SEG-D Input

SEG-D Input501 ProMAX® Reference

SEG-D Input

SEG-D Input reads data from tapes conforming to the SEG-Dstandard.

Theory

This process can handle multiplexed (gapped or gapless) ordemultiplexed SEG-D format tapes.

Read the Seismograph Instrument Parameters section forinformation on transduction, coding, and skew corrections.

Usage

Output Trace Headers

In addition to normal ProMAX® headers, SEG-D Inputcreates a number of SEGD-specific header words:

• YER_SHOT holds the year of the shot

• DAY_SHOT holds the Julian day of the year

• TIM_SHOT is the time of day of the shot as HHMMSS

• CHAN_SET is the channel set number of the trace

• CABLE_NO is the marine streamer cable number

• SEGDGAIN is the gain applied during SEG-D decoding

• TAPE_T0 is the time of first sample of the trace

Debug Option

The SEG-D Input process offers a debug option. When turnedon, you can see the following information:

• Binary format type; the number of bytes per sample

• Number of channels recorded in a channel set

• Start and end times for a channel set

• Channel set trace header extensions (THE) value

• Trace header (THE) value

Other Docs Known ProblemsSearch Page


• Trace header channel set number

• Trace header channel number

• Trace header FFID

• Block size read from tape and the calculated trace length(in bytes)

When diagnosing problems, it is important to match a traceheader with its channel set to begin unraveling the problem.

The calculated trace length is derived from the trace headerlength, channel set start and end times, sample rate andnumber of bytes per sample. It is important to know thecalculated data length when decoding super blocked data.Trace data lengths can vary based upon the channel’schannel set descriptor and the information stored in thechannel set (trace end time) can be inaccurate. For example:

Channel Set Table Index: 2

1) ST - Scan type. . . . . . . . . . . . . : 1

2) CN - Channel set . . . . . . . . . . . .: 2

3) TF - Channel set start time . . . . . . : 0

4) TE - Channel set end time. . . . . . . .: 4095 <---------------

Note: the units of the Channel set TF and TE values are in 2 msincrements (as described by SEGD standards)- 4095 is equivalent to8190 msec.

Storage type : TAPE

Original record field file I.D. # : 988

Year recorded : 98

Recording system format code : 8015

SEGD REVISION : 200

Length of data recorded : 8192.000 msec

Number of samples recorded : 4096 (value obtained from general



header)

Trace Header

1) F - Field file number . . . . . . . . .: 988

2) ST - Scan type number . . . . . . . . . : 1

3) CN - Channel set number. . . . . . . . .: 2 <-------------

4) TN - Trace number . . . . . . . . . . . : 1

5) THE - Trace header extensions . . . . . .: 0 <- No extended traceheaders

6) TR - Trace edit . . . . . . . . . . . . : 0

7) EFN - Extended file number . . . . . . .: 0

*** SEGD DEBUG:

Data recorded in super blocks.

Length of block read : 69632

Calculated size of trace : 10257

Trace header size : 20

Number of traces in block: 6

In this example, the length of the trace should be 10260 butis calculated to be 10257. Therefore, decoding of the superblock is thrown off. Even if the data are not superblocked,one or more output trace samples may be missing or corruptin this case. The Auto adjust incorrect trace data length?option can usually detect and correct many of theseproblems.

Other factors that throw off the decoding of the super block isthe existence of extended trace headers. The ProMAX®processing system only honors extended trace headers whenthe THE value in the channel set matches the THE value inthe trace header. Sometimes it is set in one place and not theother because of uninitialized data output in these headervalues (garbage). Other times, it is recorder-specific behaviorand the value should be honored. For selected SERCELinstruments, SEG-D Input knows about and performs specialinterpretation of trace header extensions.

The presence of extended trace headers affects your datadecode in two ways.

• In the presence of super blocks, the next trace headervalue is useless.



• If single trace per block, the trace’s start time is paddedby 32 times the number of extended trace headers/thenumber of bytes per sample.

Again, the Auto adjust incorrect trace data length? optioncan often detect and correct for extra or missing trace headerextensions.

