Wireline 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 line is composed of the entire waveform set recorded at each depth, preceded by the depth (multiplied by 10 to be stored as an integer). In the general case of 8 waveforms with 512 samples per waveform, this corresponds to 1 + 8x512 = 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 float'.
Any image or signal-processing program should allow 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.
For users interested in reading and converting the data to a format more suitable for their own purpose, the fortran declaration used to open the file *.bin would be:
open (1, file = *.bin,access = 'direct', recl = 4*(1+nrec*nsamples))
where nrec is the number of receivers (8 in the case of the DSI) and nsamples the number of samples per waveforms.
If the total number of depths where waveforms were recorded is ndepth (for a 150 m interval with data every 15cm, ndepth would be 1001), a generic loop to read the data would be
do k = 1, ndepth
...
read(1, rec=1+k) depth(k), ((data(i,j,k), j=1,nsamples),i = 1,nrec))
...
enddo
the first record in each file is a header with some of the file specifications:
- number of depths
- number of samples /trace
- number of receivers
- tool number = 0 (DSI)
- mode (1 = Lower Dipole, 2 = Upper Dipole, 3 = Stoneley, 4 = Monopole)
- vertical sampling interval
- scaling factor for depth
- waveform sampling rate in microseconds
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.