Marc Rodriguez Cassola

Impact of oscillator noise in bistatic and multistatic SAR

This letter addresses the impact of limited oscillator stability in bistatic and multistatic synthetic aperture radars (SARs). Oscillator noise deserves special attention in distributed SAR systems since there is no cancellation of low-frequency phase errors as in a monostatic SAR, where the same oscillator signal is used for modulation and demodulation. It is shown that the uncompensated phase noise may cause a time-variant shift, spurious sidelobes, and a broadening of the impulse response, as well as a low-frequency phase modulation of the focused SAR signal. Quantitative estimates are derived analytically for each of these errors based on a system-theoretic model taking into account the second-order statistics of the oscillator phase noise

Unexpected height offsets in TanDEM-X: Explanation and correction

This paper reports on systematic height offsets that have been observed in TanDEM-X by evaluating a large number of digital elevation model (DEM) acquisitions. Besides the expected instrument and baseline offsets, which are compensated in the calibration chain, two unexpected external error sources have been identified that apply to any formation flying bistatic SAR interferometer. The first contribution is due to relativistic effects and can be well explained within Einsteins special theory of relativity. The second effect is due to differential delays in the troposphere. It is shown that the theoretic predictions are in good agreement with the observed offsets. All necessary corrections have in the meantime been integrated in the operational TanDEM-X processing chain.