Analysis and compensation of errors of precalculated satellite overpass time and aircraft navigation system in spaceborne/airborne hybrid bistatic SAR

The impact of errors of the precalculated satellite overpass time and aircraft navigation system on some performance parameters, i.e. the footprint overlapping time, the scene extension in azimuth, the offset of the imaging scene, in spaceborne/airborne hybrid bistatic SAR (SA-BSAR) is analyzed. Several related formulae are derived and simulations were performed using parameters of TerraSAR-X as the transmitter and PAMIR as the receiver. The results indicate that predication error of only 0.01 second for the satellite overpass time would cause the scene extension in azimuth to decrease 20 percent when the aircraft navigation system error reaches 5 seconds (the maximum possible value in normal case). Under the same prerequisite predication error of 0.28 second for the satellite overpass time would miss the chance to getting overlapped. A compensation method is proposed based on the idea that the radar satellite starts the beam steering just at the instant when it passes its ideal position rather than at the precalculated instant to begin steering. To accomplish this goal a far more precise prediction for the satellite overpass time must be made on the aircraft several seconds before the satellite´s arrival. The concrete requirement for the prediction accuracy is derived. The required accuracy must be guaranteed to achieve the expected scene extension in azimuth.