Correcting I/O Systems and MDS Data Problems

The Specify Auxiliary Channel Type(s) and Specify Zero orPad Channel Type(s) are used together to work aroundgeometry assignment problems with I/O Systems and MDSrecorded data.

Geometry calculation is based upon a trace’s sequentialposition within a shot. The trace’s sequential number isbased upon this calculation:ITR_IN_RECORD-IAUXCHAN+IPADCHAN. Where:

• ITR_IN_RECORD is the trace’s physical position in therecord.

• IAUXCHAN is the current aux channel count within therecord.

• IPADCHAN is the current pad channel count within therecord.

These two parameters enable you to decide which channelsare counted as AUX and or PAD. The IAUXCHAN andIPADCHAN values are only incremented when a channel typematches the value you enter in the menu.

Work Example

In a given case the geometry is off by 6 stations. The followingsteps show how to use these parameters.

1. Turn on the SEG-D Debug Option and look at one recordin job.output.

In this record, one channel set has a channel type of 4,one channel type of 2, two channel types of 5, and fourchannels of type 6.

2. Enter 4:5:6 to Specify Auxiliary Channel Type(s).However, the number of channels defined by these groups



represents 8. We were off by 6 and now are off by 2 (theother way).

3. Again, look at the channel sets in the job.output. In thiscase there are two channel set defined with channel typeof 3.

4. Enter 3 to Specify Zero or Pad Channel Type(s).

The original geometry was off by 6. Because AUX chans 4:5:6= 8 and PAD chans 3 = 2, the relationship ofITR_IN_RECORD-IAUXCHAN+IPADCHAN is now corrected.

Bypass Adaptive Read

Some input data has different block sizes, usually due to auxtrace block being larger than trace block. The new adaptiveread algorithm in this process ignores the value entered intoMaximum data block size in bytes if the aux trace block arelarger than the data block. This can cause a very slow readspeed. To avoid this problem, you can set the CONFIG=BARto disable this function. Your read speed should improve.

Parameters

Type of storage to use

• Tape specifies a real tape dataset.

• Disk specifies a disk file.

Is the dataset in the catalog

Select Yes if the dataset is in an active catalog.

Select TAPE device(s)

This appears for Tape to Type of storage to use and No to Isthe dataset in the catalog. Select tapeN (N=ProMAX DeviceName) from the list of tape devices.

The Available Tape Catalogs

This appears if Yes to Is the dataset in the catalog. Select aa tape catalog from the list of available catalogs.



Enter/Select the tape file name

This appears if Yes to Is the dataset in the catalog. Select orenter a tape file name from the menu.

Select disk file type

This appears if Disk to Type of storage to use. Select DiskImage, ProMAX Tape on Disk, RODE Tape on Disk orLacey Tape on Disk.

Note: For SEG-A, SEG-B and SEG-C Input, only the Tape onDisk options appear.

Tape-on-disk encapsulation stores information about theoriginal tape formatting, i.e. block lengths and file marks, sothat the original tape data may be reconstituted from theinformation in the disk file.

Tape on disk hostname

This appears if Disk to Type of storage to use and anythingoption other than Disk Image is selected. Enter the name ofthe host on which the tape-on-disk file is to be read. A serveris spawned on the host; often the local machine localhost isused. In some circumstances, say for security, the tape-on-disk file may only be visible on a remote machine. Refer to theProMAX System Administration and the ProMAX Total TapeSolution guides for detailed information on setting uppermissions.

Tape on disk username

This appears if Disk to Type of storage to use. Enter thename of the user on the selected read host. Usually this is theuser running the ProMAX user interface, but can be differentif rsh or ssh configurations allow for alternate login.

Enter Disk file path name(s)

This appears if Disk to Type of storage to use. Enter thedisk filename, including the path. You do not need to enterthe full path if the file is in the Line subdirectory. Provide the



name of each individual file to be read, with one filename perline. For example:

/data/file/001.seg

/data/file/002.seg

/data/file/003.seg

Wildcard (*) is not allowed. Each filename must be explicitlyprovided.

