MOTION ERRORS IN AN AIRBORNE SYNTHETIC APERTURE RADAR SYSTEM

The Institute for Radio Frequency Technology of the German Aerospace Research Establishment (DLR) in Oberpfaffenhofen operates an experimental synthetic aperture radar, E-SAR. The Radar configuration was developed by DLR [1, 21 and consists of a L/C/X-band SAR System and antennas with a wide beamwidth in azimuth and elevation. The system is installed in a small Dornier DO 228 aircraft, which operates at low altitudes between 1000 m - 3000 m above ground. Due to atmospheric turbulences, the aircraft is displaced from its nominal flight path, causing a variation of the phase history of the returned radar signal. This eventually results in a degraded image quality and therefore a highly accurate motion compensation becomes necessary. It is intended to integrate an inertial measurement unit (IMU) within the E-SAR system to support the used motion compensation algorithm during data processing [3]. The required relative accuracy of the IMU can be determined by means of statistics i.e. an approach is demonstrated to estimate the power spectral density (PSD) of the tolerable uncompensated aircraft motion. The performance of an IMU motion compensation system has been evaluated by analysis, as well as by computer simulation.