SONIC WAVEFORMS FILES

HOLE: 720A

LEG: 117

TOOL USED: SDT (Digital Sonic Tool, also known as Array Sonic)

Recording mode: borehole-compensated mode

Remarks about the recording: The original proprietary tape was damaged and could not be loaded. The customer tape was used instead, but the data record is incomplete (uppermost 82 m are missing).

Like in all of the past legs, the sonic waveforms are not on depth with the other logs: usually, the offset is clearly visible at the base of the bottom hole assembly or casing and varies from 15 to more than 30 m downward. In Hole 720A, however, the uppermost part of the data record is missing and therefore it is difficult to assess the correct offset amount without reference to the bottom hole assembly. It is thus recommended to first process the sonic waveforms and then match the output to the other logs.

Acoustic data have been recorded in LIS format. Each of the four waveforms consists of 492 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 492 samples per waveform, this corresponds to 1 + 4x492 = 1969 columns. In this hole, the specifications of the files are:

Number of columns: 1969

Number of rows: 715 (upper section)

Number of rows: 715 (lower section)

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/NGT (upper section, bottom hole assembly at 4115 mbrf)

720A-u.bin: 4197.25-4306.06 mbrf

SDT from DIT/SDT/NGT (lower section, recorded open hole)

720A-l.bin: 4318.1-4426.92 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

E-mail: Cristina Broglia

Trevor Williams

Phone: 845-365-8626

Fax: 845-365-3182

E-mail: Trevor Williams