Wireline Sonic Waveform Data

ODP logging contractor: LDEO-BRG

Hole: 960A

Leg: 159

Location: Ivory Coast-Ghana Margin (equatorial NE Atlantic)

Latitude: 3° 34.979' N

Longitude: 2° 44.009' W

Logging date: January, 1995

Bottom felt: 2048.4 mbrf (used for depth shift to sea floor). NOTE: the mudline was originally established by the drillers at 2059.7 mbrf by direct pipe measurement. The corrected PDR reading was 2048.4 mbrf. The difference was attributed to the difficulty in "feeling" for bottom with drill pipe.

Total penetration: 451.2 mbsf (calculated using a "bottom felt" depth of 2059.7 m)

Total core recovered: 145.01 m (32.1 %)

TOOL USED: SDT (Digital Sonic Tool)

Recording mode: linear mode (8 receivers)

Remarks about the recording: The quality of the data is impaired by the bad hole conditions. The borehole size variations induced frequent cycle skipping in the log, the result of the receivers picking incorrect first arrival times.

Acoustic data are recorded in DLIS format. Each of the eight waveforms consists of 464 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 general case of 8 waveforms with 464 samples per waveform, this corresponds to 1 + 8x500 = 3713 columns. In this hole, the specifications of the file are:

Number of columns: 3713

Number of rows: 1732 (main)

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 DIT/SDT/HLDT/CNTG/NGT (main, bottom hole assembly at ~2133 mbrf)

960A-m.bin: 2133-2397 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
E-mail: Cristina Broglia

Trevor Williams
Phone: 845-365-8626
Fax: 845-365-3182
E-mail: Trevor Williams