Data Dictionary System: Users Formats (segy Trace Header)

The default fields that make up the SEGY1_TRACE structure are defined in "${DDSROOT}/src/lib/dds3/segy1.fmt.dds" and may be modified by editing that file and putting it into a directory defined by "${DDS_PATH}". These defaults are summarized by their nominal offset, name, type, and element count.

Off  Name                 Type^†       N Comment
---- -------------------- ----------  - -------------------------------------------
*    segy_green           SEGY_INT    0 "SEGY green word prefix"
0    LineTrcNum           SEGY_INT    1 "Trace sequence number within line"
4    ReelTrcNum           SEGY_INT    1 "Trace sequence number within reel"
8    FieldRecNum          SEGY_INT    1 "Original field record number"
12   FieldTrcNum          SEGY_INT    1 "Trc # within original field rec"
16   SrcPtNum             SEGY_INT    1 "Energy source point number"
20   CdpNum               SEGY_INT    1 "CDP ensemble number"
24   CdpTrcNum            SEGY_INT    1 "Trc # within the CDP ensemble"
28   TrcIdCode            SEGY_SHORT  1 "Trc identification code: 1-8"
30   VertStack            SEGY_SHORT  1 "# of vertically summed traces"
32   HorzStack            SEGY_SHORT  1 "# of horizontally stacked traces"
34   DataUse              SEGY_SHORT  1 "Data use (1 production, 2 test)"
36   DstSgn               SEGY_INT    1 "Signed src-rcv distance"
40   GrpElev              SEGY_INT    1 "Receiver group elevation"
44   SrcElev              SEGY_INT    1 "Surface elevation at source"
48   SrcDepth             SEGY_INT    1 "Src depth below surface (positive)"
52   GrpDatum             SEGY_INT    1 "Datum elevation at receiver group"
56   SrcDatum             SEGY_INT    1 "Datum elevation at source"
60   WatDepthSrc          SEGY_INT    1 "Water depth at source"
64   WatDepthGrp          SEGY_INT    1 "Water depth at group"
68   ElevScaler           SEGY_SHORT  1 "Scalar to be applied to elevations"
70   XYScaler             SEGY_SHORT  1 "Scalar to be applied to coordinates"
72   SrcX                 SEGY_INT    1 "Source coordinate X"
76   SrcY                 SEGY_INT    1 "Source coordinate Y"
80   GrpX                 SEGY_INT    1 "Group coordinate X"
84   GrpY                 SEGY_INT    1 "Group coordinate Y"
88   XYUnits              SEGY_SHORT  1 "Coordinate units (1:length 2:arc sec)"
90   WeathVel             SEGY_SHORT  1 "Weathering velocity"
92   SubWeathVel          SEGY_SHORT  1 "Subweathering velocity"
94   UpholeTmSrc          SEGY_SHORT  1 "Uphole time at source"
96   UpholeTmGrp          SEGY_SHORT  1 "Uphole time at group"
98   SrcStatic            SEGY_SHORT  1 "Source static correction"
100  GrpStatic            SEGY_SHORT  1 "Group static correction"
102  TotalStatic          SEGY_SHORT  1 "Total static applied"
104  LagTmBreak           SEGY_SHORT  1 "Lag time A. Time in ms"
106  LagTmSrc             SEGY_SHORT  1 "Lag time B. Time in ms"
108  LagTmSmpOne          SEGY_SHORT  1 "Delay recording time. Time in ms"
110  MuteStart            SEGY_SHORT  1 "Mute time--start"
112  MuteEnd              SEGY_SHORT  1 "Mute time--end"
114  TrcNumSmp            SEGY_SHORT  1 "Number of samples in this trace"
116  TrcSmpInt            SEGY_SHORT  1 "Sample interval (usec) for this trace"
118  GainType             SEGY_SHORT  1 "Gain type of field instruments: 1-4"
120  GainConst            SEGY_SHORT  1 "Instrument gain constant"
122  GainInit             SEGY_SHORT  1 "Instrument early or initial gain (db)"
124  CorrFlag             SEGY_SHORT  1 "CorrFlag (1 no, 2 yes)"
126  SwpFreqStart         SEGY_SHORT  1 "Sweep frequency at start"
128  SwpFreqEnd           SEGY_SHORT  1 "Sweep frequency at end"
130  SwpLength            SEGY_SHORT  1 "Sweep length in ms"
132  SwpType              SEGY_SHORT  1 "Sweep type (1:linear 2:par 3:exp 4:other)"
134  SwpTprStart          SEGY_SHORT  1 "Start Sweep taper length (msec)"
136  SwpTprEnd            SEGY_SHORT  1 "End Sweep taper length (msec)"
