A controlled comparison of spray drift influences. These are conceptual estimates, not AgDRIFT®, AGDISP, buffer distances or operational guidance.
Four consecutive spray passes
The square block is exactly 1,000 m × 1,000 m (100 ha), split into two 50 ha halves. Four adjacent tracks run in alternating directions, beginning left of the centre line at the default heading. The heading control rotates the full plan. The intended target is the union of all four narrow swaths. The aircraft turns automatically with the spray off; droplets already released continue drifting. Turn paths are illustrative connections, not validated aircraft manoeuvres.
The aircraft and spray markers are enlarged for visibility; map distances are to scale. Dotted contours measure distance from the first swath; bottom markers measure from the centre line. The smallest guides become readable when zoomed in.
Droplets and settling
Each pass uses 512 source trajectories sampling a lognormal volume distribution (log standard deviation 0.42) around the selected VMD. The 2,048 sources are weighted by the volume sprayed along each track. Each source is distributed into many visible droplets, sharing its motion at different release times and positions. Each marker carries part of its source weight, so extra visibility does not add spray volume or alter drift physics. Marker count is illustrative, not a count of real droplets. Up to 12,000 markers are drawn at once; all markers contribute to results. Category names are approximate examples; VMD alone does not establish a certified spray-quality class.
Settling balances gravity against sphere drag using Reynolds-dependent drag (Schiller–Naumann approximation). A fixed 0.2 s model step integrates wind transport, settling and evaporation. Deterministic eddy variations produce different paths without changing the results on each run. A short, illustrative forward-motion term depends on aircraft speed. Aircraft vortices, downwash, breakup and nozzle geometry are not resolved.
Evaporation, weather and canopy
A simplified D² evaporation law uses K = 650 × vapour pressure deficit in µm²/s, with deficit in kPa. This coefficient is illustrative and uncalibrated. Temperature and relative humidity determine vapour pressure deficit. Evaporation stops at a fixed 1% nonvolatile volume residue; chemical mass is assumed retained. This is not a formulation-specific model and does not predict vapour drift.
Release height is always above the selected canopy/target. Canopy changes near-surface wind attenuation, not the entered release height. Stability and turbulence change the illustrative eddy amplitude. Stable air mixes less; it does not switch gravity off. Inversion trapping, terrain, thermal structure and far-field transport are not resolved. A positive temperature difference activates the very-stable setting and warning.
Read the results correctly
- Average drift: mean horizontal displacement from each release point, weighted by original volume, among landed parcels only. It includes along-track and cross-track movement.
- 90% deposition distance: the 90th percentile of that same landed distribution. It is not the distance containing 90% of all emitted spray when parcels remain airborne.
- Maximum: largest horizontal displacement observed in the finite sample. “≥” indicates parcels are still airborne; it is not a bound on real-world drift.
- Off-target spray: volume deposited outside the combined four-pass target, divided by all released original volume. Unlanded material is reported separately and is not counted as on-target. This differs from the percentage outside the full 100 ha field.
- Live results: while the animation runs, distances use parcels that have landed so far; off-target uses all parcels released so far. Ready mode shows the complete four-pass forecast. Every parcel is followed for at most 180 seconds after release; any remainder is shown as unresolved airborne volume.
- Deposition colours: a smoothed, relative heat map, not measured concentration. Blue/teal show heavier deposition; pale green shows trace. Amber moving droplets and orange deposition marks identify spray outside the four target swaths. Application rate changes volume and display intensity, not droplet drift distance.
Comparisons and score
The fixed reference uses 3 m, 180 km/h, 350 µm VMD, 8 km/h wind from W, four alternating tracks starting northbound, 25°C, 60% RH, neutral stability, medium turbulence, a short crop and a 20 m swath. Height and droplet charts vary only their named setting, with 128 source trajectories per pass for each comparison point. A dagger (†) marks a result with more than 1% still airborne; landed-only means can understate that tail.
The 0–100 index combines modeled mean drift, off-target deposition and unresolved airborne volume with wind, crosswind, release height, droplet size, evaporative demand and stability. It is an unvalidated teaching index, not a measure of legal compliance or a probability of harm.
Controls
Drag the map to pan; use the wheel or + / − to zoom. Fit restores the full field. Click or drag the compasses, or type a direction. Wind direction means from; the map arrow points where it is travelling. Changes recalculate the forecast and restart an active pass. Reset clears the current pass; Reset to baseline also restores every input. Playback speed changes animation time only.
Background references
The general relationships follow these references; the numerical implementation and teaching coefficients are independent and have not been validated by these organisations.
References require internet access. The simulator itself makes no network requests.