Accurate frequency estimation for removal of orbital fringes in SAR interferograms

Abstract

ABSTRACT Differential interferogram of space-borne SAR data may be affected by residual orbital fringes resulting from errors in the orbit (i.e. baseline) determination that hinder subsequent InSAR applications (deformation or elevation measurements). In this paper, an easy-to-use method was developed to remove the orbit errors in complex SAR interferogram in the radar coordinate system by accurately estimating the frequencies of the orbital ramp phase. The method first finds an approximate integer frequency by searching for the peak of the sum of the Fourier spectra of all the rows of the interferogram. It then uses the 100-order Burg spectral estimation algorithm to estimate the power spectrum for each row of the interferogram, and calculates the high-resolution power spectrum over the frequency range Hz. Finally, the method obtains the exact frequency of the orbital ramp phase in the row direction by searching for the peak of the sum of the high-resolution power spectra of all rows. By performing the same operations on all columns of the interferogram, the exact frequency in the column direction can be obtained. The orbital ramp phase can be calculated using these exact frequencies and be removed from the interferogram. Validation tests demonstrate that our method can accurately estimate the frequencies of the orbital ramp phase in the row and column directions, and eliminate the orbital ramp fringes from the simulated and actual interferograms. The proposed method only needs to calculate the high-resolution spectrum in a small frequency range, so the burden of calculation is light. The proposed method is easy to use since phase unwrapping or a priori satellite orbit information is not required.