SEG-Y Trace Header Format

 

# Byte position Type SEG Y * SU **
1 001 - 004 4 Trace sequence number within line tracl
2 005 - 008 4 Trace sequence number within reel tracr
3 009 - 012 4 Original field record number fldr
4 013 - 016 4 Trace sequence number within original field record tracf
5 017 - 020 4 Energy source point number ep
6 021 - 024 4 CDP ensemble number cdp
7 025 - 028 4 Trace sequence number within CDP ensemble cdpt
8 029 - 030 2 Trace identification code:
-1 = Other
0 = Unknown
1 = seismic data
2 = dead
3 = dummy
4 = time break
5 = uphole
6 = sweep
7 = timing
8 = water break
9 = Near-field gun signature
10 = Far-field gun signature
11 = Seismic pressure sensor
12 = Multicomponent seismic sensor - Vertical component
13 = Multicomponent seismic sensor - Cross-line component
14 = Multicomponent seismic sensor - In-line component
15 = Rotated multicomponent seismic sensor - Vertical component
16 = Rotated multicomponent seismic sensor - Transverse component
17 = Rotated multicomponent seismic sensor - Radial component
18 = Vibrator reaction mass
19 = Vibrator baseplate
20 = Vibrator estimated ground force
21 = Vibrator reference
22 = Time-velocity pairs
23+ = optional use
(SU: 111 = complex FD, i.e. alternating samples of real and imag,
116 = real, 117 = imag, 118 = amp, 119 = phase)
trid
9 031 - 032 2 Number of vertically summed traces yielding this trace nvs
10 033 - 034 2 Number of horizontally stacked traces yielding this trace nhs
11 035 - 036 2 Data use (1 = production, 2 = test) duse
12 037 - 040 4 Distance from source point to receiver group offset
13 041 - 044 4 Receiver group elevation gelev
14 045 - 048 4 Surface elevation at source selev
15 049 - 052 4 Source depth below surface sdepth
16 053 - 056 4 Datum elevation at receiver group gdel
17 057 - 060 4 Datum elevation at source sdel
18 061 - 064 4 Water depth at source swdep
19 065 - 068 4 Water depth at receiver group gwdep
20 069 - 070 2 Scalar for elevations and depths (+ = multiplier, - = divisor) scalel
21 071 - 072 2 Scalar for coordinates (+ = multiplier, - = divisor) scalco
22 073 - 076 4 X source coordinate sx
23 077 - 080 4 Y source coordinate sy
24 081 - 084 4 X receiver group coordinate gx
25 085 - 088 4 Y receiver group coordinate gy
26 089 - 090 2 Coordinate units
1 = Length in meters or feet
2 = arc seconds
3 = decimal degrees
4 = degrees, minutes, seconds
counit
27 091 - 092 2 Weathering velocity wevel
28 093 - 094 2 Subweathering velocity swevel
29 095 - 096 2 Uphole time at source sut
30 097 - 098 2 Uphole time at receiver group gut
31 099 - 100 2 Source static correction sstat
32 101 - 102 2 Receiver group static correction gstat
33 103 - 104 2 Total static applied tstat
34 105 - 106 2 Lag time between end of header and time break in milliseconds laga
35 107 - 108 2 Lag time between time break and shot in milliseconds lagb
36 109 - 110 2 Lag time between shot and recording start in milliseconds delrt
37 111 - 112 2 Start of mute time muts
38 113 - 114 2 End of mute time mute
39 115 - 116 2 Number of samples in this trace ns
40 117 - 118 2 Sample interval of this trace in microseconds dt
41 119 - 120 2 Field instrument gain type code:
1 = fixed
2 = binary
3 = floating point
4+ = optional use
gain
42 121 - 122 2 Instrument gain constant igc
43 123 - 124 2 Intrument early gain in decibels igi
44 125 - 126 2 Correlated (1 = no, 2 = yes) corr
45 127 - 128 2 Sweep frequency at start sfs
46 129 - 130 2 Sweep fequency at end sfe
47 131 - 132 2 Sweep length in milliseconds slen
48 133 - 134 2 Sweep type code:
1 = linear
2 = parabolic
3 = exponential
4 = other
styp
49 135 - 136 2 Sweep taper trace length at start in milliseconds stas
50 137 - 138 2 Sweep taper trace length at end in milliseconds stae
51 139 - 140 2 Taper type code:
1 = linear
2 = cosine squared
3 = other
tatyp
52 141 - 142 2 Alias filter frequency afilf
