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Name: Unknown
Status: N/A
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Date: 1999


Question:
In Earth Science (9th Grade), we are learning about contour maps. We were given a scale model of a volcanic mountain in New Mexico. To make a contour map, we immersed the mountain in water and recorded where it reached on the model (for each height of water). Obviously, this is not how actual contour maps are made.

How is the height above sea level measured in reality? I am interested in both historical ways this was measured and new technological ways.

Waiting anxiously for an answer,

Kalman Strauss


Replies:
Airplanes use devices called Pitot-Static tubes (pronounced PEE-TOE- Static), which measure the static and dynamic air density. The static air density is measured at a spot on the airplane where there is relatively dead air. The dynamic density is measured where the air is rapidly passing by. Actually, I think P-T S tubes measure pressure and then calculate the density. At any rate, air density decreases the higher you go up. So, once the density is measured in the air, or at the plane, it can be compared to a reference point on the goround. The height can then be calculated above the ground or above sea level.

It can also be done using satellites I believe. I'm not familiar on the exact details, but I think radar is the basic idea. A beam of radiation is sent to the Earth, and bounces back. The time it takes to bounce back and the orbit height of the satellite tells you the elevation at that point on the Earth.

I'm sure it can get more complicated than that. Hope this helped some.

wildman jackson



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