Download Wind

Scent Theory
Understanding Human Scent
No matter how hard we try to stay clean by
showering, washing our hair, or changing into
clean clothes, each of us has an odor or scent
that is ours and ours alone.
Human Scent
Skin cells contain our genetic make-up.
Medications and changes in our age and health
affect our body’s chemical structure. Other
human chemicals such as pheromones,
hormones, adrenaline, etc., all affect our scent.
Trained dogs can detect skin cancer and oncoming epileptic seizures.
Skin glands secrete by-products of everything
we consume on the surface of our skin, which
also carries residue of the soap we use, lotions,
laundry detergent and everything we use in our
daily lives.
Skin structure and secretions differ between
races: for example, Caucasian and Black
people have more sweat glands than Asians.
Skins cells carry scent emitted from:
Eccrine Sweat Glands – regulate body
temperature and respond to emotions. More
concentrated in feet, hands and forehead.
Skins Cells
Apocrine Sweat Glands –activated by emotions
and tend to give off more odor than Eccrine Glands.
These glands also secrete Pheromones and
Adrenaline. Located at the base of hair follicles in
the arm pits and groin.
Sweat – clear liquid consisting of water, sodium,
calcium, chloride, potassium, bicarbonate, urea and
other body secretions such as amino acids.
Sebaceous Glands – located at the base of hair
follicles on your scalp, face and upper torso. They
open directly to the skin and emit fatty oils, called
sebum, that spread over the skin.
Bacterial Buddies –such as mites, fungus, yeasts
and viruses can never be completely removed by
washing.
We are constantly shedding our outside
skin layer. Skin cells or “rafts” are shed at a
rate of approximately 40,000 per minute or
roughly 57 million per day. Rafts are also
expelled every time we exhale.
Shedding
Our body temperature is usually warmer
than the surrounding air, so as heat rises,
each of us are enveloped in a thermal wind
that travels upwards at approximately 1.5
miles per hour. As the air rises around us, it
carries skin rafts upwards until they clear
the tops of our head, where they are
caught by atmospheric winds.
As rafts are caught by atmospheric winds,
the heavier rafts fall close to the source
getting caught in anything that will catch
and hold rafts. Lighter rafts will travel and
land further away.
Skin Rafts
Each skin cell or “raft” contains bacteria
that start feeding on the cell as soon as it
leaves the body. This bacteria emits a
vaporous gas or “scent”. Rafts continue to
produce scent as long as moisture and
nutrients from the skin cell last.
Once skin rafts fall away from us, many things
affect the life span of the bacteria living on it.
Temperature – Too hot or to cold… bacteria can
only thrive in perfect temperatures.
Humidity - Each skin raft is about 80% water,
which is necessary for bacteria to grow. Humidity in
the air also affects bacterial growth.
Raft Life Span
Light – Ultra-violet light from the sun can kill
bacteria and heat from the sun can dry up
necessary moisture.
Chemicals – Residues from items such as soap or
laundry detergent also affect bacterial growth.
Skin rafts that have dried out, may be re-hydrated
again when dew forms or with a light rain or mist.
The moisture can reactivate bacterial growth. As
the ground warms in the morning, heat rises up
carrying scent with it and the scent becomes
airborne again.
Scent Cone or Scent Plume
Scent hugs the ground and gradually spreads out
in a cone shape from the subject.
Scent Cone
Steady breezes carry scent longer distances,
especially in flat, open country. Gentle breezes
produce a wider scent cone.
The stronger the wind, the narrower the scent
cone will be. Stronger winds and gusts carry skin
rafts farther and disperse them higher in the
atmosphere, making it harder to find the subject.
On days with a steady breeze, a trained air scent
dog should be able to pick up and move in on
airborne scent from 200 or 300 feet away from
source.
Open Fields
With light breezes or still winds, you should still be
able to work your area in a loose grid (wider
sweeps). Your dog should be able to move in from
100 feet or more from source.
Shifting winds make searching difficult because
you may start your dog downwind and, later, the
wind direction shifts. In these cases, the best idea
is to remain with your original search plan or
pattern. The wind may continue to shift and, trying
to keep up with it, may leave you wandering
around your assigned search area.
Areas with light brush may have a combination of
open areas and wooded areas. Vegetation is not
thick enough to block or change how scent
moves. Dogs should be able to work light brush
areas about the same as open fields. With a nice
breeze, you will be able to work the area in a
loose grid (wider sweeps).
