When there is no wind or air flow, scent disperses outwards equally, in all directions (unless it is blocked). The picture shows scent spreading out in approximately a cone shape. In these pictures, brighter green represents stronger odor and lighter green represents weaker odor. You can’t see that there’s a lot of scent building up inside the box, but it’s definitely there. A sniffer dog can detect scent any green areas that reach his nose.
While searching for target odor, the dog’s nostrils dilate and he increases his sniffing rate so he can sample a larger volume of air. The dog’s left and right nostrils function independently. Mobile parts of his nose move and the shape of his nostrils is altered dynamically. When the dog is actively sampling, the inspired air travels dorsally, medially and ventrally around the obstructing alar fold. The right and left chambers of the nose are filled with scrolls of fine bone called turbinates aka conchae. Like toilet paper wrapped around a roll, this anatomical configuration maximizes the surface area available for olfactory receptors to interact with scent. When his left nostril detects more odor than his right, he adjusts his path more to the left. He alters his counter turning path, often bracketing back and forth as he tracks the scent cone back to its origin: source.
The longer you leave the scent (known as ageing aka soak time), the more widely the scent disperses into the environment. Imagine the green cone expanding until it hits the edges of the room. Experienced dogs can find hides aged weeks, including outdoors with daily temperature changes and precipitation.
Note that scent must travel through gases (like the air) or liquids (like water) to reach the dog’s nose in order for it to be detectable. If there is no medium to travel through (like space or a truly pristine, airtight vessel, scent cannot be detected. The more airtight the seal of the container holding the hide, the longer you need to let it age so the plume can escape the container and be available in the environment. This may take hours or days depending on the scenario. If you include no aging up to days or weeks of aging in your scent detection training, your dog will be better prepared to handle real-life searches.
AIRFLOW & WIND
While visualising scent plumes is helpful for human understanding, it’s actually a simplification of the complex, changing environments dogs encounter in real life. In most search environments, there is wind, or at least smaller air currents. Wind and air currents move scent around, messing up the tidy scent cone.Outdoors, wind gusts may cause chaotic, erratic, unpredictable changes to the path scent travels, including swirling in circles and even changing or reversing direction mid-search! Scent is a moving target, and no two searches are identical.
Falling back on the foremost human sense of vision, picture how smoke from a bonfire dances upward in unpredictable shapes, dropping ash some distance from the fire when it’s windy. Those shapes are closer to how your dog “sees” scent patterns with his amazing nose, as he figures out complex puzzles.
Don’t worry: when you’re just starting to learn nosework in boxes indoors, you can usually just follow your dog as he finds source. But the more you understand how wind affects scent detection, the better you’ll be able to help your dog get to productive areas in more complex searches with wind, keep reading.
- For more detailed scent detection terminology, see our Glossary of Scent Detection and Nosework Terms
- Canine Olfaction Science and Law, Advances in Forensic Science, Medicine, Conservation, and Environmental Remediation, Ed. T. Jezierski et al, Taylor & Francis Group, Boca Raton, USA, 2016
- Tenhu, Hanna, and Terhi Helkala. Canine Scent Detection in Use of Locating Contaminated Sites in Finnish Defence Forces, downloaded from https://www.defmin.fi/files/2523/26_Tenhu_Hanna.pdf