Precise computation of Doppler parameters for spaceborne SAR in elliptic orbits

There are errors in the existing formulae for calculating the Doppler parameters for spaceborne SAR. Too large errors would adversely affect the convergence speed of the estimation algorithms for Doppler parameters. This paper derives several precise analytical formulae based on the results presented in the published literature. During the deduction process, the effect of flight path angle is considered as a key issue. To the author's knowledge, the effect was neglected in all of the relevant published literature. The consequence is that the existing formulae can only be approximately used in a nearly circular orbit. If the existing formulae are applied to a satellite with large eccentricity, the error may be too large. In contrast, the formulae derived in this paper can be used in any cases, for there are no errors in our formulae. The accuracy of the derived formulae and the effect of the flight-path angle are verified by a simulation experiment using the parameters of Radarsat.