2019 E/V Nautilus Quality Assessment Report

Multibeam System: 

Executive Summary

  • Heading into the 2019 operating season, the EM302 and associated sensors aboard the E/V Nautilusare working very well compared to the 2018 NA093 Quality Assurance Test (QAT) and earlier shipboard assessments.
  • The EM302 was calibrated for residual angular offsets using the Seapath 330-5+ as the primary positioning/attitude system. The NA105 patch test revealed only very slight pitch and roll adjustments were required. These biases were entered into the SIS installation parameters for Attitude 1, COM2/UPD5, and should not be changed unless modifications are made to the system or there is evidence that another ‘patch test’ is necessary. If any changes are made please notify Johnson for amendment of this report.
  • Swath accuracy assessments were conducted over existing shallow and deep reference surfaces that had been collected during the 2017 NA079 QAT. Eight different operational settings were run (5 on the deep surface and 3 on the shallow) and analyzed. Results indicate expected and acceptable performance when comparing the data to previously collected accuracy assessments and to other system which have been evaluated. There were some issues with proper sound speed correction for the reference surfaces, which did bias the results for the outer portions of the swath. This issue was further exacerbated by the lack of a functioning surface sound speed sensor.
  • NA105 was able to collect deep data down to 3750 meters water depth for swath performance analysis (extinction) as had NA093. The NA105 swath performance was as good or better than the NA093 performance over this depth range.
  • Due to a small sample size of NA105 extinction data for depths deeper than ~2500 meters and the soft sediment bottom type for that range of depths it is somewhat difficult to assess if there has been a decrease in swath width at those depths as compared to historic data. If more data is collected during the 2019 field season, please transfer the data to Johnson for analysis.
  • Initial noise testing in the Catalina Basin area using the Built-In Self Test in SIS initially seemed to reveal a higher than expected noise floor. However, after conducting another set of noise testing offshore at the deep water ROV dive site it was shown that the E/V Nautilus’s noise floor (40-44 dB) were much lower than what had been observed during 2018 (50-54 dB) over the same speed range. The 2019 levels were similar to those observed during the initial shipboard acceptance testing done in 2013 (~40 dB).
  • A noise test was conducted to look at the noise while underway with the jet pump (~38 dB) into and with the seas at 3 knots VS no propulsion (~37 dB). This indicates that the jet pump is producing little to no acoustic noise at the frequencies detected by the EM302.
  • The heading/sea state related noise testing showed that there was significant difference in the ship’s self noise between heading going into the seas and headings with the seas. When the heading was directly into the seas or with seas on the port bow, the self-noise of the ship was ~47-~51 dB.When travelling with the seas (waves on stern) or waves on the starboard stern, the ships self-noise was ~50-~57 dB.
  • From a strictly qualitative assessment, the bathymetric data appeared very clean with few flyers and excellent bottom tracking. This was especially apparent at the patch test site where the pitch and yaw lines on the slopes were much easier to work with than the data collected on the same lines in 2017 and 2018. This was remarked on by both Johnson and Gee while undertaking the patch test.
  • Using a known seep, detected during previous E/V Nautilus mapping, a series of lines were setup to pass directly over the seep, and then be offset from the seep by 450 meters, 900 meters, and 1350 meters ranges. The seep was easily detected in the water column data on both the port and starboard side at all ranges.
  • Qimerawas used during the seep detection evaluation. It provided ray traced positions with fairly low uncertainty in position to the seep during each of the offset lines (0, 450 meters, 900, and 1350 meters).
  • A backscatter equalization assessment was done looking at inter-sector and inter-mode (medium to deep transitions) over a relatively benign area of seafloor. Historic data (2017) had indicated that FMGT was not correctly handling the balancing between modes at this site. Test data collected during NA105 showed the same imbalances in both the waterfall (raw) data and in the mosaics generated from the test data. This issue would be well worth spending some more time looking at during the next QAT.
  • The Sound Speed Manager software (https://www.hydroffice.org/soundspeed/main) was updated to the latest version and was used during NA105. The new version of the software was successfully tested for importing sound speed profiles from a Hercules ROV dive.
  • The Underway CTD (UCTD) had been sent out to recalibrated during the off season and had not been returned in time to be used for NA105. A loaner unit provided by Teledyne Ocean Science, but this unit was non-functional due to battery issues. The recalibrated UCTD was returned to the ship post-NA105.
  • The AML Surface Sound Speed Sensor was not working for the QAT. A replacement unit was delivered to the ship immediately following the end of NA105.
  • There were some issues with SIS stability. This was likely due to heat related issues (the cooling system was disabled at one point) and issues with card connectivity. Temperature in the sonar room should be carefully monitored.
  • It would be well worth clearing out the SIS list of prior surveys before continuing too long with the 2019 field season (this was an unchecked action item from NA105).
20190702_NA105_NautilusEM302_QAT_Report_Final_Version1pt1_opt.pdf10.96 MB