A plankton-style net is towed up and down through a 2D
cross-section of the water column. Any particle whose diameter
is at least the net's mesh aperture and that passes within the
net's capture radius during a tow pass is retained; smaller
particles slip straight through the mesh.
retained = (d_particle ≥ mesh_size) AND (|pos_particle − pos_net| ≤ R_net)
concentration_L = captured_count / sample_volume
sample_volume = π·R_net² · Σ(tow_speed · dt)
- Particle concentration — how many microplastic fragments drift in the sampled water column.
- Filter mesh size — the net's aperture in mm; finer mesh catches smaller fragments but the trade-off is real-world clogging (not modelled here).
- Current speed — lateral drift speed carrying particles past the net, set by real ocean currents.
- Net tow speed — how fast the net is hauled through the column; faster tows sample more volume per minute but can skip particles near the mesh threshold.
The spectroscopy scan simulates FTIR/Raman analysis of the captured
sample: each retained particle is illuminated to confirm it is a real
polymer signature, giving the detection accuracy readout.