IAMSAR Drift Modeling & USCG Search Theory
Joint IMO / ICAO Standard1. Datum Vector Summation
Datum position represents the most probable location of the target at time t. It is computed via vector addition: Drift = Total Water Current (TWC) + Leeway (LW). Current acts across the entire submerged profile, while leeway is wind-driven aerodynamic drag offset by hydrodynamic resistance.
2. Leeway Divergence & Uncertainty
Objects do not blow directly downwind; asymmetrical hulls and canopies generate aerodynamic lift, creating a divergence angle (typically ±35° for rafts, ±15° for fuselage fragments). Total Probable Error E = √(X² + Y² + dₑ²) compounds initial radar error (X), navigation error (Y), and drift error (dₑ).
3. Standard Search Patterns
Sector Search (VS): Rapid coverage for high-confidence datum (aircraft ditching with ELT/radar cutoff). Expanding Square (SS): Concentric square spirals when datum location is moderate confidence. Creeping Line (CS): Rectangular grid covering uniform linear drift corridors.