LWD Sonic Waveform Data
Science operator: CDEX-JAMSTEC
Hole: C0002S
Expedition: 358
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 33° 18.0507' N
Longitude: 136° 38.2029' E
Logging-while-drilling date: February 2 - 9, 2019
Sea floor depth (as seen on logs): 1967.5 m LRF
Total penetration: 4901.5 m LRF (2934 m LSF)
ACOUSTIC TOOL USED: SonicScope
Recording Modes: Monopole, Monopole Low Frequency, and Quadrupole.
Number of columns: 2073
Number of rows: 3385 (2-in sampling rate)
The following files have been loaded: casing at ~ 2802 mLSF)
358-C0002S_mono_2in.bin: 2761.8-2933.7 mLSF
358-C0002S_lf_2in.bin: 2761.8-2933.7 mLSF
358-C0002S_qp_2in.bin: 2761.8-2933.7 mLSF
All values are stored as '32 bits IEEE float'.
Any numerical software or programing language (matlab, python,...) can import the files for further analysis of the waveforms.
The sonic waveform files were depth-shifted to the seafloor (-1967.5 m).
IMPORTANT: Because Hole C0002S is a sidetracked hole, there is a difference between the measured depth (MD) and the true vertical depth (TVD). Because the difference is small (~1-2 m in total in expedition 358 Holes C0002Q and C0002S), the scientists decided to use the the measured depth instead of the true vertical depth for all the measurements reported in the IODP Proceedings. Accordingly, we have used the measured depth in the files included in the LogDB online database.
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 questions about the logs, please contact:
Additional information about the drilling and logging operations can be found in the Site Expedition Report and in the Methods section, Proceedings of the International Ocean Discovery Program, Expedition 358.
For questions about the logging operations and the processing performed onboard, please contact:
Yukari Kido
E-mail: ykido@jamstec.go.jp