BASIC NAVIGATION Click on ‘F5’ to start.. BASIC NAVIGATION Contents List. Click on a chapter....

BASIC NAVIGATION

Click on ‘F5’ to start.

BASIC NAVIGATION

Contents List.

Click on a chapter.

Chapter 1 Basic Navigation.

Chapter 2 The Compass.

Chapter 3 Practical Navigation.

Chapter 4 Weather.

exit

Chapter 1

Basic Navigation

Chapter 1

Basic Navigation

Good navigation is all about knowing where you are on a map.

0º 15ºE 30ºE 45ºE

Longitude

0º15ºW30ºW45ºW60ºW

Longitude

Lines of longitude converge

on the true

north and south poles.

N

S

Curved Earth to flat

map?

Curved Earth to flat

map?

Curved Earth to flat

map?

The National

Grid

Grid lines point to

Grid North.

They are parallel and

do not converge.

The National

Grid

Longitude 2° West

Longitude 2° West

Here, Grid North

exactly equals

True North

Longitude 2° West

and other lines of

longitude.

The difference between Grid

North and True North is less than 2º over most of the

UK.

When navigating with

a map it is important to

use Grid North as your

reference.

Before using a map, it is

important to turn it so that

the features on the map are in their correct

relative position to

those features on the ground.

This is known as ‘setting’ or ‘orientating’

the map.

You should keep your

map orientated at

all times when

walking.

It will help locate your

approximate location more

easily and relate any

identifiable features on the ground to those

on the map.

There are several ways of finding North without a compass. The following three methods apply in the northern hemisphere:

The Pole Star Using a watch The shadow method

The stars of the constellation known as The Great Bear or The Plough can be used to locate the Pole Star? (True North)

The Plough constellation comprises seven stars. These two are known as ‘the pointers’.

A line through the pointers, followed for a distance four times that between the pointers, will locate the Pole Star.

d

4d

Pole Star

If you can see the sun, hold your watch horizontally and point the hour hand at the sun.

Bisecting the angle between the hour hand and the 12 o’clock position will give due south.

sun

south

If you can see the sun, hold your watch horizontally and point the hour hand at the sun.

Bisecting the angle between the hour hand and the 12 o’clock position will give due south.

sun

southDuring British Summer Time remember to bisect the angle between the hour hand and the 1 o’clock position.

If the sun is shining sufficiently to cast a shadow, place a stick upright in the ground and mark the end of the shadow with a small stone.

If the sun is shining sufficiently to cast a shadow, place a stick upright in the ground and mark the end of the shadow with a small stone.

Wait 10 to 15 minutes and use a second stone to mark the new new position of the stick’s shadow.

A straight line between the two markers runs roughly West to East.

West

East

North

The Earth’s internal

‘Magnet’

Inclined to the Earth’s

Axis

Inclined to the Earth’s

Axis

Magnetic North Pole

A compass needle

will align itself

with the earth’s

magnetic field.

And point to

the magnetic

north pole.

CANADA

The North Magnetic Pole

is in currently in Northern

Canada (north of Hudson Bay).

But it moves slightly over

the years.

CANADA

1831

CANADA

1831

1904

CANADA

1831

1904

1948

CANADA

1831

1904

1948

1962

CANADA

1831

1904

1948

1962

1984

CANADA

1831

1904

1948

1962

1984

1994

CANADA

1831

1904

1948

1962

1984

1994

2000

CANADA

1831

1904

1948

1962

1984

1994

2000

CANADA

Since 1831 it has moved

steadily north.

From the British Isles

magnetic north is currently

about 5° west of true north.

1831

1904

1948

1962

1984

1994

2000

CANADA

?

but over the longer term

its movement

seems random.

Grid North is represented by an arrow with a

triangular pointer.

True North is represented by an arrow with a

diamond pointer.

Magnetic North is represented by an arrow with a half diamond pointer.

The angle between True

North and Magnetic North

is Magnetic Variation.

The angle between Grid

North and Magnetic North is called Grid

Magnetic Angle.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Information on Grid Magnetic

Angle is shown at the top of M726 series OS maps.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Information on Grid Magnetic

Angle is shown at the top of M726 series OS maps.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Information on Magnetic

Variation is shown in the right had margin of M726 series OS maps.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

The ATC manual incorrectly states

that magnetic variation is

displayed at the bottom of OS maps – it no

longer is!

BASIC NAVIGATION

Contents List.

Click on a chapter.

Chapter 1 Basic Navigation.

Chapter 2 The Compass.

Chapter 3 Practical Navigation.

