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Author Topic: Navigating the LOP with the offset method.  (Read 202556 times)

h.a.c. van asten

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  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #150 on: June 07, 2011, 11:14:40 PM »

Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used  , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth ,  by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 ,  thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course  157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.

In other words, what you're saying is that
  • Noonan was planning to use the offset method to intercept Howland,
  • At the time he was deciding when to turn off, they were flying at 1,000 feet,
  • He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
  • Noonan was using charts that had Howland's position off by 6 miles.
  • Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
  • They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.

Thank you.  I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.

Yes , I possibly started at the intricate side however , making statements is one thing , but delivering unconditional proof is another and not child´s play.
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Gary LaPook

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  • Posts: 1624
Re: Navigating the LOP with the offset method.
« Reply #151 on: June 08, 2011, 12:33:44 AM »

G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.

---------------------------

This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.

gl
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Gary LaPook

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  • Posts: 1624
Re: Navigating the LOP with the offset method.
« Reply #152 on: June 08, 2011, 12:37:13 AM »

Mr. Lapook ,

According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives :  I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening ,  you will seemingly arrive at precomptud  Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .

I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.

--------------------------------------

Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.

Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”

She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”

He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”

Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”

This illustrates  just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.

Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.

I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
 
see page 425 here:

 https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0

where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.

Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.

We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.”  Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid  improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.

See page 423:

https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0

Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.

Mr. van Asten refuses to accept these facts.

Enough for now.

gl
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Gary LaPook

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  • Posts: 1624
Re: Navigating the LOP with the offset method.
« Reply #153 on: June 08, 2011, 01:26:57 AM »

G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.

---------------------------

This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.

gl

---------------------------------

Here are some links showing how the computations are done IN FLIGHT

http://www.oceannavigator.com/content/celestial-air

http://www.avweb.com/news/avtraining/IFR_bySunAndStars_200781-1.html

https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation

They all show that Mr. van Asten is wrong again.

gl
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Gary LaPook

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  • *****
  • Posts: 1624
Re: Navigating the LOP with the offset method.
« Reply #154 on: June 08, 2011, 02:04:50 AM »

G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.

---------------------------

This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.

gl

---------------------------------

Here are some links showing how the computations are done IN FLIGHT

http://www.oceannavigator.com/content/celestial-air

http://www.avweb.com/news/avtraining/IFR_bySunAndStars_200781-1.html

https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation

They all show that Mr. van Asten is wrong again.

gl

-----------------------

Noonan himself wrote that the average time needed to compute and plot a fix was only six minutes.

gl
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h.a.c. van asten

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  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #155 on: June 08, 2011, 03:05:39 AM »

Mr. Lapook ,

According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives :  I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening ,  you will seemingly arrive at precomptud  Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .

I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.

--------------------------------------

Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.

Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”

She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”

He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”

Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”

This illustrates  just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.

Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.

I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
 
see page 425 here:

 https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0

where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.

Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.

We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.”  Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid  improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.

See page 423:

https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0

Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.

Mr. van Asten refuses to accept these facts.

Enough for now.

gl


Mr.Lapook ,

I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you  continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S  coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating  "mr.van Asten is wrong again" and "You don´t know what you are talking about"  , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used  for  his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
Logged

h.a.c. van asten

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  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #156 on: June 08, 2011, 06:00:04 AM »

Mr. Lapook ,

According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives :  I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening ,  you will seemingly arrive at precomptud  Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .

I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.

--------------------------------------

Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.

Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”

She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”

He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”

Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”

This illustrates  just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.

Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.

I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
 
see page 425 here:

 https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0

where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.

Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.

We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.”  Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid  improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.

See page 423:

https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0

Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.

Mr. van Asten refuses to accept these facts.

Enough for now.

gl


Mr.Lapook ,

I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you  continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S  coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating  "mr.van Asten is wrong again" and "You don´t know what you are talking about"  , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used  for  his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.


On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"

shouts the company executive back : "You are fired ,  Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #157 on: June 08, 2011, 07:16:01 AM »

... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...

Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.

I actually understand his theories and methodology and even his complex computations ...


Thanks for clarifying the nature of the argument.  Much appreciated!

Quote
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation.

Thanks for untangling that.

Quote
If there was no marine sextant on board
then no way to make this error.

Even if there was a marine sextant on board (with or without the bubble modification used on many Brandis instruments), there is no reason to think that Fred would have chosen to use it rather than the Pioneer instrument that was designed for use in aerial navigation.

Oh, reading further along, I see that we are already in agreement on that score:

Quote
... There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.

