Density Altitude

[tommydriver]

Can anyone tell me what (if any) Density Altitude effects a person’s sight. Would a high Density Altitude change how a person ‘sees’ their height above the ground or distances.

Thanks

 

[bigD]

It's different, but not enough for you to notice. Astronomers have to calibrate their CCD's depending on altitude, but it's on the order of a one pixel shift at a 14,000 foot difference in altitude.

By my quick math, the index of refraction of air at a 10,000 feet DA is 99.989% that of air at sea level.

 

[310]

On a different aspect of density altitude, is water vapor, measured as dewpoint taken into consideration when calculating density altitude? It's a big factor that needs attention.

If a value of 1.0 is assigned to the density of dry air, water vapor has a value of .62

 

[sbav8r]

High density altitude equals thinner air than at standard temperature; therefore, the human body is receiving less O2 per volume. Symptoms of hypoxia will be experienced and eye sight degradation is usually one of the first symptom. This is all dependent on altitude, acclimation, and time of exposure.

 

[bigD]

High density altitude equals thinner air than at standard temperature; therefore, the human body is receiving less O2 per volume. Symptoms of hypoxia will be experienced and eye sight degradation is usually one of the first symptom. This is all dependent on altitude, acclimation, and time of exposure.

Heh...that's funny, it didn't even dawn on me that the original poster may have been talking about hypoxia effects.

My astronomy/physics nerdiness took over too soon, perhaps.

 

[tommydriver]

Thanks for the replies.

I’m more interested in relatively lower DA’s. Lets say your landing at 1000’ ASL but he DA is 4,000’. Do you think that would limit a pilot’s decision-making process in regards to the visual picture, etc.?

 

[sbav8r]

Everyone has different affects and tolerances. I can’t say if a DA of 4,000 would degrade your decision making skills, but it could mess with your eyes. You would be surprised by how much night vision you loose at altitudes as low as 4,000, especially if you’re acclimated to sea level like me. The anatomy of the eye consists of rods and cones; rods are for night vision and cones are for day vision. You can remember this for your commercial knowledge by the saying; we look at cones all day and play with our rods at night. Usually, the rods become degraded before the cones. The fact that you’re aware of it is the most important thing. The best thing to do is to take a ride in an altitude chamber. It’s a great learning experience and at the end you’ll receive a high altitude endorsement. The FAA used to have a program for civilian pilots to take a ride in military chambers for a very reasonable cost; however, that may have changed. If I can find any info about it, I will post it for you. There are many other things that could be affecting your eyes other than altitude, for instance, fatigue, stress, or simply runway illusions. It could be that the airport you’re flying into is on a slope, which is making you think you are too high or low.

 

[dmspilot00]

I think he is asking if density altitude causes optical illusions

 

[sbav8r]

It's different, but not enough for you to notice. Astronomers have to calibrate their CCD's depending on altitude, but it's on the order of a one pixel shift at a 14,000 foot difference in altitude.

I don't know about the rest of us, but that went right over my head.

I would love to do a night flight with you sometime, I've always had an interest in Astronomy. I used to have an instructor with a Geology back ground and Cross Country flights with him were always a lot of fun. It was interesting to learn about how the rock formations and canyons in AZ were formed and developed over millions of years. It’s always cool to get to learn something new on down time.