19. Dog parties and how scent travels
Translated from the Finnish manual (manual/fi); the Finnish text is authoritative.
Matches version: 0.9.1 (phase 9, 2026-10-28). Status: dog parties and the scent model work; the numbers come from the literature and our own estimates and are meant to be corrected with dog handlers (calibration page, chapter 13).
This chapter explains how the simulator's dog parties work and how scent travels, so the drone crew can read the dogs' radio traffic and work with them. The Dog parties section of chapter 7 is a summary of this; chapter 13 tells what the instructor sees and can adjust.
The party
A dog party is a handler, a navigator (kartturi) and a dog. The split of work depends on the party and its experience, but mainly the navigator navigates and the handler can concentrate on the dog. The party gets a segment from the search leader like the drone crew does and walks the segment's route at about 1.6 km/h.
Each party makes its search plan by its own and its dog's strengths, so parties differ:
- A close-working dog searches about 40–80 m from the handler (it is called back from further). A free-ranging dog works well beyond that, 120–300 m in the simulator, and the party's sweep lines are wider apart (up to 150 m), so it covers the segment faster. About half the dogs in the simulator range freely.
- About 60 % of parties quarter across the wind, the dog ahead of the handler and upwind. The rest follow their own plan: the dog works both sides of the route whatever the wind, and the party does not necessarily enter the segment from downwind.
When the party has walked the route, the leader logs the segment as searched with the dog party's POD and gives the party the next segment. The shares and distances are estimates on the calibration page.
A search has 0–3 parties: none in 10 % of exercises, one in 50 %, two in 30 % and three in 10 %. The first party usually works in the same segment as the drone. A party is normally on site at the same time as the drone crew or earlier (in about 40 % it is already at work, up to an hour), rarely 10–90 min later. The briefing gives the estimated times, and the radio says "Koira 1 paikalla, aloittaa lohkossa 7" (Dog 1 on site, starting in segment 7), or "Koira 1 jo työssä lohkossa 7, aloitti 20 min sitten" (already working in segment 7, started 20 min ago). A party already at work has searched its segment and may be on a trail when the drone crew arrives; its work time (Fatigue and heat, below) has run for that long too.
The dog's states
The dog is always in one of these states. The instructor sees the state on the map; everyone else infers it from the radio.
| State | What the dog does | On the radio |
|---|---|---|
| not on site yet | the party is on its way | – |
| searching | quarters across the wind ahead of and upwind of the handler, or both sides of the route by the party's own plan; close-working 40–80 m, free-ranging 120–300 m | on site, starting in segment n |
| in scent | has air scent and works into the wind toward the source; at the cone's edge it tries for the stronger side, close in it goes straight | the dog has scent, working into the wind / the dog lost the scent |
| on the trail | follows the ground scent of the person's footsteps toward the fresher end, a few metres downwind of the prints | the dog takes the trail / on the trail, the trail continues toward 240° (every 5 min) / the trail broke |
| moving to a find | a find reported by the drone: the party goes there to pick up the trail | leaving for the find to take the trail / at the find, the dog takes the trail |
| indicating | at a source: an item or the person (30 s) | the dog indicates an item: bucket / the dog indicates — the missing person is found |
| resting | an hour's rest after two hours of work | the dog needs a break, 60 min / break over, continuing |
| done for the day | after the hour that follows the break the dog is finished for the day; its segment goes to the next team; 12 h later the dog comes back to a new segment | the dog is done for the day, party returning / the dog has rested, back to the search |
| with the subject | the person was found, the party's work ends | – |
So the dog can find the missing person itself. The search then ends with the dog's find, and the debrief logs both the drone's and the dog's finds.
Air scent
The missing person and the items they dropped give off scent that travels downwind as a cone. The cone widens with distance (about a 14° half angle, 25 m of widening per 100 m) and thins in two ways: the widening spreads the scent over a larger area, and air that has travelled long has lost part of it (after a minute of travel only about a third is left). Around the source there is also a scent pool, which is all there is in calm air.
