth and measurement modeling——band division correlation technique and three delay method. Simulations are presented for point thermal source and extended thermal source of one-dimensional and two-dimensional SAIR. With the aid of two methods, it is shown that the performance of SAIR is little influenced by the spatial decorrelation phenomenon occurring with large aperture synthesis radiometers.