Subject: Water recoveries
Date: Thu, 26 Dec 1996 13:15:27 -0500
From: Henry Santeford <hssantef@mtu.edu>
To:
sar-l-d@islandnet.com
Mike Larish wrote:
>Unfortunately, the "exact point scent is detected surfacing from
> underwater" is often times rather nebulous for a variety of reasons
> including wind direction and speed, water direction and speed, water
> temperature, air temperature and more.
>
>If it is real cold out with little or no wind, the scent often will pool
>along the surface of the water making it difficult to pinpoint the exact
>exit of scent from the water. If the water is moving, especially rapidly,
>it can carry the scent downstream quite a ways from the actual location of
>the subject. If the wind is blowing fairly hard, it will also make it
>difficult for a dog to pinpoint exact exit from the water (insofar as down
>to a few feet). There is also discussion whether or not thermoclines in
>the water have an affect on scent as they do on sound. The K9 itself also
>obviously has a lot to do with accuracy...
It is important to realize that the scent leaving the body under water
behaves just like scent leaving a body on land, i.e. there is a scent cone,
which under the simplest conditions rises straight up to the surface and
forms a circle, the circumference of which is determined by the distance.
In the real world of scent however, that is seldom the case. As Mike
stated, many variables influence the 'circle of scent'.
Water temperature gradient plays a role in the vertical circulation. If the
water is isothermal, there is no circulation. The greater the temperature
gradient in water with temperatures above 4 degrees centigrade, the greater
the circulation. (Less than 4dc involves density issues) Thermoclines seem
to act as a wall to scent penetration - they can be broken up by mechanical
mixing.
The vertical circulation is also dependent on velocity and depth of the
water in addition to the temperature gradient between the air and water.
THis is somewhat simplified by incresed water velocity, which decreases the
influence of the temperature gradients.
I'm not sure what Mike means by "real cold". When we have "real cold" and
no wind with open water, there is alot of veritical circulation due to the
huge temperature gradient produced. It is possible for the frost formed by
water vapor leaving the water surface to reach the tops of trees. With a
lesser gradient, i.e. fog conditions, there is a pooling of scent, not
unlike a scent pool on land. A temperature gradient always produces
circulation.
High wind conditions on large lakes are usually dangerous for divers, but
the wind at the water surface is minimal (watch snow blow across an open
field), so if you can work the dog close to the water, he can usually, if
worked into the wind with a good boat operator (hard to go slow enough and
control a boat in high winds) do the job.
It is important for the search manager to know all of the details so that
he can plot alerts in complicated recoveries. Dog handlers need to
concentrate on where their dog is alerting and be careful not to try to
'out-think their dog'. I am less concerned with having another dog confirm
my dog's alerts than I am with having a knowledgeable person help interpret
what the dog is telling us based on all the variables.
Sally Santeford
D.O.G.S.-north
