Monthly Archives: October 2015

Index/Instrument Error Correction in Sextant Measurements

Sextants make measurements that are subject to systematic errors – all instruments are subject to systematic errors. Alas, much of my career has been spent on calibrating out systematic instrument errors. Even with all my efforts, residual systematic errors remain. Continue reading

 
Posted in Naval History, Navigation | 2 Comments

Refraction Error Correction in Sextant Measurements

Refraction is probably the most difficult to understand of all the altitude observation corrections. It is also the most difficult to estimate accurately because it depends so strongly on atmospheric conditions, particularly the rate of temperature variation with altitude (see lapse rate). I will derive in this post a commonly used expression for the refraction correction required for a celestial object with an altitude greater than or equal to 15°. The accuracy of this expression degrades significantly for objects below 15°. Continue reading

 
Posted in Astronomy, Naval History, Navigation | 3 Comments

Correcting for Sextant Parallax Error

Navigators use the altitudes of solar system objects to assist them with determining their positions. The most commonly used solar system objects are the Sun, Moon, Venus, and Mars. There is a small error caused by the fact that navigators are making their sextant measurements from the surface of the ocean and not from the center of the Earth, which is the reference point used by nautical almanacs. Parallax has no practical significance when measuring the positions of stars because they are so far away relative to the radius of the Earth. Continue reading

 
Posted in Astronomy, Naval History, Navigation | 1 Comment

Correcting Sextant Measurements For Dip

I love to read stories of the sea and about the voyages made during the age of sail. I personally have never thought that I would have an opportunity for ocean sailing, but I recently began working with an engineer who is an avid sailor and teacher of sailing. He has sailed all over the world and recently trained another engineer in my group to sail. This newly trained sailor just returned from a trip to Bora Bora, which he found to be enjoyable and the sailing uneventful. Continue reading

 
Posted in Naval History, Navigation | 7 Comments

My Phone Stops a Road Rage Incident

Quote of the Day Remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious. And however difficult life may … Continue reading

 
Posted in Personal | Leave a comment

Rogue Software Engineers and Responsibility, Accountability, and Authority

I have always liked Volkswagen (VW) cars – I actually rebuilt a Beetle engine during a shop class in high-school (Figure 1). My respect for VW took a serious downturn this morning when read the following headline,"Top U.S. VW Exec Blames 'A Couple of Software Engineers' for Scandal". Continue reading

 
Posted in Management | 2 Comments

Samsung S5 Field of View

I use a Samsung S5 phone for my daily smart phone work. Recently, I have even started to use its camera/video system for some rough measurement work (examples here and here). This work has made me a bit curious about the how the camera subsystem was designed. In this post, I will document a very rough experiment that I performed over lunch today in which I measured the S5 camera's Field of View (FOV). I will also compute the field of view using some information that Samsung provides. The agreement between the results seem reasonable considering my crude approach. Continue reading

 
Posted in optics | 5 Comments