2 Altitude Corrections

8/14/2019 2 Altitude Corrections

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Intro to Principles Navigation Altitude corrections /October 2008/MH/Altitude corrections /October 2008/MH/ 1111

Nautical almanac is ..


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Nautical almanac is a compilation of astronomical data

for the entire year. It provides ..

p 161


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OBJECTIVE1.Define :

Rational horizon

Visible horizon

Sensible horizon

True altitude


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Rational horizon

Z

Nadir


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Vertical circle

Z

Nadir


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Zenith to the rational horizon = 90

Z

R

Nadir H


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True altitude

Z

R

Nadir H


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Zenith distance = 90 - true altitude

= ZX or ZD

Z

R

Nadir H


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True altitude

Z

R

Nadir H


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True altitude

RH


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Intro to Principles Navigation Altitude corrections /October /MH/Altitude corrections /October /MH/

True altitude Z

RH


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True altitude Z

RH


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Zenith distance Z

90 - true altitude = zenith distance

= ZX

= ZD

RH

X


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True altitude

RH

X


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Visible horizon

RH


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Sensible horizon

RH


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Rational, visible and sensible horizon

SH

VH

RH

X


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OBJECTIVE1.Define :

Observed altitude

Dip

Apparent altitude

Parallax

Refraction

Semi-diameter


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Observed altitude

RH

X


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Rational, visible and sensible horizon

SH

VH

RH

X


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Dip

SH

RH

X


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Observed altitude dip = apparent altitude

RH

X


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Refraction


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True altitude

SH

RH

X


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Upper limb(UL)

SH

upper limb

RH

X


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Lower limb(LL)

SH

upper limb

RH

X

lower limb


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upper limb

lower limb


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Semi-diameter


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upper limb

SD

lower limb

ld Cl i i d


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upper limb

SD

SD

lower limb

T B A W ld Cl M i i A dT B A W ld Cl M iti A d


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upper limb (UL)

UL = -ve SD

LL = +ve SD

lower limb (LL)

ld l i i dT B A W ld Cl M iti A dT B A W ld Cl M iti A dT B A W ld Cl M iti A d


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Parallax= angle at body

RH

X

T B A W ld Cl M iti A dT B A W ld Cl M iti A dT B A W ld Cl M iti A dTo Be A Wo ld Class Ma itime Academ


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a = b + c

RH

b c X

a

T B A W ld Cl M iti A dT B A W ld Cl M iti A dTo Be A World Class Maritime AcademyTo Be A World Class Maritime Academy


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a = b + c

True altitude = apparent altitude + parallax

RH

b c X

a

To Be A Wo ld Class Ma itime AcademTo Be A World Class Maritime AcademyTo Be A World Class Maritime AcademyTo Be A World Class Maritime Academy


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SI

O

D

A

R

S



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Sextant altitudeI

O

D

A

R

S



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Sextant altitude Index error

O

D

A

R

S



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Observed altitude

D

A

R

S



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Observed altitude

- Dip

A

R

S



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Observed altitude

- Dip

Apparent altitude

R

S



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Observed altitude

- Dip

Apparent altitude

- Refraction

S



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To Be A World Class Maritime AcademyTo Be A World Class Maritime AcademyTo Be A World Class Maritime Academyo e o d C ass a t e cade y



Observed altitude

- Dip

Apparent altitude

- Refraction

Semi-diameter



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To Be A World Class Maritime AcademyTo Be A World Class Maritime Academyyy


SI

O

D

A

R

S



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To Be A World Class Maritime Academyyyy



Observed altitude

- Dip

Apparent altitude

- Refraction

Semi-diameter



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yyyy



Observed altitude

- Dip

Apparent altitude

- Refraction

Semi-diameter

+Parallax



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yy



Observed altitude

- Dip

Apparent altitude- Refraction

Semi-diameter

+Parallax

=True altitude



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y



Observed altitude

- Dip

Apparent altitude

- Total correction (refraction,parallax and semi-diameter)

=True altitude



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Observed altitude

- Dip

Apparent altitude

- Refraction Semi-diameter

+Parallax

=True altitude




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Observed altitude

- Dip

Apparent altitude- Total correction

=True altitude




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Next : find total correction to be applied



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OBJECTIVE

1.Find total correction to be applied



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Total correction = ?

