The RADARSAT-2 synthetic aperture radar diagnostics and calibration

The RADARSAT-2 antenna is an active phased array, which uses two-dimensional beamforming and beamsteering to form the many (over 200) different beams required for the RADARSAT-2 imaging modes. For calibration purposes it is necessary to have a means for obtaining information about the characteristics of the array in-orbit. This paper is concerned with the in-orbit measurement operations, which are planned for characterisation of the antenna. These operations do not involve any interaction with any hardware units on the ground, thus they can be performed at any point in the orbit where the ground has the required backscatter characteristics. The purpose of these operations and the information that is to be obtained is described in this paper, followed by assessment of the accuracy of the information. The set of measurements described use special sequences involving transmissions or receptions with individual transmit receive modules (TRMs), rows or columns or subsets of the TRMs, rows or columns. An outline description of the operations, the required spacecraft and ground resources required, and the accuracy of the derived data is then presented. Analysis and simulation have shown that all the test and measurement accuracy goals can be met with data from a single cycle of each of the test sequences, but provision has been made for multiple successive cycles to be performed to increase accuracy if required.