06/13/2013 — admin
The transducer impedances are similar to baseline measurements with exception of the EM710 transducer impedances. This latter potential issue is being examined with the manufacturer but we do not feel, after consultation with the manufacturer, that there is any cause for concern. Noise levels have not changed significantly since the 2012 trials in “Science” mode. Review of the noise results by Tim Gates indicates that there are some modules reporting higher noise levels compared to measurements taken by Gates in early 2012 and may warrant a closer investigation
even though the system performance does not appear to have degraded. Despite the uncertainty associated with the EM710 transducer impedances, the consistency of achievable coverage relative to the 2012 results is a strong indicator that both systems, as a whole, have not experienced any acoustic degradation over their first year of life in terms of acoustic performance.
Calibration of the two systems was performed with much more ideal seafloor imaging geometry compared to the 2012 patch test. The systems have been updated with the new calibration results.
Both multibeam systems provide bathymetric measurements that are in agreement with the expected performances of the systems and that are consistent with previous examinations. There is no evidence of degradation of ancillary sensor performance since the previous accuracy tests. Furthermore, the EM710 “FM wobble” data artifact identified in 2012 has indeed been corrected by increasing the MRU’s data output rate for the Doppler velocity corrections required for FM waveforms.
Seabed imagery quality is good and is generally artifact free. There are residual interVsector imbalances with the EM302 despite the signal balancing routines undertaken in 2012. The EM710 has slight signal imbalances, however, it is not currently possible to correct for this using the same mechanism that is used for the EM302. In both cases, the residual offsets are easily corrected in commercial processing software.
As a whole, the two multibeam systems are in satisfactory working condition and we do not anticipate any problems with either system for the 2013 mapping season.