02/05/2013 — admin
The accuracy (repeatability, strictly speaking) analysis indicates that the system is performing within expected levels. The EM122 appears to be configured correctly and adequately calibrated. A full patch test calibration was conducted with the offsets being applied in SIS; follow up confirmation calibrations indicate that the offsets are correct. A residual bias exists in the system that is associated with the multibeam system itself and not the MRUs (as it was common to both the Hydrins and Seapath). The bias, though typical of a surface sound speed bias, cannot be explained by this and must have another cause. The bias should be raised with the manufacturer to better understand if this has been observed before.
Coverage performance of the EM122 is as expected and is consistent with Lurton’s model predictions in DEEP mode. Discrepancies in MEDIUM and SHALLOW mode indicate that further refinement of the model is required, however, the good agreement with the DEEP mode increases confidence in the predicted system coverage performance in deep water and indicate that it will be reasonable and on par with what is achievable with similar EM122 systems in the US academic fleet.
Data quality is satisfactory in terms of bathymetry, seabed imagery and water column imagery. No sector specific artifacts were observed in the bathymetry or seabed imagery. Slight signal level offsets were observed between sectors in the dualNswath geometry in water column imagery but they are typical of what is usually observed for Kongsberg Maritime dualNswath systems. Bubble sweep events were observed in typical sea states, however, SIO personnel indicate that their standard procedure is to ballast the vessel to trim the bow down slightly to mitigate these effects.
Small (<1 m) transmitter/receiver sensor offset errors were found during the review of the vessel geometry. These were corrected in SIS so the system is correctly configured to the best of our knowledge. Past data sets should be examined to determine at what point the system was incorrectly configured to aid in QA efforts undertaken by R2R and GMRT.
The following recommendations are made with respect to patch test calibration design and execution:
- Yaw/Pitch stabilization should be enabled for calibration routines to give nearly constant along-track sounding density.
- Dual swath should be enabled for calibration routines to give increased along-track sounding density.
- Vessel speeds should be slower than those typically used for mapping in order to increase the alongNtrack sounding density, especially when
attempting to resolve smaller topographic features. Smaller and more discrete topographic features should be chosen for pitch/heading calibration site.
- If stationary roll calibrations (holding station with dynamic positioning system and then reversing direction) are to be pursued, the MRU pitch and heading offsets must first be resolved and pitch stabilization should be enabled.
|2013 Revelle QAT Final Report (.pdf)||6.31 MB|
|2013 Revelle System Configuration (.pdf)||955.04 KB|