Using synthetic aperture sonar as an effective hydrographic survey tool

SAS is becoming a powerful tool for hydrographic surveys in addition to its original use as a mine detection sensor. This technology can provide very high resolution seafloor imagery and bathymetry over the full extent of the swath. SAS lends itself for use with Autonomous Underwater Vehicles (AUVs) because of the stable nature of these platforms. As the hydrographic industry begins to adopt AUV technology, especially given the efficiencies they can bring, it is clear that SAS will have a greater role to play. This trend is driving a requirement to support this data effectively in the data processing software tools that are used by the hydrographic industry. This involves new requirements and workflows to handle the increased data volumes that result from the centimeter level resolutions that these sensors are capable of generating. Another key concept is understanding the difference in geometries involved in SAS data collection as it compares to multibeam, the concept of frames of data instead of swaths requires some changes in approach, which will be explained. The data processing emphasis from a survey utilizing a SAS is different from traditional vessel based operations. For example, early experiences suggest that more attention needs to be given to dataset combining rather than data cleaning. Another important observation is understanding how to run a survey with SAS, what line configurations are appropriate when conducting a route survey and how does this differ for an area based survey for the purposes of charting. There are also some technological advancements that could streamline the SAS workflow and aid its adoption as a hydrographic tool. One such technology is variable resolution surface creation. This emerging terrain modelling technique would allow high resolution SAS data and lower resolution multibeam data to be stitched seamlessly together into a single terrain model allowing for more efficient data transfers, more integrated and robust data cleaning techniques and easier object detection. Another advancement that will benefit surveys utilizing this technology is onboard and near real-time data processing solutions. This is being driven by the nature of this data; its density and the autonomous way in which it is collected. This concept will also be explained. The paper's aim will be to not only highlight the new considerations that need to be understood when using this technology as a hydrographic mapping tool, but to also demonstrate this through appropriate use cases.