Evaluation of Several Filtering and Unwrapping Methods for the Interferometric Imaging Radar Altimeter

  • Hong TanEmail author
  • Shengyang Li
  • Zhiwen Liu
  • Wanfeng Zhang
  • Leijuan Li
Conference paper
Part of the Lecture Notes in Electrical Engineering book series (LNEE, volume 541)


Radar altimeters using interferometric synthetic aperture radar (InSAR) techniques at near-nadir angles have been proposed to measure elevations of the ocean and the inland water with wide swath and high spatial resolution. The Ku-band Interferometric Imaging Radar Altimeter (InIRA) on the Tiangong-2 space laboratory, which was launched on 15 September 2016, is the first spaceborne instrument of such kind. Another similar instrument is the forthcoming Ka-band Radar Interferometer (KaRIn) of the Surface Water and Ocean Topography (SWOT) mission. In the interferometric processings, which have to be done to derive the elevations with the interferometric altimeter, the phase filtering and the phase unwrapping are two key steps. There are many filtering and unwrapping methods for conventional InSAR published in literature, but very few for interferometric altimeters. In this paper, several common filtering and unwrapping methods were evaluated with real InIRA acquisitions over three different scenes, including an open ocean, a coastal area, and a land with a mountain. The phase filtering was evaluated by the pseudo-correlation coefficient, the residue number, and the Root Mean Square (RMS) of the difference between the filtered phase and the original phase. The phase unwrapping was evaluated by the statistics of the difference between the rewrapped phase and the input wrapped phase, the ε value, and the discontinuity number. The evaluation results were shown and some recommendations were made on the method selection and the parameter setting for interferometric altimeters.


Tiangong-2 Altimetry Interferometry Phase filtering Phase unwrapping Synthetic aperture radar 



Thanks to China Manned Space Engineering for providing space science and application data products. Thanks to Xiao Dong and Yunhua Zhang in the Key Laboratory of Microwave Remote Sensing, Chinese Academy of Sciences, for their discussions on the instrument design and for their help in generating the complex images.


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© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Key Laboratory of Space UtilizationChinese Academy of SciencesBeijingChina
  2. 2.Technology and Engineering Center for Space UtilizationChinese Academy of SciencesBeijingChina

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