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Airmanship, Air Safety and Emergency Procedures > Nav Revision > Flashcards

Nav Revision Flashcards

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1
Q

What are the features of a conformal projection?

A

Produce charts that represent bearings accurately

Projection on which angles are preserved

Bearing on Earth’s surface should be represented by the same angle on the chart

For a given point on the chart, scale expansion is the same in all directions

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2
Q

At what angle do meridians and parallels intersect on conformal charts?

A

90 degrees

same as on Earth’s surface

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3
Q

What is another name for a conformal chart?

A

Orthomorphic

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4
Q

How can the figure/shape of the Earth be modelled for navigation and charts?

A

Geoid

Ellipsoid/spheroid

Sphere

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5
Q

What are the two categories of projection?

A

Perspective (true/geometric|)

Non-perspective (mathematical)

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6
Q

What are perspective projections?

A

Drawings of shadows cast by meridians and parallels on a transparent model Earth onto a plane surface.

Aka True (geometric)

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7
Q

What is a non-perspective projection?

A

A perspective projection which has been adjusted mathematically by relocation of the graticule to attain a more accurate representation so that some distortions are removed.

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8
Q

What are the 3 types of perspective projection?

A

Azimuthal - Shadows projected onto a flat surface

Cylindrical - Shadows projected onto a cylinder surrounding the model

Conical - Shadows projected from a light source in the centre of the reduced Earth onto a cone tangential to the model that can then be developed

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9
Q

How can scale be represented on maps/charts?

A

Graduated scale (i.e. ruler on chart)

Representative fraction (e.g. 1:500,000)

Plain Statement (e.g. 2cm is 1 mile)

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10
Q

What is scale?

A

The ratio of chart length to Earth length.

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11
Q

It is impossible for scale to be …. over an entire projection.

A

Constant

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12
Q

How many times larger is the apex angle than the point of tangency in a conical projection?

A

2

E.g. tangential point = 45 degrees, apex angle = 90 degrees

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13
Q

What is a standard parallel?

A

A line of latitude in a conical or cylindrical projection in normal aspect, where the projection surface touches the globe.

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14
Q

What are the 4 types of standard parallel?

A

Conical one Standard Parallel projection
Conical two Standard Parallel projection

Cylindrical one Standard Parallel projection
Cylindrical two Standard Parallel projection

Note - Be able to recognise from pictures in course manual

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15
Q

What are the types of conical projection?

A

Perspective projection

Conical One Standard Parallel projection (1 red line)

Conical Two Standard Parallel projection (2 red lines)

Non-perspective projections

Note - Be able to recognise all from pictures.

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16
Q

What are conical projections used for?

A

Producing maps of SMALL AREAS on the Earth’s spherical surface onto a cone that is subsequently developed

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17
Q

What is the constant of the cone/Convergence Factor?

A

The ratio of the convergence between any two meridians on a map or chart to the change of longitude between them.

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18
Q

What is the Lambert Conformal Conical Projection?

A

NON-PERSPECTIVE projection.

Assumes that the reduced Earth is a PERFECT SPHERE.

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19
Q

Where are Lambert Conformal Conical Projections used?

A

LFC (1:500,000)

Note - Unsuitable for use at the poles

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20
Q

What azimuthal projections can we produce?

A

Polar azimuthal

Equatorial azimuthal

Oblique azimuthal

(Be able to recognise all of the above from the pictures in the course manual)

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21
Q

What are the TYPES of Azimuthal Projection?

A

Stereographic projection

Polar graticule meridians

Gnomonic projection

Azimuthal equidistant

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22
Q

Explain stereographic projection.

A

Azimuthal projection

Perspective and conformal

Mainly used for polar based navigation

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23
Q

Explain Polar graticule meridians.

A

Azimuthal projection

Radial straight lines from the point of tangency

Scale expands away from the point of tangency

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24
Q

Explain Gnomonic projection.

A

Azimuthal projection

Perspective and NON-conformal

Meridians and parallels are projected onto a surface from the centre of the reduced Earth

Displays great circles as straight lines

Scale increases away from the point of tangency

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25
Q

Explain Azimuthal equidistant.

