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PROCESS SEGDIN
------- ------
Parameters, alphabetically:
DECIMF DESCALE DEVICE FCSET FDAY FFILEN
FGMT FILINC FORMAT FTR IUNIT LCSET
LDAY LFILEN LGMT LTR NEWFILE NFSKIP
NTRGAT OFFLINE RENUM RETRAC REWIND SECS
STIME TRINC TR0
Document date: June 2005
Modifications:
July 2004 - Add parameter DESCALE.
PROCESS SEGDIN reads seismic tape formatted in the SEG-D format
or the SEG-D, Revision 1 format (see Geophysics, April 1994).
Three demultiplexed data formats are available:
1) 20 bit binary format.
2) IBM floating point (SEG-D hexidecimal).
3) IEEE floating point (SEG-D, Revision 1.).
Reel changes and job termination may be done in the normal tape
manner, that is; the new tape unit number should be inserted in a
file named "IN" when the new tape is loaded and ready. A negative
tape unit number indicates that there are no more tapes and the job
should be terminated.
The tape change file "in" is deleted during the edit phase of
sioseis. When end-of-tape is detected, process segdin waits in a loop
until file "in" exists and then reads it to determine which tape unit
the next read is to be done on. File "in" is immediately deleted so
that a new file "in" must be created for every tape change.
SIOSEIS considers the SEG-D file number to be a count of the
file marks on tape. The file number is used as the SEG-Y "Original
field record number", word 3, as well as the "Energy source point
number", word 5, EXCEPT on the LDEO system. The LDEO system "shot
point number" is put in SEG-Y trace header word 3 and the file number
in word 5.
The SEG-D File number is used to control SEGDIN though parameters
FFILEN and LFILEN.
Example:
segdin
iunit 5 end
end
PARAMETER DICTIONARY
--------- ----------
PARAMETERS FOR READING BY FILE NUMBER
-------------------------------------
FFILEN - The first file number to read from tape. File numbers
less than FFILEN will be omitted. FFILEN 99999 indicates
that all shot files should be read, in the order on tape,
until LFILEN is reached or end-of-tape is detected.
Preset = 99999
LFILEN - The last file number to read from tape. File numbers
greater than LFILEN will be omitted.
Preset = 999999999
FILINC - The increment between FFILEN and LFILEN. FILINC 99999
indicates that all shots between FFILEN and LFILEN will
be used regardless of order. Only valid when FFILEN is
given.
Preset = 99999
PARAMETERS FOR READING BY GMT
-----------------------------
NOTE: GMT as used by these parameters is the time contained
in the SEG-D General Header. On the Ewing, this is the
Syntron clock, not the external GPS clock used as
"the Official Shot Time".
FDAY - The Julian day of the first shot to be read from tape.
preset = the day of the first shot on tape e.g. fday 365
LDAY - The Julian day of the last shot to be processed.
preset = fday. e.g. lday 366
FGMT - The GMT of the first data to extract from the tape. Shots
prior to FGMT will not be processed.
preset = the GMT of the first shot on tape.
LGMT - The GMT of the last shot to extract from tape.
preset = the last shot on the FIRST tape.
PARAMETERS USED BY BOTH GMT AND FILE NUMBERS
--------------------------------------------
DEVICE - The UNIX device name to use rather than /dev/nrst. IUNIT
should be given also, especially when tape changes will be
made, in which case use the IUNIT value in file "in" when
the new tape is ready. USE A NO-REWIND DEVICE so that Unix
does not rewind the tape when an end-of-tape is encountered.
USE A BSD DEVICE because SIOSEIS expects to read past
end-of-files when it detects the filemark between each
SEG-D shot. Any valid (a number from 0 to 50) unit number
may be used in file IN for tape changes.
********** ALWAYS USE BSD and NO REWIND (b and n)
e.g. Solaris 5.8 says:
/dev/rmt/[][]
Where density can be l, m, h, u/c (low, medium, high,
ultra/compressed, respectively), the BSD behavior option is
b, and the no rewind option is n.
Preset = none e.g. device /dev/rmt/0cbn
IUNIT - Obsolete, but still functional. Parameter DEVICE is preferred.
IUNIT - The tape unit number of the first input tape. Tape units may
be changed by changing IUNIT in a new FNO/LNO list or by the
use of file "in" as discussed above. The default on various
Unix machines is:
Sun: /dev/nrstIUNIT
SGI: /dev/mt/tps0dIUNITnrns
HP: /dev/rmt/IUNITmbn
Linux: /dev/nstIUNIT (nfiles > 1 will not work)
Preset 0. e.g. IUNIT 1
On R/V Ewing in May 2001 on grampus:
DLT was /dev/rmt/0 and /dev/nrst29 -> rmt/0cbn
DDS-3 was /dev/rmt/1 and /dev/nrst43 -> rmt/1cbn
3490 was /dev/rmt/2 and /dev/nrst35 -> rmt/2cbn
LOADER - The sleep time, in seconds, to sleep after each tape is
automatically loaded on the IBM 3480 cartridge auto-loader.
