Wireline Sonic Waveform Data

ODP logging contractor: LDEO-BRG

Hole: 998-B

Leg: 165

Location: Cayman Rise (Caribbean Sea)

Latitude: 19° 29.387' N

Longitude: 82° 56.160' W

Logging date: December, 1995

Bottom felt: 3190.7 mbrf (used for depth shift to sea floor)

Total penetration: 904.8 mbsf

Total core recovered: 287.9 m (83.1 %)

TOOL USED: SDT (Digital Sonic Tool)

Recording mode: depth-derived, borehole compensated mode.

Remarks about the recording: good quality data recorded.

Acoustic data have been 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 has been 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 4 waveforms with 464 samples per waveform, this corresponds to 1 + 4x640 = 18571 columns. In this hole, the specifications of the file are:

Number of columns: 1857

Number of rows: 2469 (main pass)

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.

SDT from DIT/SDT/HLDT/CNTG/NGT (main, bottom hole assembly at 3363 mbrf)

998B-m.bin: 3363-4075 mbrf

The sonic waveform files are not depth shifted to a reference run or to the seafloor. Because the DIT/SDT/HLDT/CNTG/NGT run was chosen as the reference file for depth shifting, only a depth shift of -3190.7 m is necessary.

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