This report covers the Simrad EM120 Multibeam data collection and processing for the RVIB Nathaniel B. Palmer cruise NBP0709. This cruise started at Punta Arenas, Chile on September 1, 2007 (GMT) and ended at Punta Arenas, Chile on October 31, 2007. Multibeam data logging started at 19:44 (GMT), September 28, 2007. Data was collected during the rest of the cruise with the exception of a few hours ... when it was turned off so as not to interfere with recording of underwater seal calls. 1862 kilometers of data consisting of 222,829 records were collected during this cruise. Most of the data collected was collected during the Ice Station Belgica Drift. Data quality during the drift was good except when the bow thrusters were operating. When the ship was drifting parallel to the swath width, not much new data was collected. After ending the drift, the ship traveled through pack ice for several days and data quality was poor during this period. The raw Multibeam data were logged in approximately one hour-long files in the Kongsberg Simrad EM120 raw format. This is a complex format that is not described in this report. The MBSystem1 software package may be used to access the files if additional work is to be done with the data. MB-System version 5.0.7 was used for processing of data on this cruise. MB System versions 5.0.9 and 5.1.0 are available, but these newer distributions do not correctly handle sides can data for the EM120 system. It is recommended that users who are interested in this data continue to use MB System 5.0.7 until a distribution that correctly handles the EM120 sides can data is released. These raw data files are named xxxx_yyyymmdd_hhmmss_raw.all where xxx x is a consecutive line number within the survey, yyyy is the year, mm is the month, dd is the day, hh is the hour, mm is the minute, and ss is the seconds that the file was started. The logged Multibeam data files were transferred from the data acquisition computer to a data storage area just after the end of each day. The raw hourly data files were converted from MB System format 56 (the raw Simrad format) to format 57 using mbcopy and were made available for manual editing. The format 57 files are named xxx_yyyymmdd_hhmmss.mb57 where the first part of the name is identical to the raw file. All data files were edited while at sea.
The Bellingshausen Sea area, because of ice cover and remoteness, has not been the subject of intensive study of its fundamental properties, including bathymetry. Therefore the swath bathymetric system on NB Palmer was used to fill in some of the blanks in bottom topography and bottom characteristics. Data was coordinated with J. Anderson, Rice Univ, and Julian Dowdeswell, Scott Polar Research ... Institute to provide more complete bottom mapping of the region by combining this swath information with that from previous cruises of NB Palmer and JC Ross in the region. Particular features of interest were the depressions and channels on the shelf and continental slope which has origins in glacial melt water erosion at the retreat of the last ice age and, on the shelf, were thought to be pathways for warm deep water to access the sub glacial cavities of Pine Island Glacier, Thurston Glacier and other glaciers. The warm waters were hypothesized to be a source for the excess melting recently observed for these West Antarctic glaciers and ice shelves.