Enhancing Foundation Models for Imbalanced SAR Ship Classification via Targeted Oversampling

Ch Muhammad Awais; Marco Reggiannini; Davide Moroni

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arXiv · 2609.31657

Enhancing Foundation Models for Imbalanced SAR Ship Classification via Targeted Oversampling

Ch Muhammad Awais·Marco Reggiannini·Davide Moroni

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Abstract

Remote-sensing foundation models offer strong representations for SAR imagery, but their behavior under severe long-tail class imbalance is still not well characterized. We benchmark DOFA and SAR-JEPA on the imbalanced OpenSARShip dataset and compare them with ImageNet-pretrained baselines under a fixed, training-efficient protocol that keeps the backbone frozen. To mitigate imbalance without fine-tuning, we apply four oversampling methods in embedding space exclusively to minority classes and train a lightweight classifier head on the augmented embeddings. Across both foundation models, oversampling improves Macro-F1 and test accuracy relative to their respective baselines, with the largest Macro-F1 gains observed for DOFA using ADASYN (34.39 to 38.56) and for SAR-JEPA using SVM-SMOTE (25.89 to 32.30). We also report class-wise behavior, showing that aggregate improvements can coexist with persistent failures on specific rare classes. Code for embedding extraction and reproducible multi-seed evaluation is provided to support rapid experimentation on free-tier hardware.

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BibTeX RIS

Ch Muhammad Awais, Marco Reggiannini, Davide Moroni. 2026-09-15. Enhancing Foundation Models for Imbalanced SAR Ship Classification via Targeted Oversampling. https://arxiv.org/abs/2609.31657

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