SEGDIN issues a rewind/offline command when two consecutive
file marks are sensed. It then sleeps while the loader is
changing tapes. A 90 second sleep works on the Fujitsu
M2485. The normal tape change scheme (via file in) is used
after the last tape in the loader, enabling another stack of
tapes to be inserted and SEGDIN notified via file in. (-1 in
file in terminates the SIOSEIS run). IUNIT should be given
also. Parameter NEWFILE is honored on each tape within the
stacker.
Preset = 0 e.g. loader 5
FTR - The first trace within each file to process. Trace numbers
less than FFILEN will be omitted.
Preset = 1 e.g. ftr 97
LTR - The last trace within each file to process. Traces with
numbers larger than LTR will be omitted.
Preset = The largest data trace number in the channel scan.
TRINC - The increment between traces. The trace skip increment.
preset = 1 e.g. trinc 2 every other trace is skipped
SECS - The maximum number of seconds of data to process.
Preset = length in the header. e.g. secs 6
STIME - The time of the first data to output. The delay of the
trace after reformatting. The data times will be from STIME
to STIME + SECS. The first portion of the data trace will
be discarded whenever STIME is greater than the delay of the
recorded data. STIME less than the recorded delay will NOT
result in zero padding. e.g. STIME must be greater than or
equal to the deep water delay.
Preset - The recorded delay. e.g. stime 4.0
DECIMF - Sample rate decimation factor.
Preset = 1, e.g. decimf 2 decimates by a factor of 2
NTRGAT - The number of traces per gather. SIOSEIS requires RPs to be
terminated with a -1 in word 51 of the SEGY trace header.
Because this is unique to SIOSEIS, gathers from other
computers may be converted by setting NTRGAT to the proper
value. SEGDIN will set every NTRGAT trace to be a
terminator. e.g. ftr 91 ltr 96 ntrgat 6 will read only
traces 91 - 96 and will set every trace 96 (the sixth trace
to be read) to be a gather terminator.
Preset = 0, e.g. ntrgat 12
RENUM - Renumbers the shots (file numbers) so that the first shot
read will be RENUM and successive shots will be incremented
by 1.
Preset = 0, e.g. renum 1
REWIND - Rewinds the input tape PRIOR to reading the first shot file.
= YES, rewind.
= NO, NO rewind.
Preset = yes, e.g. rewind no # don't rewind
FCSET - First channel set. The SEG-D format allows all traces with
similar characteristics to be grouped together. If traces
have different trace length, all traces with the same length
are grouped together. Likewise, auxillary traces belong
to a different set from seismic traces. e.g. The "UTIG"
data has 16 auxillary channels, each being a separate
channel set, and 96 seismic traces in the 17th channel set.
= 99, then all channel sets are processed.
Preset = 99
LCSET - Last channel set. Each channel set numbers it's traces
starting with 1; use retrac 1 when using multiple channel sets.
Preset = total number of channel sets.
RETRAC - Renumber the trace numbers within each shot/rp so that the
traces of each shot/rp start with retrac and each successive
trace is one larger. RETRAC is very important when using
multiple channel sets because each SEG-D channel set starts
it's trace numbers with 1.
Preset = none; = 1 when lcset > fcset e.g. retrac 1
NFSKIP - The number of files to skip before reading the first file
(in SEG-D, each shot is terminated by a filemark).
Preset = 0. e.g. nfskip 1 skips 1 file
FORMAT - The type of SEG-D format of the data tape.
=UTIG, The UTIG "EOFless" (no file marks) format.
Preset SEGD
OFFLINE - A YES/NO switch when set to YES means that the tape is set
offline during every tape change. This is quite useful on
3480 drives without a stack loader since it ejects the tape
from the drive, signaling that a new tape should be mounted.
File "in" is still used as a means of communicating with sioseis.
Preset = NO e.g. offline yes
TR0 - A YES/NO switch indicating that the SEG-D external header
should be written and saved in a disk file similar to the
old Digicon/LDGO trace 0. The disk file will start with
'tr0' and have the Syntron date of the first shot appended to it.
Preset = no e.g. tr0 yes
NEWFILE - A YES/NO switch when set to YES will cause PROCESS OUTPUT and
DISKOX to start a new SEG-Y file. This is useful when the SEG-Y
file should correspond to the input SEG-D tape.
DESCALE - A yes/no switch indicating whether to apply the SEG-D
"descalar" multiplier to every amplitude. The descalar
brings the data back to the recording system input
level, See the SEG standard for further information.
PRESET = NO e.g. descale yes
************************************************************************
SPECIAL INFORMATION FOR THE LDEO R/V MAURICE EWING
************************************************************************
LDEO uses a "shot point" counter that is incremented every
time the guns are fired. The shot point number is set at the
beginning of every cruise and is allowed to increment each time
a trigger is sent to the guns, thus the guns may not fire but the
shot point number is incremented.
