SAR Fundamentals/Navigation instruments theory


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[edit] Subject

What is this lesson plan about?

This lesson gives the students a theoretical (class room) understanding of the instruments that they may be using in the field to aid navigation.

The instruments covered are:

  • compass
  • GPS
  • altimeter
  • stride tally counter

For each instrument, the theory of how it operates is discussed along with how to select an instrument for purchase.

[edit] Authors

List who wrote this lesson plan.

  • Brett Wuth

[edit] Scope

What is included in this lesson, what's not and why.

SAR Fundamentals Ch.13 "Navigation"
Basic SAR Skills Manual: Ch.7 "Navigation"
stride count

Only basic use of a GPS is shown. Advanced features such as waypoints, tracks and maps are left to another lesson beyond the SAR Fundamentals course.

  • Waypoints are not an essential skill for using GPS. Students should be recording locations on paper, and should be able to estimate relative direction and distance to a new location.
    • This material can be covered in additional material presented by a SAR group outside the SAR Fundamentals course.

[edit] Prerequisites

What should students already know/have accomplished before the lesson is presented.

Prior to this lesson, students should have already been introduced to the following concepts:

  • direction measured in degrees
  • directions measured from True North (this lesson will introduce declination and magnetic north)

Parts of a compass which can be used on a map

  • straight edge
  • ruler
  • rotatable bezel and interior north-south lines
  • roamer
  • magnifying lens

Specifying a location in UTM

  • the three components of a UTM: Zone, Easting, Northing
  • map datums: NAD27 vs WGS84
  • the 6 digit short form of UTM


  • contour lines

[edit] Objectives

At the conclusion of this lesson the participants will be able to:

  1. explain how a GPS works
  2. identify purposes for which a GPS is sufficient, a help, not useful
  3. identify circumstances under which a GPS may fail
  4. identify the significant configuration options of most GPS models
  5. identify when to use NAD27 vs. NAD83/WGS84
  6. configure a particular model of GPS for local SAR usage
  7. read a UTM off a particular model of GPS and translate that to and from the UTM notation used with topographic maps.
  8. determine the UTM of the location where they are at and the accuracy of their reading
  9. given a destination UTM know what direction and distance to go to get to it
  10. select a GPS for purchase
  11. identify the parts of a compass
  12. explain how a compass works
  13. select a compass for purchase

[edit] Time Plan

Total Time: 1 hour 45 minutes

  • 2013-02: 1 hour 16 min


Time Material


3 min


Introduce topic title

Introduce Instructor

Present Objectives

Determine experience level of students.

  • Who uses GPS regularly?
  • Who uses a compass regularly?
  • Who is comfortable reading UTM's off a map?
  • Recruit more advanced students to assist in illustrating material.


1 min


SAR workers use navigation instruments to make measurements in the field.

The measurements are used to calculate your location or that of other things.

The four instruments we will discuss:

  • pace counter
  • compass
  • altimeter
  • GPS

No one instrument is perfect. Each is better in some circumstances.

Each instrument has different ways of failing.


2 min

Pace Counter

Measuring distance with your feet.

When a GPS isn't working this is the best that can be done in the field.

Will be practiced in a separate exercise.

Pace is landing with the same foot.

Need to count each pace.

beads - slide bead on every 10 paces. Slide other for every 100 paces.

pedometer - measures the jiggle from each pace.


  • count in your head
  • use note book.
  • less accurate: know your speed and measure your time.


1 min


So far having been using the compass on the map.

Can also be used in the field. Because of magnetic needle.


2 min

Magnetic North

The needle of the compass points in the direction of Magnetic North towards the North Magnetic Pole.

This is not the same as True North. The North Magnetic Pole isn't the same location as the north pole.

North Magnetic Pole is currently (2019) 8634 deg N 175.3 deg E northwest of of the tip of Ellsmere Island, now in Russia Arctic.

It moves. About 55 km closer to Russia each year.


4 min


The difference between True North and Magnetic North is called Declination.

It's expressed in degrees and fractions of degrees (minutes).

If Magnetic North is to the east of True North, the declination is degrees EAST. Opposite is degrees WEST.

Declination changes from year to year.

It also changes from area to area.

