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Change the answer mode for this tool by selecting elevation (HP), station pressure (QFE), or sea level pressure (QNH) as the parameter to calculate instead
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Related Tools
- ICAO Standard Atmosphere Altitude and Pressure Calculator
- US Standard Atmosphere Altitude and Pressure Calculator
- Pressure unit conversion
- Height unit conversion
User Guide
This tool which is based on the icao standard atmosphere model will calculate the station elevation relative to mean sea level, station pressure or the sea level pressure used for QFE or QNH setting altimeters.
The method and formulas used are based on the ICAO Standard Atmosphere 1993 model and is implemented here over the range of 5000 metres below mean sea level up to a height of 11,000 metres above mean sea level.
A station is the location where the atmospheric pressure is measured, but it comes from the term ‘Weather Station’, which is where meteorological measurement instrumentation is housed to monitor and report current conditions for aviation purposes.
The atmospheric model assumes the air is a dry ideal gas, with an atmospheric pressure of 101325 Pa and a temperature of 288.15 K at mean sea level. In order to improve accuracy when closer to the ground, altimeters are adjustable to the local atmospheric pressure, or the equivalent pressure at sea level.
In order to determine the altimeter setting, the standard atmosphere pressure (P0) of 101325 Pa at sea level usually used for the icao standard atmosphere calculation, is replaced in this case by the station pressure reduced to the equivalent pressure at sea level.
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Formulas
The formulas used by this elevation, station pressure and sea level pressure calculator to determine each individual parameter are:
HP = ((((P / P0) –βb · R / g – 1) / βb) * Tb) + Hb
P = P0 · (1 + (βb · (HP – Hb) / Tb))-g / (βb · R)
P0 = P / (1 + (βb · (HP – Hb) / Tb))-g / (βb · R)
Symbols
- HP = Station elevation relative to mean sea level
- P = Station atmospheric pressure at height HP = QFE
- P0 = Sea level pressure by reducing station atmospheric pressure to equivalent at mean sea level = QNH
- Hb = Altitude of interfaces between atmosphere transitional layers from b = 0 to 6, but b = 0 up to 11000m, therefore only H0 = 0 m is needed for this calculation, corresponding to mean sea level
- Tb = Reference temperature at interface between atmosphere transitional layers from b = 0 to 6, but b = 0 up to 11000m, therefore only T0 = 288.15 K is needed for this calculation
- βb = Standard temperature lapse rate to change reference temperature (Tb) between atmosphere transitional layers from b = 0 to 6, but b = 0 up to 11000m, therefore only β0 = -0.0065 K/m is needed for this calculation
- g = Standard acceleration due to gravity = 9.90665 m/s2
- R = Specific gas constant = 287.05287 J/K·kg, constant value defined by ICAO Standard Atmosphere 1993, and derived from ideal gas law equation; P = ρ·R*·T/M0, where P = 101,325 Pa, ρ = 1.225 kg/m3, R* = 8,314.32 J/K·kmol, T = 288.15 K, M0 = 28.964420 kg/kmol), P/(ρ·T) = R* / M0 = R
Station Elevation (HP)
This is the geopotential height of the station above or below mean sea level.
Station Pressure (QFE)
This is the absolute pressure of air measured at the station. It can be used to set an altimeter so that the altitude reads zero when on the ground at the stations location, and shows the altitude above ground during flight within the vicinity of the station.
QFE is a radio operator query code for ‘Field Elevation’ pressure.
Sea Level Pressure (QNH)
This is the absolute pressure of air at sea level, which is derived from reducing the station pressure to the equivalent pressure at sea level using the icao standard atmosphere model formula.
This is also called the ‘Altimeter Setting’ because this is often the pressure reading that an altimeter is set to when landing or taking off from a runway located at the same place as the station, so that the altitude reading corresponds to the station elevation above sea level when on the ground.
The altimeter will show altitude relative to sea level during flight within the vicinity of the station.
QNH is a radio operator query code for ‘Nautical Height’ pressure.
