Navigation During Search and Rescue
In order to locate and access a patient or point, personnel must have a good working knowledge of outdoor terrain features and how to efficiently navigate that terrain. Personnel must know where they are, where they need to go and how to get there efficiently. Along the way clues, hazards, or other items may be discovered and the coordinates of those locations need to be collected and transmitted to others. There are a variety of technologies available to aid in backcountry navigation. These include the use of a map and compass or the GPS system. Often both are effectively used together.
The location of the patient(s) or points can be as simple as receiving that location verbally from the patient or reporting party, or as complicated as a multi-day search. Once the location is known, SAR teams must access the patient as quickly and safely as possible. Many hours and even days have been lost to poorly navigating the outdoors to the waiting patient(s).
If there is a choice between having a map, a compass, or a GPS as the only source of navigation information, choose the map. Good navigators often only occasionally use the compass and GPS but frequently look at the map. Maps come in a variety of different formats and sizes, each with its advantages and disadvantages. The bottom line is, never leave the Incident Command Post for an assignment in the field without a paper map of the area. GPS maps are a good tool, but if the GPS or mapping software fails, or if batteries fail, a paper map is essential as a backup and often easier to read for a larger comprehensive view than a map on a small GPS screen.
MAPS
Maps come in a variety of scales and are generally referred to as small-scale maps or large-scale maps. A small-scale map provides a large overview and covers many square miles. A large-scale map provides a more detailed view of an area and encompasses a smaller area. This seems counterintuitive but think about looking at a house on each of these types of maps. On a small-scale map, the house appears very small and shows neighbouring houses and structures, whereas on a large-scale map the house would appear larger and more detail can be seen.
There are several different map datums in use. It’s important to know the map datums and to make sure that the datum of the GPS units in use on the incident matches the map datum used on the incident. Simply stated, the map datum is a mathematical model of the size and shape of the earth. Not all map datums agree.
Suppose one cartographer believed that the earth was a cube and devised a mathematical model based on that notion while another cartographer believed that the earth was a sphere and devised a mathematical model based on that notion. A particular point on the earth would have significantly different descriptions in each of those models. While that is an extreme example it does help to understand the issue. The same location on the Earth’s surface in the same coordinate system has different coordinates under different datums.
COMPASS
There are several types of compasses available. The best compass for search and rescue use is the orienteering base plate compass with a declination adjustment feature. A term that is used frequently when working with compasses is Azimuth. An azimuth is the angle of horizontal deviation, measured clockwise, of a bearing from a standard direction such as north or south. The compass is a relatively simple instrument for finding direction.
The compass works by aligning its magnetic compass needle with the magnetic force lines of the Earth’s magnetic field at that location. The compass needle does not necessarily point to the magnetic north pole or to the true north. To determine true north, it is necessary to apply a declination adjustment to the reading obtained. There are rules for doing this but using a declination adjustable compass is the preferred method for working with azimuths from the map to field and vice versa.
Once the declination is set for the area all the azimuths are true and match the map that also uses true geographic directions and not magnetic directions. This can serve to reduce navigation errors. The biggest contributor to compass error is the user. One degree of error equates to almost 100 feet of error over the course of one mile.
GLOBAL POSITIONING SYSTEM
The Global Positioning System (GPS) has become an essential tool for SAR and other emergency services. This system allows locations to be marked accurately on a map. It also allows users to input coordinates into a GPS receiver and navigate to those coordinates very accurately in all types of weather, in the dark, and in flat featureless terrain that makes navigating with other techniques difficult. GPS receivers can also track the movements of SAR teams, providing a variety of benefits. A team could use the track to safely return to base. The track can be downloaded to a map for further use in searches. Teams also used saved tracks to more efficiently navigate to future incidents.
GPS has become very prevalent outside of emergency services as well. It is a relatively cheap but sophisticated technology that more members of the public are relying upon. Many GPS users do not receive any training about the technology and its limitations. The use of GPS without training or other navigation skills to back up the GPS has been a contributor to more than a few SAR missions around the country.
When a GPS receiver is turned on it begins searching for satellites. Once it has acquired signals from three satellites it displays a location. This location is commonly known as a 2-D location and when additional satellites are received the location becomes a 3-D location with horizontal location information as well as elevation information. Just like a map, GPS receivers use a datum, which must correspond to the maps being used. GPS coordinates can be given in several different formats. The format used is not as important as all parties using the same format. This is imperative for successfully navigating with the GPS.
ALTERNATIVE WILDERNESS NAVIGATION TECHNIQUES AND COMMON SENSE
Obviously, having a map and compass or GPS receiver (and the knowledge of how to use them) will be the most effective way to navigate to an incident scene in the wilderness. Sometimes, these tools are not available or even needed. Often a patient may be located at a known place on a known trail. SAR teams typically know most or all the trails in the area they serve and would simply hike that trail to the location, only needing to consult the map to confirm progress.
There are some alternative techniques that may help locate or navigate when a map or GPS is unavailable. Recognizing and identifying prominent landmarks can help. Knowing which way is north will help. The sun rises in the east and sets in the south. North slopes are typically greener than south-facing ones, and moss usually grows on the north side of a tree trunk. Small streams run downhill to larger ones and eventually to bodies of water. Small trails typically follow the same pattern, becoming larger trails and then to roads, usually downhill or at the bottom of drainages or canyons. As SAR personnel are the ones doing the search and rescue, they shouldn’t need alternative methods of navigation, but these alternative methods may be useful when gathering information verbally from patients or reporting parties.
In conclusion, SAR personnel cannot stabilize a patient until successfully locating and accessing the patient(s) involved in an incident. It is therefore essential they have a strong working knowledge of backcountry navigation techniques and experience using those techniques.
