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PROCESS INPUT (READS MAGNETIC TAPE)
Document Date: July 2002
Process INPUT reads seismic data from magnetic tape. The data must be
in SEG-Y format. INPUT is trace oriented rather than shot or rp
oriented. Process INPUT reads a single trace from tape and immediately
passes it on to the next process in the PROCS list.
The data may be read from tapes using one of three different controls.
Field tapes may be controlled by either shot numbers or GMT time. Tapes
that have been processed through process GATHER must be controlled by rp
numbers. Stacked tapes may be read using either rp numbers or by GMT
time.
Input tape changes are handled by process INPUT through operator
intervention when either end of tape is reached (a file mark) or when
the user specifies a new tape number via the IREELN parameter. Operator
tape changes are accomplished by passing the new tape unit number to
SIOSEIS via file "in" when the new tape is mounted and ready. The file
"in" must be in the same directory that the SIOSEIS job is running.
A -1 unit number terminates the job. The file may be created using the
editor.
The tape change file "in" is deleted during the edit phase of sioseis.
When the end-of-tape is deteceted, process input 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 allows the user to "break" the SEG-Y standard by putting more
than one file on a single tape. In order to read multiple files on a
tape, INPUT parameter NFILES should be used. Each file should contain
both SEG-Y headers (see document segy.header).
SIOSEIS assumes that shot numbers increase on the tape unless parameter
ORDER is used. If the shot numbers do not increase, or if the shots are
not to be processed in the order they are on tape, multiple parameter
list may be used. For example if the shots on tape are ordered 10001 to
11000 followed by shots 500 to 600, use either fis 99999 or use two lists
e.g. fis 10001 lis 11000 end
fis 500 lis 600 end
THE PARAMETER DICTIONARY
--- --------- ----------
Required Parameters
-------- ----------
DEVICE - The UNIX device name to use rather than /dev/nrst. IUNIT is
ignored when DEVICE is given, but may be specified by the
user. 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. Any valid
positive unit number may be used in file IN for tape changes.
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
Parameters for processing by shot
---------- --- ---------- -- ----
FIS - The first input shot number of a set of shots (of a fis-lis-end
LIST). A negative FIS means that the first shot of the set is
in a reverse or backwards direction on tape from the previous
shot input. The shots will be read from tape in the order
specified by: FIS to LIS in increments of SINC. e.g.
fis 1 lis 5 means that the shots must be ordered 1, 2, 3, 4, 5
on tape. If a shot within FIS - LIS is missing, the program
will continue to search for the missing shot and will stop at
the end of tape without finding the shot. A fis of 99999 will
cause the program to read all shots on the input tape regard-
less of shot number (the shot numbers do not have to be con-
secutive). Use of fis 99999 causes lis to be ignored, thus the
only way the job can be stopped is at the tape change when the
operator responds with a -1 unit number. FIS 99999 still
assumes that all the traces are as described in FTR/LTR.
Preset = first on tape. e.g. fis 41
LIS - The last input shot number of a set of shots (of a list).
Preset = 32767. e.g. lis 201
NIS - The number of input shots to read when fis = 99999.
Preset = 32767 e.g. nis 5
SINC - The shot increment between the first shot (iabs(fis)) and the
last shot (lis) of a list. Alternate shots may be processed by
using sinc 2. A negative sinc must be used if shot lis is
before shot fis on tape.
Preset = 1. e.g. sinc 2
FTR - The first trace of each shot to process. A trace with a trace
number on tape less than ftr will be ignored. An FTR of 99999
indicates that all traces will be read regardless of trace
number or trace order.
Preset = 1. e.g. ftr 23
LTR - The last trace of each shot to process. A trace with a trace
number on tape larger than LTR will be ignored.
Preset = tape header. e.g. ltr 23
TRINC - The increment between traces FTR and LTR. Alternate traces may
be processed by using trinc 2.
