Rune Hagelund, WesternGeco Stewart A. Levin, Halliburton 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