How Scent and Airflow Works
How do those dogs find missing people?
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. These are what dogs smell.
Some skin rafts are lighter in air, 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 pay attention to physics. Warm Air rises
and Cool air sinks. Cold and moisture make air heavier. Your skin rafts first leave your body at about 2mph up in the air traveling along the current of air your 98.6 degree F produces.
Without any air movement
scent diffuses evenly
But of course, there is always something making air move.
When things are perfect, scent moves predictably like this:
Objects and other factors often cause air to move like this:
Turbulent Air Flow
Turbulent air flow causes handlers and their canines to mutter choice words under their breaths.
Different Types of Airflow
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.
- movement of scent from subject downwind in the shape of a cone
- during cloud covered days or nights
- travels long distances
- ideal for dogs
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 before sunup
- scents travel down valleys like water
- subjects on a hill can be detected by dog down below
- It is good to get dogs out before sunrise
- Occurs after sun sets
- 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 as scent can 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 next to an open field
- 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 by putting his head up, but will lose the scent.
- Happens when air currents move straight up an object
- alerts may occur nearby -but-
- scent may come down as much as several hundred meters away from the subject
- This makes it nearly impossible for the dog to find the subject
- You should check around tall objects in the area
- caused by significant temperature and humidity differences in short distances
- changes in elevation
- drastic changes in shade and sunny spots
- creates a wall like barrier of scent
Handlers use their knowledge to help the dog find the subject
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.
A good book to read on the subject is: