7. Variation of atmospheric pressure with altitude

Atmospheric pressure is due to the weight of the air column rising from the Earth's surface. It therefore varies with altitude. For our purposes, this translates into a gas column correction that can be considered from a number of angles. Firstly, we can use the pressure measured at a given point, using a barometer, to determine the atmospheric pressure existing at a slightly different altitude (in a neighbouring room, for example), but with practically the same accuracy as that given by the barometer. The second case, considered in meteorology, is that of measuring atmospheric pressure in a location at altitude a, and then deducing the pressure at sea level (altitude 0). Finally, for air navigation problems, it is important to know statistically, or as a function of pressure at a given altitude, the variations in atmospheric pressure over a wide range of altitudes.

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