What it means in practice:
| Wind | The dog picks up a person's scent from downwind |
|---|---|
| calm | 20–25 m from any direction |
| 1 m/s | about 120 m |
| 3 m/s | about 150 m |
| 8 m/s | about 100 m (strong wind dilutes) |
The wind is the wind at the dog's height: the same power-law profile as for the aircraft (chapter 10), so on the forest floor the wind is lighter than at the weather station.
- A dropped item (a garment, a beanie, a bucket, a backpack) smells about a third of a person and fades: after eight hours only about a third of that is left.
- Of a missing person inside a building only about 15 % of the scent escapes: the dog finds them only from close by.
- Scent does not travel upwind: a person upwind of the segment goes unnoticed by the dog even 50 m away. That is why many parties quarter across the wind ahead of the handler, and why the wind direction is worth checking before a party is sent.
- Once the dog has scent it does not go straight: it works into the wind and tests which side is stronger until it reaches the pool. At the cone's edge it may lose the scent (the dog lost the scent) and return to searching.
Trailing
The missing person's footsteps leave ground scent the dog can follow. It fades with time, and the ground matters a great deal (Vapepa notes, 2026-10-29):
| Ground | Trail can be followed (mild, calm weather) |
|---|---|
| shaded forest, moss | 48–72 h |
| bog | about 50 h |
| open heath, field, meadow | about 36 h |
| gravel, sand, rock | about a day |
| yards and built-up areas | about 14 h; other people's scent confuses, the dog loses the trail more easily |
| asphalt | a few hours |
| snow, frost and calm | 12–24 h |
| snow, thaw or rain | a few hours |
Weather wears it:
| Condition | Effect on ground scent |
|---|---|
| cool, humid air | keeps it; dry air wears it (95 % humidity about 0.8 ×, 40 % about 1.25 ×) |
| direct sun | dries it on open ground; the canopy's shade protects it |
| light rain or drizzle (up to 1 mm/h) | binds the scent, the trail lasts a little longer |
| heavy rain (over 1 mm/h) | washes the trail |
| heat above +15 °C | wears it a little per degree |
| wind above 6 m/s (on snow above 4 m/s) | wears it; on snow the wind blows the scent out of the track |
| snowfall | fills a trail on snow fast; covers one on bare ground a little |
| snow at −3…0 °C | wet snow binds the scent of the prints well |
The same snow and weather record (chapter 10) drives both the visible tracks in snow and the ground scent, so a two-day-old trail is weak in both.
The dog takes the trail when it quarters across the footsteps (about one time in three, scent permitting) or when the party is sent to a find. On the trail it moves toward the fresher end, a few metres downwind of the prints where the scent lies, and the party reports on the radio every five minutes which way the trail continues (±15°). That is the hint for the drone crew: the segment's next search direction is worth choosing from the trail. At the end of the trail the person's own air scent takes over and the dog switches to in scent.
Air currents and terrain
The air-scent cone changes with the time of day and the terrain (Hajujen käyttäytyminen ilmavirtojen ja sään vaikutuksesta, VS Pelastuskoirat 2024). The simulator picks the state from the sun's height, the cloud and the wind once a minute:
| State | When | What the dog meets |
|---|---|---|
| wedge with the wind | cloudy day, windy night | the ordinary cone: good scent |
| rises and falls | clear midday, wind under 6 m/s | convection lifts and drops the scent in about 40 s cycles: the dog picks it up and loses it in turns |
| rises (evening) | after sunset, clear, light wind | the ground cools under warm air and the scent rises: a dog more than 3 m below the source gets only about a third |
| drains down (morning) | before the air warms, clear, light wind | the scent drains down the slope at about 0.6 m/s: a target higher up is found from below |
| hovers (calm night) | night, wind under 1 m/s | the scent hangs over a wide area (about 2.5 × the usual pool): the dog reacts but pinpointing is hard |
Terrain:
- Hollows: in a light wind (under 2 m/s) scent collects in hollows and pits. With the source in a hollow the dog struggles to follow the scent all the way to it.
