Density Altitude, Temperature Altitude, Geometric Altitude, Geopotential Altitude, Absolute Altitude, Value of Gravitational acceleration g
and Standard Atmosphere Table...
The pressure, density and temperature can be defined as the functions of the altitude. This is known as the standard atmosphere. The standard atmosphere is useful as it gives us a way to find out the pressure, density and temperature values at a certain altitude above the surface of the earth or above sea-level.
Secondly, the standard atmosphere is useful as it gives us a way to determine altitude if we know the local density, pressure and temperature values. We can use the standard atmospheric data and by comparison we can calculate the altitude which can be either pressure, density or temperature altitude.
One standard atmospheric method is to defined the temperature as a function of the altitude. The temperature values are computed in Kelvin. The temperature of the atmosphere and this standard atmosphere method is based on experiment using hot air balloons to measure pressure, density and temperature above the surface of the earth.
There are two layers which are important in the standard atmosphere plot if the temperature versus altitude is being used. One is the gradient layer and the other is the isothermal layer. In the gradient layer the temperature of the atmosphere either decrease or increase according to a fixed slope value. If the slope is negative temperature decreases in that region. If the slope is positive the temperature rises in that region. Secondly, in the isothermal region as the name suggests the temperature of the atmosphere remains constant in that region. Here in this region the temperature of the atmosphere neither increase nor decrease.
How to Calculate Standard Atmosphere Experimentally:
The standard atmosphere can be calculated experimentally and thus generating the pressure, density and temperature plots versus altitude by using hot air balloons. Pressure, density and temperature sensors are mounted in large helium filled balloons and released. The balloons rise high in the air and record the surrounding pressure, density and temperature values at different increments of height. The data is then transmitted to a ground station where the data is collected and thus analyzed.
Altitude of a flying vehicle is defined as the distance above the ground to the point where the aircraft is flying. In simple words, altitude is the distance above the ground.
Types of Altitudes:
- Geometric Altitude
- Geopotential Altitude
- Absolute Altitude
- Pressure Altitude
- Density Altitude
- Temperature Altitude
The geometric altitude of a flying vehicle is the height or the distance above the surface of the earth to the point where the vehicle is flying.
Absolute Altitude of a flying vehicle or a space vehicle is the height or the distance from the center of the earth to where the vehicle is flying. Mathematically, Absolute Altitude = Geometric Altitude + Radius of the Earth.
Pressure altitude is the altitude above the ground to the point where the atmospheric pressure has some fixed value defined by that altitude.
Density altitude is the altitude above the ground to the point where the atmospheric density has some fixed value defined by that altitude.
Temperature altitude is the altitude above the ground to the point where the atmospheric temperature has some fixed value defined by that altitude.
Free Calculation Programs on Standard Atmosphere
- Calculate Standard Atmosphere Table
- Calculate Geopotential Altitude
- Calculate Pressure Altitude
- Calculate Density Altitude
- Calculate Temperature Altitude
- Calculate Value of g at Altitude
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