Van Asten's bottom line appears in Figure 6 of "Where to Search for the Earhart Lockheed Electra."  Using his system, he calculates that the plane came down in an area roughly 85 miles NNW of Howland Island--the area immediately searched by the Itasca on 2 July 1937.  I'm not sure how close this is to Elgen Long's calculations or whether the two Nauticos searches have covered that area.
LTM,

           Marty
           TIGHAR #2359A
 
« Last Edit: June 08, 2011, 07:36:03 AM by Martin X. Moleski, SJ »
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h.a.c. van asten

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Re: Navigating the LOP with the offset method.
« Reply #158 on: June 08, 2011, 12:21:48 PM »

... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...

Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.

I actually understand his theories and methodology and even his complex computations ...


Thanks for clarifying the nature of the argument.  Much appreciated!

Quote
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation.

Thanks for untangling that.

Quote
If there was no marine sextant on board
then no way to make this error.

Even if there was a marine sextant on board (with or without the bubble modification used on many Brandis instruments), there is no reason to think that Fred would have chosen to use it rather than the Pioneer instrument that was designed for use in aerial navigation.

Oh, reading further along, I see that we are already in agreement on that score:

Quote
... There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.

Van Asten's bottom line appears in Figure 6 of "Where to Search for the Earhart Lockheed Electra."  Using his system, he calculates that the plane came down in an area roughly 85 miles NNW of Howland Island--the area immediately searched by the Itasca on 2 July 1937.  I'm not sure how close this is to Elgen Long's calculations or whether the two Nauticos searches have covered that area.

I do not know about Nauticos searches , Waitt discoveries searched along E.Long´s ´circles of uncertainty´ , southwards of 1 deg 49 - N . That the area would have been visited by Itasca confirms nothing : there have been numerous aircraft on sea accidents without trace.
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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #159 on: June 08, 2011, 11:44:44 PM »

The problem I see with the concept of making this flight by the offset method is based in the uncertainty associated with flight parameters and the accumulated errors produced by them.

Offsets only make sense if they don't add more risk or error than they compensate for.  For example, if you're flying from Havana to Key West (roughly 020T) and for some reason don't have enough fuel to continue on to mainland Florida if you miss to the west, it makes sense to shade your course to the right (say 030T) and turn west when you see the Keys.  The Keys are fixed, visible to the naked eye, they lead to Key West and you have a very high probabliity of finding them, so you're not introducing new error or uncertainty.  You are, however, guaranteeing a longer flight.

Doing the same thing based on a DR track buys you very little, and at quite a price in terms of risk and uncertainty.  For simplicitys sake, consider a flight from a point on the equator to a small island 1000 nm east on the equator.  If you think an offset is a good idea, go ahead and fly to a spot in the ocean (not an island, coastline, depth contour or lighted range, just a random-looking patch of ocean) exactly 100 nm south of the island, then hang a left.  The island will be exactly 100 nm ahead of you.  Piece of cake.

If:  You were able to hit the correct longitude.  At night.  No identifiable landmarks.  No decent winds aloft data.  Maybe a single LOP a couple hours before ETA.

If AE and FN intended to try this, it would require that they not home in on the RDF bearings they intended to be picking up.  As Itasca and/or Howland came into range, they would have to watch the bearing move from almost dead ahead to straight off the port wing and then and only then only then turn at that point.  Then fly into their destination from a direction 90 degrees from their origin.

Without telling the people that would be looking for them that they would be coming in from the south. 

Seems a bit of a stretch to me.

-----------------------------

Except that the two methods to use to find the island are not mutually exclusive. The RDF should have picked up the Itasca's signals several hundred miles out. They used radio bearings that were more than 600 NM on the flight to Hawii. So there is no problem aiming directly towards Howland expecting to be able to get radio bearings when within 200 NM. When they didn't get a signal there is no problem with turning off to start the landfall since that procedure is accurate enough to get them to Howland in case they never do get the radio signal. If, on the way to the offset point they do start receiving the signals then they would not have to continue all the way to the sun line LOP but would turn to head directly toward Howland as soon as they got the signals.

This is common when flying an instrument approach. You follow a routing to the  initial approach fix at which point you will turn away from the destination airport to fly a procedure turn and only after completing the procedure turn are you then heading towards the airport. This "full instrument procedure" adds 9 or 10 minutes to the flight time so you don't want to do it you do not have to. So, if you are flying toward the IAF and you happen to be below the clouds and you see the airport, say off to your left, then you tell the controller "airport in sight" and he then clears you for a "visual approach" which then allows you, at that point, to turn directly towards the airport. There is no reason to complete the full approach and waste all that time.

Same thing with a landfall approach.


See:

https://sites.google.com/site/fredienoonan/topics/landfall-procedure

https://sites.google.com/site/fredienoonan/discussions/navigation-to-howland-island

gl
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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #160 on: June 11, 2011, 03:16:36 AM »

Mr. Lapook ,

According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives :  I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening ,  you will seemingly arrive at precomptud  Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .

I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.

--------------------------------------

Imagine...you have taken your wife, .....
Enough for now.

gl


Mr.Lapook ,

I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you  continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S  coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating  "mr.van Asten is wrong again" and "You don´t know what you are talking about"  , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used  for  his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.


On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"

shouts the company executive back : "You are fired ,  Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
------------------------------------------------------------------------------



(Continuing on with our romantic vignette.)

...

“Noticing the confused look on her face he goes on ‘we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.’”

“But wait, I wanted to see a romantic sunset, this sucks. How do you even know that the sun is
below the true horizontal?” she asks.

“Because I figured out a way to determine it without help from anybody else, and I am pretty
proud of myself, I looked in lots of navigation manuals and this method is not in any of them! I
did find in these manuals that navigators have to allow for the fact that the visible horizon is
actually below the true horizontal when taking sights with their marine sextants. Since it is below
zero and it is used as the reference for the measurements, all altitudes measured with a marine
sextant are too large so navigators must subtract the amount that the visible horizon is below the
true horizontal from all of their sextant readings. They call this the “dip” correction and it varies
according to the height the observer’s eye is above sea level. They find this correction tabulated
in the “dip correction table” in the Nautical Almanac. I looked in the dip table and found that for
our height above the sea, one thousand feet, the dip correction is a little more than half a degree,
thirty-one minutes of arc, actually. So, I just set the index arm on my marine sextant to thirty-one
minutes, looked at the horizon through the horizon mirror on the sextant and waited until the
upper limb of the sun, that I was viewing in the index mirror, sank down until it appeared to be
lined up with the visible horizon reference in the sextant mirror so I then knew that the upper
limb was at the true horizontal and so the sun had set.”

She says “OK, that’s great. So that’s what you were doing over there by yourself, I thought... oh
never mind.”

“You’re RIGHT, it is great, I FIGURED IT OUT, nobody else had ever discovered this method
for finding the true horizontal!” he replied.

“O.K. but can we please wait a little while longer so I can actually see the sun disappear behind
the horizon, I’d like to see the green flash” she begs.

“No!, I know when the true sunset is, so we are leaving now.”


(We will now leave this couple to work our their “issues.”)



In fact, this method would work if anybody needed to find the point of “van Asten
sunset/sunrise” which no navigator has yet to discover the need to do.

I communicated with Mr. van Asten about this and asked him how Noonan would have known
his height above the sea so that he could look in the dip table to determine the correct value of
dip to place on his sextant. He responded that Earhart said that she was at a thousand feet and
that she knew that from her altimeter.

On May 16th I wrote to Mr. van Asten:

“To have an accurate altitude from a barometric altimeter  you need to have a local altimeter
setting (QNH)  for a reporting station within 50 nm of your location and Earhart had set her
altimeter on the ground in Lae, 2222 nm away and had not received any altimeter setting since
then. Over such a great distance it is possible for an altimeter to be off by a 1000 feet since the
change in atmospheric pressure for the different locations will cause the altimeter to read
incorrectly.

Just to give you an example, I just checked the weather at Minneapolis, Minnesota and at
Billings, Montana, two airports separated by only 644 nm. At 0600 Z the altimeter setting at
Minneapolis is 31.18 inches of hg and at Billings the altimeter setting is only 29.72 inches of hg.
With this difference in altimeter settings, a pilot taking off from Minneapolis and flying only 644
nm to Billings  without getting the local Billings altimeter setting (QNH) would end up 460 feet
lower than what his altimeter is indicating, and this in only 644 nm. A pilot flying in the opposite
direction would find himself 460 feet too high.  Noonan would not have used a mariner's sextant
because he would know of the uncertainty in the altitude and the resulting uncertainty in the
correct dip correction to use. Since Noonan did not have a current altimeter setting then his
height could easily have been off by plus or minus 500 feet so the dip might be anywhere
between 22' and 38'  giving the marine sextant altitude 16' of uncertainty But using the
methodology that you laid out of setting the marine sextant to 31' (the dip at 1000 feet) and then
waiting for the upper limb of the sun to come up into alignment with the visible horizon seen in
the marine sextant then causes you to see the upper limb of the sun aligned with the true
horizontal . Then you said to subtract 53' (37' refraction and 16' of semi-diameter) from this zero
altitude to arrive at the true altitude of the center of the sun of minus 53'.

