Monday, February 3, 2014

ManTracking - Detecting Speed from Tracks

Rebel wrote me to ask "I found your website from the videos on You Tube. I am not into horses, but was looking for tracking information as I am helping to teach classes to Explorer and Boy Scouts. I also serve as a volunteer on a regional Search and Rescue (SAR) Team. Can you explain how to tell how fast the person who are tracking is going? Thanks, Rebel."

Aside from the obvious extended stride length, there are some pressure release clues. Any one of them could be helpful when the others are harder to discern.

Stride length. From a normal walk on level ground to a man running on level ground, stride length can double. From the picture below you can see the stride stick (aka tracking stick) and the tight fitting rubber grommets I use so I can slide them up and down to measure a stride, track width, off set, etc. of any track I'm on. The picture shows the increase in the stride length from a person walking, to walking fast to running. In this case the stride length from the previous toe to the subsequent heel, which is how I measure stride, is 17 inches for the walk, 24 inches for the fast walk and 31 inches for jog - for example. That will change depending upon the hardness of the ground, weight the person is carrying and the degree of slope. It can be also influenced by the physical condition of the person. Tired people will have a shorter stride and get a little careless on foot falls. Toe gouges and trips may be evident.

With the increased speed and force with a person's foot hitting the ground, the disturbance to the ground soil, vegetation and/or rocks can change significantly. The pressure release would be altered because of the change of pressure on the surface has changed.

The pressure release may be hard to discern on hard soil or ground that is covered by vegetation. Torn pieces of vegetation and bruising on stems, stalks and flowers can be discernible. While you may not be able to see tracks because of ground vegetation, you may be able to feel the pressure-release or gently separate the vegetation in order to get a visual idea on the track.

The picture below shows tracks in sand where it is easy to tell the difference in the pressure releases, changed by speed. The easiest pressure releases to read are toe dirt visible on the fast walk and the wave around the ball of the foot that is created by the foot pushing off. At the print at right, where the person is running you will see a more significant wave and less toe dirt as the person's foot are coming of the ground with the knee bent more, therefore reducing the amount of toe dirt thrown forward. This can change in deeper soil or be indiscernible on much harder ground.

A gouge is another pressure release that is enhanced from speed and sometimes weight being carried. On the above print at the right you will see a gouge created by the heel striking the ground more forcefully at a shallower angle. You will sometimes see a ledge opposite the gouge. This is usually evident on wet soil or soil that was wet when the track was laid then has dried. The ledge visible in the heel of the track at left is due to the foot making a more vertical strike on the ground.  

Hope this helps Rebel.  When you are trying to determine the speed of a track (the person you are tracking), you shouldn't make a determination based on stride along or any one aspect of the pressure release, unless that's all you have. You should pretty much take all the signs together to tell you what that person is doing.

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