SEGY header description

The following tables show SIA header names and byte/format assignments for the standard SEGY binary reel and trace headers, and also two extensions of trace header format used in PASSCAL and Seismic UNIX files.

Data sample format is normally controlled by the corresponding value of the reel header.

Input and output in SEGY format is performed by modules readbf and write, respectively.

Binary reel (file) header

Name in SIA
First byte
Length
Format in file
Format in SIA
Description
jobid
1
4
INTEGER
INTEGER
 
line
5
4
INTEGER
INTEGER
Line number
reelnum
9
4
INTEGER
INTEGER
 
numtrac
13
2
INTEGER
INTEGER
 
numaxtr
15
2
INTEGER
INTEGER
 
sampint
17
2
INTEGER
INTEGER
Sample interval (microseconds)
sampin0
19
2
INTEGER
INTEGER
 
nsamp
21
2
INTEGER
INTEGER
Number of trace samples
nsamp0
23
2
INTEGER
INTEGER
Same
sampfrm
25
2
INTEGER
INTEGER
Sample format.  The following values are recognized by program readbf::
  • 1 - IBM 4-byte real
  • 2 - 4-byte integer
  • 3 - 2-byte integer
  • 5 - IEEE 4-byte float
  • 6 - 1-byte integer (byte)
cdpfold
27
2
INTEGER
INTEGER
 
trcsort
29
2
INTEGER
INTEGER
 
vstack
31
2
INTEGER
INTEGER
 
swpst
33
2
INTEGER
INTEGER
 
swpend
35
2
INTEGER
INTEGER
 
swplen
37
2
INTEGER
INTEGER
 
swptyp
39
2
INTEGER
INTEGER
 
swpchan
41
2
INTEGER
INTEGER
 
swpstp
43
2
INTEGER
INTEGER
 
swpetp
45
2
INTEGER
INTEGER
 
swptpt
47
2
INTEGER
INTEGER
 
swprcs
49
2
INTEGER
INTEGER
 
bingain
51
2
INTEGER
INTEGER
 
amprec
53
2
INTEGER
INTEGER
 
units
55
2
INTEGER
INTEGER
 
polarit
57
2
INTEGER
INTEGER
 
vibrpol
59
2
INTEGER
INTEGER
 

Binary trace header

Name in SIA First byte Length Format in file Format in SIA Description
linetrc
1
4
INTEGER
INTEGER
  
reeltrc
5
4
INTEGER
INTEGER
  
ffid
9
4
INTEGER
INTEGER
  
chan
13
4
INTEGER
INTEGER
  
espnum
17
4
INTEGER
INTEGER
  
cdp
21
4
INTEGER
INTEGER
  
cdptrc
25
4
INTEGER
INTEGER
  
traceid
29
2
INTEGER
INTEGER
  
vstackt
31
2
INTEGER
INTEGER
  
fold
33
2
INTEGER
INTEGER
  
datause
35
2
INTEGER
INTEGER
  
offset
37
4
INTEGER
INTEGER
  
relev
41
4
REAL
REAL
  
selev
45
4
REAL
REAL
  
sdepth
49
4
INTEGER
INTEGER
  
rdatum
53
4
INTEGER
INTEGER
  
sdatum
57
4
INTEGER
INTEGER
  
wdepths
61
4
INTEGER
INTEGER
  
wdepthr
65
4
INTEGER
INTEGER
  
ed-scal
69
2
INTEGER
INTEGER
  
c-scal
71
2
INTEGER
INTEGER
 Coordinate scalar for the following coordinates
sht-x
73
4
INTEGER
REAL
 Shot X coordinate
sht-y
77
4
INTEGER
REAL
 Shot Y coordinate
rec-x
81
4
INTEGER
REAL
 Receiver X coordinate
rec-y
85
4
INTEGER
REAL
 Receiver Y coordinate
coounit
89
2
INTEGER
INTEGER
  
