Wireline Sonic Waveform Data
ODP logging contractor: LDEO-BRG
Location: Great Bahama Bank (tropical NW Atlantic)
Latitude: 24° 32.763' N
Longitude: 79° 15.650' W
Logging date: March, 1996
Bottom felt: 494.5 mbrf
Total penetration: 677 mbsf
Total core recovered: none.
TOOL USED: SDT (Digital Sonic Tool)
Recording mode: linear mode (8 receivers)
Remarks about the recording: none.
As most Schlumberger logs, acoustic data are recorded in DLIS format. Each of the eight waveforms consists of 428 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 428 samples per waveform, this corresponds to 1 + 8x428 = 3425 columns. In this hole, the specifications of the file are:
Number of columns: 3425
Number of rows: 6115
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/GPIT/NGT (main, bottom hole assembly at ~ 600 mbrf)
1003D-m.bin: 600-1532 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
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)
For further information about the logs please contact:
E-mail: Cristina Broglia