53 143 - 144 2 Alias filter slope afils
54 145 - 146 2 Notch filter frequency nofilf
55 147 - 148 2 Notch filter slope nofils
56 149 - 150 2 Low cut frequency lcf
57 151 - 152 2 High cut frequency hcf
58 153 - 154 2 Low cut slope lcs
59 155 - 156 2 High cut slope hcs
60 157 - 158 2 Year data recorded year
61 159 - 160 2 Day of year day
62 161 - 162 2 Hour of day (24-hour clock) hour
63 163 - 164 2 Minute of hour min
64 165 - 166 2 Second of minute sec
65 167 - 168 2 Time basis (1 = local, 2 = GMT, 3 = other) timbas
66 169 - 170 2 Trace weighting factor for fixed-point format data trwf
67 171 - 172 2 Geophone group number of roll switch position one grnors
68 173 - 174 2 Geophone group number of first trace of original field record grnofr
69 175 - 176 2 Geophone group number of last trace of original field record grnlof
70 177 - 178 2 Gap size (total number of groups dropped) gaps
71 179 - 180 2 Overtravel associated with taper (1 = down/behind, 2 = up/ahead) otrav
72 181 - 184 4 X cdp coordinate d1
73 185 - 188 4 Y cdp coordinate f1
74 189 - 192 4 In-line number d2
75 193 - 196 4 Cross-line number f2
76 197 - 200 4 SP number ungpow
77 201 - 204 4 unscale
78 205 - 206 2 mark
79 207 - 208 2 mutb
80 209 - 212 4 dz
81 213 - 216 4 fz
82 217 - 218 2 n2
83 219 - 220 2 shortpad
84 221 - 224 4 ntr
77 201 - 202 2 SP number scalar (applies to #76)
78 203 - 204 2 Trace value measurement unit:
-1 = Other (should be described in Data Sample Measurement Units Stanza)
0 = Unknown
1 = Pascal (Pa)
2 = Volts (V)
3 = Millivolts (mV)
4 = Amperes (A)
5 = Meters (m)
6 = Meters per second (m/s)
7 = Meters per second squared (m/s2)
8 = Newton (N)
9 = Watt (W)
79 205 - 210 6 Transduction constant
80 211 - 212 2 Transduction Units
-1 = Other
0 = Unknown
1 = Pascal (Pa)
2 = Volts (V)
3 = Millivolts (mV)
4 = Amperes (A)
5 = Meters (m)
6 = Meters per second (m/s)
7 = Meters per second squared (m/s2)
8 = Newton (N)
9 = Watt (W)
81 213 - 214 2 Device Identifier
82 215 - 216 2 Scalar for times and statics (applies to #29-39)
83 217 - 218 2 Source Type/Orientation
-1 = Other
0 = Unknown1 = Vibratory - Vertical orientation
2 = Vibratory - Cross-line orientation
3 = Vibratory - In-line orientation
4 = Impulsive - Vertical orientation
5 = Impulsive - Cross-line orientation
6 = Impulsive - In-line orientation
7 = Distributed Impulsive - Vertical orientation
8 = Distributed Impulsive - Cross-line orientation
9 = Distributed Impulsive - In-line orientation
84 219 - 224 6 Source Energy Direction
85 225 - 230 6 Source Measurement
86 231 - 232 2 Source Measurement Unit
-1 = Other
0 = Unknown
1 = Joule (J)
2 = Kilowatt (kW)
3 = Pascal (Pa)
4 = Bar (Bar)
4 = Bar-meter (Bar-m)
5 = Newton (N)
6 = Kilograms (kg)
87 233 - 240 6 unassigned - for optional information

*The SEG Y trace header length is 240 bytes. The original SEG Y definition (rev 0) leaves the trace header positions 181-240 unformatted and unassigned for optional storage of information (Barry et al., 1975,  Recommended Standards for Digital Tape Formats, Geophysics 40(2), 344-352). A revision to this standard extended the assigned header, leaving only bytes 233-240 for optional information (SEG Technical Standards Committee, 2002,  SEG Y rev 1 Data Exchange format, Technical Standard Report, 45 pp).
Revision 1 also extended the reel/file header to previously unassigned positions. In the new standard, the byte positions 3501-3506 are used to store information about the format (rev 0 or 1), variable trace length (not permitted in rev 0), and the number of extended textual file headers (non-existent in rev 0). Note that the new interpretation may result in backward incompatibility.
**Header Mapping to Seismic Unix. Beyond byte position 180 the interpretation between SEG Y and SU differs (grey). This may lead to problems in SU, which can be avoided using  segyclean to erase the header positions 181-210 .