Preset = 1. e.g. trinc 24
Parameters for Processing by RP (cdp gathers)
---------- --- ---------- -- -- -----------
FRP - The first input rp number of a set of rps (of a frp-lrp-end
list). A negative frp means that the first rp of the set is
in a reverse or backwards direction on tape from the previous
rp input.
Preset = first on tape. e.g. frp 41
LRP - The last input rp number of a set of rps (of a list).
Preset = 32767. e.g. lrp 201
RPINC - The rp increment between the first rp (iabs(frp)) and the last
rp (lrp) of a list. Alternate rps may be processed by using
rpinc 2. A negative rpinc must be used if rp lrp is in front
of rp frp.
Preset = 1. e.g. rpinc 2
FTR - The first trace of each rp to process. A trace with a trace
number on tape less than ftr will be ignored. An ftr of 99999
indicates that all traces will be read regardless of trace
number or trace order.
Preset = 1. e.g. ftr 23
LTR - The last trace of each rp to process. A trace with a trace
number on tape larger than ltr will be ignored.
Preset = tape header. e.g. ltr 23
TRINC - The increment between traces ftr and ltr. Alternate traces may
be processed by using trinc 2.
Preset = 1. e.g. trinc 24
Parameters for Processing by time (gmt)
---------- --- ---------- -- ---- -----
All shots prior to fday, fgmt are ignored. All shots are then processed
as they are read from tape until lday, lgmt is exceeded.
FDAY - The first julian day of the data to be read from tape.
Preset=0. e.g. fday 364
LDAY - The last julian day of the data to be processed.
Preset=fday
FGMT - The first time of day fday of the data to be read from tape.
GMT is expressed as hhmm or hours and minutes of the 24 hour
clock (0000-2359).
Preset=0. e.g. fgmt 1400
LGMT - The last time of lday to be read from tape.
Preset=0. e.g. lgmt 0605
FTR - The first trace of each shot to process. A trace with a trace
number on tape less than ftr will be ignored. An ftr of 99999
indicates that all traces will be read regardless of trace
number or trace order.
Preset = 1. e.g. ftr 2
LTR - The last trace of each shot to process. A trace with a trace
number on tape larger than ltr will be ignored.
Preset = all traces e.g ltr 1
TRINC - The increment between traces ftr and ltr. Alternate traces may
be processed by using trinc 2.
Preset = 1. e.g. trinc 24
USEFUL OPTIONAL PARAMETERS
------ -------- ----------
FNO - First shot/rp number. FNO may be used instead of FIS or FRP.
Ordinarily SIOSEIS insists that the users know whether the
input tape is sorted by shot or rp and will not run if the tape
is described incorrectly. The use of FNO and LNO simplifies
this! As with FIS and LIS, FNO 99999 reads all traces from
tape regardless of their numbers and will stop reading only
when a negative tape unit number is given in file "IN" at the
end of a tape (see tape change).
Preset = none e.g. FNO 101
LNO - Last shot/rp to read.
Preset = none e.g. LNO 200
NOINC - The increment between FNO and LNO. The shots/rps on tape will
be read in the order FNO to LNO in increments of NOINC. If a
shot/rp is missing, PROCESS INPUT will continue searching until
it finds it. e.g. FNO 1 LNO 5 but the shot/rps on tape are 1,
2, 4, 5 then SIOSEIS will search the entire tape for shot 3,
stopping when it finds end of tape, and never reading shots 4
or 5. Use FNO 99999 when this occurs.
Preset = 1
NO XN - The word type and the index of the SEG-Y trace header to use
for searching rather than the shot or rp number.
X = I, means short integer (16 bit integer trace header)
= L, means long integer (32 bit integer trace header)
= R, means real word (host floating point)
N = the index with the SEGY trace header.
Example: no l10 means long word 10 (the range) will be used
instead of FIS/FRP/FNO and LIS/LRP/LNO.
