Multibeam Bathymetry

Multibeam swath bathymetry data were acquired throughout cruise MGL0812 using the Langseth's  1°x1° beam Simrad EM120 multibeam swath sonar. Nominal sonar frequency is 12 kHz with an angular coverage sector up to 150 degrees and 191 beams per ping. Achievable swath width is approximately six times the water depth. In our working water depths of 2500-3000 m, the system acquired a useable swath width of ~12-13 km.

Multibeam data were ping edited onboard with preliminary bathymetric grids created during the expedition. Ping edited data quality is excellent and far exceeds the quality of much of the existing swath bathymetry for the region. Prior to our survey the best quality bathymetry grid for the survey region was an 80 m grid  from  Cochran (1999) and was limited to  -104°09’-23’ and 9°32’-9°58’. In 2005 a 6 km wide EM300 swath was run along the ridge axis by Scott White et al. using the R/V Thompson. The figure below shows a comparison between the EM300 data (gridded at 30x50 m) for the EPR 9°50'N bulls eye region with our bathymetry for the same region gridded at 50x50 m.

 

 

Based on the theoretical footprint of the sonar beam on the ocean floor in our survey area, the EM120 data can be reliably gridded to 75 m. However, our survey experience indicates the data can be usefully gridded to even finer interval in areas of redundant data coverage.

 

Other Underway Data

A proton precession magnetometer and the BGM3 gravitmeter, cross-decked from the Ewing, were operated for most of the cruise.