A

Azimuthal projection

NON-Perspective

NON-Conformal

Distances from the point of tangency are correct to scale

Bearing and distance can be measured accurately from the point of tangency

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26
Q

What is Mercator’s Projection?

A

A type of cylindrical conformal or orthomorphic projection.

Uses straight meridians and parallels that intersect at right angles.

Straight lines on the map are lines of CONSTANT AZIMUTH (RHUMB lines)

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27
Q

What are the different types of Mercator’s Projection?

A

General Mercator’s projection

Plane/Oblique

Transverse

Note - See course manual for extra details + be able to recognise from pictures.

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28
Q

What are the different types of year?

A

Year

Sidereal Year

Tropical Year

Civil Year

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29
Q

What is a year?

A

Length of time taken for the Earth to orbit the Sun

30
Q

What is a sidereal year?

A

Time taken by the Earth to orbit the Sun as measured against a fixed star

31
Q

What is a tropical year?

A

A Tropical Year is one complete orbit of the Sun measured as the PERIOD between TWO successive VERNAL EQUINOXES relative to the First point of Aries.

Approx. 365 days, 6 hrs

32
Q

What is a civil year?

A

Civil year = Calendar year using the Gregorian calendar

Assumes 1 yr = 365 days, with every 4th being a leap year (366 days)

33
Q

What are the 2 types of day?

A

Apparent Solar Day

Mean Solar Day

34
Q

What is an Apparent Solar Day?

A

The interval between two successive returns of the sun to the local meridian.

35
Q

What is a Mean Solar Day?

A

Average length of Apparent Solar Days observed over a period of years.

Measured relative to a fictional Mean Sun moving at a constant rate.

24 hrs

36
Q

What is Apparent Solar Time?

A

Kept according to the actual position of the Sun in the sky, measured at successive crossings of the Sun at a local meridian at noon.

Varies throughout the year, not exactly 24hrs.

37
Q

What is Local Mean Time (LMT)?

A

Uses a theoretical Mean Sun which orbits Earth every 24hrs in the plane of the equator.

Errors averaged out to give LMT.

38
Q

How is LMT calculated at different longitudes?

A

1 degree of longitude = 4 mins
15 degrees = 1hr

Going East = +
Going West = -

OR

Air Almanac Conversion of Arc to Time Table

39
Q

What is UTC?

A

Coordinated Universal Time

World standard reference time for aviation

LMT at the Greenwich Meridian

40
Q

How can UTC be converted to LMT?

A

LMT = UTC + Long E

or

LMT = UTC - Long W

Depends which way you’re going

41
Q

What is TAI?

A

International Atomic Time

Based on the measurement of a particular vibration of the Caesium-133 atom.
Forms the basis of UTC.

42
Q

How are Radio Time Signals transmitted?

A

Transmitted by numerous NATIONAL and COMMERCIAL broadcast stations throughout the world.

Normal time check 6 pips prior to the hour

43
Q

What is the Prime Meridian?

A

0 degrees longitude

Greenwich Meridian

ZULU time

44
Q

What is the International Date Line?

A

180 degrees

Anti-Meridian

Zone boundary separating +12 and -12 hours

Crossing West adds one day, crossing East subtracts one day

Not a straight line (learn picture in book)

45
Q

What is Standard Time?

A

A particular LMT that a national authority has decreed will be kept throughout its country.

46
Q

What is Daylight Saving Time (DST)?

A

Clocks advance 1 hour in Spring to maximise evening daylight.

British Summer Time (BST) starts on the last Sunday in March and 01:00 GMT.

BST ends on the last Sunday in October at 02:00 BST.

47
Q

What is Zone Time?

A

Countries with significant East/West extent have further subdivisions of time within the, e.g. USA, Australia.

48
Q

How can we convert from zone time to UTC?

A

UTC = Zone Time - East change in longitude

49
Q

What are the dimensions of the Twilight Zone?

