Computer and network configurationThe 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 recordingPython 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 conversionSEG-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 stackRealtime 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