There is a limit of 204,000 characters. For example, if thepathname for each file is 50 characters long, you are limitedto about 4080 files. You can workaround this limit byinputting filenames relative to the Line/Subproject directoryor by creating a soft-link to make a much shorter pathnameto your files.

Browse for DISK file path name(s)

Click on Browse to launch an interactive X-Windows dialoguebox to select the disk file name. Note that for tape-on-diskfiles, the browser is launched on the remote system underthe remote user name specified with X display pointing backto the screen running the ProMAX user interface. If nothingappears, you should check host and rsh/ ssh connectivitywith that remote system and ensure that you allow (via thexhost command) the remote system to display on yourdesktop.

Tape LABEL type

This appears for Tape and Tape-on-Disk if No to Is thedataset in the catalog. Select the type of tape label from thefollowing options:

• None

• ANSI

• IBM

Enter the tape file name for internal label

This appears if ANSI or IBM to Tape LABEL type. Enter thetape file name.



Specify MASK for external labels

This appears if No to Is the dataset in the catalog. Enterthe Volume Serial Number for the external tapes. For roboticdevices, this field is required. For other tape devices, this fieldis optional. If you choose to use it, the tape mount messagewill contain the label of the next tape to mount.

The mask is used in conjunction with the parameter below tobuild tape label names.

For example, if the tape labels for a job are

PB001, PB002, PB003

The mask is

PB000

Specify MASK list for external labels

This appears if No to Is the dataset in the catalog. Enterthe Volume Serial Number lists for external tapes. Forexample, if the tape labels for a job are

PB001, PB002, PB003

The mask list will be

1-3/

Note: The mask list is limited to 6 characters. This parametersubstitutes the list values for trailing zeros in the mask. Forexample, if the mask is B60ST0 and the list is 1, the programwill drop the last zero and substitute 1, making the masklistB60ST1.

If the ProMAX tape catalog, TopCat, is active and being used,an external, non-catalog, job automatically bypasses thecatalog. However, for a labelled tape, the Volume SerialNumber is checked against the catalog to ensure this tape isnot an element of the catalog.

Update LIN database at end of input?

Select Yes, the default, to update the LIN database. Select Noif you are loading data into an already populated ProMAX lineand want to avoid changing values in its LIN database.



Override input data’s sample interval?

Select Yes to supply this value manually instead of letting theprogram automatically determine it from the input data.

Super block Warning : Adjusting the following twoparameters will fool SEGD read into anticipating SuperBlocked data if the numbers supplied are different from thevalues found in the general file header. Therefore theyshould be input only if the general file header is found to bemissing or corrupt by SEGD read. To alter the length oftraces sent to subsequent ProMAX processing please see"RECORD LENGTH to input" below.

Correct sample interval

Enter the input data’s sample rate in ms.

Input data’s TRACE LENGTH

The default value of 0.0 determines the length of each datatrace from information in the input dataset. Supplying anonzero number of milliseconds overrides the default.

End of Super block warning.

Starting sequential FILE number

This appears for Tape to Type of storage to use. Enter thesequential field record number you wish to start with on thetape. Default is 1, i.e. the first file on tape.

SEG-D tape format

Select the SEG-D tape format from the following choices:

• Demultiplexed, also referred to as trace sequential, cor-responds to tape data formats such as 8015, 8048. Inthis format, traces are written as individual blocks ontape. Revision 2 of the SEG-D standard is alwaysdemultiplexed.

• Multiplexed, also referred to as long block, correspondsto tape data formats such as 0015, 0048. In the format,trace samples are written in scans and all traces arecontained within a single block on tape.



Maximum data block size in bytes

Enter the maximum data block size in bytes on the tape.Multiplexed data has two blocks per record: the header blockand the data block. The data block holds the trace headerand data sample information.

Note: For values greater than 65536, you must have a longblock driver configured for the tape device.

Turn on SEG-D debug option?