Brush
Areas with heavy brush can be found in thick
woods or un-mowed fields. Tall grasses are
harder for dogs to work, as there is little air flow
slightly above the ground (where the dog’s nose
is located). On hot, still days, in heavy vegetation,
the scent stays close to the source. It will be
necessary to work the area in a tighter grid
(closer sweeps).
Forests can vary from open woods, where deadfall and dense underbrush has been cleared, to
thick woods, where no clearing has taken place
and dense underbrush has grown up under the
trees.
Woods
Open woods are basically worked the same way
as light brush. With a nice breeze, you will be
able to work the area in a loose grid (wider
sweeps).
Thick woods are worked the same way as dense
brush, work the area in a tighter grid (closer
sweeps). Working thick woods at night should be
done carefully to avoid unseen hazards.
A river, creek or drainage search during the day
should be conducted along ridge lines or hilltops
on the downwind side whenever possible. This will
cover the waterway and the slopes as well. Since
cool air falls, an evening search should be
conducted in the waterway itself.
Waterways
Waterways can also act as a funnel, where scent
flows downwind. If your dog is alerting or showing
interest with his nose in the air and unable to
locate source, work your dog upwind to where the
source may be located.
When doing HRD searches in waterways, here
again, if your dog is alerting or showing interest in
the water, work your dog upstream to where the
source may be located.
As SAR canine handlers, we are always aware of
which direction the wind is coming from so we can
work our dogs in the most effective manner.
Wind
Wind basically has the same effect on scent as it
does on smoke, dust or some other lighter-thanair substance. One of the best ways of
determining how wind will affect scent is by
watching smoke as it is swirled around by the
wind. Another good method is to imagine water
rushing in the same direction the wind is blowing
and picture in your mind how that water would
react as it reaches obstacles. Water and wind will
always take the path of least resistance.
Gentle breezes carry scent long distances,
especially in flat, open country.
Gusty, strong winds disperse scent, making it
harder to locate the source.
If you have a NNW wind, wind is coming from the
NNW direction. Winds are identified by the
compass point or direction they are coming from.
Wind
To determine wind direction (and possibly wind
speed), some handlers may hold out a small
length of flagging tape, some pull a few blades of
grass and throw them in the air, some use a puffer
bottle with scent-free talc or powder, many just
turn around until the wind is hitting them in the
face.
Some handlers carry a wind meter that accurately
measures wind speed and air temperature.
No matter what method you use, remember to test
the wind at your dog’s nose level. Vegetation and
terrain will also affect wind speed and direction
down where your dog’s nose is located.
How wind moves and how human scent travels
are greatly affected by local terrain and
vegetation.
Terrain
Upslope Winds: Morning sunshine heats the
sides of hills and mountains, carrying human
scent uphill. On hilltops, mountain tops and
along ridges, winds are stronger due to upflowing air and converging winds from opposite
slopes. In the mornings, work your SAR dog on
hilltops, mountain tops or along ridges to take
advantage of upslope winds.
Down-slope Winds: Evening around sunset, at
night or under heavy daytime cloud cover, air
cools and flows to the bottom of valleys, carrying
human scent downhill. In the evening, work
your SAR dog in valleys.
Up-valley winds form when valley walls are
cooler than the valley floor. The “Venturi Effect”
happens when air is forced through a narrow
opening such as a mountain pass, accelerating
the wind speed.
Valleys
Down-valley winds result from air moving
down-slope in the evenings or at night. As the
down-slope winds converge at the valley floor,
winds move down the valley, which can be
stronger on clear nights.
During morning and daytime hours, land heats
up faster than water. When the warm air over
land rises, the cool air over the water moves in
towards land. These are called Lake or Sea
Breezes. When working a water HRD problem,
dogs may be worked from the shoreline.
Lake/Land
Breezes
During evening or early night, land cools faster
than water. In the evenings, warm air over the
water rises and cool air from the land moves in
towards the water. These Land Breezes are
strongest along shore and weaken further
inland. When working your SAR dog on land
areas with water, working shorelines may be
best in the evenings.
Rising warm air creates a void that pulls in other
air from the surface to fill it. The resulting air
movement is called convection current.
