Optical and SAR Cross-Modal Hallucination Collaborative Learning for Remote Sensing Missing-Modality Building Footprint Extraction

Building footprint extraction using optical and synthetic aperture radar (SAR) images enables all-weather capability and significantly boosts performance. In practical scenarios, optical data may not be available, leading to the missing-modality challenge. To overcome this challenge, advanced methods employ mainstream knowledge distillation approaches with hallucination network schemes to improve performance. However, under complex SAR backgrounds, current hallucination-network-based methods suffer from cross-modal information transfer failure between optical and hallucination models. To solve this problem, this study introduces a cross-modal hallucination collaborative learning (CMH-CL) method, consisting of two components: modality-share information alignment learning (MSAL) and multimodal fusion information alignment learning (MFAL). The MSAL method facilitates cross-modal knowledge transfer between optical and hallucination encoders, thereby enabling the hallucination model to effectively mimic the missing optical modality. The MFAL method aligns semantic information between OPT-SAR and HAL-SAR fusion heads to strengthen their semantic consistency, thereby improving HAL-SAR fusion performance. By combining MSAL and MFAL, the CMH-CL method collaboratively alleviates cross-modal transfer failure problem between the optical and hallucination models, thereby improving performance in missing-modality building footprint extraction. Extensive experimental results obtained on a public dataset demonstrate the effectiveness of the proposed CMH-CL.