  • Pincher Creek has about half a degree more declination than Lethbridge.
  • Banff is about one degree more declination than Pincher Creek.
  • Pincher Creek, February 2020: 13 deg 38' E
  • Lethbridge, February 2020: 13 deg 12' E
  • Banff, February 2020: 14 deg 36' E

Look up online Declination:

Calculation on topo maps is old, not accurate.

Ask the person briefing you.


4 min

Compass failures

Compasses don't work:

when there's magnetic distrubances

  • other magnets nearby
  • things that generate magnetic fields
    • power lines
    • generators, electric motors

attracted to certain metals

  • don't hold close to building, vehicle, belt buckle

when the needle doesn't settle

  • don't use when vibrating, turning

when the needle scrapes the housing

  • doesn't work close to magnetic poles because needle points down
  • the further from the equator, the more the magnetic field points down
  • compass needles are built for zones
    • don't use a compass from the southern hemisphere in the northern hemisphere
  • unless compass has "Global" needle bearings


7 min

Choosing a compass

Features to look for in compass:

  • straight edge
  • ruler (scale)
  • roamer
  • bezel (barrel) in 360 degrees (not 4 x 90 degrees, mils, or named directions)
  • interior north-south lines
  • adjustable declination
  • nice: magnifying lens
  • sighting mirror
    • sighting line
    • sighting notch
      • nice: both top and bottom of mirror
  • needle zones (nice: Global)
  • nice: luminous
  • nice: clinometer

Good compasses:

  • Silva Ranger
  • approx $70


4 min


Measures the weight of the air above you - air pressure.

The higher you go up, the less pressure - displays elevation is feet or meters.

Air pressure also affected by weather - high and low pressures

  • needs to be recalibrated when the weather changes

Can be bought as separate device, or built into watches, radios, cell phones.

Does not require clear view of sky. Works when GPS's fail. Works indoors, in caves.

Only useful when elevation helps is determining location.

  • e.g. following a feature (ridge line) until hit certain elevation
  • e.g. traversing along same elevation until hit certain feature (creek)
  • terrain has a lot of elevation details : big hills, mountains : Kananaskis, Waterton, BC


1 min

Satellite navigation systems

There are two satellite navigation systems available

  • GPS - Global Positioning System
    • controlled by the US military
    • most commonly used
  • GLONASS - Global Navigation Satellite System
    • controlled by the Russian military
    • starting to be found in devices
    • works substantially the same as GPS and can be combined

Other systems will soon arrive from the Chinese and the Europeans.


3 min

How a GPS works

3 major components

  • 1. radio receiver
    • compares time for radio signal to arrive from satellites
    • receives information on satellite locations
    • optional WAAS: receives corrections to satellite location, signal distortions
  • 2. computer
    • computes where GPS currently is (needs 4 separated satellites)
      • 10-15m accuracy
      • applies corrections: ~ 1m accuracy
    • records where GPS has been
    • allows entry of remote locations
    • calculates distance and direction between points
    • calculate speed/time
    • draw a route on a map
    • place points on map
  • 3. magnetic sensor (only some models)
    • determines direction GPS is facing
    • GPS without magnetic sensor tells what direction GPS has moved, but not direction GPS is facing
    • test GPS by turning it. Does the direction arrow change?


10 min

How a GPS fails

radio signal not received from 4 satellites

  • heavy tree cover
  • blocked view of sky (hills, mountains, building)
  • blocked view of geosynchronous WAAS satellites (32 deg elevation around Pincher Creek)
    • North America only
  • satellites not in right positions (below/at horizon, clustered)
  • satellites not working/disabled (military selective availability)
  • radio interference (jamming; spoofing)
  • multipath (reflected) signals[3]
  • weather does not affect signal

computer fails

  • batteries (-15C)
  • temperature (too hot)
  • water/condensation (if not sealed)
  • electromagnetic interference (industrial sites)

magnetic sensor fails (same as compass)

  • metal (belt buckles, cars)
  • magnetic fields (power lines)
  • magnetic anomalies (far north)


4 min

Alternatives/Aids to GPS

  • location: dead recogning / distance-bearing / triangulation
  • recording: paper
  • distance/direction: subtraction & estimation; plot on map
  • map (better choice)
  • bearing: compass (better choice)


