SAR Fundamentals/Navigation instruments theory

Subject
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.

Authors

 * Brett Wuth

Scope

 * 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.

Prerequisites
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

elevation
 * contour lines

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

Time Plan
Total Time: 1 hour 45 minutes
 * 2013-02: 1 hour 16 min

Introduction

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.

Instruments

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.

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.

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

Compass

So far having been using the compass on the map.

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

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 (2012) 85.9 deg N 147.0 deg W northwest of of the tip of Ellsmere Island.

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

Declination

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.

Look up online Declination: http://magnetic-declination.com/

Calculation on topo maps is old, not accurate.

Ask the person briefing you.

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

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:
 * SUUNTU MC-2G
 * Silva Ranger
 * approx $70

Altimeter

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

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.

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?

How a GPS fails

radio signal not received from 4 satellites computer fails magnetic sensor fails (same as compass)
 * 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
 * batteries (-15C)
 * temperature (too hot)
 * water/condensation (if not sealed)
 * electromagnetic interference (industrial sites)
 * metal (belt buckles, cars)
 * magnetic fields (power lines)
 * magnetic anomalies (far north)

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)

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

determine location when at

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

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

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

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

GPS UTM exercise

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

Manual determination of Distance and Direction Example:
 * 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

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

Summary

Review objectives

Aids

 * compasses for students
 * 5 Pincher SAR Garmin eTrex GPS's
 * 1 Brett Wuth's Garmin eTrex GPS
 * 5 copies topo map of locale (82 H/5)
 * copy for each student of local street map
 * copy for each student of PCSAR Doc-69 GPS - Set-Up and Maintenance


 * [[Image:GPS-lesson-plan.odt|GPS lesson plan (odt)]] (pdf)

Alternate resources, deeper understanding:

Frequently Asked Questions
How does global compass work at any latitude?

From http://www.mapworld.co.nz/global.html

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?'''

http://en.wikipedia.org/wiki/European_Geostationary_Navigation_Overlay_Service

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

License
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 http://creativecommons.org/licenses/by-nc/2.5/ca/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Reference Material
[1]

To Do

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