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TraceHeader

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TraceHeader

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     Geocluster

     Reference Documentation

     Seismic Trace Header Format

     CGG

     Geocluster

     Copyright

     This documentation, or any of the information included herein, may not be modified without the prior consent of the owner. The information included in this documentation does not form in any way a contractual agreement of sales promise on the part of the owner. The software mentioned in this documentation is sold under a precise license agreement and as such, the documentation may cover technical areas for which the user may not have a final license. No part of this documentation may be copied in any form or by any means without the prior written consent of the owner.

     Geocluster is a trademark of CGG.

     Ref: GCT-HEADER-0304-VA

     Gct 2.1 Seismic Trace Header Format - April 2003

     Compagnie G??n??rale de G??ophysique 1, rue L??on Migaux, 91341 MASSY CEDEX, FRANCE Telephone: +33 1 64 47 38 95

     Seismic Trace Header Format

     Table of Contents

     A

     Seismic Trace Header Format

    Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .

     . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 Trace Header Components . . . . . . . . . . . . . . . . . . . . . . . . . . . .

     . . . . . . . . . . . . . A-3 Module-Specific

    Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    A-11

     Compagnie G??n??rale de G??ophysique

     i

     ii

     Chapter

     A

     Seismic Trace Header Format

     This chapter contains information concerning the format of GeoclusterTM seismic trace headers. You will find the following sections:

     I Introduction I Trace Header Components I Module-Specific Formats

     Compagnie G??n??rale de G??ophysique

     A-1

     A

     Seismic Trace Header Format Introduction

     Introduction

     The header of each trace consists of 64 words of 32 bits each. These words are in integer format with the exception of word 14 which is in real format. The meaning of some of the words is fixed (e.g. the word containing the value of the last non-zero sample and the word containing the value of the sampling interval). Many header words are automatically updated by batch programs (e.g. the word containing the value for trace offset). Most header words can easily be modified by the user using the processing module MODET. This lends great power and flexibility to seismic job construction. Header words are the primary means of trace selection.

     A-2

     Seismic Trace Header Format

     Trace Header Components

     The table below gives the contents of these words :

     Word Bit Contents

     1 2

     1 to 32 1 to 16

     Time in ms of the last non zero sample counted from the delay time (see word 16).

     Physical shotpoint number.

     17 to 32 Order number of record before vertical stack (see LIBRI IT). 3 1 to 32 1 Type of trace =1 Trace whose geophone position is greater than or equal to the shotpoint position (Direct Trace) (word3=1). Trace whose geophone position is less than shotpoint position (Reverse Trace) (word 3=2). Distances are in feet (word 3=4). Stacked trace (from STAPA). The trace is composed of multiple elements (word 3=16).

     A

     2 3 4 5 6 8

     =1 =1 =1 =1

     Vapor choc or STARJET trace with signature samples packed 3x10 bits each. =1 Vapor choc trace containing the signature in the header. The signature is packed by 2 samples per word (word 3=128). The trace contains (time, velocity) pairs resulting from TRVEL, option INTERP9.

     9

     =1

     Compagnie G??n??rale de G??ophysique

     A-3

     A

     Seismic Trace Header Format Trace Header Components

     Word

     Bit

     Contents

     3

     (cont'd)

     10 to 13 Number of the receiver line in WLP. 14 to 18 CDP line number. 19 20 21 22 23 24 25 26 27 28 29 31 =1 =1 =1 =2 =1 =1 =1 =1 =1 =1 =1 KIDMO, DMSTK and FXMIG output trace. If FANMO was applied. Zeroed by reverse FANMO (DENMO). HABIN output trace. The trace was processed by SDICO, option FW. Set to 0 by SDICO, option RV. Pseudo-trace created by GVTRD or trace duplicated by HABIN. Trace created by a migration or DMO program. After EGRID and TDETQ. After TOPRD Interpolated trace created by FXINT After MUTES if a taper has been applied at end of trace. Output stack trace from STAPA.

     is used by DECSC as an internal flag. CDP number. CDP surface position expressed in receiver positions multiplied by 4. Time in ms of the first non zero sample counted from the delay time (see word 16). Length, in ms, of the mute tapering. 99999 for a radionavigation tape.

