11/04/2015 — admin
The research vessel icebreaker (RVIB) Nathaniel B. Palmer (NBP) undertook cruise NBP1505 in the vicinity of the continental shelf break between Talcahuano and Puerto Montt, Chile, from June 10-15, 2015 (Fig. 1) in order to assess performance of the vessel’s 12-kHz multibeam echosounder (MBES). The MBES consists of a Kongsberg Maritime (KM) EM122 transceiver installed in June 2014 and transmit (TX) and receive (RX) arrays installed in June 2015, prior to NBP1505.
A Sea Acceptance Trial (SAT) for the EM122 transceiver performed in June 2014 (NBP1405) revealed extensive degradation of the original EM120 TX array and motivated the upgrade of both EM120 TX and RX arrays to the latest-generation EM122 models (see NBP1405 MAC SAT report for more detail). A primary expected advantage of the EM122 array upgrade is wider swath coverage through frequency-modulated (FM) transmission compared to traditional continuous waveform (CW) operation. FM capabilities were available with the EM122 transceiver but not fully supported by the original EM120 arrays.
Additionally, the damaged polycarbonate ice window on the EM120 TX array was replaced completely prior to NBP1505; the titanium ice window on the EM120 RX array was observed to be in good condition and reinstalled for the EM122 RX array. A survey of the installed arrays, GPS antennas, and the two MRUs (Seapath 330 and Seapath 200) was conducted while the NBP was in dry dock in Talcahuano. The survey results were provided in preliminary form to KM and MAC personnel for implementation during NBP1505.
The primary MAC objectives during NBP1505, which are documented in this report, were to:
- Assist KM representatives with the SAT of the EM122 TX and RX arrays
- Review and update the system geometry per the 2015 Talcahuano survey
- Determine residual angular offsets between the MBES and primary MRU
- Evaluate the depth accuracy across the swath using a reference surface
- Examine RX array noise conditions at various speeds and headings relative to the swell
- Determine the achieved swath coverage over a wide range of depths
- Outline steps for transformation of all MBES sensors to a common reference frame