LWD Sonic Waveform Data - IODP Exp 372 Hole U1518A

LWD Sonic Waveform Data

Science operator: Texas A&M University

Hole: U1518A

Expedition: 372

Location: Hikurangi Subduction Margin (SW Pacific Ocean)

Latitude: 38° 51.5368' S

Longitude: 178° 53.7606' E

Logging date: December 20, 2017

Sea floor depth (driller's): 2647.3 m DRF

Sea floor depth (logger's): 2642.4 LRF

Total penetration: 2747.4 m LRF (123 m LSF)

Oldest sediment recovered: Early-Middle Pleistocene (NB: LWD Hole - Site cored during IODP 375)

Lithology: silty clay(stone) alternating with thin beds of silt(stone) with variable amounts of sand

ACOUSTIC TOOL USED: SonicScope

Recording mode: Monopole P&S, Low Frequency Monopole, Quadrupole.

Remarks about the recording: none.

MONOPOLE P&S MODE: measures compressional slowness in all formations and shear slowness in fast formations.

LOW FREQUENCY MONOPOLE: for stoneley waves analysis.

QUADRUPOLE MODE: measures shear slowness in slow formations.

Acoustic data are recorded in DLIS format. Each of the twelve waveforms 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).The original data in DLIS format were first loaded into the Techlog suite software. The packed waveform data were run through a module that applies a gain correction and the depths were converted to meters below seafloor. The waveforms data were then converted into binary format and gif images.

Each line of the binary file is composed of the entire waveform set recorded at each depth, preceded by the depth. In the general case of 12 waveforms with 256 samples per waveform, this corresponds to 1 + 12x256 = 3073 columns. In hole U1518A, the specifications of the files are:

Number of columns: 3073

Number of rows: 2452 (5.08 cm sampling interval)

Number of rows: 817 (15.24 cm sampling interval)

The following binary files are available at Hole U1518A:

372-U1518A_mono_2in.bin ( -0.952 to 123.559 mbsf)
372-U1518A_mono_6in.bin ( -0.952 to 123.559 mbsf)
372-U1518A_mono_lf_2in.bin ( -0.952 to 123.559 mbsf)
372-U1518A_mono_lf_6in.bin ( -0.952 to 123.559 mbsf)
372-U1518A_qp_2in.bin ( -0.952 to 123.559 mbsf)
372-U1518A_qp_6in.bin ( -0.952 to 123.559 mbsf)

All values are stored as '32 bits IEEE float'.

Any image or signal-processing program should allow to import the files and display the data.

The sonic waveform files were depth-shifted to the seafloor (-2642.4 m) . Please refer to the "DEPTH SHIFT" section in the standard processing notes for further information.

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

Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition 372.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.