Use of Pseudo-Random Noise sequences in microwave radiometer calibration

The calibration of large aperture synthesis interferometric radiometers such as the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) aboard ESApsilas SMOS mission is a crucial issue. Due to the large number of receiving channels, calibration techniques based on the centralized noise injection from a single noise source would require a large and stable distribution network, which is unfeasible from the point of view of mass, volume and phase equalization. Distributed noise injection techniques have been proposed, but are unable to correct for all types of errors. This work analyzes the possibility of using pseudo-random noise (PRN) instead of a centralized noise source. PRN sequences are signals with very long repetition period and relatively flat spectrum over a bandwidth determined by the length of the sequence and the symbol rate. Since their spectrum looks like that of the noise, calibration of a microwave correlation radiometers can benefit from their use.