Abstract: In line with sea reef terrain characteristics, POS-aided low altitude photogrammetry of sea islands and reefs without Ground Control Points (GCP) was researched using VTOL (Vertical Take-Off and Landing) system. The technical requirements of POS-aided UAV low altitude photogrammetry were analyzed in the aim of offering technical basis for acquiring the terrain of coastal zone of South China Sea islands and reefs in future. The technical feasibility of photogrammetry of sea islands and reefs without GCP is demonstrated by verifying the accuracy of mapping through field test and comparing the accuracy indicators between POS data based on low altitude OEM POS-borne UAV photogrammetry system and CORS stations and POS data based on PPP technique. Based on previous investigations, suggestions on typical equipment and UAV specification were given. In the present test, the high resolution digital images of the test area and the 1:2000 digital line drawing (DLG) mapping result of high precision were obtained. Moreover, some technical requirements of low-altitude POS-aided photogrammetry for the survey of islands and reefs in the South China Sea are put forward in the purpose of forming technical specification for the mapping of islands and reefs. The test results validate that the POS-aided UAV photogrammetry technology meets the accuracy requirements of 1∶2000 large-scale hydrographic survey without GCP.

Key words: POS-aided, UAV, sea island and reef, without GCP, low altitude photogrammetry