Select Yes to turn on the SEG-D debug option. When turnedon, it shows a record’s general headers, channel sets, traceheader and extended trace header information. See the Usagesection for more information about the Debug Option. Usethis option sparingly as it generates a lot of printout and canslow down data input by a factor of 10.

Bypass Fatal Errors?

Select Yes to ignore fatal errors caused by damaged records.In the past, a damaged record caused the ProMAX®processing system to exit with a fatal error when, forinstance, the FORMAT TYPE could not be determined. Thisoption will allow the systemX to skip to the next record andcontinue processing. For Disk Image data, this option isignored.

Override the Additional General Header Block count(GH)?

Select Yes to correct a faulty count in the first nibble of byte12 of general header block 1 of the SEG-D main header. Insome rare instances this has been set wrong, most often isvery old SEG-D data made at a time when these generalheader block bits were undefined and used for some privatepurpose, causing the channel set information, which appearsdirectly after the general header blocks, to read from thewrong locations in the main header leading to disastrousresults.

Number of additional general header blocks

This appears if Yes to Override the Additional GeneralHeader Block count (GH)? Enter the number of additional32 byte general header blocks in the SEG-D main header that



follow the first general header block. For SEG-D Rev 1 and 2,this number is at least 1.

Extract geometry from extended trace headers?

Select Yes to use the geometry information in the extendedtrace headers. At times the information in the extended traceheaders is invalid and may not be useful. This option extractsgeometry information from the extended SEG-D traceheaders and assigns it to the internal ProMAX® traceheaders.

Extract extended geometry from extended trace head-ers?

Select Yes to extract extended geometry from the extendedtrace header.

Honor the Trace Header Extension value (THE)?

Select Yes to honor the trace header THE value. The valuestored in the THE location is used to calculate the start ofdata offset within a trace data block.

|<-- start of data?-> Start of data (offset) = 20 + THE*32

|<-- Trace header ->|<---------- SEGD trace data ----------->|

|<---------------- SEGD trace --------------------------------->|

The start of data offset is wrong:

• If recorded in super block, the next trace header in blockhas bad values (very large or negative channel numbers).

• If the data are recorded one trace per block, the start ofdata will be (time) shifted by: THE*32/(number of bytesper sample).



Override the Trace Header Extension value (THE)?

This appears if No to Honor the Trace Header Extensionvalue (THE)? Select Yes to override faulty values in thechannel set and trace header.

Number of trace header extensions

This appears if Yes to Override the Trace Header BlockExtension value (TH)E? Enter the number of additional 32byte trace header extension blocks on each trace.

Auto adjust incorrect trace length?

For Disk Image input, which has no direct indication of traceor record boundaries, select Yes to automatically round thenumber of samples per trace calculated from each channelset down to the nearest even number. This is useful in thefar too common situation where the channel set end time isrecorded as the time of the sample just past the last oneactually recorded.

For Tape or Tape-on-Disk input, select Yes to dynamicallyadjust the calculated trace length in the presence of anincorrect channel set end time. When decoding super blockeddata, SEG-D checks for a valid channel set number andexpected channel number for the next trace in the superblock. If an error condition is detected, such as the channelnumbers are too big or negative, this option forces SEG-D tosearch down the trace buffer until the expected values arefound. The calculated data length for channel set (in error) iscorrected for the shot. This option also auto-adjusts forunflagged trace header extensions. Some Syntron systemswrite an extra 32 bytes in the SEG-D trace header, but fail toflag its presence in either the channel set or the regular traceheader.

The ProMAX® system uses the calculated trace length for thechannel set. This enables the accurate decode of varying datalengths within a shot, in particular, the auxiliary channels.

Use this option with: Honor the Trace Header Extensionvalue (THE)?

Note: An incorrect trace header offset can also have the sameeffect. It is recommended to use the Turn on SEGD debug



option to determine what the issues are and enable the rightcorrections.