But if they were only at 500 feet instead of 1000 feet then the dip correction is only 22' so setting
the sextant as you said would not cause it to define the true horizontal but would actually set the
reference at  9' above the true horizontal so the observation would be in error by the same 9'
meaning that the true altitude of the center of the sun would be minus 44' not the minus 53' of
your computation, resulting in a 9 nm error in the line of position which would eventually place
them 9 nm east of Howland.

If, instead, they were actually at 1500 feet then the dip correction would have been 38' instead of
the 31' that you have set your marine sextant to which would then result in a 7' error, placing
them 7 nm west of Howland. There is 16' of uncertainty from this possible altimetery error
causing 16' of uncertainty in the correct dip correction to use. This results in a 16 nm uncertainty
in the derived position of the aircraft. Noonan would have gotten a more accurate LOP using the
bubble sextant which doesn't require a correction for dip. This would also cause the “van Asten
sunrise” to occur up to 36 seconds early or late compared to your computations.”

(You can see the dip correction table at:

https://sites.google.com/site/fredienoonan/resources/nautical-almanac-1937/almanac-1937-277.J
PG?attredirects=0

You can also read about the dip and refraction corrections in the American Practical Navigator,
1888 and 1914 editions here:

https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888

and

https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914

These excerpts also contain the complete sections on the methods of determining longitude and
you can review them and you will find no mention of the “van Asten’s sunrise” method.)



Mr. van Asten’s response actually made me laugh out loud.  He said Noonan could just use his
bubble sextant to measure the dip of the visible horizon to place on his marine sextant and then
look in the dip table for that amount of dip and so determine the altitude of the plane.

I responded:

“You come up with an interesting use for the dip table. But if they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.”

Mr. van Asten has a bubble sextant and plays with it while standing on the ground so he doesn’t
understand the use of a bubble sextant in the air. Due to the constant accelerations a plane feels,
the bubble is in constant motion even if the air feels smooth to the occupants. In turbulence it
really moves around. So when taking an observation you are constantly turning the altitude knob
on the sextant to chase the bubble with the image of the sun. The extreme readings might actually
differ from the true reading by more than a full degree (60'). You must take many sights over a
short period and average the readings to get any kind of accuracy at all and you must accept an
uncertainty of plus and minus 7'. This would also apply to a measurement of the dip of the visible
horizon, so this uncertainty would then be transmitted to the marine sextant and would carry
through to the horizontal established by the “van Asten method..” The uncertainty introduced this
way is just about the same as that introduced by lack of a current altimeter setting.

Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.

I also pointed out to Mr. van Asten:


“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”

Mr. van Asten wrote back:

“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”

-To which I responded:

“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “

(to be continued)



gl

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Gary LaPook

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Re: Navigating the LOP with the offset method.
« Reply #161 on: June 11, 2011, 03:27:52 AM »

Mr. Lapook ,

Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.



---------------------------------

I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be  more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!

gl
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #162 on: June 11, 2011, 07:40:03 AM »

... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.  ...

Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?

Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
LTM,

           Marty
           TIGHAR #2359A
 
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Chris Owens

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Re: Navigating the LOP with the offset method.
« Reply #163 on: June 11, 2011, 08:32:58 AM »

... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.  ...

Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?

Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?

A marine sextant measures the angle between
  • A line between your eye and the observed object, and
  • A line between your eye and the observed horizon
   The higher up you are, the lower the observed horizon is, and so the angle will change based upon your altitude.

The bubble sextant measures the angle between
  • A line between your eye and the observed object, and
  • The horizontal plane, as measured by what is essentially a very precise refinement of a carpenter's level.
In this case, ascending or descending doesn't change anything, so your altitude doesn't need to be taken into consideration, except for the special case when the observed object is very close to the horizon and subject to atmospheric refraction.
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Martin X. Moleski, SJ

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Re: Navigating the LOP with the offset method.
« Reply #164 on: June 11, 2011, 09:58:26 AM »

The bubble sextant measures the angle between
  • A line between your eye and the observed object, and
  • The horizontal plane, as measured by what is essentially a very precise refinement of a carpenter's level.
In this case, ascending or descending doesn't change anything, so your altitude doesn't need to be taken into consideration, except for the special case when the observed object is very close to the horizon and subject to atmospheric refraction.

I'll take your word for this that this works.

The fact that the altitude of the observer makes no difference in the calculation of the LOP derived from an observation must be due to the inability of the instrument to detect the tiny difference in altitude compared to the vast distance from the celestial object.  It must be a difference that makes no difference.  If, instead of measuring the eye angle from the observer to a stars we were measuring the eye angle from the observers to a weather balloon, the difference in altitude between the observers would make a difference in the angles measured--wouldn't it?

To put it the other way around, looking at the situation from the standpoint of the star being observed, the two different observers are, for all practical purposes, at the same altitude (?).
LTM,

           Marty
           TIGHAR #2359A
 
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