Acronyms and abbreviations

  • AGC – automatic gain control
  • CDP – Common Depth-point
  • CD-ROM – Compact Disc Read-Only Memory
  • CMP – Common Midpoint
  • DB – decibel
  • DMO – dip move-out
  • EBCDIC – Extended Binary Coded Decimal Interchange Code
  • EPS – Encapsulated PostScript Format
  • EPSG – European Petroleum Survey Group
  • FFT – Fast Fourier Transform
  • FIRE – Finnish Reflection Experiment
  • Gb – gigabyte
  • GTK – Geological Survey of Finland
  • Hz – hertz
  • IBM – International Business Machines Corporation
  • I/O – input/output
  • JPEG – Joint Photographic Experts Group
  • KKJ – kartastokoordinaattijärjestelmä (National Grid Coordinate System)
  • Km – kilometre
  • Mb – megabyte
  • NMO – normal move-out
  • RMS – root mean square
  • SEG-Y – Society for Exploration Geophysicists Y-format
  • SU – Seismic Un*x
  • TIFF – Tagged Image File Format
  • TWT – two-way travel time
  • UH – University of Helsinki

Original field recordings

General

The original, demultiplexed and correlated field recordings from Specgeofizika are available as a set of SEG-Y files. Each SEG-Y contains 500 to 700 megabytes of field recordings or about 20 to 30 shots.

Noise tests and accidental or failed measurements are included in this data set and can be identified using the original observer’s logs. The samples are in IBM floats. The sampling interval is 2 milliseconds and the number of samples per trace is 15 000.

The data is very elementary and raw, so we do not recommend anyone to look into these unless you really want to start processing from scratch. Carefully chosen, quality-controlled shot gathers with all relevant trace headers set are available under Shot gathers and have been prepared at the University of Helsinki, Institute of Seismology during the year 2016.

Geometry

Finnish Reflection Experiment is a 2-D crooked-line seismic survey conducted using 4 to 5 Vibroseis sources per shot point. The nominal shot point interval is 100 meters.

The recording geometry is split-spread (asymmetric at the end of lines) with 362 active channels separated by a nominal group interval of 50 meters. This results in a nominal fold of ~ 90 for the entire survey.

Naming of files

The naming of files follows the general pattern

Fire_(line)_(subdivision)_(min)-(max).sgy

where the last two numbers separated by a dash specify a range of field records in observer’s logs. The range varies irregularly.

Textual and binary header

The 3200-byte textual header does not contain anything significant. The 400-byte binary header has not been set.

Trace headers

In the trace headers, set are only bytes 9-12 (field record number) and bytes 13-16 (trace number within shot gather). The field record number refers to a row in observer’s logs. The trace number is also the channel number and usually varies between 1 and 362. At the beginning of FIRE 1-2, up to 410 active channels were used.

Original observer's notes

The original observer's notes from the I/O recording system are available and can be downloaded using the OpenFIRE table view. The quality-controlled versions should always be preferred to these. The original notes are only preserved for historical purposes.

Miscellaneous notes

The observer’s logs are man-made and always prone to errors. At times the original notes have not been found and have been reproduced by a simple visual comparison of traces. A comprehensive erratum is available for all lines and can be downloaded using the OpenFIRE table view.

Quality-controlled shot gathers are available under Shot gathers.