Omit records of type

Enter records to omit if your data was initialized with a valuewhich signifies a test record. For example, given the followinggeneral header information:

F - Field file number (<9999). . . . . : 988

Y - Format code . . . . . . . . . . . .: 8015

K - General Constants. . . . . . . . . : 830000

YR - Year (0-99) . . . . . . . . . . . .: 98

GH - Additional General Header blocks . : 1

DY - Julian Date (1-366) . . . . . . . .: 230

H - Hour of day (0-23) UTC Time. . . . : 23

MI - Minute of hour (0-59) . . . . . . .: 31

SE - Second of the minute (0-59.) . . . : 58

M - Manufacturer’s code . . . . . . . .: 22

M - Manufacturer’s serial number . . . : 3020

I - Base scan interval. . . . . . . . .: 32

P - Polarity . . . . . . . . . . . . . : 0

Z - Record type . . . . . . . . . . . .: 2 <---------------

You determine that a record type of 2 is a test record. To omitthis record type you would enter the 2. To omit a group ofrecords, you would enter, for example, 2:3:4:5:6. The default,-1 disables this feature.

Specify Seismic Data Channel Type(s)

Enter the channel set value, that is channel type, foroverriding the default seismic data channel type (1). Forexample, a record consists of AUX channels only of type:2,3,6,7. To interpret these channels as seismic datachannels, enter 2:3:6:7.

Note: In this example, we are using four different channeltypes from four different channel sets. With this example, youcan expect to see duplicate channel numbers. Therefore, setGet Channel Number from trace headers to No andrenumber based upon sequential input. And set Maximum



traces per record to a typical shot. The default maximumnumber of traces per shot is calculated from only onechannel set and is of type 1.

Specify Auxiliary Channel Type(s)

Enter the channel type(s) to define auxiliary traces. Enter -1to disable this parameter. See Correcting I/O Systems andMDS Data Problems in the Usage section for informationabout using this parameter.

Specify Zero or Pad Channel Type(s)

Enter the channel type(s) to define zero or pad traces. Enter-1 to disable this parameter. See Correcting I/O Systems andMDS Data Problems in the Usage section for informationabout using this parameter.

Number of errors in a row before aborting job

Enter the number of errors in a row before aborting the job.Enter 0 to ignore all errors. Any value greater than 0 willoutput dead traces until this value is reached.

Some older tapes will error out on every block. This isespecially true on 800 bpi and 3200 dpi 9-track tapes whichare not supported by several computer operating systems. Aslong as the tape drive can read these tapes the data buffermay be valid.

SEG-D main header length (bytes)

Enter the length of the main header in bytes. Enter 0 tocalculate the header length as follows:

header length = 32 * [GH + ST * (CS + SK) + 1 + EC + EX]

GH = number of additional general header blocks (first half of byte 12)

ST = number of scan types per record (byte 28)

CS = number of channel sets per scan type (byte 29)

SK = skew fields per scan type (byte 30)

EC = extended header length (byte 31)

EX = external header length (byte 32)



Typically, you will leave this value at the default of 0. If any ofthe above header values are incorrect, you must specify themain header length.

Display ensemble information?

Select Yes to display information about input ensembles.When an end of ensemble is reached, the program writes tothe job.output file:

The ensembles are CDP sorted:

CDP = 123 SOURCE = 1 TRACES IN ENSEMBLE = 120

The ensembles are SHOT sorted:

FFID = 600 SOURCE = 1 TRACES IN ENSEMBLE = 120

The ensembles are RECEIVER LOCATION sorted:

RECEIVER = 200 SOURCE = 1 TRACES IN ENSEMBLE = 120

SEG-D data format code?

Select the format code of the data samples on tape. In thefollowing list, the 80xx formats are demultiplexed data, andthe 00xx formats are the corresponding multiplexed formats:

• Get from header gets format code from general header.This is the default.

• 8015, 0015 is 2.5-byte bin foreary exponent (demulti-plexed, multiplexed)

• 8022, 0022 is 1-byte quaternary exponent (demult.,mult.)

• 8024, 0024 is 2-byte quaternary exponent (demult.,mult.)

• 8036, 0036 is 3-byte 2’s complement integer (demult.,mult.)

• 8038, 0038 is 4-byte 2’s complement integer (demult.,mult.)

