FPUNet: A Fourier-Enhanced U-Net for Robust 2-D Phase Unwrapping of Noisy InSAR Interferograms.

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Title: FPUNet: A Fourier-Enhanced U-Net for Robust 2-D Phase Unwrapping of Noisy InSAR Interferograms.
Authors: He, Yuxiao1,2 (AUTHOR), Wu, Yuming1,2 (AUTHOR) wuym@lreis.ac.cn, Gao, Xing1 (AUTHOR)
Source: Remote Sensing. Mar2026, Vol. 18 Issue 5, p808. 29p.
Subjects: Phase unwrapping (Digital image processing), Radar interferometry, Frequency-domain analysis, Deep learning, Signal denoising
Abstract: Highlights: What are the main findings? We propose FPUNet, a Fourier-enhanced phase unwrapping network that integrates frequency-domain global context modeling with multi-scale spatial feature aggregation for robust 2-D unwrapping under steep deformation gradients and multi-source noise. FPUNet improves unwrapping fidelity while preserving physical consistency, as validated by rewrapping checks and closed-loop phase consistency on synthetic and real interferograms. What are the implications of the main findings? The proposed framework provides a practical learning-based alternative to classical unwrapping pipelines for challenging coseismic/complex scenes, with fast inference suitable for large-scale InSAR processing. The physics-informed constraints offer a general strategy to regularize deep unwrapping models, enabling reliable deformation retrieval when the Itoh condition is frequently violated. Two-dimensional phase unwrapping (PU) of interferometric synthetic aperture radar (InSAR) data remains difficult when steep deformation gradients and multi-source disturbances violate the Itoh condition. This study proposes FPUNet, a Fourier-enhanced encoder–decoder for joint denoising and 2-D PU, in which frequency-domain global context modeling is combined with complementary multi-scale spatial aggregation and attention-based feature refinement. Specifically, the bottleneck cascades a Fourier Mixed Residual Block (FMRB), atrous spatial pyramid pooling (ASPP), and a convolutional block attention module (CBAM) to suppress noise while preserving deformation-related fringe structures. FPUNet is trained end-to-end on realistically simulated Sentinel-1 interferograms generated from Shuttle Radar Topography Mission (SRTM) digital elevation models using a physics-informed composite loss that enforces data fidelity, gradient consistency, spectral regularization, and selective rewrapping consistency. On a synthetic benchmark of 1800 test interferograms, FPUNet achieves an RMSE of 0.79 rad, improving over a plain U-Net (1.61 rad) and producing fewer large fringe-number errors than least-squares, SNAPHU, PUNet, and DLPU. Experiments on real Sentinel-1 data over the Datong mining area and the 2022 Menyuan and Luding earthquakes further indicate improved phase closure and rewrapping consistency, particularly in high-gradient coseismic fringes, supporting FPUNet as a robust PU module for InSAR deformation monitoring. [ABSTRACT FROM AUTHOR]
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  Data: FPUNet: A Fourier-Enhanced U-Net for Robust 2-D Phase Unwrapping of Noisy InSAR Interferograms.
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  Data: <searchLink fieldCode="JN" term="%22Remote+Sensing%22">Remote Sensing</searchLink>. Mar2026, Vol. 18 Issue 5, p808. 29p.
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– Name: Abstract
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  Data: Highlights: What are the main findings? We propose FPUNet, a Fourier-enhanced phase unwrapping network that integrates frequency-domain global context modeling with multi-scale spatial feature aggregation for robust 2-D unwrapping under steep deformation gradients and multi-source noise. FPUNet improves unwrapping fidelity while preserving physical consistency, as validated by rewrapping checks and closed-loop phase consistency on synthetic and real interferograms. What are the implications of the main findings? The proposed framework provides a practical learning-based alternative to classical unwrapping pipelines for challenging coseismic/complex scenes, with fast inference suitable for large-scale InSAR processing. The physics-informed constraints offer a general strategy to regularize deep unwrapping models, enabling reliable deformation retrieval when the Itoh condition is frequently violated. Two-dimensional phase unwrapping (PU) of interferometric synthetic aperture radar (InSAR) data remains difficult when steep deformation gradients and multi-source disturbances violate the Itoh condition. This study proposes FPUNet, a Fourier-enhanced encoder–decoder for joint denoising and 2-D PU, in which frequency-domain global context modeling is combined with complementary multi-scale spatial aggregation and attention-based feature refinement. Specifically, the bottleneck cascades a Fourier Mixed Residual Block (FMRB), atrous spatial pyramid pooling (ASPP), and a convolutional block attention module (CBAM) to suppress noise while preserving deformation-related fringe structures. FPUNet is trained end-to-end on realistically simulated Sentinel-1 interferograms generated from Shuttle Radar Topography Mission (SRTM) digital elevation models using a physics-informed composite loss that enforces data fidelity, gradient consistency, spectral regularization, and selective rewrapping consistency. On a synthetic benchmark of 1800 test interferograms, FPUNet achieves an RMSE of 0.79 rad, improving over a plain U-Net (1.61 rad) and producing fewer large fringe-number errors than least-squares, SNAPHU, PUNet, and DLPU. Experiments on real Sentinel-1 data over the Datong mining area and the 2022 Menyuan and Luding earthquakes further indicate improved phase closure and rewrapping consistency, particularly in high-gradient coseismic fringes, supporting FPUNet as a robust PU module for InSAR deformation monitoring. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
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  Data: <i>Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.3390/rs18050808
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        Text: English
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      – SubjectFull: Radar interferometry
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      – SubjectFull: Frequency-domain analysis
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      – SubjectFull: Deep learning
        Type: general
      – SubjectFull: Signal denoising
        Type: general
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      – TitleFull: FPUNet: A Fourier-Enhanced U-Net for Robust 2-D Phase Unwrapping of Noisy InSAR Interferograms.
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            NameFull: He, Yuxiao
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              M: 03
              Text: Mar2026
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              Y: 2026
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