How Scent and Airflow Works
How do those dogs find missing people?This article was orginally published on the Hound and Found Blog: http://houndandthefound.wordpress.com/2012/02/22/how-scent-and-airflow-works/
Remember PigPen from Charlie Brown? He always appeared to have clouds of dust coming off of him wherever he went. This is not far from the truth.
You have thousands of tiny pieces of your body leaving you every minute; 40,000 pieces to be exact. These tiny cornflake-like bits are called rafts .
They are made up of skin cells, hygiene products, bacteria, fungus, parasites, sweat, hormones, and enzymes. They are unique to each individual human. Even skin rafts from identical twins are different. Dogs can smell these rafts, and distinguish between different people.
Some skin rafts are lighter, and easily carried by air currents. Others are heavier than air, alighting on vegetation or falling to the ground.
Dog Handlers pay attention to air currents. Skin rafts are carried along currents of air like millions of fluffy dandelion seeds. We also pay attention to physics. A great tool for visualization is smoke.
→ In the image to the right, the origin of the smoke is higher on the hill, and the smoke is falling.
- Can you guess what time of day it is?
- The weather?
- (*answer at the end)
Warm Air rises and Cool Air sinks
Cold and moisture make air heavier and dense. Warmth and lack of moisture make air rise up like bubbles on a summer day. Your skin rafts first leave your body travelling upwards at 2mph along an air current your 98.6 degree Farenheit body produces.
Without any air movement
Scent difuses evenly.
But, of course, there is always something making air move.
Factors that affect Air Movement: Scent Threory
In idealistic theory: scent moves predictably like this:
Laminar Air: straight flow of air, without ahy interference.
Turbulent Air Flow: laminar air hits an obstacle that creates chaotic behavior, which causes handlers and their canines to mutter choice words under their breaths.
Normal Daytime Air
When the ground heats up during the day time, air begins to rise.
Normal Nighttime Air
- When the ground begins to cool, air cools and begins to fall.
- It flows downhill like water.
- Dogs work great at night!
- movement of scent away from subject in the shape of a cone
- occurs with a elevated subject, during cloud covered days or nights without wind
- travels long distances with a solid breeze
- ideal for dogs
- K9 Demonstrating a Scent Cone - Video
A dog will run perpendicular to the flow of the scent crossing in and out of the scent cone zeroing in to its source.
- occurs in the morning, as the warm sunlight hits stable air, and churns the cooler air.
- Scent is "overloaded" near source, and K9 might have trouble pinpointing.
- subjects on a hill can be detected downhill
- it is ideal to get dogs searching before sunrise
- occurs after sun sets - PM
- the ground is cooling, but aloft air is still warm
- usually occurs in valleys first then other areas later on
- work dogs on the high ground in the evening
- at night in stable air
- scent holds at the same elevation level without falling or rising
- dog may alert across a drainage or canyon at the same level, but can’t find a person
- be sure to report your alerts (changes in your dog's behavior) as scent will carry
- collects in an area like a pool of water
- usually occurs in a low area
- occurs where there is little dispersal of scent by the wind
- It hard for dog to follow a scent pool to the subject
- circular air forms behind an object (turbulence)
- prevents scent from traveling along prevailing wind
- example: eddies form at a line of trees (border), next to an open field
- Visualize: Take two chalk board erasuers and clap them together outside on a windy day next to a wall.
- occurs in clear sky or with high clouds
- occurs at midday, a high convection situation
- scent rises, cools, falls, heats up, rises, cools, falls, etc.
- Dog will alert (change behavior) by putting his head up, but will lose the scent.
- occurs when air currents move straight up an object
- scent may come down as far as several hundred meters away from the subject
- This makes it very difficult for the dog to find the subject, without Handler problem-solving.
- the Handler should detail the K9 around tall objects in the area, for scent pooling up high, against trees and brush
- your dog may show changes of behavior (alerts) in several different places, usually all up high and without pinpointing.
- caused by significant temperature and humidity differences in short distances
- occurs around changes in elevation
- drastic changes in shade and sunny spots
- creates a wall like barrier of scent
- behave exactly like thermoclines under water
The Dog is only Part of the Team
You are the brains. Your dog is the nose.
A search dog team will prefer to search into the wind, often zigzagging into the wind on small areas. A canine team can also perform searches along parallel sweeps perpendicular to the wind in larger areas. Remember to search ridges when air is likely to be rising and down in drainages when air is likely to be falling.
Time of day: Morning.
Weather: high humidity. Cool + wet = air falling down slope. What is not also obvious, is that there was a prevailing wind at the photographer's back, which moved the smoke away as well as down.
A good book to read on the subject is: Scent and the Scenting Dog by William G Syrotuck
For more information about Scent Theory with regards to searching with a dog: Hatch Graham’s 1979 Article on Convectional Turbulence and the Airscenting Dog
This article was orginally published on the Hound and Found Blog : http://houndandthefound.wordpress.com/2012/02/22/how-scent-and-airflow-works/