A file number on the LDEO Syntron system is a count of the
files written to tape. In SEG-D, each shot is terminated by a
file mark and the file number incremented. If the shot fails to
be written to tape, the file number is NOT incremented. The file
number is reset to 1 everytime the Syntron is restarted.
SIOSEIS extracts the "official shot time" from an external
GPS clock rather than from the Syntron clock. The "official
shot time", the shot number, navigation (lat/long), and
Hydrosweep water depth are also extracted from the SEG-D
external header and placed in the SEG-Y trace headers.
LDEO supplies a daily navigation file that lists every shot
point number, "official shot time", and position. This file is
called a ts.n file. ts.n files do not contain the SEG-D file
number.
SEGDIN optionally carries the old DIGICON "trace 0" forward.
Trace 0 contains the nonseismic information in the SEG-D General
and External Headers. SIOSEIS process OUTPUT parameter
TRACE0 YES will write these headers as SEG-Y trace number 0 and
trace id 28 (see the SEG-Y documentation).
The Hydrosweep water depth is inserted as a floating point
number into the 54th real word of the SEG-Y trace header and is
converted to time by dividing by 750. and placed in real word 50.
The new (2001) Spectra/Syntron system does not put the Digicourse
streamer depth in SEG-D data, instead it is now in an external
UKOOA navigation file.
The SEGDIN code is:
(where ibuf is 16 bit integers, lbuf is 32bit integer, buf is REAL)
lbuf(3) = ldgo_shotno ! or SEGD shot number if not LDEO
lbuf(4) = itrcno ! shot trace number
lbuf(5) = ifilen ! SEGD file number
ibuf(15) = 1 ! SEGY trace id
buf(46) = AMAX1(delay(icsn),stime) ! REAL delay
ibuf(55) = NINT(buf(46) * 1000.) ! delay in mils
ibuf(58) = (nsamps + decimf - 1) / decimf ! number of samples
ibuf(59) = micros * decimf ! sample interval in micros
buf(49) = si * decimf ! REAL sample interval in seconds
lbuf(16) = wdepth ! integer water depth
ibuf(79) = ldgo_yr ! year of "official shot time"
ibuf(80) = ldgo_day ! day of "official shot time"
ibuf(81) = ldgo_hr ! hour of "official shot time"
ibuf(82) = ldgo_min ! minute of "official shot time"
ibuf(83) = ldgo_sec ! second of "official shot time"
ibuf(84) = ldgo_mil ! "millisecond of "official shot time"
*** This use of word 84 is an SEG-Y violation ****
ibuf(36) = -10 ! scalar for coordinates
lbuf(19) = NINT(ship_long*360.*60.*10.) ! shot x-coordinate
lbuf(20) = NINT(ship_lat*360.*60.*10.) ! shot y-coordinate
lbuf(21) = NINT(ship_long*360.*60.*10.) ! shot x-coordinate
lbuf(22) = NINT(ship_lat*360.*60.*10.) ! shot y-coordinate
ibuf(45) = 2
buf(50) = wdepth / 750.
buf(54) = wdepth
If process GEOM parameter GXP and BGP are used, the group offset and
streamer depth are added as:
lbuf(10) = NINT(range)
lbuf(11) = -NINT(depths(lbuf(4))*100.) | streamer depth in cm
.
SIOSEIS/LDEO SEGDIN error messages:
1) *** WARNING *** Syntron error or guns did not fire.
This message is printed when the the LDEO "official shot time" has
a '-' quality flag between the year and day of year. The Syntron
system did not acknowledge the firing trigger beacause a) the
trigger was not sent and the guns didn't fire, or b) the Syntron
failed in some other way.
2) *** WARNING *** Bad LDEO clock.
This message occurs when the LDEO "official shot time" does not
have a '+' or '-' quality flag between the year and day of year.
3) *** WARNING *** Bad LDEO block.
This message occurs when the LDEO nav block has garbage in place
of the GPS fix.
4) *** WARNING *** Bad LDEO Hydrosweep of XXXXXX
This message occurs when the Hydrosweep center beam depth is
greater than 10000 or less than 100. The previous depth is substituted.
5) LDEO "nav" block does not have Digicourse.
This message occurs when the streamer birds do not report back to
the recording system. The streamer bird communications is single
duplex; they can not talk when being talked to. Setting the bird
depths will cause this message until the Digicourse program is
reset to the "run" mode.
TAPE ERROR CODES
status = -6 means a tape read error. Dirty tape can cause parities.
Blank or no data might also cause this.
status = -1 means end-of-file. SIOSEIS may interpret parities as
file marks on some tape drives.
status >0 is the number of 16 bit words read.
Copyright (C) Seismic Reflection Processors, San Diego, Ca.
ALL RIGHTS RESERVED.
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