Chapter 4 Weather.

exit

Chapter 2

The Compass

The ‘Silva’ compass

consists of a base plate

N

E

SW

N

E

SW

N

E

SW

N

E

SW

N

E

SW

N

E

SW

N E

SW

N E

SW

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E

S

W

N

E S

W

NE

S

W

NE

S

W

NE

S

W

NE

S

W

N

ES

W

N

ES

W

N

ES

W

N

ES

W

N

E

SW

N

E

SW

N

E

SW

N

E

SW

N

E

SW

a rotating bezel

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

a rotating bezel

marked with compass

points and bearings

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

and a freely suspended

red and white

magnetic needle

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

and a freely suspended

red and white

magnetic needle

- red end pointing to Magnetic

North

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The needle is in a liquid

filled capsule which

‘damps’ movement and helps it settle down

quickly.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass

must be held horizontally when taking readings to ensure the

needle floats freely.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

The compass needle is a small magnet, so it is

affected by ferrous metals

close by.

N

E

SW

20340

280

300

320 40

6080

100120

140160200220240

260

This causes the compass needle to deviate from its true position.

A nearby cattle grid, for

instance, would cause

considerable deviation.

Setting or Orientating a Map with a Compass

To set a map with a

compass we must first set

the Grid Magnetic

Angle (GMA) against the direction

arrow - say five degrees.

N

E

S

W

N010350 020

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Place the compass on the map so

that the long edge

matches the N-S grid

lines.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

Cheshire

Ordnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

CheshireOrdnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

CheshireOrdnance Survey

Sheet 117

1:50 000

Now turn the map and

compass together until the compass

needle falls inside the orienting

arrow.

CheshireOrdnance

Survey

Sheet 117

1:50 000Now turn

the map and compass together until the compass

needle falls inside the orienting

arrow.

CheshireOrdnance

Survey

Sheet 117

1:50 000The map is

now correctly

orientated.

Taking a Bearing between Two Features on a Map

If we cannot see the

church to walk to it

from the trig point -

- we can take a

bearing from the

map

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

Place the long edge of the compass

along the intended

route

N

E

S

W

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

ES

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

SW

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

N

E

S

W

then turn the bezel until the lines in the capsule are parallel

with the grid lines

2040

N

E

S

W

In the UK Magnetic North is

west of Grid North

2040

N

E

S

W

So we must add the Grid

Magnetic Angle

(GMA)

5 degrees

2040

N

E

S

W

So we must add the Grid

Magnetic Angle

(GMA)

5 degrees

2040

N

E

S

W

So we must add the Grid

Magnetic Angle

(GMA)

5 degrees

N

E

S

W

We can now take the compass

away from the map -

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

SW

and turn the whole

compass until the

needle falls inside the red arrow

N

ES

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

and turn the whole

compass until the

needle falls inside the red arrow

N

E

S

W

The black arrow on the

base plate now shows

your direction of

travel

N

E

S

W

The black arrow on the

base plate now shows

your direction of

travel

N

E

S

W

Keep the compass needle

inside the arrow whilst you walk on the bearing

N

E

S

W

Pick out a feature in

the distance along your

line of travel and walk

towards it.

Taking a Bearing on a Distant Object

To take a bearing on a

distant object, point the direction

of travel arrow at the

object.

N

E

S

W

To distant feature

Now turn the bezel

and capsule until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N E

SW

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

SW

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

N

E

S

W

To distant feature Now turn

the bezel and capsule

until the orienting arrow is

beneath the North end of the compass

needle.

In the UK magnetic north is west of grid

north

N

E

S

W

To distant feature

In the UK magnetic north is west of grid

north

- so we must subtract the

Grid Magnetic Angle – five

degrees

N

E

S

W

To distant feature

In the UK magnetic north is west of grid

north

- so we must subtract the

Grid Magnetic Angle – five

degrees

N

E

S

WE 100

080

In the UK magnetic north is west of grid

north

- so we must subtract the

Grid Magnetic Angle – five

degrees

N

E

S

WE 100080

In the UK magnetic north is west of grid

north

- so we must subtract the

Grid Magnetic Angle – five

degrees

N

E

S

WE 100080

In the UK magnetic north is west of grid

north

- so we must subtract the

Grid Magnetic Angle – five

degrees

N

E

S

WE 100080

Place the compass on the map – it

does not have to be

orientated

N

E

S

W

Place the compass on the map – it

does not have to be

orientated

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid linesN

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid linesN

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

NE

SW

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N E

SW

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

SW

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Next turn the whole

compass until the orienting lines in the capsule are

parallel to the N-S grid lines

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

Keeping the lines parallel,

slide the compass until the long edge

is over the symbol

representing the object you first took the bearing upon

N

E

S

W

The top edge of the compass

now runs through your own position

and the symbol of the distant object.

