Comparison of Target Detectors to Identify Icebergs in Quad-Polarimetric L-Band Synthetic Aperture Radar Data

Abstract

Icebergs represent hazards to ships and maritime activities and therefore their detection is essential. Synthetic Aperture Radar (SAR) satellites are very useful for this, due to their capability to acquire data under cloud cover and during day and night passes. In this work, we compared six state-of-the-art polarimetric target detectors to test their performance and ability to detect small-sized icebergs <120 m in four locations in Greenland. We used four single-look complex (SLC) ALOS-2 quad-polarimetric images from JAXA for quad-polarimetric detection and we compared with dual-polarimetric detectors using only the channels HH and HV. We also compared these detectors with single-polarimetric intensity channels and we tested using two scenarios: open ocean and sea ice. Our results show that the multi-look polarimetric whitening filter (MPWF) and the optimal polarimetric detector (OPD) provide the most optimal performance in quad- and dual-polarimetric mode detection. The analysis shows that, overall, quad-polarimetric detectors provide the best detection performance. When the false alarm rate (PF) is fixed to 10−5, the probabilities of detection (PD) are 0.99 in open ocean and 0.90 in sea ice. Dual-polarimetric or single-polarimetric detectors show an overall reduction in performance (the ROC curves show a decrease), but this degradation is not very large (<0.1) when the value of false alarms is relatively high (i.e., we are interested in bigger icebergs with a brighter backscattering >120 m, as they are easier to detect). However, the differences between quad- and dual- or single-polarimetric detectors became much more evident when the PF value was fixed to low detection probabilities 10−6 (i.e., smaller icebergs). In the single-polarimetric mode, the HV channel showed PD values of 0.62 for open ocean and 0.26 for sea ice, compared to values of 0.81 (open ocean) and 0.77 (sea ice) obtained with quad-polarimetric detectors.

Review of Ice Characteristics in Ship-Iceberg Collisions

“…The U.S. National Ice Center is also using satellites to track large icebergs found near Antarctica. In addition, the Canadian Ice Service or the time of day or night (Frost et al, 2016;Choi, 2018;Barbat et al, 2019;Soldal et al, 2019;Bailey et al, 2021).…”

Iceberg Detection With RADARSAT-2 Quad-Polarimetric C-Band SAR in Kongsfjorden, Svalbard—Comparison With a Ground-Based Radar

“…Thirdly, the size of the window being used is important; bigger windows can include more image pixels, diluting targets during averaging, while smaller windows can exclude pixels of iceberg edges and present more speckle noise. Attempts to address these problems include the implementation of a guard window, in between the testing and training windows, which has been shown to increase performance [21]. Another limitation to these iceberg detection methods is that even in areas such as open ocean, numerous rocks and small islands can increase the number of false alarms.…”

“…Previous work has been carried out on icebergs of a similar size and shape in east and west Greenland [21] using ALOS-2 L-Band SAR images. Here, several detectors, were tested for two scenarios: icebergs in open ocean, and icebergs embedded within sea-ice floes.…”

Adaptive logarithmic retinex enhancement for iceberg detection in visible imagery

“…This diversity poses complex classification challenges in visible imagery, often leading to ambiguous categorizations and hindering the development of reliable predictive models [2]. Consequently, extensive manual analysis is required to minimize false positives and address undetected targets, constraining the scalability of iceberg detection efforts based on visible imagery [3].…”