Wireline Sonic Waveform Data
ODP logging
contractor: LDEO-BRG
Hole: 504B
Leg: 148
Location: Costa Rica Rift (tropical NE Pacific Ocean)
Latitude: 1° 13.611' N
Longitude: 83° 43.818' E
Logging date: March, 1993
Water depth (from Leg 111): 3474 mbrf
Total penetration: 2111 mbsf
Total core recovered: 9.58 m (8.7 %), 2000-2111 mbsf interval
TOOL USED: SDT (Digital Sonic Tool)
Recording mode: Linear Array Mode (8 receivers)
Remarks about the recording. In all of the past legs, the sonic waveforms were not on depth with the other logs: they generally showed an offset ranging from a few meters to about 40 m downward, depending on the length of the tool string. This offset was very clearly visible at the base of the bottom hole. In Hole 504B, there not seem to be any offset. It is recommended, however, to process the sonic waveforms and then match the output to the other logs before drawing any conclusion.
Acoustic data have been recorded in LIS format. Each of the eight waveforms consists of 500 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 8 waveforms with 500 samples per waveform, this corresponds to 1 + 8x500 = 4001 columns. In this hole, the specifications of the files are:
Number of columns: 4001
Number of rows: 6805 (upper section)
Number of rows: 1100 (middle section)
Number of rows: 4381 (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 DLL/SDT (upper section, casing at 374 mbrf)
504B-u.bin.bin: 3748.28-4785.21 mbrf
SDT from DLL/SDT (middle section, open hole)
504B-mid.bin: 4762.80-4930.29 mbrf
SDT from DLL/SDT (lower section, open hole)
504B-l.bin: 4884.57-5552.08 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