Preset = none
TR XN - The word type and the index of the SEG-Y trace header to use
for searching rather than the shot/rp trace number.
X = I, means short integer (16 bit integer trace header)
= L, means long integer (32 bit integer trace header)
= R, means real word (host floating point)
N = the index with the SEGY trace header.
Example: tr l10 means long word 10 (the range) will be used
instead of the shot/rp trace number for FTR and LTR.
Preset = none
ALLNO - Read all shots/rps yes/no switch.
= YES, all shots between between FIS and LIS will be read
regardless of number.
= NO, the shots/rps will be read in strictly monotonic
increasing order. i.e. Only shots FIS, FIS+SINC, FIS+2*SINC,
FIS+3*SINC, ....., LIS will be read.
Preset = YES e.g. allno no
ALLTR - Read all traces yes/no switch.
= YES, all traces between between FTR and LTR will be read
regardless of order or number.
= NO, the traces will be read in strictly monotonic
increasing order. i.e. Only shots FTR, FTR+TRINC, FTR+2*TRINC,
FTR+3*TRINC, ....., LTR will be read.
Preset = YES e.g. alltr no
RENUM - Renumbers every shot/rp so that the numbers are monotonically
increasing by 1, starting with the number specified by renum.
Renumbering the shot/rp numbers is helpful when the input
shot/rp numbers are nonunique and some parameter needs to be
spatially varied. The renumbering is done after the shot/rp is
read.
Default = not given. e.g. renum 1
C - Comment card images to replace in the tape header. The comment
card must start with the letter c and must be followed
immediately by a 2 digit number, followed by a blank. The
number is the card number within the header to replace. The
comment itself must be enclosed in single quotes.
Preset=none. example c15 'this is an example of a comment'
STIME - Start time of the data to process. Data prior to STIME will be
discarded and the deep water delay will be set to STIME. If
STIME is less than the deep water delay, STIME will be ignored.
Preset = delay of each trace e.g. stime 3.0
SECS - The number of seconds of data to process. SECS is held
constant for all traces within the job. The total time length
of each trace is the sum of the delay and secs. If the data
is not SECS long, zeroes are NOT added or padded and the trace
will be less than SECS long.
Preset= all of the data on the trace.
SET - The start and end times of the data to read from tape. SET is
a pair of times in seconds. The use of SET causes the deep
water delay and the number of samples to be changed. If either
SET is outside of the data, the data are padded with zeroes.
The data will always be SET(2) - SET(1) long.
Preset = none e.g. set 2.0 3.0
IREELN - The input reeln number. This is useful when the input tape
should be changed and the previous tape is not at the end of
tape (2 file marks). e.g.
fis 1 lis 10 ireeln 1 end fis 11 lis 20 ireeln 2 end
causes a tape change to occur after shot 10 is read. The
normal tape change procedures should be followed (using file
"IN").
IFMT - The input tape format. Used to override the format indicator
on the tape itself.
= 0, Use the value from the tape.
= 1, IBM 360 32 bit hex based floating point.
= 2, 32 Bit integer.
= 3, 16 Bit integer.
= 4, 16 Bit fixed point with gain codes. (not SEG-Y)
= 5, host floating point. IEEE
Preset=0
SI - The input sample interval in seconds. Used to override the
sample interval contained in the trace header.
Preset=tape
DELAY - The input deep water delay in seconds. Used to override the
delay contained in the trace header.
Preset=tape
NTRCS - The number of traces per input record (shot or rp). Used to
override the number of traces contained in the binary tape
header.
Preset=tape header.
NTRGAT > 0, number of traces per gather. NTRGAT converts a shot sorted
tape into a rp sorted tape, or converts a foreign rp sorted
tape into a SIOSEIS rp sorted tape. Each gather will contain
NTRGAT traces. The rp numbers will be the same as the shot
numbers. Every NTRGAT traces will be flagged as the end of
gather, so process stack will stack ntrgat traces. This
parameter is useful for processing tapes that have been
gathered outside of SIOSEIS.
