Three themes have emerged during the initial discussions and will be addressed and discussed
1. Sonar system design and configuration
- User requirements (expected performance and functionalities)
- Instrument uncertainty level to be suggested to sonar manufacturers
- Best practices for sonar configuration, for seafloor backscatter and water-column data collection
- Definition of a terminology
- Methodology/best practices for backscatter acquisition
- Methodology/best practices for water-column multibeam data acquisition
- Compatibility with hydrography requirements (bathymetry best practices)
- Guidelines for standardized levels of data processing
- Best practices for backscatter processing, for different applications
- Standard basic products, providing consistent results (to be defined) whatever the processing software.
- Benchmark datasets from various sonars usable to verify/compare processing results from different manufacturers
Based on group feedback and discussion, the scope of the working group will be limited in the following ways:
- The focus should be on the fundamentals of backscatter recording and processing.
- The limit of the “processing” to consider here corresponds to backscatter data cleaned from the sensor artifacts (directivity patterns…) and the acquisition configuration (SVP refraction, seafloor slope…), and displayed in a way (flattening of the backscatter/angle, mosaicking…) making it readily usable for further interpretative tasks.
- Post-processing issues related to data manipulation and interpretation (e.g., segmentation, texture analysis, classification, modelling, etc.) will not be addressed.
- While processing matters are consensual within the backscatter community, post-processing issues are still evolving considerably and remain a more “open” domain; varied contributions and innovation still dominate, making it difficult to write a consensual document.
- SAS (Synthetic Aperture Sonar) is relevant but cannot reasonably be addressed now.
- “Non-MBES” bathymetric systems, in this case the limited family of “interferometric side-scan sonars” aka “phase-measuring bathymetric sonars”, will be included. These systems provide basically the same type of data as MBES – i.e. co-located bathymetry and reflectivity – while under a different array geometry. So all the concepts elaborated in the document with MBES in mind should be de facto applicable to these systems. Inevitably some specific points will have to be mentioned about the particularities of these sonars – we propose that the people who requested the inclusion of these systems take it upon themselves to write this part of the appropriate chapters, so that this does not impact the workload of the people working on MBES, which remains our priority.
- We will not address classical side-scan sonars, which are imaging systems without bathymetry or intensity measurement capabilities.
The main deliverable from the group activity will consist in a report featuring:
- common terminology and concept definitions applicable to the physical phenomena, to the processing operations, and to the data at their various stages of elaboration;
- a summary of the needs expressed by users from various fields, and the associated technical requirements;
- recommendations for system calibration and data acquisition, including survey configuration; environmental conditions control; and ancillary sensor quality control;
- recommended operations for data processing limited to the first-level stages of the backscatter data conditioning, aimed at presenting physically consistent backscatter data (while excluding post-processing operations such as image segmentation, classification and characterization).