A

.

50
Q

What are the types of Twilight?

A

Civil twilight - Up to 6 degrees

Nautical twilight - Up to 12 degrees

Astronomical twilight - Up to 18 degrees

Morning Civil Twilight (MCT) and Evening Civil Twilight (ECT)

51
Q

What factors affect the duration and time of twilight for a stationary observer?

A

Latitude

Sun’s declination

Alitude

52
Q

How does twilight vary with latitude?

A

Duration increases with increasing latitude.

Sun’s declination in the SAME hemisphere = Earlier sunrise, later sunset

Sun’s declination and observer’s latitude are CONTRARY, sunrise occurs later and sunset earlier with increasing latitude.

53
Q

How does twilight vary with altitude/height?

A

At height, sunrise becomes earlier, sunset later.

Duration of twilight DECREASES.
(atmosphere is less deep, reduction in refracted light and diffused light to do a decrease in scattered particles)

54
Q

How does flying West affect sunset and twilight?

A

GS > Earth’s rotational speed = Sun’s position in sky remains constant or appears to move in reverse

Sun takes longer to set and Twilight becomes longer.

Opposite is true if flying East

55
Q

What does the UK Air Almanac provide?

A

Convenient form of astronomical data:

Time conversion tables, sunrise, sunset, twilight, moonrise, moonset, duration and time of astronomical phenomena, etc.

56
Q

Explain TDAs.

A

Tactical Decision Aids

Uses Numeric Weather Prediction (NWP) and Met Office Night Illumination Model (MONIM) to forecast light levels 24/7 for anywhere in the world.

Request to Met Office TDA allows decisions to be made re use of electro-optical night vision devices/timing for operations, etc.

57
Q

What is the Earth’s rate of rotation?

A

15 degrees per hour

58
Q

What does every projection have?

A

Central Meridian - Its middle longitude

Central Parallel - Middle latitude/latitude of origin

Natural Origin - Where the Central Meridian and Central Parallel intersect. Starting point of the projected coordinates

59
Q

What is sometime done to the Natural Origin to avoid negative coordinate values or extremely large values?

A

It is shifted, giving a COORDINATE SYSTEM ORIGIN.

Shifts are described using False Eastings and False Northings

Note - Be able to recognise picture in course manual

60
Q

What is the National Grid at its largest extent?

A

Starts as a 5x5 series of 500km x 500km grids, labelled A to Z (but omitting I).

61
Q

What is the National Grid base on and where is the natural origin?

A

Transverse Mercator Projection

49 N 2 W

62
Q

Where is the BNG false origin?

A

100km North and 400km West of grid origin

63
Q

The UK is covered by 6 of the 500km x 500km grid squares of the BNG, how are these split up and labelled?

A

Each is split into 100km squares, lettered A to Z (omitting I).

A is in the TOP LEFT.

64
Q

What is UTM?

A

Universal Transverse Mercator

World map

NUMBERS along the bottom

60 longitude zones, 20 latitude bands

65
Q

What is UPS?

A

Universal Polar Stereographic

Circular (azimuthal projection)

One for N pole, one for S pole, origin for each is at the pole.

66
Q

How is the North Pole divided for UPS?

A

Divided by the Greenwich meridian and the 180 degree meridian.

West longitudes = Y

East longitudes = Z

67
Q

How is the South Pole divided for UPS?

A

Divided by the Greenwich meridian and the 180 degree meridian.

West longitudes = A

East longitudes = B

68
Q

What is the MGRS?

A

Military Grid Reference System

Used with the UTM and UPS girds.

69
Q

What is GEOREF?

A

Geographic Reference System

LETTERS along the bottom

24 longitudinal zones
12 bands of latitude

Applied in UK coastal and air defence

70
Q

What Datum is used for most charts/maps/GPS?

A

WGS 84 - World Geodetic System

71
Q

What are some common datums?

A

WGS 84

ED 50 - European Datum

Local Datum - Best fits a local area of interest

Airmanship, Air Safety and Emergency Procedures (8 decks)

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