wvel
91
2
INTEGER
INTEGER
  
subsvel
93
2
INTEGER
INTEGER
  
suphole
95
2
INTEGER
INTEGER
  
ruphole
97
2
INTEGER
INTEGER
  
shtstat
99
2
INTEGER
INTEGER
  
rcstat
101
2
INTEGER
INTEGER
  
stapply
103
2
INTEGER
INTEGER
  
lagtima
105
2
INTEGER
INTEGER
  
lagtims
107
2
INTEGER
INTEGER
  
delay
109
2
INTEGER
REAL
  
mutstrt
111
2
INTEGER
INTEGER
  
muteend
113
2
INTEGER
INTEGER
  
nsampt
115
2
INTEGER
INTEGER
  
smpintt
117
2
INTEGER
INTEGER
  
gaintyp
119
2
INTEGER
INTEGER
  
ingcnst
121
2
INTEGER
INTEGER
  
inigain
123
2
INTEGER
INTEGER
  
corrflg
125
2
INTEGER
INTEGER
  
swpst
127
2
INTEGER
INTEGER
  
swpend
129
2
INTEGER
INTEGER
  
swplngt
131
2
INTEGER
INTEGER
  
swptyp
133
2
INTEGER
INTEGER
  
swpstpr
135
2
INTEGER
INTEGER
  
swpetpr
137
2
INTEGER
INTEGER
  
taptyp
139
2
INTEGER
INTEGER
  
aliafil
141
2
INTEGER
INTEGER
  
alialop
143
2
INTEGER
INTEGER
  
notcfil
145
2
INTEGER
INTEGER
  
notcslp
147
2
INTEGER
INTEGER
  
lowcut
149
2
INTEGER
INTEGER
  
highcut
151
2
INTEGER
INTEGER
  
lowslop
153
2
INTEGER
INTEGER
  
hicslop
155
2
INTEGER
INTEGER
  
year
157
2
INTEGER
INTEGER
 Record start - year
day
159
2
INTEGER
INTEGER
 Record start - day
hour
161
2
INTEGER
INTEGER
 Record start - hour
min
163
2
INTEGER
INTEGER
 Record start - minute
sec
165
2
INTEGER
INTEGER
 Record start - second
timebas
167
2
INTEGER
INTEGER
  
tweight
169
2
INTEGER
INTEGER
  
nstswp1
171
2
INTEGER
INTEGER
  
rsttcr1
173
2
INTEGER
INTEGER
  
rsttrcn
175
2
INTEGER
INTEGER
  
gapsize
177
2
INTEGER
INTEGER
  
overtrv
179
2
INTEGER
INTEGER
  

PASSCAL extension

This SEGY trace header format extension is used in PASSCAL programs, such as ref2segy, segygather, or txn2segy.  Like  Seismic UNIX, PASSCAL SEGY does not use reel header.

Name in SIA First byte Length Format in file Format in SIA Description
station 181 6 CHARACTER CHARACTER Station name
sensor 187 8 CHARACTER CHARACTER Sensor type
channel 195 4 CHARACTER CHARACTER Channel name
static 199 2 INTEGER REAL Record time start - msec
sampin2 201 4 INTEGER REAL Sample interval
datafrm 205 2 INTEGER INTEGER Data format
msec 207 2 INTEGER INTEGER Record start - millisecond
e_year 209 2 INTEGER INTEGER Event year
e_day 211 2 INTEGER INTEGER Event day
e_hour 213 2 INTEGER INTEGER Event hour
e_min 215 2 INTEGER INTEGER Event miniute
e_sec 217 2 INTEGER INTEGER Event second
e_msec 219 2 INTEGER INTEGER Event millisecond
gain 221 4 REAL REAL
inst_no 225 2 INTEGER INTEGER Number of the instrument
filter 227 2 INTEGER INTEGER
nsampt2 229 4 INTEGER INTEGER Number of samples
maxsamp 233 4 INTEGER REAL
minsamp 237 4 INTEGER REAL

Seismic UNIX extension

SEGY trace header parameters used by Seismic UNIX programs.

Name in SIA FIrst byte Length Format in file Format in SIA Description
su.d1 181 4 REAL REAL Sample spacing for non-seismic data
su.f1 185 4 REAL REAL First sample location for non-seismic data
su.d2 189 4 REAL REAL Sample spacing between traces
su.f2 193 4 REAL REAL First trace location
su.ungp 197 4 REAL REAL Negative of power used for dynamic range compression
su.unsc 201 4 REAL REAL   Reciprocal of scaling factor to normalize range
su.ntr 205 4 INTEGER INTEGER   Number of traces
su.mark 209 2 INTEGER INTEGER   Mark selected traces
Copyright (c) 1995-1999, I. B. Morozov, Rice University and University of Wyoming
This document updated Oct 02, 1999