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» Online Classroom   »   » Public Discussion of Inland and Coastal Navigation   » Question 6-7 and 6-11, among others

   
Author Topic: Question 6-7 and 6-11, among others
Michael Mitgang


 - posted February 05, 2005 10:27 PM      Profile for Michael Mitgang           Edit/Delete Post 
When do you use the formula 1.15 (or 1.17) times (the square root of hight of eye) + (the square root of hight of object)? The answers have sometimes used 1.15, 1.17 or just nothing (ie. 1.0). What is the correct formula to use and if it is different in different situations, when do you use 1.15, 1.17 or 1.00?

Thanks

From: Menlo Park, CA
David Burch


 - posted February 05, 2005 10:47 PM      Profile for David Burch           Edit/Delete Post 
Do a search of this forum under "geographic range" to find the topic discussed. The latest best average value is 1.15 for visible light and 1.22 for radar (microwaves). The visible light constant has bounced around some as scientists learn more about refraction in the first meter of air above the water, which is where the light is bent.

The amount of water vapor in that layer changes with sea-air temp difference, the wind, and sea state, and this affects the refraction, and hence that constant.

Note also that these formulas presume flat seas. With much sea state your visible range is much reduced, for much of the time.

By the way, the "use of nothing" meaning constant = 1.0 is used in some of our discussions as a simplification... ie geo range or distance to the horizon in nautical miles is about square root of eye height in feet.

From: Starpath, Seattle, WA


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