Efficient sar azimuth ambiguity reduction in coastal waters using a simple rotation matrix: The case study of the northern coast of jeju island

Joon Hyuk Choi, Joong Sun Won

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1 Citation (Scopus)


Azimuth ambiguities, or ghosts on SAR images, represent one of the main obstacles for SAR applications involving coastal monitoring activities such as ship detection. While most previous methods based on azimuth antenna pattern and direct filtering are effective for azimuth ambiguity suppression, they may not be effective for fast cruising small ships. This paper proposes a unique approach for the reduction of azimuth ambiguities or ghosts in SAR single-look complex (SLC) images using a simple rotation matrix. It exploits the fact that the signal powers of azimuth ambiguities are concentrated on narrow bands, while those of vessels or other true ground targets are dispersed over broad bands. Through sub-aperture processing and simple axis rotation, it is possible to concentrate the dispersed energy of vessels onto a single axis while the ghost signal powers are dispersed onto three different axes. Then, the azimuth ambiguities can be easily suppressed by a simple calculation of weighted sum and difference, while preserving vessels. Applied results achieved by processing TerrSAR-X SLC images are provided and discussed. An optimum weight of 0.5 was determined by Receiver Operating Characteristic (ROC) analysis. Capabilities of ship detection from the test image were significantly improved by removing 93% of false alarms. Application results demonstrate its high performance of ghost suppression. This method can be employed as a pre-processing tool of SAR images for ship detection in coastal waters.

Original languageEnglish
Article number4865
JournalRemote Sensing
Issue number23
Publication statusPublished - 2021 Dec 1

Bibliographical note

Funding Information:
Funding: This study was funded by the Korea Ministry of Environment (MOE) under the Service Program for Demand-Responsive Water Supply (2019002650004) and partially supported by the Korea Institute of Marine Science and Technology Promotion funded by the Ministry of Ocean and Fisheries for the “Base research for building a wide integrated surveillance system of marine territory” projects for field data acquisition.

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)


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