< 0, Converts tapes sorted by rp (if the rp has a non zero trace
number) to a tape sorted by shot (rp trace number (segy trace
header word 7) to zero.
Preset=0. e.g. ntrgat 1
FORGAT - Foreign gather tape switch. The use of FORGAT indicates that
the input gather tape was not generated by SIOSEIS and thus
does not have the end-of-gather convention used by SIOSEIS
(a -1 in SEG-Y header word 51). FORGAT is similar to NTRGAT
but allows each gather to have a different number of traces.
FORGAT causes process INPUT to wait for the next trace to be
read from tape and sets the end-of-gather flag to -1 if the
next gather number is different, or the next trace number is
greater than LTR. End-of-gather will also be set if the
parameter LTR is used and the trace on tape is equal to LTR.
The value of forgat indicates the number of rps to concatenate
into a single gather which is terminated by the end-of-gather
flag. The penalty for this is significantly slower throughput
on non-Unix computers (computers that allow asynchronous or
overlapped I/O). LDGO gather tapes start with the largest
trace number first, which breaks the SIOSEIS monotonically
increasing assumption; LDGO gather tapes may be read using
forgat 1 and ftr 99999, in which case SIOSEIS will use all
traces within the gather.
Preset = 0 e.g. forgat 1
DECIMF - Decimation factor. The data will be decimated or resampled by
a factor of decimf, thus reducing the number of samples in the
trace. ** Note ** no anti-alias filter is applied prior to
decimation.
Preset=1. e.g decimf 2 takes every second sample
NFSKIP - The number of files to skip before reading the SEG-Y tape
header. Some places (LDGO) sometimes put multiple lines or
logical tapes on a single physical tape, a violation of the
SEG-Y standard!
Preset = 0. e.g. nfskip 1 skips 1 file
REWIND - A YES/NO switch indicating whether the input tape should be
rewound PRIOR to reading any data (including tape positioning
with NFSKIP). REWIND is set to YES after the first tape is
read so that subsequent tapes will be rewound when using the
"operator" tape change method (file "in"). Likewise, REWIND
is set to YES on every INPUT list (a list is terminated with
"END").
= YES, rewind.
= NO, NO rewind.
DEFAULT = YES, e.g. rewind no # don't rewind
NRSKIP - The number of tape records (traces) to skip before reading the
first trace. This is useful when 2 or more SEG-Y files are
concatenated into 1 file on tape.
> 0, the record skip is done AFTER the SEG-Y tape header is read.
< 0, the record skip is done BEFORE the SEG-Y tape header is read.
Preset = 0. e.g. nrskip 3 skips 3 records
ORDER - SIOSEIS normally assumes that the shot/rp numbers are in
ascending order on tape. In order to reverse this assumption,
set order to -1, which will then force process INPUT to assume
that the shot/rp numbers are in decreasing order on tape. The
parameter sinc/rpinc/noinc usually needs to be a negative number
when order -1 is given. e.g. If the order of rps on tape is
9100, 9099, 9098, 9097,... the following parameters would work:
frp 9100 lrp 9097 rpinc -1
Preset = 0 e.g. order -1
NFILES - The number of files to use. The tape files must be consecutive
on tape. A filemark on tape is the end of file indicator. Two
consecutive file marks are considered end of information and
will cause input to rewind the tape and expect a tape change
using the normal SIOSEIS tape change procedures (by creating a
file named "IN"). NFILES will only work on "Berkeley style"
tape drivers, which permits reading past the file make. (see
parameter DEVICE and read the man pages for mtio).
Preset = 1 e.g. nfiles 2
Written and copyrighted (c) by:
Paul Henkart, Scripps Institution of Oceanography, January 1980
ALL RIGHTS RESERVED.
Go to the list of seismic processes.
Go to SIOSEIS introduction.