Page 61 - Acquisition and Processing of Marine Seismic Data

52 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.12 Comparison of (A) pressure, (B) velocity sensor measurements, and (C) computed final upgoing pressure field
data. Corresponding amplitude spectra are shown in the bottom panels. After Carlson, D., Long, A., S€ ollner, W., Tabti, H., Ten-
ghamn, R., Lunde, N., 2007. Increased resolution and penetration from a towed dual’sensor streamer. First Break 25, 71–77.

as a separate tilt sensor to correct the orientation dealiasing in crossline direction (Bunting et al.,
of the sensors for each recording channel to 2013). Since the ghost effect is eliminated by Iso-
obtain a true vertical and horizontal measure- Metrix technology, it becomes possible to tow
ment. Mellier et al. (2014) have shown that the streamer at higher depths, which provides
hydrophone data separates the signal and noise more low frequencies and widens the overall
at very low frequencies, whereas the accelerom- frequency band (Breistøl, 2015).
eter data is quite noisy at frequencies up to Dual sensor data needs some specific prepro-
24 Hz. Therefore, the accelerometer signal is cessing applications. The velocity sensor data is
used to reconstruct higher frequency compo- incorporated only for the frequencies typically
nents, especially those lost at the ghost notches, higher than 20 Hz since it is too noisy at lower
for a careful summation process between hydro- frequencies. Therefore, velocity sensor data for
phone and vertical accelerometer data. low frequencies must be predicted from hydro-
The IsoMetrix system utilizes a single-sensor phone record. The data is separated into up- and
triaxial microelectromechanical accelerometer downgoing pressure and velocity wave fields,
technology on Nessie-6 (Western Geco) point where both sets of data can be extrapolated to
receiver seismic streamer, which measures pres- any desired recording depth, and then a conven-
sure and accelerations related to the vertical tional processing flow can be applied (Carlson
and crossline gradients of the pressure field. The et al., 2007).
acceleration measurements are used to obtain Recording with dual sensor streamers has
pressure gradients for recovering the missing fre- several significant advantages. First, the band-
quency components at the ghost notches and for width of the data is considerably extended by