Thermal
Turbulence
As warm air rises, it mixes with cooler air at
higher levels. Winds increase and flow back down
to the ground in spurts or gusts, increasing
surface wind speed. This mixing of air is called
thermal turbulence.
Surface winds are stronger in the afternoon (the
hottest part of the day) than at night. When
surface temperatures start cooling at night and in
early morning hours, the air becomes more
stable. These hours of stable air are usually the
best times to work your SAR dog.
If rising warm air meets a layer of very cold air, a
thermal layer may form causing turbulence two
or three feet above the surface. This turbulence
will keep human skin rafts airborne longer.
Mechanical Turbulence slows down surface
winds. Winds hitting buildings, rocks, or any
stationary object causes the air to divide and flow
around the object. Picture how water moves as it
hits a rock in a fast flowing stream.
Mechanical
Turbulence
Eddies, or swirling pockets of air, form on the lee
side (the side that is sheltered from the wind).
There will be areas of turbulence and areas of
calm (dead spots). In the calm areas, human
scent will settle more quickly.
The air traveling around an object will be denser
and/or traveling faster than the surrounding air.
In this area, human scent will settle slower and
tend to travel farther than the particles caught in
eddies or surrounding areas.
Air flowing over a ridge is influenced by the shape
of the ridge, the wind speed and the wind
direction.
Mechanical
Turbulence
Higher wind speeds on sharp ridges, bluffs or
canyon rims cause turbulence and large rolling
eddies, updrafts and downdrafts on the lee side
(downwind side). Upslope winds can be felt on the
surface of the lee side.
Depending on the terrain, dead spots with no air
movement can also occur on the lee side of
mountains.
These chaotic air movements make it more
difficult for your SAR dogs to find scent.
Surface
Winds
Mechanical Turbulence (an object on the
surface) changes the wind path and direction.
Thermal Turbulence (surface heating) causes
pressure differences which can increase or
decrease wind speed. Both work together to
change winds at the surface, which are
measured up to 20 feet above the ground or any
vegetation.
Additional Mechanical Turbulence such as
bushes, rocks, gravel, plowed fields, grasses,
etc. on the surface can also slow down surface
winds due to surface friction. Slide your hand
over a sheet of typing paper and then over a
sheet of rough sandpaper, and you’ll get the idea
of how surface friction works.
Human scent tends to flow with surface winds
until they eventually land or get caught by
objects.
Tall buildings act much like canyon walls, causing
Urban Canyon Winds.
Urban
Canyons
When wind hits the face of an object (in this case
a building) the wind scatters. How the wind reacts
depends on the angle of building to the wind (flat
or at a corner). Wind streams down the sides of
the building and eddies form at the back, or
downwind side of the building.
Vertical Eddies form when winds converge at the
corners of buildings or at the mouth of steep
canyons. Whirlwinds and dust devils are
examples of vertical eddies.
Horizontal eddies are cylindrical air formations
that roll along the surface.
How air moves within a building affects
scenting conditions. Heating and air
conditioning systems, for instance, may
circulate scent within the room or throughout
the entire building. Even with the system shut
down, ducts between rooms will continue to
move air. Holes and cracks in the walls and
ceiling, open windows or doors will also move
scent around. When you enter a building, try to
determine which way air currents are moving.
Exterior walls will also affect scent. The side of
the building exposed to the sun will be warmer
than the side that is shaded. Scent tends to
move to the interior or cooler walls.
Buildings
Thermals usually occur by the sun heating darker
surfaces such as the ground, open areas in
woods or parking lots. Darker surfaces do not
reflect back many of the suns rays thereby
heating them faster than surrounding areas.
Thermals
This uneven heating causes the air to rise in a
column. The rising column of hot air cools as it
rises until it reaches the same temperature as the
surrounding air. The air then turns downward,
flowing around the outside of the hot air column.
Think of water spouts in fountains. The water
shoots up so high, then collapses and falls back
down on the sides.
This is the basic principle behind the Chimney
Effect.
Open meadows in wooded areas form natural
chimneys. Chimneys draw cool air from under
surrounding shaded areas into the sunny meadow
or opening where warm air is rising.
Chimney
Effect
If your SAR dog loses scent in open areas or
meadows, the rising air may be carrying the scent
too high for your dog’s nose to catch it. As the
scent drops back down to the ground, you may be
able to cast your dog in the surrounding shady
areas and pick up scent again.