Computer and network configuration
    The GeoEel digital streamer is attached to a PC (DOS?) which
is connected to a server PC (Windows 7?) and terabyte raid disk.
The server has a second raid disk for a backup of the SEG-D raw data
as well as the near-realtime processing (SEG-Y raw data and SEG-Y 
brute stack).  Only the near-realtime disk partition is accessible
through the ship's network.
    The ship's NTP (Network Time Protocol) is used for precise shot 
timing.
    The GeoEel also accepts a  XXXXX  connection which receives 
NMEA strings for navigation and water depth.
SEG-D recording
    Python script realtime runs on the server pc and backs up the SEG-D files
by copying to the second raid.
    This script also executes a csh script to convert the SEG-D files to SEG-Y.
realtime SEG-Y conversion
    SEG-D to SEG-Y script.
    This script runs on the Shipboard Geophysical Group's (SGG) server computer.
    Sioseis process segddin reads the SEG-D files from the GeoEel's computer and 
writes a SEG-Y file on the server's raid disk.  Segddin inserts the navigation 
and water depth NMEA strings into the SEG-Y trace headers.  The output disk
file may be exported to the ship's computer network.
    The key to creating the SEGY file in realtime is Sioseis segddin continually
looking for a new segd file (segddin format geometrics assumes the GeoEel
produces monotonically increasing file numbers).
Near realtime stack
    Realtime SEG-Y constant velocity stack test script.
    This script should be run on the scientist's computer rather than the SGG
server in order to prevent and conflicts with either the recording or SEGD
to SEGY conversion.
    The key to reading a SEGY file in realtime is the sioseis parameter "realtime"
which signals process diskin to sleep rather than exit when a read fails.

    Several sioseis parameters MUST be changed in the script:
1)  diskin   ipath /home/seismic/data/test10-10-2011/SEGY/site1/line1.sgy
ipath is the file pathname of the near-realtime raw SEG-Y file.
2)  diskin   ftr 1 ltr 48 is used to exclude any auxiliary channels.
3)  geom   gxp 1 -250
The correct distance from the source to group 1 should be used rather than -250.
The combination of gxp 1 -250 and ggx -12.5 indicates that group 1 is closest 
to the source.
4)  nmo    addwb yes vtp 1500 0 1600 .5 2000 2.0  
The velocity function is "hung" from the water bottom and can be changed.
5)  diskoa   opath /home/seismic/data/test10-10-2011/line1_stack.segy
opath should be changed and should be exported to all other computers.

Screen plots of realtime stack