I was reading on the plane yesterday an article on takeoff calculations; how the temperature and pressure have an effect on the density of the air. It got me thinking. When we adjust the temperature and pressure in a total station, what exactly is happening in the total station?
The speed of light in the atmosphere depends on the density of the air, which is affected by temperature, pressure, and, to a lesser extent, humidity. Think of it as the light will slow down as the air becomes more dense. A similar phenomena exists with airplane performance. When it is hot and humid, the "apparent" altitude is much greater than the listed altitude. This means the density of the air is less, and the plane's performance is less. If the air is hot and humid at a high altitude airport, it is possible that some planes cannot takeoff at full weight. If you ever listen to a ATIS report from an airport (Automated Terminal Information Service), they will often mention the density altitude if it is significantly different than the field altitude, as that is what affects performance.
I departed on a US Airways flight once from Mexico City direct to Pittsburgh. We landed in San Antonio to fuel up because we were not able to take off with a full fuel load.
And, last week I was departing from mexico City again and they stopped before takeoff to burn some fuel off because they put too much in and that put us over the maximum takeoff weight for that density altitude.
So the mechanisms in the total station increase/reduce the speed of the signal similarly to the procedure with an echosounder when adjusting the speed of sound in a bar check?
I was trying to scan my old ppm wheel in to post in reply but my scanner is on the fritz. I still cary this thing in my work case because I feel lost without it:-| in this day of the gun does everything. To make a long math explanation into english it develops a correction value for the density of the air the EDM beam travels thru.
So in that relics place I will post the topcon example of what this does.
Thank you - a good refresher on the topic, I had forgotten.
For the firearms folks on board, you also might find it interesting how temperature, pressure, humidity affect your sighting and shooting.
i have read that the temperature and pressure also affects a baseball's flight, both as a pitched ball and a batted ball.
apparently the pitches with more 'stink' on them (curves, sliders, sinkers, knuckles) are the most affected. fastballs are still fastballs
For me, the change in pressure value is small. For example, for the next seven days, the lowest predicted pressure during our working hours is 29.81 and the highest predicted is 29.94. My standard setting is 29.9.