2018 E/V Nautilus Quality Assessment Report

Multibeam System: 

Executive Summary

  • Heading into the 2018 operating season, the EM302 and associated sensors aboard the E/V Nautilusare working well compared to the 2017 Quality Assurance Test (QAT) and earlier shipboard assessments.
  • The EM302 was calibrated for residual angular offsets using the Seapath 330+ as the primary positioning / attitude system. The patch test revealed that only very slight roll and heading adjustments were required. These biases were entered into the SIS installation parameters for Attitude 1 motion sensor, and should remain unchanged unless modifications are made to the system or there is evidence that another ‘patch test’ is necessary.
  • Swath accuracy assessments were conducted over existing shallow and deep reference surfaces that had been collected during the NA079 QAT. Seven different operational settings were run (4 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. Further work will be done on the crosslines to see if synthetic sound speed profiles applied to the data can better quantify the accuracy of the system.
  • NA093 was able to collect deeper data for swath performance analysis (extinction) than was able to be done during NA079. The NA079 testing had revealed that the EM302’s swath width as a function of depth was not performing at the level it had been historically been able to. This issue was eventually identified to be due to marine growth on the hull and array faces causing flow noise. After cleaning the surfaces, data collected during a long deep transit showed that the EM302 was able to match the historic swath performance.
  • NA093’s extinction data showed that the EM302 was performing better than it had during NA079, but due to the lack of a large sample size for the deeper portion of the extinction test, it is unclear if the EM302 is performing as well as it did during the NA089 transit. If more data is collected during the 2018 field season, please transfer the data to Johnson for analysis.
  • Noise testing using the Built-In Self Test in SIS initially seemed to reveal a large ship self-noise problem. However, after consulting with the bridge it was revealed that a doppler speed log was running during the tests. Subsequent testing revealed that noise levels were significantly lower (~48 dB) than those seen during NA079 (~50-54 dB). However, the levels were not as low (~40 dB) as those seen during the initial shipboard acceptance testing done in 2013.
  • 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 there were seas on the port bow, the self-noise of the ship was ~55 dB.When travelling with the seas or waves on the starboard bow, the ships self-noise was ~48 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.
  • 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.
  • The determination of geolocation of seeps using Qimera instead of FM midwater showed significantly less variation in position than when using FM midwater. It is recommended that this method be used for future geolocation.
  • The Sound Speed Manager software (https://www.hydroffice.org/soundspeed/main) was updated to the latest version and was used during NA093. The new version of the software was successfully tested for importing sound speed profiles from a Hercules ROV dive. Ideally, both temperature and salinity should be included with the ROV CTD profile for future archiving and for absorption calculation.
  • The Underway CTD (UCTD) was recalibrated during the off season, and after a minor cabling issue during recovery, the system was successfully used to collect data for determination of sound speed profiles.
  • There were some issues with SIS stability, especially during the early parts of NA093. This was likely due to heat related issues (the cooling system was disabled after power blackout). Temperature in the sonar room should be carefully monitored.
  • As has been historically the case, TX board 4 in the TRU caused downtime during data collection and needed to be reseated and power cycled to continue collecting data.
  • A long time action list item was finally completed at the conclusion of NA093 when the SIS survey list of prior cruise was finally cleaned out. This amounted to removing over 100 surveys, which done over the last 4 years, from the database.
  • The surface sound speed pump was changed out for a spare due to a worn bearing. No noise issues were detected using the RxnoiseBIST following the change of the unit.
  • WAAS was forced enabled in the Seapath control software as the automatic SBAS was not functioning.
  • During NA093 there was a temperature gradient error with the Seapath which had not been seen before. The error was acknowledges and no further issues were noticed.
  • The Seapath Control software was unable to export the Seapath configuration files for backup. This issue should be followed up with Kongsberg to see how it can be resolved.
NA093_NautilusEM302_QAT_Report_Final_v1pt2.pdf25 MB