Wireline Sonic Waveform Data
ODP logging contractor: LDEO-BRG
Hole: 909-C
Leg: 151
Location: Yermac Plateau (Arctic Ocean)
Latitude: 80° 15.894' N
Longitude: 6° 35.430' W
Logging date: September, 1993
Bottom felt: 2529 mbrf
Total penetration: 1061.8 mbsf
Total core recovered: 604.77 m (61%)
TOOL USED: SDT (Sonic Digital Tool, also known as Array
Sonic)
Recording mode: linear array mode.
Remarks about the recording: none.
As most Schlumberger logs, acoustic data are recorded in
DLIS format. Each of the eight waveforms consists of 472 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 472 samples per waveform,
this corresponds to 1 + 8x472 = 3777 columns. In this hole, the specifications
of the files are:
Number of columns: 3777
Number of rows: 4155 (upper)
Number of rows: 2718 (lower main)
Number of rows: 624 (lower repeat)
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/HLDT/CNTG/NGT (lower main, bottom hole
assembly at ~ 3109 mbrf)
909C-lm.bin: 3109-3523 mbrf
SDT from DIT/SDT/HLDT/CNTG/NGT (lower repeat, recorded open
hole)
909C-lr.bin: 3119-3214 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
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