Wireline Sonic Waveform Data

DSDP operator and logging contractor: Scripps Institution of Oceanography

Hole: 612

Leg: 95

Location: Baltimore Canyon (NW Atlantic)

Latitude: 38° 49.21 N

Longitude: 72°46.43 W

Logging date: August 1983

Sea floor depth (drillers' mudline): 1414.3 mbrf

Sea floor depth (step in GR log): logs did not reach the mudline

Total penetration: 675.3 mbsf

Total core recovered: 580.66 m (86 % of cored section)

Oldest sediment cored: late Campanian

Lithologies: muds and sands, oozes and chalks, mudstones and shales.

Tool used: LSS (Long Spacing Sonic)

Recording mode: depth-derived, borehole compensated mode

Remarks about the recording: the sonic waveforms were digitized by Schlumberger on tape with a 500 msec delay. The data available on the original tapes, however, does not cover the entire logged interval. Analog copies of the logs show that the entire section from 1680 mbrf to total depth is missing. The available section (1453.44-1680.97 mbrf) seems to have been recorded entirely open hole, though the log header indicates the bit depth to be at 1518 mbrf. Also, the waveforms carry the notation that they are not on depth with the other logs; in fact, a comparison of the delay time from this run with that from the DIT/LSS/GR/MCD run used as depth reference shows an offset of 51.5 m upwards. Therefore, it is recommended to first process the sonic waveforms and then depth-match the output to the logs from other runs.

Each of the four waveforms consists of 512 samples and is recorded at a sampling rate of 0.1524 m. The original data is first loaded on a Sun system using GeoFrame software. The 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 4 waveforms with 512 samples per waveform, this corresponds to 1 + 4x512 = 2049 columns. In this hole, the specifications of the file are:

Number of columns: 2049

Number of rows: 1494

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/GR (recorded open hole)

612.bin: 1453.43-1680.972 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.

Also, please refer to the 'Remarks about the recording' note above.

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