- A tree line beside open ground: on the open side behind it (10–40 m) eddies turn the scent regardless of the wind direction.
- Chimney: next to a building or a cliff (about 12 m) the scent climbs the face and comes down further off (60–150 m downwind). Close by the dog gets little scent and does not pinpoint the source easily; check the surroundings of tall objects.
- Snow: the scent of a person on the snow or in a snow pit carries far, and further still in cold powder (below −5 °C) as it rises from the light snow. On snow the handler sees false tracks, so other tracks confuse half as much.
- Crust: when snow has thawed and frozen again a step does not break the surface: the trail ages about 1.3 × faster and the wind wears it from 2.5 m/s. 5 cm of new snow buries the crust.
- Valley: on a valley floor a light wind (under 4–8 m/s) and the scent turn along the valley.
- Other searchers: a ground team or another dog party moving within 40 m stirs the scent (the dog's threshold 1.6 ×), and on a trail others have trampled the dog loses it more easily.
- Mist: in low mist or fog the scent stays low and travels further with the air in a narrower plume.
Hard pinpointing (hovering scent, a hollow, a chimney) shows in the dog's work: over the last metres it searches wider and less surely, and the in scent state can last long without an indication.
Working with the drone
- When the drone crew reports a find (I, chapter 9: a bucket or a beanie, for example), the nearest free dog party leaves for it and takes the trail onward from the item. A resting party or one not yet on site does not go; then the leader sends a ground team.
- End of the trail: when the prints run out, the dog circles out from the end (10 m growing to 60 m, up to 10 min) for the person's air scent.
- Trail lost: the party radios where it followed the trail from and to (coordinates, distance and direction), and the trail shows as a dashed line on the debrief map. The search leader judges whether it matters: a stretch under 100 m, or a spot already reported, is only logged; otherwise the segments in the trail's direction (800 m, ±35°) are raised and the nearest free Vapepa ground team is sent to the segment where the trail went cold to support the dog.
- A party on the trail radios the direction every five minutes; the drone can fly ahead in that direction.
- The dog does not see the drone's coverage and the drone does not see the dog's scent cone: information is exchanged only by radio, as in a real search.
- In the thermal camera a dog party is three warm figures, one of them small and moving fast ahead of the others. It is the most common "person-like" thermal distractor in a segment where a party is working.
Fatigue and heat
A dog's working day is 2 hours of continuous work in scent in good conditions, an hour's break and one more hour of work. After that the dog is done for the day: the party returns, and the leader gives its unfinished segment to the next free team. In the last half hour of each work period the nose is about 30 % less sensitive (threshold 1.43×). In heat the work periods shrink: from +20 °C on, down to half (1 h and 30 min) at +30 °C. A party on its break or done for the day does not leave for a find; if no dog is coming back to work, the leader leaves the find to the ground teams.
For the instructor
On the instructor station and in coach mode the map shows the scent cones of the person and the items in the current wind (purple) and each dog's state. The debrief shows the dogs' routes, the cone in the final wind and the indications. The pilot and the observer do not see the cones.
Every number in this chapter is in the calibration page's group Koirat ja haju (dogs and scent, chapter 13): air-scent sensitivity, cone widening and reach, the pool, an item's scent and its fading, ground-scent fading and the weather effects, work and rest times, fatigue, heat, speeds and the dog's distance from the handler. The calibration sheet (docs/calibration/kalibrointi.md) puts them to dog handlers as questions.
What the model does not have
- The wind direction is the same over the whole segment: terrain does not channel it into valleys. Morning drainage, evening rise, hollows, tree-line eddies and the chimney are in (above), simplified.
- Vegetation does not damp air scent: a dense spruce stand and an open field are alike in the air (for ground scent the forest keeps a trail longer).
- Crust is simplified: snow that thawed and froze again turns load-bearing (no change of bearing strength over the day).
- Water neither carries nor breaks scent; the party only walks around water.
- One dog per party; individual dogs and their training show only through the calibration.
- The dog does not follow other searchers' or animals' scent; the confusing scents of yards and roads appear only as the trail breaking more easily.