basic navigation click on ‘f5’ to start.. basic navigation contents list. click on a chapter....
TRANSCRIPT
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.
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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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