| Summary: | Maintenance and Update Frequency: asNeeded Statement: Original field data. This record describes sub bottom profiler data collected on RV Tangaroa voyage TAN2021_V01 (NIWA TAN2113), which was carried out on a contract to the CSIRO MNF from 9th November to 4th December 2021. The voyage had two objectives, which were to recover 27 Ocean Bottom Seismometers which had been deployed around Macquarie Island on IN2020_v06, and complete multibeam and sub bottom profiler mapping along the crest of the Macquarie Ridge and collect new multibeam data during transits. The Kongsberg Maritime TOPAS PS 18 Parametric Sub-bottom Profiler was used to acoustically image the strata and structure in the seafloors's shallow sub-surface. Sediment penetration can achieve 120-150 m in ideal conditions. Sub bottom profilers in general do not perform well with hard rocky substrates, water depths less than 150 m, steep and irregular terrain. The working area was subject to these limitations which made SBP data acquisition challenging and affected the resultant data. The data recorded in water depth greater than 4000 m at transit speeds when synced with multibeam acquisition was of little use as the time between pings was too long to maintain bottom lock. The transmitted waveform used was a linear frequency-modulated chirp (LFM) which was externally triggered with K-Sync to avoid interference with the EM302 and EM2040 multibeams. The frequency range of the chirp was from 2.0 to 6.0 kHz, with a chirp length of 20 or 15 ms or 50 ms for deep water. Transmitter output level was set to 0 dB and gain set to 0 dB and the high-pass filter was set to 1.0 kHz. The sub bottom profiler beam is stabilised for heave, roll and pitch via motion data fed from the PosMV. Beam steering was set to automatic. Raw data files were written in WGS 84 and SEG-Y files were written with UTM57S projection in the survey area and NZTM projection on transit. Data are stored in *.raw (123 files 3.82 GB) raw and *.seg (156 files 3.78 GB) segy formats at CSIRO. Additional ...
|
|---|