Processing steps
While some processing software retains L2 MBES backscatter data in proprietary formats during the mosaicking process, others only preserve the final L3 MBES backscatter. This variation in data retention can significantly influence how the data can be accessed, analysed, and reused in future projects.
Retaining L2 backscatter offers several advantages, such as the ability to revisit and refine the data with different processing techniques or to apply additional corrections that may be necessary as new methodologies emerge. This flexibility is particularly valuable in scientific research, where data integrity and the ability to reprocess information are critical for reproducibility and long-term studies.
On the other hand, software that retains only L3 backscatter offers a streamlined process aimed at delivering a final product—a backscatter mosaic ready for interpretation and analysis. Although this method is efficient, it may limit the ability to revisit the data for new requirements or additional validation without reverting to the original L0 MBES data.
Regardless of the specific software or data retention strategy, AusSeabed recommends following the standardised processing flowchart illustrated in Figure xx. This flowchart ensures that all steps, from data acquisition to final mosaic creation, are conducted systematically, promoting consistency and accuracy across different surveys and projects. By adhering to this recommended workflow, users can ensure that their backscatter data meets the highest standards of quality, whether it’s used for immediate analysis or archived for future research and development.
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Figure 1. Recommended backscatter processing flowchart
Starting with L2 MBES data that includes backscatter measurements, the following steps outline the process for backscatter data processing (Figure xx):
Gain Correction: Adjust for any gain discrepancies in the backscatter data to ensure consistency across the dataset.
Propagation Effects Correction: Apply corrections for propagation effects, such as Time-Varying Gain (TVG) and insonified area adjustments, to account for variations in signal strength due to distance and angle.
Physical Properties Correction: Correct for physical factors like beam pattern distortions and apply dB offset calibration values to standardize the backscatter measurements.
Angular Dependence Removal: Address angular dependence by applying methods such as averaging, setting window sizes, and defining reference angles to minimize distortions related to the sonar's viewing angle.
Pre-Mosaicking Adjustments: Implement pre-mosaicking steps like anti-aliasing and despeckling to reduce noise and prepare the data for seamless integration.
Mosaicking: Create the backscatter mosaic by selecting grid size, choosing the appropriate operation and blending methods, and applying post-mosaicking enhancements to refine the final product.
L3 MBES Backscatter Product: The final L3 MBES backscatter grid, which integrates all corrections and adjustments to produce a high-quality backscatter mosaic ready for analysis.
Depending on the software, the first 4 or 5 steps may have already been completed for systems that retain L2 MBES backscatter, eliminating the need to repeat them. However, for software that does not retain L2 MBES backscatter, all 6 processing steps are required.
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[1] Based on NOAA’s, AHO’s HIPP and correspondences with Dr Calder.
[2] 20.707xGrid_Resulution (NOAA, 2014; HIPP version 1.2).
[3] HIPP version 1.2 and NOAA (2014).
[4] CARIS automatically reset to 100, a maximum value allowed