TITLE: Processed Multibeam data, BEST KNORR 195-10 Cruise - Summer 2009

Steve Roberts
NCAR/EOL
sroberts@ucar.edu

1.0 DATA SET OVERVIEW

During this cruise the Knorr's multibeam system (SeaBeam 3012) operated
for part of the time with minimal supervision. Thus sound speed
profiles were not kept current but it appears to have received valid
surface sound speed values during the duration of the cruise. Also,
this is not a shallow water system so the data in shallow water is of
low quality with a lot of noise. The original format of the raw data
is the vendor specific ELAC/SeaBeam XSE or mb94 based on the mbsystem
format nomenclature. The open source software package
mbsystem (http://www.mbari.org/data/mbsystem/) was used to apply new
sound speed profiles using the CTD data collected during this
cruise. In addition, mbsystems tool "mbclean" was used as a first pass
to remove the noise and artifacts from the shallow water sections. The
results were visually scanned and those files that still had obvious
problems were manually cleaned. This process is by no means
perfect. Due to the large number of files involved only a quick visual
scan was possible with only the most obvious artifacts being
removed. The Knorr multibeam also appears to have installation bias
issues which are most obvious in shallow water. No attempt was made to
address this issue at this time.  

2.0 INSTRUMENT DESCRIPTION

R/V Knorr, SeaBeam 3012-P1
See the web page at http://www.whoi.edu/page.do?pid=8576 for a
description of the multibeam system onboard the Knorr ship.

3.0 PROCESSING

This is a brief outline of the processing steps.

3.1 New sound speed profiles were manually generated using the CTD
data generated on this cruise. The processed CTD files already
included a column for sound speed so there was no need to calculate
this value. So a simple text editor and gnuplot were the only tools
needed for this step. The ocean climatology database Levitus was used
for extrapolating in deep water for areas where there were no deep CTDs.

3.2 A simple perl script(svp.pl) was written to read each multibeam
file and parse out it's latitude & longitude. It then used this
information to compute the great circle distance for all the CTDs to
that multibeam file and use the closest one for it's new sound speed
profile. An example output for each file: 

 mbset -PSVPFILE:../svp/218.sv -PHEAVEMULTIPLY:-1 -POUTFILE:svp_fix/sb20090711010933.xse -I sb20090711010933.xse
 mbprocess -F94 -I sb20090711010933.xse

The original xse files were saved in a directory for each day with
names of the form "20090705". So each directory contained a days worth
of xse files. This script was used to generate the above output for a
days worth of xse files and saved to "svp_process.sh". The script was
then run at the command line. The corrected files are saved to a
subdirectory "svp_fix". 

3.3 These corrected xse files were then cleaned using the mbsystem
  tool "mbclean". A typical command used: 

 mbclean -F94 -X6 -U10 -G.970/1.030 -I sb20090711010933.xse

However, the values for the parameters had to be occasionally tweaked
depending on the results. See the script mbclean.sh for examples. For
the example above the outputs will be: 

 sb20090711010933p.mb94
 sb20090711010933p.mb94.fbt
 sb20090711010933p.mb94.fnv
 sb20090711010933p.mb94.inf
 sb20090711010933.xse.esf
 sb20090711010933.xse.par

Please see the mbsystem documentation for a complete description of
these file formats. 

This script was only useful on the shelf where the bottom was
generally flat. Off the shelf and over deep water where the bottom was
generally not flat this step was not done and each file had to be
cleaned manually using mbedit.

After the processing of all the data was completed, the original and
intermediate xse files were deleted leaving only the final velocity
corrected and cleaned sb20090XXXXXXXXXp.mb94 files. 

4.0 DATA FILES

20090XXX.tar - The processed multibeam files along with auxiliary
                files generated during the processing  
                with a days worth of data per tar file

svp.tar.gz  - The sound speed profiles that were manually generated
              from CTD's along with the script svp.pl 

mbclean.sh  - Simple script with examples of mbclean usage.

5.0 REFERENCES

R/V Knorr, SeaBeam 3012-P1 information: http://www.whoi.edu/page.do?pid=8576
mbsystem information: http://www.mbari.org/data/mbsystem/
Information for program "geod": http://trac.osgeo.org/proj/