     4 5 6 7

     1 to 32 1 to 32 1 to 32 1 to 32

     A-4

     Seismic Trace Header Format

     Word

     Bit

     Contents

     8

     1 to 9

     Before total of partial stack, number of traces of the CDP.

     10 to 18 Order number of the trace within a CDP. 1 to 32 1 to 32 9 10 11 1 to 32 1 to 32 1 to 20 After stack, (word 3=8): number of stacked traces (stacking fold). After TRVEL, option INTERP9 (word 3=9): number of (time, velocity) pairs Sample interval in microseconds. Number of samples multiplied by the sampling interval in milliseconds. = 0 for a non valid trace. = 7 for a valid trace. = 15 for a history trace.

     A

     21 to 32 Trace format (read by RUNET, written by WUNET) set to 0 after read. 12 1 to 16 Output type (TSD).

     17 to 32 Sequence number. This number increments by 1 at every trace. 13 14 15 1 to 32 1 to 32 1 to 16 Cumulated bit shifts reset to zero after INPTR. Maximum trace value (in real format). Negative if this maximum is unknown (-1). Twice the distance between two consecutive CDPs (usually interval between field traces).

     17 to 32 Physical number of the shotpoint closest to the CDP. Each

    shotpoint is shown at one CDP only, the other CDPs have zero as their value.

     Compagnie G??n??rale de G??ophysique

     A-5

     A

     Seismic Trace Header Format Trace Header Components

     Word

     Bit

     Contents

     16

     1 to 3

     = 1 Fixed format 16 bits/word. = 2 12 bits for data + 4 bits for gain. = 3 IBM floating point, 32 bits. = 4 RDS floating point, 32 bits. = 7 Host internal floating point format. Formats 1, 2, 3 and 4 are converted to 7 by INPTR. Delay in milliseconds. Trace number on the spread.

     4 to 32 17 1 to 16

     17 to 32 Trace number before vertical stack (see LIBRI IT). This information is eliminated by the input program. 18 19 1 to 32 1 to 32 Receiver position. Projected shot distance. Line number in 3D (after TDETQ or EGRID). 20 1 to 32 Real shot distance. After KIDMO, first input WORD20 or center of the offset gather (ID parameter coded), or center of the partial stacks (PS option). 21 1 to 32 1 to 16 Shotpoint surface position expressed in receiver positions multiplied by 4. After STAPA, these bits contain either the value of the N parameter (if coded), or if 65535 if the NP parameter is coded.

     17 to 32 After STAPA, stack fold of the first non-zero sample, multiplied by 100.

     A-6

     Seismic Trace Header Format

     Word

     Bit

     Contents

     21

     (cont'd)

     After TRVEL, option LT: 7 if VINT (time-sampled interval velocities) 8 if VINT + NODIX (time-sampled interval velocities) 9 if INTERP (time-sampled average velocities) After TRVEL, option IT: 7 if output trace defined in time (interval velocities) 17 if output trace defined in depth (interval velocities) After TRVEL, options GO, MD: 17 (depth-sampled interval velocities)

     22

     1 to 32 1 to 32

     Maximum signature value before normalization. Following the

    LISTA-HISTA A sequence: static correction value (SI/64). Number of labelling velocities in the case of VSCAN.

     A

     22 to 41

     1 to 16 After STAPA, stack fold at regular intervals between WORD6 and WORD1 times. and 17 to 32 If i is the interval, then the first value is determined at WORD6+i, the second at WORD6+2i, and so on, up to the last, at WORD1. The stack folds are then multiplied by 100 and packed on 16 bits, giving two values per word. Case of the STARJET traces before WAPCO. 1 to 18 1 to 30 Signature samples after normalization and packing, 2 samples per 18-bit word (bit 8 of word 3 equal to 1). Signature samples after normalization and packing, 3 samples per word of 30 bits (bit 6 of word 3 equal to 1).

     22 to 64 23 to 64

     Compagnie G??n??rale de G??ophysique

     A-7

     A

     Seismic Trace Header Format Trace Header Components

     Word

     Bit

     Contents

     23

     1 to 32 1 to 32

     Flag: 1 transmitted by SATAN to STACK at the end of CDP. After VSCAN: output length in ms for each velocity. After LISTA - HISTA A: maximum value of the window picked by LISTA option NC1, YMX1.

