Finding Ground-based Radars in SAR images: Localizing Radio Frequency Interference using Unsupervised Deep Learning

Synthetic Aperture Radar (SAR) satellite images are used increasingly more for Earth observation. While SAR images are useable in most conditions, they occasionally experience image degradation due to interfering signals from external radars, called Radio Frequency Interference (RFI). RFI affected i...

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Bibliographic Details
Published in:IEEE transactions on geoscience and remote sensing Vol. 61; p. 1
Main Authors: Sorensen, Kristian Aa, Kusk, Anders, Heiselberg, Peder, Heiselberg, Henning
Format: Journal Article
Language:English
Published: New York IEEE 01.01.2023
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
Anomalies
anomaly classification and localization
Classification
convolutional autoencoder
Deep learning
Image degradation
Image reconstruction
Radar
Radar imaging
Radio
Radio frequency
Radio frequency interference
radio frequency interference (RFI)
SAR (radar)
Satellite imagery
Ships
Synthetic aperture radar
synthetic aperture radar (SAR)
ISSN:0196-2892, 1558-0644
Online Access:Get full text
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Summary:Synthetic Aperture Radar (SAR) satellite images are used increasingly more for Earth observation. While SAR images are useable in most conditions, they occasionally experience image degradation due to interfering signals from external radars, called Radio Frequency Interference (RFI). RFI affected images are often discarded in further analysis or pre-processed to remove the RFI. However, few on-ground radars can cause RFI in SAR images and such information can thus increase domain awareness greatly over both land and sea, where, e.g ., localizing and characterizing RFI signals in the ocean could help classify otherwise overlooked ships. The aim of the current study is to detect and localize RFI signals automatically in Sentinel-1 level-1 images and further characterize the on-ground radar. The spatial structure of RFI signals vary greatly. A convolutional autoencoder was therefore developed to reconstruct RFI-free Sentinel-1 images. Conversely, RFI-affected images could not be well reconstructed. Anomalous heatmaps were then developed to automatically detect and localize RFI anomalies in the images under varying environmental and geographical conditions whereafter the external radar characteristics were extracted manually from Sentinel-1 level-0 data. We could consequently classify and localize RFI signals believed to originate from both stationary radars and ship-borne radars. We further argue that the calculated ship-borne radar characteristics correspond to those of air-surveillance radars. Empirically, the method showed better detection results than those of previous studies. Our study shows that more information can be extracted from certain detected objects, such as ships, from SAR images.
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ISSN:0196-2892
1558-0644
DOI:10.1109/TGRS.2023.3295002