This will reduce contamination of the area with extraneous or confusing scents. The dog begins tracking as soon as possible because success often depends on the strength of the available scent. The passage of time, wind strength, and other environmental conditions will affect the strength of the scent. Human scent adheres well to grass and brush which can improve the chances of success. Paved or gravel areas and strong scents such as fertilizer, burned grass, or spilled oil or gasoline impede the tracking ability.
Human scent remains longer on cool, moist ground.
Direct sunlight, extremely dry ground, or heavy rain dissolves scent rapidly, making tracking more difficult. The methods used to track lost personnel, especially children, are different from those used to track a fleeing suspect. Only dogs who have been trained to track successfully for lost personnel are used, to avoid any danger of harming innocent persons. Not all patrol dogs have been trained to track. Among the dogs trained to track, not all have the same tracking ability.