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.

The SonicScope data were acquired by Schlumberger/Anadrill in DLIS format. The data was sent onshore to Schlumberger Information Solution for processing. Each of the twelve waveforms acquired with the SonicScope tool consists of 256 samples, each sampled every 20 (monopole P&S) and 40 microsec (quadrupole and low frequency monopole modes), at depth intervals of 5.08 cm (2 inches) and 15.24 cm (6 inches). For Hole C0002S, only the SWF with 2-inch sampling rate were available on the JAMSTEC web site. The processed data in DLIS format were first loaded into the Techlog suite software and were depth shifted to the sea floor. The packed waveform data were run through a module that applies a gain correction and were output in LAS format. Finally, the waveforms were converted into binary format and gif images. Each line of the binary files is composed of the entire waveform set recorded at each depth, preceded by the depth. In the case of 12 waveforms with 256 samples per waveform, this corresponds to 1 + (12x256 )= 3073 columns. In hole C0002S, the specifications of the files are:

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

For database-related questions you may contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu