Navigation and positioning QC

Part 6 — QC during acquisition

Learning objectives

Identify the three environment regimes: streamer, OBN, land RTK
Quote deviation tolerances: streamer feather ≤15°, OBN landing ≤5% depth, land ≤2 m
Link cross-current to streamer feather and water depth to OBN drift
Apply threshold-based QC flagging for each mode

Every shot and receiver in a modern survey is GPS-logged or acoustically positioned. The actual geometry is never identical to the planned geometry; QC measures the deviations and flags anything outside tolerance.

Streamer feather

Streamers behind a towed vessel drift sideways in cross-current. Feather angle is roughly atan(cross-current / sail-speed). At 1 kt cross with 4.5 kt sail that is ~13° — borderline at the industry 15° limit. Lateral steering birds (e.g. Sercel Nautilus) close part of the loop with a correction lag of ~100 m; a fully active bird system reduces feather by 60–80%. Un-feathered 2–3 kt currents push a 6 km streamer tail 150–200 m off plan, well beyond any usable bin-fold tolerance.

OBN landing

Nodes drop through water at ≈1 m/s terminal velocity. In 1500 m of water with a 0.3 m/s current, the node drifts 450 m during descent. USBL (Ultra-Short Baseline) acoustic ranging during descent and post-deploy multi-shot triangulation refine the actual landed position to ≈3 m in deep water. Industry rule: landed position within 5% of water depth of the drop plan.

Land RTK

Real-Time Kinematic GPS gives 2–5 cm horizontal precision under open sky. Lost fixes (under trees, in urban canyons, with satellite geometry issues) degrade the position to metres or worse. A few percent of stations per day typically report a degraded fix and need a follow-up visit with total station or UAV photogrammetry to obtain a clean coordinate.

References

Sheriff, R. E., Geldart, L. P. (1995). Exploration Seismology (2nd ed.). Cambridge University Press.
Vermeer, G. J. O. (2002). 3-D Seismic Survey Design. SEG Geophysical References 12.
Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.