How do SAR Dogs work? All humans, alive or dead, constantly emit microscopic particles bearing human scent. Millions of these are airborne and are carried by the wind for considerable distances. Many air scenting dogs are also cross trained in body recovery........ Human Remains Detection Dogs are trained to detect and find the odor of human remains.... Air scent dogs range well away from their handlers and can cover huge areas in a much shorter time span than a typical man tracking search party. Using air scenting dogs has a much higher probability of detection rate than using a regular search party. The dog is not restricted to the missing person's track and can search long after the track is obliterated. Many air scenting search dogs are also trained in body recovery, and trailing/scent discrimination.
HUMAN REMAINS (CADAVER) DETECTION DOGS are trained to detect and find the scent of human remains. Cadaver dogs are trained to find decomposing, skeletal, submerged, buried and/or scattered human remains in varied locations such as water, collapsed structures and wilderness areas. They are used for forensic detection such as finding trace evidence of blood, bone fragments, charred tissue and teeth in homicide situations.
TRAILING/TRACKING SEARCH DOGS are mostly scent specific, meaning they are looking for a specific person's scent trail. They will follow one person's trail and totally ignore other individual's trail having been at the site before. The dog is presented with an article of clothing or anything the missing person had touched. The dog then will try to find the one scent in the area and follow it. The trails can be up to several days old and on varied surfaces such as dirt or on streets.
http://www.southgeorgiasearchdogs.com/sar_fact.htm