The Synthetic Aperture Interferometric Radiometer Performance Simulator (SAIRPS) is a three-year project sponsored by the European Space Agency (ESA) to develop a completely generic end-to-end performance simulator of arbitrary synthetic aperture interferometric radiometers. This means, on one side, a generic radiative transfer module from 1 to 100 GHz, including land and ocean covers, as well as a fully 3D atmosphere and Faraday ionospheric rotation based on variable TEC. On the other hand, the instrument can have an arbitrary array topology (number of antenna elements, and their time-dependent position and orientation). Receivers’ topology can also be modified, starting from a very generic one to connecting and disconnecting subsystems, whose parameters can be individually configured. These parameters can be defined either by mathematical functions or by input data files, including the frequency and temperature dependence. Generic calibration and image reconstruction algorithms that are suitable for arbitrary array topologies have also been implemented, as well as tools to compute the instrument performance metrics, i.e., radiometric accuracy, sensitivity, angular resolution, etc. This manuscript presents the generic architecture of the SAIRPS, the algorithms implemented in the Radiative Transfer Module, and simulation results showing its performance. A companion manuscript (Part II) describes the instrument and calibration modelling, the image reconstruction algorithms, and the validation tests that were performed.

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