     1 to 32 24 1 to 32

     Number of samples eliminated in a gather (NOISE and HARMO auxiliary output). After VSCAN: gap length in milliseconds. Following the LISTA (or LISTS) HISTA A sequence: weight of the static correction calculated by LISTA (or LISTS).

     25 to 33 25 26 27 28 29 30 to 39 34 35

     1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32

     Words 25 and following: labelling velocity from VSCAN. After HISTA H/V = applied velocity. Time from which the stack fold is equal to word 8 (after STACK) = maximum of words 6 of stacked trace. After SEGIN in SEGD format: number of the channel in the 4th byte of the input trace label. CDP position of the receiver. CDP position of the shotpoint. After QCAMP, the values of words 30 to 39 contain real values. After HABIN: number of traces belonging to the same offset class. Duplicating distance for duplicated traces. After HABIN: distance to the center of the bin for original traces.

     A-8

     Seismic Trace Header Format

     Word

     Bit

     Contents

     36 43 1 to 32

     After HABIN: this word is set to 1 in the trace closest to the center of the bin. By default, it is set to 2. CDP abscissa (X) (after DTBXY). In 3D (after EGRID, TDETQ): abscissa of the midpoint on the shotpoint-receiver segment.

     44

     1 to 32

     CDP ordinate (Y) (after DTBXY). In 3D (after EGRID, TDETQ): ordinate of the midpoint on the shotpoint-receiver segment.

     45 46 47 48 49 50 51 52 53

     1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32 1 to 32

     Regional static correction in milliseconds. Auxiliary DP in milliseconds. Water depth in milliseconds. Source code (shotpoint) updated by PSUPD. Receiver static correction in milliseconds. Source index (shotpoint) updated by PSUPD. Shotpoint static correction in milliseconds. Receiver code updated by PSUPD. CDP static correction in milliseconds. Receiver index code updated by PSUPD. Total of static corrections applied by TDPIK. Offset class number after HABIN. Amplitude correction in millibels (by AMPSO and DYNQU SG, R or RX). Mean value of the trace (AMPOF).

     A

     54 56

     1 to 32 1 to 32

     After TDETQ and EGRID: azimuth expressed in degrees, relative to the shot direction. Time in ms of the TDPIK model. Shotpoint abscissa expressed in receiver positions (TDETQ).

     Compagnie G??n??rale de G??ophysique

     A-9

     A

     Seismic Trace Header Format Trace Header Components

     Word

     Bit

     Contents

     57

     1 to 32

     Time in ms of the pick carried out by TDPIK. Shotpoint ordinate expressed in receiver positions (TDETQ).

     58

     1 to 32

     After EGRID or TDETQ: (RCDP ?Á 100)/DX where RCDP is the CDP axis

    midpoint coordinate, and DX is the interval in CDPs between bin centers. After EGRID or TDETQ: (RLINE ?Á 100)/DY where RLINE is the LINE axis midpoint coordinate, and DY is the interval in LINEs between bin centers. After DTBXY or TDETQ: geophone abscissa. After EGRID: receiver-position abscissa. After OUTGR 3D: relative abscissa (CDP number ?Á 10)

     59

     1 to 32

     60

     1 to 32

     61

     1 to 32

     After DTBXY or TDETQ: geophone ordinate. After EGRID: receiver-position ordinate. After OUTGR 3D: relative ordinate (line number ?Á 10)

     62

     1 to 32

     After DTBXY or TDETQ: shotpoint abscissa. After EGRID: shotpoint abscissa. After OUTGR 3D: absolute abscissa.

     63

     1 to 32

     After DTBXY or TDETQ: shotpoint ordinate. After EGRID: shotpoint ordinate. After OUTGR 3D: absolute ordinate.

     64

     1 to 32

     Flag used to avoid a repeated application of HISTA RG.

     A-10

     Seismic Trace Header Format

     Module-Specific Formats

     Refer to the documentation for the following modules for information concerning these module-specific header formats: DTBXY WILOC PFLIB TDSAT GVTWR

     A

     Compagnie G??n??rale de G??ophysique

     A-11

     A

     Seismic Trace Header Format Module-Specific Formats

     A-12

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