N

E

S

W

The top edge of the compass

now runs through your own position

and the symbol of the distant object.

N

E

S

W

Plotting further ‘back

bearings’ from other features will accurately

locate your position.

Plotting further ‘back

bearings’ from other features will accurately

locate your position.

Plotting further ‘back

bearings’ from other features will accurately

locate your position.

This is known as

‘resection’.

Grid References

The country is covered in

100 km squares.

Each of the 100km

squares are divided into

1km squares.

The vertical lines are

‘eastings’ and are

numbered.

41 42 43 44

The horizontal lines are

‘northings’ and are also numbered.

41 42 43 44

72

71

70

69

68

67

A four figure grid reference

defines the bottom left hand corner

of a 1km square.

41 42 43 44

72

71

70

69

68

67GR 4369

’43’ the easting

41 42 43 44

72

71

70

69

68

67GR 4369

’43’ the easting

41 42 43 44

72

71

70

69

68

67GR 4369

’69’ the northing

This is the 1km square described by

the four figure

reference.

41 42 43 44

72

71

70

69

68

67GR 4369

The easting ’43’ is always

given first, followed by the northing

’69’

41 42 43 44

72

71

70

69

68

67GR 4369

Exactly as in mathematics

where the ‘x’ axis figure is

given before the ‘y’ axis component.

41 42 43 44

72

71

70

69

68

67GR 4369

Dividing the 1km square into 100m

squares enables us

to give accurate 6-figure grid references.

43 4469

70

A six-figure reference describes

the bottom left hand

corner of a 100m

square.

43 4469

70

GR 437692

’43’ is the easting of this 1km square.

43 4469

70

GR 437692

’43’ is the easting of this 1km square.

43 4469

70

GR 437692

’43’ is the easting of this 1km square.

43 4469

70

GR 437692

The ‘7’ moves us a further 7

100m squares east.

’43’ is the easting of this 1km square.

43 4469

70

GR 437692

The ‘7’ moves us a further 7

100m squares east.

1 2 3 4 5 6 7 8 9

’69’ is the northing of

this 1km square.

43 4469

70

GR 437692

’69’ is the northing of

this 1km square.

43 4469

70

GR 437692

’69’ is the northing of

this 1km square.

43 4469

70

GR 437692

The ‘2’ moves us a further 2

100m squares north.

’69’ is the northing of

this 1km square.

43 4469

70

GR 437692

The ‘2’ moves us a further 2

100m squares north.

2

1

43 4469

70

GR 437692

This is the point

described by the six-figure

reference,

This is the point

described by the six-figure

reference,

43 4469

70

GR 437692

and this is the 100m square it refers to.

Note that a six-figure reference describes

the southwest corner of a

100m square.

43 4469

70

2468

2

4

6

8

Most compass bases will have

one corner marked with a

grid of numbers.

This is a ROAMER

2468

2

4

6

8

Roamers can be used to find six figure grid references very

accurately.

246

2

4

6

8

37

07

38

08 Place the corner of the roamer on the

feature and read from where the

scales intersect the grid lines,

eastings first.

246

2

4

6

8

37

07

38

08 The first three figures in the grid reference of the church

are 373

37 from the grid square

3

the final 3 from the roamer.

246

2

4

6

8

37

07

38

08 The last three figures in the grid reference of the church

are 078

07 from the grid square

8the final 8 from

the roamer.

2468

2

4

6

8

37

07

38

08 Here the first three figures in

the grid reference of the Hostel are 377

37 from the grid square

7

the final 7 from the roamer.

2468

2

4

6

8

37

07

38

08 The last three figures in the grid reference of the Hostel

are 075

07 from the grid square

5the final 5 from

the roamer.

BASIC NAVIGATION

Contents List.

Click on a chapter.

Chapter 1 Basic Navigation.

Chapter 2 The Compass.

Chapter 3 Practical Navigation.

Chapter 4 Weather.

exit

Chapter 3

Practical Navigation

It is important to measure distances accurately when hillwalking.

Measuring Distances

By measuring distances accurately you can calculate and gauge your speed of

travel.

If you know how fast you walk, you can work out how long it will take you to

cover a known distance.

Timing

For instance, if a cadet is able to walk 1km over reasonably flat ground in 15

minutes, it would take one hour to cover 4km in similar terrain.

