ng mirrors to aid in obtaining bearings in the field.
59 FACTORS AFFECTING COMPASS OPERATION The compass needle is magnetic and will be attracted toward any large iron or steel object or it will respond to local magnetic fields. If you are near a car, snowmobile, ATV, or outboard motor, especially if they are running, the needle may be way off. Radios, GPS units, knives, axes, clipboards and even metal belt buckles will affect the operation of the compass. If you are unsure of how far the local magnetic attraction of an object extends, simply move away from the object while watching the compass needle. When it no longer wavers towards the object, the compass is set for operation.
60 BEARINGS Bearings are angular measurements with respect to the position of the observer, and the position of a distant object or intended destination course. Bearings may be expressed in terms of: Azimuths (used by Nova Scotia SAR teams) Quadrants (not used by Nova Scotia SAR teams)
61 AZIMUTHS BEARINGS Azimuths are bearings, expressed as angles, measured clockwise from north throughout the full range of the directional circle. Azimuths range from 0 o 360 o.
62 MAGNETIC DECLINATION There are three primary references that are used to indicate direction: Magnetic North (on compass) the direction to the earth s north magnetic pole. This is where all compass needles point. True North (on globe) the direction to the earth s north geographic pole. All lines of longitude meet there. Grid North (on map) the direction indicated by the N-S lines on the grid which overlies the map. Grid north is slightly different than true north. Since this difference is so little, for GSAR purposes, grid north and true north are the same.
63 MAGNETIC DECLINATION The angular difference between true north and magnetic north is called Magnetic Declination. All topographic maps display a declination diagram. Depending on your location, declination will be either East or West. In Nova Scotia declination is West.
64 MAGNETIC DECLINATION Example of a Map s Declination Diagram
65 Magnetic North 20 degrees East 21 degrees west 0 degrees Declination Across Canada
66 CONVERTING BEARINGS Whenever you take a bearing from a map and want to follow it with a compass, you must take into account the magnetic declination. The same holds true when you want to plot a bearing taken from your compass, onto a map.
67 CONVERTING BEARINGS The declination for the searcher maps used by ESGSAR is 21 o West. During a search, bearings are always MAGNETIC. During a search, bearings given by the command centre (via radio and on taskings) include declination.
68 CONVERTING BEARINGS For West Declinations (ie. the Maritimes): To convert a grid bearing (taken from a map) to a magnetic (compass) bearing: Add Declination To convert a magnetic bearing (taken from a compass) to a grid (map) bearing: Subtract Declination
69 CONVERTING BEARINGS EXAMPLE: Converting grid (map) bearing to a magnetic (compass) bearing. Declination: 21 degrees West. Grid bearing: 60 degrees Magnetic bearing = Grid bearing + 21 Magnetic bearing = 81 degrees
70 CONVERTING BEARINGS EXAMPLE: Converting magnetic (compass) bearing to a grid (map) bearing. Declination: 21 degrees West. Magnetic bearing: 90 degrees Grid bearing = Magnetic bearing - 21 Grid bearing = 69 degrees
71 CONVERTING BEARINGS EXERCISE Convert the following bearings: 1. Declination: 21 o W 2. Declination: 21 o W Magnetic bearing: 264 o Grid bearing: 167 o Grid bearing:??? Magnetic bearing:??? 3. Declination: 21 o W 4. Declination: 21 o W Grid bearing: 69 o Magnetic bearing: 10 o Magnetic bearing:??? Grid bearing:???
72 CONVERTING BEARINGS EXERCISE ANSWERS 1. Declination: 21 o W 2. Declination: 21 o W Magnetic bearing: 264 o Grid bearing: 167 o Grid bearing: 243 o Magnetic bearing: 188 o 3. Declination: 21 o W 4. Declination: 21 o W Grid bearing: 69 o Magnetic bearing: 10 o Magnetic bearing: 90 o Grid bearing: 349 o
73 DETERMINING BEARINGS FROM A MAP To follow a route in the field between two points on a map, the direction (bearing) between these points must be determ