7 min 7,6

When to use a GPS or other tools discuss examples, compare with other alternatives

determine location when at

determine location when at ...GPSCompassAltimeter
hill top+ triangulatehelps
valley bottomdepends on tightnesstriangulate-
heavy treesdepends on type of trees, wetness-helps
south side of a lone hill+triangulatehelps
north side of a lone hillpoorer -- no WAAStriangulatehelps
downtown citymultipathpoor: metal-
under power lines+-helps
heavy fog+-helps
blizzard+-pressure change?
determine direction/distance to ...GPSCompassAltimeter
known UTM+direction onlyelevation change
some place you can seenot helpful or only poor with magnetic sensordirection only-
some place you've beensufficient if you recorded UTM-elevation change
a Lat/Longsufficient-elevation change
a street addressfor street GPS--
other purposes ...GPSCompassAltimeter
route selectionpoor unless street--
remembering a UTM+--
convert between Lat/Log and UTM+--


5 min 5,6

Significant configuration settings

Most GPS's allow you to configure:

  • True North vs. Magnetic North
    • use True North
    • GPS's don't generally allow you to set declination to exact same value used on compasses.
  • UTM vs. Lat / Long
    • UTM generally used by SAR
  • Map Datum: NAD27 vs NAD83/WGS84
    • measurement of the shape of the Earth
    • NAD - North American Datum
    • WGS - World Geodetic Survey
    • should use same as the topo map being used
    • Pincher SAR maps generally NAD27


9 min

configure a particular model for local SAR usage

Handout PCSAR GPS Configuration sheet

Exercise: Students configure their GPS

'Help students to configure if their particular model not same as PCSAR GPS


5 min

Long/Short UTM

Assume students have basic background in UTM

  • Distribute: topo maps
  • ZEN (Zone Easting Northing)
  • long form of numbers
    • read off corner of topo maps
    • northing: number of meters north of the equator
    • easting: number of meters east of imaginary zone line (500km center line)
    • converting to short form


5 min

Reading UTM on a GPS

  • Read the current/last known UTM
    • last location where GPS was turned on and could see satellites
    • instructions on front of Pincher SAR GPS's
    • determining accuracy
      • Garmin eTrex: on Satellite Page


8 min

GPS UTM exercise


  • Record last known UTM in long form
    • some GPSes may be sensitive enough to get fix in the classroom
  • Give last known UTM in short form
  • assist students that don't have Pincher SAR GPS


10 min

Manual determination of Distance and Direction

  • use map
  • without map
    • subtract Easting/Northing
    • estimate distance or Pythagorean theorem
    • estimate direction or calculate Tangent
    • or draw scale map


  • I'm at Zone:12U Easting: 0286623 Northing: 5484642
  • I'm going to:12U Easting: 0287134 Northing: 5484419
  • location is: 511 meters East and 223 meters South
  • estimate: ESE 620m
  • map/calculation: 129 degrees 661m


10 min

Choosing a GPS

Discuss GPS model selection/shopping

  • Packaging: hand held, cell phone, car
  • Features: sensitivity, WAAS, map, computer interface
  • Brands: Garmin, Magellan
  • Prices: low $200


1 min


Review objectives

[edit] Aids

What materials are needed or useful in presenting this lesson.

Alternate resources, deeper understanding:

[edit] Question bank

List of questions suitable for an review/exam of this section.

Question bank

[edit] Frequently Asked Questions

What are some of the questions that students typically ask. Include the answers.

How does global compass work at any latitude?


In the global compass, this problem has been solved with a structural innovation. The needle and magnet are built as separate units functioning independently from each other, so that the inclination of the magnetic field cannot tilt the needle. The needle can no longer move vertically. It is the compass magnet, separated from the needle, which absorbs the vertical force of the magnetic field. The needle itself is fixed at the lid by means of a double jeweled bearing. The magnet rotates with its jewel bearing on a pin. Such a compass works reliably in all zones of the world. Due to the strong magnet, the needle settles very quickly and stops immediately at the right position, allowing for an extremely accurate reading.

My GPS has EGNOS. What is that?

EGNOS is similar to WAAS, but works best in Europe.

[edit] Feedback

When has this lesson been presented. What was the feedback.

[edit] License

What can others do with this lesson?

Copyright © 2004-2013, Brett Wuth. This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 Canada License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

[edit] Reference Material

If you need to cite sources, do so here.

[edit] Notes

Any additional notes, etc.


Altitude/Azimuth calculator for WAAS geosynchronous satellites



Galileo - European

COMPASS - Chinese

[edit] To Do

  • Get example of altimeter
  • Create a checklist sheet for shopping
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