• 8042, 0042 is 1-byte hexadecimal exponent (demult.,mult.)





• 8058, 0058 is 4-byte IEEE floating point (demult, mult.)

MAXIMUM traces per record

Enter the maximum number of input traces or channels perrecord/shot. Enter 0, the default, to calculate the maximumchannels from header values. You must include auxiliarychannels in this number to read in the auxiliary channels.

Input AUXILIARY traces?

Select Yes to input the auxiliary traces. Select No to omit theauxiliary channels. If Yes, then include auxiliary channels inthe maximum traces per record parameter.

Auxiliary traces are assigned negative numbers. Formultiplexed SEG-D, the timing word is treated as anauxiliary channel.

RECORD LENGTH to input

Enter the amount of data to input to subsequent ProMAX®processes in ms. Enter 0 to read all available data. The datalength will be read from the header. Entering a value willoverride the value read from the tape header. The start timeof each trace is recorded (in ms) in the ProMAX® headerTAPE_T0. Inspect this header word for nonzero values beforeapplying subsequent processes depending upon the firstsample of the trace appearing at time 0. Use Header Staticsto adjust the trace start time using the TAPE_T0 header.

If the number is less than the trace length on tape the outputdata is truncated. If any trace from tape is shorter than thislength it will be padded with zeros to this length to satisfy theProMAX® requirement that all traces in a dataset are thesame length.

SERCEL instrument type?

Select additional required SEG-D information for Sercelinstruments:

• Not Sercel indicates that it is not a SERCEL instrument,or data is not from a SERCEL 356, 368, 388 or 408 seis-mograph. It can also be specified to disable special SER-CEL-only header processing.



• 358 Demux indicates that the SEG-D input is demulti-plexed data from a SERCEL 358 seismograph. SERCEL358 instruments store the preamplifier gains in a non-standard format in the channel set header. To convertthe data to millivolt level, these gains must be used. TheSERCEL 358 also records the shotpoint number in byte39 of the general header extension and this is trans-ferred to header SOU_SLOC when this option is selected.

• 368 indicates that the SEG-D data is from a SERCEL368 seismograph. SERCEL 368 seismographs store thepreamplifier gains in byte 110 of the general headerextension and byte 16 of the trace header when the datais correlated within the seismograph. To convert the datato millivolt level, these gains must be used. SERCEL 368seismographs also record shotpoint line and geophonepositions in general header extension bytes 18-20 andbytes 21-23 and receiver station line numbers and stakenumbers within the line in trace header bytes 17-18 and19-20. These are transferred into headers S_LINE,SOU_SLOC, R_LINE and SRF_SLOC respectively whenthis option is selected.

• 388 indicates that the SEG-D data is from a SERCEL388 instrument. SERCEL 388 seismographs produce aSEG-D Revision 1 format dataset with optional field pro-cessing. SEG-D Revision 1 geometry extensions to thegeneral header and trace header are transferred intoProMAX® headers S_LINE, SOU_SLOC, R_LINE andSRF_SLOC on output.

• 408 indicates that the SEG-D data is from a SERCEL408 instrument. SERCEL 408 seismographs use SEG-Dtrace header extensions to supply trace gain factors that,when nonzero, override the standard SEG-D MP conver-sion exponent. SEG-D Revision 1 geometry extensions tothe general header and trace header are transferred intoProMAX® headers S_LINE, SOU_SLOC, R_LINE andSRF_SLOC on output. In addition, SEG-D Input alsoretrieves SOU_X, SOU_Y, SOU_ELEV, REC_X, REC_Y,and REC_ELEV information from the SERCEL 408extended trace headers.

Apply preamplifier gain (2 ** MP factor)?

Select Yes to apply the preamplifier gain to the trace data.For SERCEL seismographs, information in the extended



general and/or trace headers is used to compute the propergain. For other instruments, the gain is obtained from theSEG-D standard MP exponent that occupies bytes 7 and 8 ofthe channel set descriptor. Most data should have thepreamp gain applied, the exception being certain instrumenttest records. Whatever gain is applied is recorded inProMAX® header word SEGDGAIN.

pre-amp gain = 2 ** MP

trace data = trace data(raw) * pre-amp gain

Scan correction option (sample skew statics)?

