Sonic Waveform Data

Science operator: Texas A&M University

Hole: U1520C

Expedition: 375

Location: Hikurangi Subduction Margin (SW Pacific Ocean)

Latitude: 38° 58.1532' S

Longitude: 179° 7.9112' E

Logging date: April 9, 2018

Sea floor depth (driller's): 3533 m DRF

Sea floor depth (logger's): 3531 m WRF

Total penetration: 4587.1 m DRF (1054.1 m DSF)

Total core recovered: 235.4 m (57.7 % of cored section)

Oldest sediment recovered: Probably Cretaceous

Lithology: Cemented sandstone and conglomerate with grains of volcaniclastics and altered basalts

ACOUSTIC TOOL USED: DSI (Dipole Sonic Imager)

Recording mode: Monopole P&S, Upper and Lower Dipole, and Stoneley mode (all passes).

Remarks about the recording: none.

MONOPOLE P&S MODE: measures compressional and hard-rock shear slowness. The monopole transmitter is excited by a high-frequency pulse, which reproduces conditions similar to previous sonic tools.

UPPER DIPOLE MODE: measures shear wave slowness using firings of the upper dipole transmitter.

LOWER DIPOLE MODE: measures shear wave slowness using firings of the lower dipole transmitter.

STONELEY MODE: measures low-frequency Stoneley wave slowness. The monopole transmitter, driven by a low-frequency pulse, generates the Stoneley wave.

Acoustic data are recorded in DLIS format. Each of the eight waveforms generally consists of 512 samples, each recorded every 10 (monopole P&S) and 40 microsec (dipolemodes), at depth intervals of 15.24 cm (6 inches).The original waveforms in DLIS format are first loaded on a virtual PC machine using Schlumberger's Techlog log analysis package. The packed waveform data files are run through a module that applies a gain correction. After they are exported from Techlog in LAS format they are converted into binaryand GIF format (images) are cconverted using in-house software.

Each row is composed of the entire waveform set recorded at each depth, preceded by the depth value. In the general case of 8 receivers with 512 samples per waveform, this corresponds to 1 + 4x512 = 4097 columns. In this hole, the specifications of the files are:

Number of columns: 4097

Number of rows: 5906 (downlog)

Number of rows: 6165 (main pass)

Number of rows: 613 (repeat pass)

The following files have been loaded:

DSI from HRLA/DSI/HLDS/EDTC-B (Downlog, drill pipe at 596 m WMSF, casing at 642 m WMSF)

375-U1520C_ldip_d.bin: 0-907.8 m WMSF

375-U1520C_mono_p1.bin: 0-907.8 m WMSF

375-U1520C_st_d.bin: 0-907.8 m WMSF

375-U1520C_udip_d.bin: 0-907.8 m WMSF

DSI from HRLA/DSI/HLDS/EDTC-B (Main pass, drill pipe at 596 m WMSF, casing at 642 m WMSF)

375-U1520C_ldip_main.bin: 0-947 m WMSF

375-U1520C_mono_main.bin:0-947 m WMSF

375-U1520C_st_main.bin:0-947 m WMSF

375-U1520C_udip_main.bin:0-947 m WMSF

DSI from HRLA/DSI/HLDS/EDTC-B (Repeat pass, recorded open hole)

375-U1520C_ldip_rep.bin: 844.9-946.1 m WMSF

375-U1520C_mono_rep.bin: 844.9-946.1 m WMSF

375-U1520C_st_rep.bin: 844.9-946.1 m WMSF

375-U1520C_udip_rep.bin: 844.9-946.1 m WMSF

All values are stored as 32 bits IEEE floating point.
Any image or signal-processing program should be able to import the files and display the data.

The sonic waveform files are depth-matched and depth-shifted to the seafloor (-3531 m) . Please refer to the 'depth_matches' folder in the hole index page for the depth-matching values and 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 375.

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