Dec 13

Apparent altitude 30

Sun LL



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May 13


Sun UL



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Acamar



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May 13


Venus



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May 13


Mars



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May 13

Apparent altitude 9

Sun LL



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May 13


Moon LL


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OBJECTIVE

1.Find the zenith distance



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Q1

Suns UL Sextant altitude 35 19.1

Index error(IE) = nil

Height of eye(HE) 12.8m on 14 Oct

Find the zenith distance



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Observed altitude

- Dip


=True altitude




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Sextant altitude 35

19.1 Index error

Observed altitude 35 19.1

- Dip


=True altitude




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Sextant altitude 35

19.1 Index error

Observed altitude 35 19.1 (14 oct UL)

- Dip 6.3 (HE 12.8m)


=True altitude




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Sextant altitude 35

19.1 Index error


- Dip 6.3 (HE 12.8m)

Apparent altitude 35 12.8- Total correction 17.4

=True altitude




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Sextant altitude 35

19.1 Index error


- Dip 6.3 (HE 12.8m)

Apparent altitude 35 12.8- Total correction 17.4

=True altitude 34 55.4




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Sextant altitude 35

19.1 Index error


- Dip 6.3 (HE 12.8m)

Apparent altitude 35 12.8

- Total correction 17.4



ZD = ZX = 55 04.6



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Q2

Capella sextant altitude 23 12.7

Index error(IE) = 1.2off the arc

Height of eye(HE) 11.0m




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Observed altitude

- Dip


=True altitude




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Sextant altitude 23

12.7 Index error

Observed altitude

- Dip


=True altitude




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Sextant altitude 23

12.7 Index error + 1.2(off the arc)

Observed altitude

- Dip


=True altitude




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Sextant altitude 23


Observed altitude 23 13.9 on 02 Feb

- Dip - 5.8 (HE) 11.0m


=True altitude




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Sextant altitude 23



- Dip - 5.8 (HE) 11.0m

Apparent altitude 23 8.1- Total correction

=True altitude




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Sextant altitude 23



- Dip - 5.8 (HE) 11.0m

Apparent altitude 23 8.1- Total correction - 2.3

=True altitude




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Sextant altitude 23



- Dip - 5.8 (HE) 11.0m

Apparent altitude 23 8- Total correction - 2.2





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Sextant altitude 23 12.7

Index error + 1.2(off the arc)


- Dip - 5.8 (HE) 11.0m


- Total correction - 2.3



= 66 54.2



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Q3

Mars sextant altitude 42 54.3

Index error(IE) = 0.7on the arc

Height of eye(HE) 9.0m on 02 Feb




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Sextant altitude 42

54.3 Index error

Observed altitude

- Dip


=True altitude




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Sextant altitude 42

54.3 Index error - 0.7 on the arc

Observed altitude

- Dip


=True altitude




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Sextant altitude 42


Observed altitude 42 53.6 (9.0m on 02 Feb)

- Dip


=True altitude




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Sextant altitude 42



- Dip - 5.3


=True altitude




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Sextant altitude 42



- Dip - 5.3

Apparent altitude 42 48.3- Total correction

=True altitude




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Index error - 0.7 on the arc


- Dip - 5.3



+ 0.1

=True altitude




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- Dip - 5.3



+ 0.1





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- Dip - 5.3


- Total correction - 1.0+ 0.1



= 47 1236



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Sextant altitude

Index error

Observed altitude

- Dip

Apparent altitude

- Refraction Semi-diameter

+Parallax

=True altitude




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Sextant altitude

Index error

Observed altitude

- Dip


=True altitude




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Total correction includesrefraction, parallax and semi-

diameter values



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The corrections to be applied to the sextant altitudes

of the various celestial bodies are listed at page 152



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2 Altitude Corrections