1. Project Overview
The Project is a high-resolution offshore seismic survey conducted in 2024 along the eastern continental margin.
The survey aimed to delineate near-surface stratigraphy, identify potential geohazards, and characterize shallow sedimentary sequences for the planned offshore infrastructure corridor.
Data acquisition was carried out using an ultra-high-resolution seismic (UHRS) system combined with multibeam echosounder (MBES), side-scan sonar (SSS), and magnetometer (MAG) datasets to provide an integrated geophysical understanding of the site.
2. Data Acquisition Summary
| Parameter | Description |
|---|---|
| Survey Area | ~250 km² off the coast of an Asia country |
| System | UHRS boomer array with 96-channel streamer |
| Sample Rate | 0.25 ms |
| Record Length | 500 ms |
| Shot Interval / Trace Spacing | 0.5 m / 1.0 m |
| Navigation System | DGPS with positional accuracy ±0.5 m |
| Water Depth Range | 30 – 80 m |
Environmental conditions included moderate swell (0.5–1.2 m) and variable sound-speed structure due to seasonal thermocline development, both influencing source-receiver coupling and wavefield consistency.
3. Processing Objectives
The core objective of the processing workflow was to extract true subsurface reflections with minimal contamination from source, receiver, or environmental effects.
Specific goals included:
- Removal of ghost and bubble oscillations from the source signature.
- Suppression of surface-related and interbed multiples.
- Enhancement of signal-to-noise ratio (SNR) in the 200–2000 Hz band.
- Accurate time-to-depth conversion and isopach mapping for interpretation.
4. Processing Challenges
Offshore presents unique challenges related to both source mechanics and environmental acoustics:
- Ghost Effects – The shallow streamer (1.5 m) caused destructive interference between direct and surface-reflected arrivals, producing notches near 330 Hz and 1000 Hz.
- Bubble Noise – The untuned boomer source generated low-frequency bubble oscillations, masking early arrivals and requiring frequency-domain de-bubbling.
- Multiples & Reverberations – Strong impedance contrast between soft sediments and underlying volcanic tuffs produced persistent water-bottom multiples and peg-leg reverberations.
- Sound-Speed Variability – Daily temperature gradients caused slight statics variations and travel-time anomalies across adjacent lines.
- Complex Seabed Morphology – Steep escarpments and pockmarks enhanced scattering and mode conversions.
5. Processing Workflow
The data were processed using RadexPro 2024.2 with a customized workflow as outlined below:
- Geometry Definition & Navigation Merge
- GPS and shot files merged; geometry QC performed in SEG-Y headers.
- Trace Editing & Amplitude Recovery
- Noisy channels muted; spherical divergence and gain corrections applied.
- De-ghosting
- Phase-adaptive operator derived from shallow water model;
filter applied in τ–p domain to restore high-frequency spectral balance.
- Phase-adaptive operator derived from shallow water model;
- De-bubbling
- Source signature analyzed in the frequency domain;
inverse bubble filter designed from measured oscillation period (~80 ms).
- Source signature analyzed in the frequency domain;
- De-convolution
- Spiking deconvolution with time-variant operator (200 ms window, 20 ms step).
- Multiple Attenuation
- Surface-related multiple elimination (SRME) applied;
residual peg-legs addressed using Radon transform demultiple.
- Surface-related multiple elimination (SRME) applied;
- Velocity Analysis & NMO Correction
- Velocity picking every 250 m CDP interval; smoothed using median filter.
- Stacking & Band-Pass Filtering
- 200–2000 Hz band retained;
f-k noise suppression before stacking to preserve lateral continuity.
- 200–2000 Hz band retained;
- Time-to-Depth Conversion
- Check-shot calibration with nearby borehole data.
- Seabed-Referenced Amplitude Correction & Final Migration
- Kirchhoff post-stack migration with 4 m grid step.
6. Results
The processed sections revealed:
- Clear imaging of sedimentary layering to depths of 80–120 m below seabed.
- Identification of paleochannels and buried erosional surfaces.
- Recognition of shallow gas pockets and minor fault offsets (<2 m vertical throw).
- Enhanced frequency content up to 1.8 kHz after successful de-ghosting and de-bubbling.
Amplitude preservation was sufficient for semi-quantitative impedance analysis, while coherence attributes delineated structural discontinuities critical for foundation design.
7. Quality Control and Validation
- Spectral QC: Pre- and post-processing spectra verified notch suppression.
- Signal-to-Noise Ratio (SNR): Improved from 8 dB (raw) to ~22 dB (final stack).
- Repeatability: Cross-line correlation exceeded 0.9 in stable zones.
- Comparison with MBES: Seismic seabed reflector matched bathymetric DEM within ±0.3 m.
8. Conclusions
The Project offshore seismic processing in Asia demonstrates that shallow-water marine environments impose substantial complexities, primarily due to source ghosting, bubble oscillations, and reverberations.
Through a combination of adaptive de-ghosting, model-based de-bubbling, and robust multiple attenuation techniques, reliable subsurface images were achieved.
The success of this workflow underscores the importance of physics-driven source modeling, frequency-adaptive filters, and rigorous QC for any high-resolution seismic campaign in acoustically challenging environments such as Asia area.