Select the scan correction option from the following choices:

• Get from header reads the sample skew static valuesfrom the trace headers and puts them into the traceheaders.

• User specified allows you to specify the scan correctionsin the next field.

• Do not apply ignores any sample skew static values inthe input headers and sets the trace header SKEWSTATto 0.

Multiplex scan corrections are necessary because of thesequential sampling of the different recording channels.There is a resulting slight time offset between the samples ofvarious channels. If selected, these shifts will be stored in thetrace header SKEWSTAT which is automatically included indatum statics application.

Specify multiplex scan corrections list

This appears if User specified to Scan correction option.Enter the scan correction string for each channel.

The static times must be entered in ms. Static times forchannels not entered into the string are interpolated usingthe existing values.

Get Channel Number from trace headers?

Select Yes to get the channel number from the trace headers.Select No to number the channels sequentially within anensemble. Auxiliary traces are assigned negative numbers.



Input PRIMARY selection choice?

Select the SEG-D or Promax header key on which the inputprimary trace list is based. The choices are:

• Input All inputs all file numbers on this tape, or multi-tape input.

• File No. selects input records based on SEG-D FileNumber.

• Source Index No. selects input records based on thesequential source number within the tape.

Specify PRIMARY input records list

This appears if any option, except Input all, to Inputprimary selection choice. Enter the input records/traces.

Since data from a tape/file is input sequentially, you shouldtry to build the list based upon sequential location within afile. If the primary selection choice is decreasing within thetape/file then the list should be decreasing. For example:

100-1/

Input SECONDARY selection choice?

Select a secondary selection choice. The choices are:

• None uses no secondary sort key. All channels/tracesare input.

• Channel inputs a subset of the channels in a record.

Specify CHANNEL input list

This appears if Channel to Input Secondary selectionchoice. Enter the channels in the following format:

Selection key value values range /

1-120 / 1-60,62-120 / 1-240(2)

The first example reads in the first 120 channels within adataset. The second example reads in channels 1-60,inclusive, and 62-120, inclusive. The third example reads inevery other channel beginning at channel 1 and ending atchannel 240.



Streamline CHANNEL selection?

If Yes, SEG-D Input quickly forward spaces its input to thenext record once it encounters channels beyond the selectedrange. The default is No, examining every trace in the recordfor possible inclusion. In multistreamer configurations, it iscommon to have channel numbers reoccur several timeswithin a record, once per streamer.

Remap SEGD main header values?

Select Yes to input/override/remap SEG-D main headervalues. Select No to accept the default.

Input/override main header entries

This appears if Yes to Remap SEGD main header values.Enter ProMAX® header entries to input or override from theSEG-D main header, using a supplied format, increment, andposition. Header entries are created if they do not exist.Format can be 2I, 4I, #B, #C, 4RIBM, 4RIEEE, 8RIEEE. Anincrement can be specified that is based upon channel setnumber. Position is anywhere inside the SEG-D main header.For example:

cab_off,cable\shipboard offset,4RIBM,,,793/cab_num,cable num-ber,1I,,32,865/ ffid,field file id,4B,,,0.5/

An override entry consists of six fields plus a / at the end ofeach entry. Each field is separated by a comma. For example:

wat_dep,cable water depth,4RIBM,1:2:3,32,204/

wat_dep,cable water depth,4RIBM,flex,10,204/

Field 1: wat_dep is the name of the ProMAX® header word.This can be a new word defined by you or an existing word asdefined in header.inc. This field can be 1 to 8 characters.

Field 2: cable water depth is the description of theProMAX® header word. If you are overriding a current headerword existing in header.inc, this field may be left blank. Thisfield can be 1 to 32 characters.

