Indirect levelling. Barometric Levelling This method depends on the principle that atmospheric pressure depends upon the elevation of place. Barometer is used to measure the atmospheric pressure and hence elevation is computed. However it is not accurate method since the atmospheric pressure depends upon season and temperature also. It may be used in exploratory surveys. Hypsometric Levelling This is based on the principle that boiling point of water decreases with the elevation of the place.
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If we put these words in a scientific form, it turns out that the pressure density of the gas depends on its altitude in a gravitational field. On this phenomenon method of barometric leveling is built. Barometric leveling - method of determining the height difference between two points by atmospheric pressure measured at these points. Since the atmospheric pressure, in addition to the altitude above the sea level is also dependent on the weather, for example, on the water vapor content of air, if it is possible to the method is applied to make measurements at points with the smallest interval between the measurements, and the points themselves should not be located too far from each other.
The difference in altitude is calculated as follows. There is a rather complicated formula of Laplace: It is, in addition to temperature and pressure also takes into account the absolute humidity and latitude of the measuring point, that is, in practice it seems to be not in use. And use a simple Babinet formula , where - Gas expansion factor equal to Indeed, in an era without computers and calculators, even this formula was Barometric stage - the height at which we must ascend so the pressure drop by 1 mm Hg That is, we took and simplified Babinet formula to expression and calculate h for different values of temperature and pressure.
It is clear that the formula gives the result with a margin error, but at the same time it is approved that the error does not exceed 0. The method of barometric leveling allows to determine the height of a point above sea level, without resorting to the geodetic leveling.
In practice, the height of the point above sea level is determined by using the closest ranging mark, height above sea level of which is known. For example, the ranging mark meters. Barometer shows that ranging mark at mmHg, being transferred to the defined point, barometer shows mmHg. The average temperature is 15 degrees Celsius. Using the Babinet formula obtain Taking the average pressure of mmHg and using barometric table we get The calculator below illustrates everything said above.
Barometric leveling Pressure at the first point mmHg Pressure at the second point mmHg Average air temperature degrees Celsius Calculation precision Digits after the decimal point: 2 Calculate.
On this phenomenon method of barometric leveling is built. Definition of barometric leveling — glossary Levelliny method is thoroughly explained in next article. It is, in addition to temperature and pressure also takes into account the absolute humidity and latitude of the measuring point, that is, in practice it seems to be not in use. Recent Comments France Haule.
Methods of Levelling