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» Online Classroom   » Emergency Navigation   » Public Discussion of Emergency Navigation   » New moon photo sights

   
Author Topic: New moon photo sights
David Burch


 - posted August 16, 2007 12:21 PM      Profile for David Burch           Edit/Delete Post 
Here is a sample of another photo sextant sight. This was made with a samsung sync phone. the sight was taken from 47° 40.5' N, 122° 24.5' W. There was no wrist watch available but the phone said 905 PM PDT at the time of the sight.... this means the actual time was 04 05 30 ± 30s on Aug 16, 2007 UTC. Without any special care, the height of the LL was found to be about 49 pixels and the diameter of the moon was about 13 pixels as shown in the picture.

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this gives Hs LL = 49x30/13 = 113.1' = 1° 53' (from the almanac, the SD of the moon at sight time was 15.0').

Doing a sight reduction of this sight from the HE of 15 feet, gives the remarkable result of a = 0.1' A 264.2, with about ± 5' if you take 00s and 060s, since we do not know where the time was within the 0905 display, and it was not estimated.

In short, even from this very crude cell phone picture we get an LOP well within 10 nmi of our true position. Had we included uncertainty from the pixel measurements we would likely add 5 nmi to what we had to end up with ± 10 nmi. this was a fortuitous result, almost certainly.

.... However, we might soon learn more on this regard. At the same time this cell phone photo was taken professional photographer Jack Vieg was on the scene with a good camera taking the same pictures and he said he will share one with us for a better analysis... we will post this when we receive it. His camera has an accurate time stamp to the second on it. Stand by...

[There are several other samples of photo sextant sights in this discussion forum.]

From: Starpath, Seattle, WA
David Burch


 - posted August 17, 2007 01:14 PM      Profile for David Burch           Edit/Delete Post 
Here is the analysis of the good photo from Jack Vieg (this is a 6-second exposure, and just a snippet of a beautiful phtograph showing the Olympic Mountains viewed to the west across Puget Sound from Seattle). The cel nav results speak for themselves.

So it seems the answer is if you get a good photo and the body is low — let's say within 5° of the horizon — then chances are you will get a good LOP.

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From: Starpath, Seattle, WA


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