Wireline Sonic Waveform Data

ODP logging contractor: LDEO-BRG

Well name: 646B

Leg: 105

Location: Eirik Ridge (Labrador Sea)

Latitude: 58° 12.559' N

Longitude: 48° 22.147' W

Logging date: October, 1985

Bottom felt: 3458.7 mbrf (used for depth shift to sea floor)

Total penetration: 766.7 mbsf

Total core recovered: 402.9 m (53 %)

TOOL USED: LSS (Long Spacing Sonic)

Recording mode: depth-derived borehole compensated mode

Remarks about the recording: the sonic waveforms are not on depth (they need to be shifted  upward by about 5m).

Acoustic data have been recorded in LIS format. Each of the four waveforms consists of 512 samples and is recorded at a sampling rate of 0.1524 m. The original data in LIS 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 512 samples per waveform, this corresponds to 1 + 4x512 = 2049 columns. In this hole, the specifications of the files are:

Number of columns: 2049

Number of rows: 3693

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:

LSS from DIT/LSS/GR (main pass recorded open hole; bottom  at pipe ~ 3670 mbrf)

105-646B_lss.bin: 3645.103-4207.764 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. The sonic waveforms are not on depth and need to be shifted up by ~5m.

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 LogDB support.