1 km

15 mins

If you know how fast you walk, you can work out how long it will take you to

cover a known distance.

Timing

For instance, if a cadet is able to walk 1km over reasonably flat ground in 15

minutes, it would take one hour to cover 4km in similar terrain.

1 km

15 mins

1 km 1 km 1 km

15 mins 15 mins 15 mins

If you know how fast you walk, you can work out how long it will take you to

cover a known distance.

Timing

For instance, if a cadet is able to walk 1km over reasonably flat ground in 15

minutes, it would take one hour to cover 4km in similar terrain.

4 km

60 minutes

In 1892 a Scottish climber called Naismith devised a rule to calculate walking speeds.

Naismith’s Rule

His basic rule assumed a walking speed of 4km per hour over normal (flat) terrain.

4 km

60 minutes

Naismith’s Rule

Climbing took more time, so he added 30 minutes for every 200m of climbing.

Steep descents also need extra care and time, so he added 10 minutes for every

200m of steep descent.

400m

600m

+30 mins+10 mins

Distance can be measured by counting paces, or every other pace, and with

practise can be very accurate -

Pacing

but only over short distances!

No method of estimating distance is entirely accurate, and when you add errors in measuring direction as well, your ‘area

of uncertainty’ can grow very quickly.

Errors

If you assume a possible error of plus or minus 10% measuring distance and plus or

minus 4% measuring direction:

Errors

After 1 km the area of uncertainty is about the size of 4 football pitches.

Errors

1 km

The area of uncertainty continues to increase with distance travelled

Errors

2 km

and after only 3 km is the size of 36 football pitches!

Errors

3 km

?

To keep the area of uncertainty to a minimum it is important to measure bearings and

distances as accurately as possible.

Errors

3 km

Good navigators rely on a number of useful techniques to improve their navigation.

Aids to Navigation

If a track or path leads directly to where you want to go, it would make sense to

follow it.

Aids to Navigation Handrailing

You could also use a wall, stream, ridge, electricity pylons, or any other linear

feature that leads the right way.

You would be using the linear feature as a ‘handrail’.

Aids to Navigation Handrailing

v

v

v

v

Imagine you wish to cross a river at the bridge, if you aim directly for the

footbridge you may miss it.

Aids to Navigation Aiming Off

On reaching the stream you would not know which way to turn to find the bridge..

Aids to Navigation Aiming Off

?

?

Instead, if you deliberately ‘aim off’ you would know which way to turn when you

do reach the stream.

Aids to Navigation Aiming Off

Is it better to go round a hill or up and over the top?

Aids to Navigation Contouring

Going round the hill, neither gaining or losing height is called ‘contouring’.

Contouring – following the lines of the contours – takes less effort, but may take

longer.

An attack point is an easily identifiable feature close to your target.

Aids to Navigation Attack Points

It sometimes pays to go slightly out of your way to increase your chances of

successfully reaching your final objective.

BASIC NAVIGATION

Contents List.

Click on a chapter.

Chapter 1 Basic Navigation.

Chapter 2 The Compass.

Chapter 3 Practical Navigation.

Chapter 4 Weather.

exit

Chapter 4

Weather

There are six main air

masses that affect the

weather in the British Isles,

each having its own distinct

characteristics.

Arctic Maritime

Polar Continental

Tropical Continental

Tropical Maritime

Polar Maritime

Returning Polar

Maritime

There are six main air

masses that affect the

weather in the British Isles,

each having its own distinct

characteristics.

These characteristics also change by season.

Tropical Continental

Tropical Continental air

originates in North Africa.

In Summer it is very hot and

hazy with occasional

thunderstorms.

Tropical Continental

Tropical Maritime

Tropical Maritime air

originates over the warm

Atlantic Ocean near the equator.

It brings warm and wet air all year round.

Tropical Continental

Tropical Maritime

Polar Maritime

Polar Maritime originates in

North Canada and Greenland.

It brings cool winds and

heavy showers to the U.K. in both summer and winter.

Tropical Continental

Tropical Maritime

Polar Maritime

Returning Polar

Maritime

Returning Polar Maritime

originates in Canada as cold

dry air, but moves south

over the Atlantic and picks up water vapour.

It is much warmer and wetter than Polar Maritime air.

Arctic Maritime

Tropical Continental

Tropical Maritime

Polar Maritime

Returning Polar

Maritime

Arctic Maritime air originates in cold Arctic

seas and picks up little

moisture as it travels south.

Always very cold, with heavy showers in summer and heavy snow in winter.

Arctic Maritime

Polar Continental

Tropical Continental

Tropical Maritime

Polar Maritime

Returning Polar

Maritime

Polar Continental air

originates in Siberia.

