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Objectives: On 14th and 15th January 2022, the Hunga Tonga‑Hunga Ha̓apai (HTHH) underwater volcano in Tonga in the South Pacific Ocean violently erupted and caused a tsunami, which has attracted widespread international attention. In this paper, we attempted to rapidly investigate this oncein‑a‑millennium massive event using integrated remote sensing techniques. Methods: We comprehensively used multi‑temporal satellite optical images, radar images, global navigation satellite system (GNSS) observations and other datasets to quickly interpret and analyze the volcanic eruption process and its impacts. The damage assessment in parts of Tonga was also performed. Based on the integrated remote sensing techniques, we presented a technical framework for the rapid interpretation and analysis of volcanic eruptions, which comprises of six components, namely multi‑source data acquisition, geomorphology monitoring, deformation monitoring, environmental response detection, damage assessment and recovery decision. Results: Our results show that the HTHH underwater volcano in Tonga had exhibited obvious surface displacements in the satellite radar line of sight direction with a maximum accumulated displacement of 6.0 cm since June 2020, and erupted since around 22nd December 2021. During the volcanic eruption, the local magnetic field and ionosphere exhibited obvious abnormal signals, and the continuous GNSS data in Tonga suggested clear surface displacements with an uplift up to 50.2 cm. Most areas of Tonga were blanketed in ash, but it appeared that, in northern part of Tonga̓s capital, little damage was observed in the coastlines and the main buildings and roads remained intact. Conclusions: This study shows how to use integrated remote sensing techniques to quickly respond to underwater volcanic eruptions, including the topography evolution of the HTHH volcano and the damage assessment of its eruption. It is believed that the remote sensing integrated technical framework shall not only contribute to the speedy recovery and reconstruction of the society after the HTHH volcanic eruption, but also to the mitigation of future geohazard events. [ABSTRACT FROM AUTHOR]