Wireline Sonic Waveform Data

ODP logging contractor: LDEO-BRG
Hole: 801C
Leg: 185
Location: Pigafetta Basin (tropical NW Pacific)
Latitude: 18° 38.5380' N
Longitude: 156° 21.5880' E
Logging date: May, 1999
Bottom felt: 5685 mbrf (assumed)
Total penetration: 926 mbsf
Total core recovered: 160.42 m (47.28%)

TOOL USED: SDT (Array Sonic)

Recording mode: depth-derived, borehole compensated mode (long spacing)

Remarks about the recording: none.

As most Schlumberger logs, acoustic data are recorded in DLIS format. Each of the four waveforms consists of 400 samples and is recorded at a sampling rate of 0.1524 m. The original data in DLIS format is first loaded on a Sun system using GeoFrame software. The packed waveform data files are then converted into ASCII and finally binary format.

Each row of the binary file is composed of the entire waveform set recorded at each depth, preceded by the depth. In the case of 4 waveforms with 400 samples per waveform, this corresponds to 1 + 4x400 = 1601 columns. In this hole, the specifications of the file are:

Number of columns: 1601

Number of rows: 2232

All values are stored as 'IEEE floating point numbers' (= 4 bytes ).

Any numerical software or programing language (matlab, python,...) can import the files for further analysis of the waveforms.

The following files were converted:

SDT from FMS/GPIT/SDT/NGT (casing at ~ 6172 mbrf)

801C.bin: 6172-6512 mbrf

The sonic waveform files are not depth-shifted to a reference run or to the seafloor. For depth shift to the sea floor, please refer to the DEPTH SHIFT section in the standard log documentation file.

NOTE: For users interested in converting the data to a format more suitable for their own purpose, a simple routine to read the binary files would include a couple of basic steps (here in old fashioned fortran 77, but would be similar in matlab or other languages):

The first step is to extract the files dimensions and specification from the header, which is the first record in each file:

  open (1, file = *.bin,access = 'direct', recl = 50) <-- NB:50 is enough to real all fields

  read (1, rec = 1)nz, ns, nrec, ntool, mode, dz, scale, dt

  close (1)

The various fields in the header are:
      - number of depths
      - number of samples per waveform and per receiver
      - number of receivers
      - tool number (0 = DSI; 1 = SonicVISION; 2 = SonicScope; 3 = Sonic Scanner; 4 = XBAT; 5 = MCS; 6 = SDT; 7 = LSS; 8 = SST; 9 = BHC; 10 = QL40; 11 = 2PSA)
      - mode (1 = Lower Dipole, 2 = Upper Dipole, 3 = Stoneley, 4 = Monopole)
      - vertical sampling interval *
      - scaling factor for depth (1.0 = meters; 0.3048 = feet) *
      - waveform sampling rate in microseconds *

All those values are stored as 4 bytes integers, except for the ones marked by an asterisk, stored as 4 bytes IEEE floating point numbers.

Then, if the number of depths, samples per waveform/receiver, and receivers are nz, ns, and nrec, respectively, a command to open the file would be:

  open (1, file = *.bin, access = 'direct', recl = 4*(1 + nrec*ns))

Finally, a generic loop to read the data and store them in an array of dimension nrec × ns × nz would be:

  do k = 1, nz

    read (1, rec = 1+k) depth(k), ((data(i,j,k), j = 1,ns), i = 1,nrec)

  enddo

For further information about the logs please contact:

Cristina Broglia
phone: 845-365-8343
fax: 845-365-3182
email: Cristina Broglia