Field 3: 4RIBM is the format of the value in the SEG-Dheader. This field can be a 1I (1 byte integer), 2I (2 byteinteger), 4I (4 byte integer), #B (1-9 BCD digits), #C (1-9integers in character format), 4RIBM (4 byte IBM floatingpoint), 4RIEEE (4 byte IEEE floating point), or 8RIEEE (8 byteIEEE double precision floating point). The BCD or character



digit field is entered as a number*B, as in 9B for nine BCDdigits or 9C for 9 characters. The character data that is in thefile must be integers that were converted to character format.

Field 4: 1:2:3 or flex is the channel set manipulation field. Ifthe field is blank, then all channel sets are selected. This fieldcan be 1 to 32 characters.

When the field contains channel set numbers (1:2:3:...), thestarting byte position is incremented by the channel setnumber taken from the trace header times the byteincrement (Field 5). The channel sets must be separated by acolon, :. As in the example, channel sets 1, 2, and 3 areselected. Only channels set listed in this field will be used.Trace headers with a different channel set number will notload a valid override.

byte position = start byte position + (channel set - 1) * increment

When the field contains flex, the starting byte position isincremented by the total channels sets (byte 29 of generalheader) times the byte increment (field 5). Use flex when thesize of the main header is changing due to a different numberof total channel sets.

byte position = start byte position + (total channel sets) * increment

Field 5: 32 is the byte increment. Use this field inconjunction with Field 4 to move around the main header. If avalue is entered in this field, the starting byte position, Field6 is incremented by this byte amount for each channel set ortotal channel sets. If field is left blank, the increment is 0.This field can be 1 to 8 characters.

When BCD digits are input, the increment can be less than abyte. There are two BCD digits per byte. For example, if theentry is

wat_dep,cable water depth,5B,,2.5,0.5/

the value for channel set one occupies BCD digits 1-5. Thevalue for channel set two occupies BCD digits 6-10.

Field 6: 204 is the starting byte position within the SEG-Dheader to extract the override value. This field can be 1 to 8characters. When BCD digits are being input, the positioncan be less than a byte. To begin a BCD digit at the firstnibble (4 bits) of a byte you must subtract .5. The first nibbleof byte 2 is 1.5, the first nibble of byte 100 is 99.5. Thesecond nibble of byte 100 is 100.



Remap SEGD trace header values?

Select Yes to input/override/remap SEG-D trace headervalues. Select No to accept the default.

Input/override trace header entries

This appears if Yes to Remap SEGD trace header values.Enter ProMAX® header entries to input or override from theSEG-D trace header, using user-supplied format, andposition. Header entries are created if they do not exist.Format can be 2I, 4I, #B, #C, 4RIBM, 4RIEEE, 8RIEEE.Position is anywhere inside the SEG-D trace header. Forexample:

chan,channel number,2B,,,3.5/

See the override entry explanation above for override details.Field 4, the channel set number and Field 5, the channel setbyte increment are not used.

Input Global XY reference coordinates?

Select Yes to input the global x,y reference coordinates. Theglobal x,y reference parameters are stored with the dataset.The reference parameters are subtracted from the input Xand Y source and receiver coordinates.

ProMAX® coordinate = ProMAX® coordinate - reference

Global X reference coordinate

This appears if Yes to Input global XY referencecoordinates. Enter the global X reference coordinate. If youuse the remapping feature and override the trace headerwords, SOU_X and/or REC_X, then the X referencecoordinate will be subtracted from the remapped value.

Global Y reference coordinate

This appears if Yes to Input global XY referencecoordinates. Enter the global Y reference coordinate. If youuse the remapping feature and override the trace headerwords, SOU_Y and/or REC_Y, then the Y referencecoordinate will be subtracted from the remapped value.



Save trace IFP values for NGAIN Instrument Test?

Select Yes to save the trace sample IFP values to a file. Thefile is required to run the Ngain Instrument Test. Thiscannot be used with formats x036, x038, x048, or x058.

Enter NGAIN disk file path name

This appears if Yes to Save trace IFP values for NGAINinstrument test. Enter the disk file path name to save theIFP values for the Ngain Instrument Test. The full path is notnecessary if the file is in the database.




Documents

SEG-D Input