The short sea track to the south of England means it stays quite dry with little cloud.

It is cold in winter but warm

in summer.

Arctic Maritime

Polar Continental

Tropical Continental

Tropical Maritime

Polar Maritime

Returning Polar

Maritime

Polar Continental air

originates in Siberia.

The longer North Sea track means much wetter weather for Scotland and Northern England.

It is cold in winter but warm

in summer.

Fronts and depressions are the cause of most of the poor weather we experience.

Fronts and Depressions

To try and understand what is happening in the atmosphere meteorologists draw

charts joining points of equal pressure – isobars.

Isobars appear similar to contours on relief maps – and have many similarities.

Fronts and Depressions

The distance between contours indicates the steepness of hills.

shallow slopesteep slope

The distance between isobars indicates the pressure gradient which in turn

determines the strength of the winds.

Fronts and Depressions

shallow pressure

gradient = light winds

steep pressure

gradient = strong winds

Depressions are areas of low atmospheric pressure.

Fronts and Depressions

L

They are the cause of much of the poor weather in the U.K.

Fronts and Depressions

Fronts and Depressions

At our latitudes a typical depression moves slowly from

west to east.

Fronts and Depressions

and a segment of warm tropical

maritime air in the south.

They usually have cold polar air to

the north -cold air

warm air

Fronts and Depressions

Fronts occur where a warm air mass meets a cold air

mass.

cold air

warm air

Semicircles denote a warm front.

Fronts and Depressions

Fronts occur where a warm air mass meets a cold air

mass.

cold air

warm air

Triangles denote a cold front.

Fronts and Depressions

Cold fronts move slightly faster than

warm fronts.cold air

warm air

When both fronts meet, the warm segment air is lifted off the

ground by the colder air.

Fronts and Depressions

Cold fronts move slightly faster than

warm fronts.cold air

When both fronts meet the warm segment air is lifted off the

ground by the colder air.

Fronts and Depressions

The result is an occluded front -cold air

symbolised by alternate

semicircles and triangles.

Upper Winds

High level (normally westerly) winds are responsible for the movement of weather

systems, particularly depressions.

In this diagram the dotted lines

represent the upper winds pushing the depression east.

Upper Winds

If you were stood at point ‘Y’ with your back to the lower wind and the upper

wind moving from left to right:

then the depression has not yet reached you and the weather

is likely to deteriorate.

Anticyclones

Regions of high pressure with widely spaced isobars and light winds.

They are stable, slow moving systems

bringing long periods of warm,

fine weather.

H

An anticyclone is:

a) An area of low pressure. b) An area of high pressure.

c) A depression. d) An area between two areas of high pressure.

An anticyclone is:

a) An area of low pressure. b) An area of high pressure.

c) A depression. d) An area between two areas of high pressure.

Generally an area of high pressure will tend to bring:

a) Fast moving wet weather systems.

b) Fast moving fine weather systems.

c) Long periods of fine weather. d) Long periods of poor weather.

Generally an area of high pressure will tend to bring:

a) Fast moving wet weather systems.

b) Fast moving fine weather systems.

c) Long periods of fine weather. d) Long periods of poor weather.

Clouds

Clouds are named according to shape and height.

Cirrus clouds are found only at high levels and

are composed of ice crystals. Cirrus means

‘thread’ or ‘hair’.

Cirrus

Clouds

Clouds are named according to shape and height.

Cumulus clouds are formed by rising air and

appear lumpy or heaped.

Cumulus

Clouds

Clouds are named according to shape and height.

Stratus describes a featureless layer cloud.

Stratus

Clouds

Clouds may be given prefixes which identify the height of the cloud.

Clouds prefixed with Cirro are high level

clouds, above 18000 ft (5500 m). Cirrus, cirrostratus and

cirrocumulus are examples.Cirrus

Clouds

Clouds may be given prefixes which identify the height of the cloud.

Clouds prefixed with Alto are medium

level clouds, between 6500 ft (2000 m) and 18000 ft. Altostratus and altocumulus are

examples.Altostratus

Clouds

Clouds without prefixes are low level clouds found below 6500 ft (2000 m).

Examples are stratus, cumulus and

cumulonimbus - the nimbus suffix

meaning a raincloud.

Cumulonimbus

BASIC NAVIGATION

Contents List.

Click on a chapter.

Chapter 1 Basic Navigation.

Chapter 2 The Compass.

Chapter 3 Practical Navigation.

Chapter 4 Weather.

exit

Basic Navigation Revision

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