138  SwpTprType           SEGY_SHORT  1 "Taper type (1:linear 2:cos^2 3:other)"
140  AntiAliasFreq        SEGY_SHORT  1 "Alias filter frequency, if used"
142  AntiAliasSlope       SEGY_SHORT  1 "Alias filter slope"
144  NotchFreq            SEGY_SHORT  1 "Notch filter frequency, if used"
146  NotchSlope           SEGY_SHORT  1 "Notch filter slope"
148  LowCutFreq           SEGY_SHORT  1 "Low cut frequency, if used"
150  HighCutFreq          SEGY_SHORT  1 "High cut frequency, if used"
152  LowCutSlope          SEGY_SHORT  1 "Low cut slope"
154  HighCutSlope         SEGY_SHORT  1 "High cut slope"
156  Date.DateYear        SEGY_SHORT  1 "Year data recorded"
158  Date.DateDay         SEGY_SHORT  1 "Day of year"
160  Date.DateHour        SEGY_SHORT  1 "Hour of day (24 hour clock)"
162  Date.DateMin         SEGY_SHORT  1 "Minute of hour"
164  Date.DateSec         SEGY_SHORT  1 "Second of minute"
166  DateType             SEGY_SHORT  1 "Time basis code (1:local 2:gmt 3:other)"
168  TrcWeight            SEGY_SHORT  1 "Trace weighting factor"
170  RollSwtch1           SEGY_SHORT  1 "Geophone group # of roll switch pos 1"
172  RollTrace1           SEGY_SHORT  1 "Geophone group # of trace number one"
174  RollTraceN           SEGY_SHORT  1 "Geophone group # of last trace"
176  RollGapSize          SEGY_SHORT  1 "Gap size (total # of groups dropped"
178  OverTravel           SEGY_SHORT  1 "Overtravel associated with taper"
180  CDPBCX               SEGY_INT    1 "CDP Bin Center X Coordinate"
184  CDPBCY               SEGY_INT    1 "CDP Bin Center Y Coordinate"
188  LinInd               SEGY_INT    1 "Line Index"
192  DphInd               SEGY_INT    1 "Depth Index (crossline index)"
196  SrcLoc               SEGY_INT    1 "Source Index times 10"
200  SrcLocScaler         SEGY_SHORT  1 "Source Index scaler"
202  TrcUnit              SEGY_SHORT  1 "Trace value measurement unit"
204  TranConstMan         SEGY_INT    1 "Transduction Constant - mantissa"
208  TranConstExp         SEGY_SHORT  1 "Transduction Constant - exponent"
210  TranUnits            SEGY_SHORT  1 "Transduction Units"
212  DevId                SEGY_SHORT  1 "Device/Trace Identifier"
214  MsecScaler           SEGY_SHORT  1 "Scalar to be applied to times"
216* Spare1.I1            unsigned1  24 "Unassigned--for optional information"
216* Spare1.I2            integer2   12 "Unassigned--for optional information"
216* Spare1.I4            integer4    6 "Unassigned--for optional information"
216* Spare1.F4            float4      6 "Unassigned--for optional information"
216* Spare1.F4ibm         float4ibm   6 "Unassigned--for optional information"
216* Spare1.Hdr.SrRcMX    SEGY_INT    1 "Source-Receiver Mid Point X Coordinate"
220* Spare1.Hdr.SrRcMY    SEGY_INT    1 "Source-Receiver Mid Point Y Coordinate"
224* Spare1.Hdr.SrcPnt    SEGY_SHORT  1 "Source Point above this Depth Pt"
226* Spare1.Hdr.SoPtNm    SEGY_SHORT  1 "Source point Number"
228* Spare1.Hdr.RecInd    SEGY_SHORT  1 "Receiver Location Index (GI)"
230* Spare1.Hdr.RecNum    SEGY_SHORT  1 "USP RecNum"
232* Spare1.Hdr.FlReFN    SEGY_SHORT  1 "Field Record File #"
234* Spare1.Hdr.CdpStatic SEGY_SHORT  1 "Total Static Applied"
236* Spare1.Hdr.DePtEl    SEGY_SHORT  1 "Depth Point Elevation"
238* Spare1.Hdr.FlDtEl    SEGY_SHORT  1 "Floating Datum Elevation"
240  Samples              *          -1 "trace samples"
*    segy_PadTrace        unsigned1   0 "excess bytes after trace samples"
*    segy_GREEN           SEGY_INT    0 "SEGY green word suffix"

where * indicates overloading of fields for the same byte locations.

The Spare trace header fields begins at byte offset 216 in the segy1 format which accommodates 24 bytes of non-standard, but often vital, information. This spare area is a union (Fortran equivalences) which is used to divide the spare area into meaningful fields. The entire area can be accessed as an array of integers or floats, using I1, I2, I4, F4, and F4ibm. Locations commonly used by contractors have also been predefined (see, for example, RecInd, and RecNum).