# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: dip angle refraction correction
From: Greg Rudzinski
Date: 2011 Dec 2, 14:57 -0800

John H.,

There might be enough information for this problem if a given dip short is compared to a measured dip from a horizon level.

Greg Rudzinski

[NavList] dip angle refraction correction
From: apacherunner---com
Date: 2 Dec 2011 17:35

I have a somewhat esoteric question, but I thought I'd pose it to the list to see if anyone knew of a program or website that could do this.

Here's the situation - some students are doing a final project where they went to the tallest building in Boston and used a water level to establish a horizontal and then sighted down to the horizon. They then had measurements of the height of the building and want to turn this into a curvature of the earth.

They'd like to improve on things and correct for refraction. I don't know of any ready made formulas for correcting for the shift in the position of the horizon due to refraction, since you'd need some model of temperatures etc.

I suggested that they could make a 'model' atmosphere that had maybe 4 layers from the surface to the top of the building and then assume either a uniform temperature or a mild uniform gradient and then just do the ray tracing. I'd imagine this is a bit of pain, but not outside of their capabilities.

On a related note, since I talked about this effect, they keep asking me about whether they need to correct their dip angle for refraction and it takes a bit of time and patience to show them the relative size of the two effects for an observer only a few feet above sea level.

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