SEGD rev 3.0 proposal

Rune Hagelund, WesternGeco

Stewart A. Levin, Halliburton

Overview of rev 3.0 proposal

• All features discussed at SEG New Orleans have been implemented– With a few additions

• SEGD Tape Label, General Header 1 and Demux Trace Header left as is (with a few exceptions)

• Be an efficient format for transferring information between acquisition and QC/processing– SEGD is not a processing format

• More space for user-defined header blocks

Overview of rev 3.0 proposal• Increased flexibility

– Header blocks tagged to allow shot specific (attached to general header) or trace specific information

– Flexible samplerates, header sizes, reclength etc.• Increased robustness

– Tagged header blocks– Size of shot/data in General Header

• Simplified encoding/decoding – No complex datatypes, using 4byte float, int etc– Explicit values (ex. #samples/trace)– No dependencies between header blocks

• Additional functionality

New functionality in rev 3.0

• Positions can be tagged to all traces/equipment– Multiple positions (in space and time)– Format TBD by pos group

• Support for multi-component data– Node number, trace grouping, orientation header

• New General Trailer format– Flexible, allows any data-block to be appended

• Standardized edits can be appended to General Trailer– Allows easy addition of edits post-acquisition

• 8068: IEEE 8 byte samples

New functionality in rev 3.0

• Supporting complex shooting schemes– Multiple source efforts per shot record– Multiple sources firing simultaneously

• Supporting complex source configurations– Traces and measurements for sources and

parts of sources

• Align SEGD with SPS

New functionality in rev 3.0• All measurements now properly tagged with

accurate, absolute timestamp (if available)– Positions, traces, shot, etc.

• All header sizes extended– More room for acquisition system defined blocks– Existing trace ext hdr blocks may be used....– ...but remember to use correct block tag

• Standardizing storage of SEGD– One header block spanning multiple tape blocks– A trace spanning multiple tape blocks– Fixed/variable block devices– Disk storage– Transfer across network

New functionality in rev 3.0

• Standardizing storage of common survey information– Vessel/crew identification– Survey area name– Client identification– Job identification– Line identification (Record set identification)

• Size of record, data, and header explicit in General Header

New functionality in rev 3.0

• Logical numbering of traces/source points extended to handle all operation types– Line number– Point number– Point index– Group index– Depth index– Reshoot index

New functionality in rev 3.0

• More sensor types/channel types explicitly supported– Wind, depth, reference signals, source

measurements etc.

• Sensor sensitivity value stored per channel– Convert to actual physical unit– Support non-voltage measurements

New functionality in rev 3.0

• Table Of Contents file– Stored at end (or beginning) of tape– Lists all SEGD records on a tape– Enable fast access to data– May be stored on disk (to simplify data mgt)

New functionality in rev 3.0

• Line number -> Record set number– To be usable for all types of operation

• Only 3 General Header blocks required in rev 3– Everything else optional

Header sizes

• Channelset header block 96 bytes• Header block sizes

– General header - 65536 blocks (2 MB)– Channelset header – 65535 blocks (~6MB) – Skew blocks – 65535 blocks (~2MB)– Extended header – 16777215 blocks (~512MB)– External header - 16777215 blocks (~512MB)– Trace Header Extension – 255 blocks (8160 bytes)– General Trailer – 4294967295 blocks (~128GB)

Samplerate / timestamp

• Sample rates steps of 1 microsecs• No longer a base scan rate

– Dominant Sample interval used for backwards compatibility

• Timestamp – counting microsecs since 6 jan 1980 (GPS epoch)– 8 byte integer– Negative timestamps allowed– 292471 years range

Trace size

• Traces can be 2147 secs long

• Negative start times allowed

• Extended recording mode allows up to 140735340 secs (1628 days) of data to be stored in one record

Filters

• Extended filter definitions– Frequencies and slopes are IEEE floats (4

bytes) – Filter type– Filter delay