Application of airborne LiDAR to identification of underwater geomorphology and fine interpretation of faults.

The airborne lidar bathymetry (ALB) is a new equipment for efficient survey of offshore seabed topography with high precision, high accuracy, high efficiency and wide operation area. By study of the high-resolution submarine topography data collected by the CZMIL Nova Ⅱ ALB system from an island in the South China Sea, it is found that the data can be used for efficient identification of geomorphic types and precise interpretation of submarine fractures, and the principles and methods adopted are very similar to the remote sensing interpretation for land structures. Through the detailed interpretation of the images acquired by lidar sounding, many seabed geomorphic types are found in the study area, for examples, the sand spit, headland, bay, ancient wave-cut platform, bank slope, fault depression, valley, submarine plain and residual fault block. The submarine landform and coastline surrounding the island are mainly controlled by fractures. Four groups of faults in NW, NNW, NNE and NEE directions are found on the seafloor, basically in consistent with the regional tectonic patterns. The extension of submarine rift system on land surface is proved by the high-resolution images acquired synchronously by the digital camera of CZMIL Nova Ⅱ system. Our experience in this survey proves that to extend the technique of remote sensing interpretation for land structures to the underwater fault interpretation offshore is a good solution to the precise detection of fault structures in coastal shallow waters.