LWD Sonic Waveform Data
IODP coring and logging operator: CDEX
Hole: C0012H
Expedition: 338
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 32 ° 44.8783 ' N
Longitude: 136° 5.0351' E
Logging-while-drilling date: December 3-6, 2012
Sea floor depth (as seen on logs): 3538 m LRF
Total penetration: 4248 m LRF (710 m LSF)
TOOL USED: sonicVISION
The original LWD sonic data have been unpacked by Schlumberger Drilling and Measurements using GeoFrame's Preprocessor module, which also applies a gain correction. At LDEO-BRG the four waveforms have first been converted into ASCII and then binary format. Each of the four waveforms consists of 151 samples at depth intervals of 15.24 cm (6 inches). Each line of the binary files is composed of the entire waveform set recorded at each depth, preceded by the depth value. In the case of 4 waveforms with 151 samples per waveform, this corresponds to 1 + 4x151 = 605 columns. In this hole, the specifications of the files are:
Number of columns: 605
Number of rows: 4496 (15.24 cm sampling rate)
The following files have been loaded:
338-C0012H_6in.bin: 0-713.35 m LSF
The binary files are depth-shifted to the sea floor (- 3538 m).
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.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 Logging-while-drilling sections of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 338.