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Altitude - Density Altitude
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Konstantinos


Apr 13, 2013, 8:39 AM
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Registered: Jan 7, 2013
Posts: 3

Altitude - Density Altitude
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Hello all. I am trying to understand the difference between altitude and density altitude. The only difference is that density altitude depends on my position's current air temperature and altitude does not?

If my position's current air temperature is increased, then the density altitude is also increased, but the altitude remains fixed. If my position's current air temperature is decreased, then the density altitude is also decreased, but the altitude remains fixed. I am right?

According barometric formula of wikipedia (http://en.wikipedia.org/wiki/Atmospheric_pressure#Altitude_atmospheric_pressure_variation), the altitude depends on my position's current atmoshperic pressure, current seal level atmospheric pressure and current sea level temperature.

According wikipedia (http://en.wikipedia.org/wiki/Density_altitude#Calculation), the density altitude depends on my position's current atmoshperic pressure, current seal level atmospheric pressure, current sea level temperature AND MY POSITION'S CURRENT AIR TEMPERATURE.

Have I understood well?

Also, I have created two scripts on matlab which calculate altitude and density altitude. Here are the codes and two simple running of them. Tell me your opinion:

Altitude:
In reply to:
CODE --> Matlab

fprintf ( 1,'Hello, I will calculate your altitude.\n' );
cslt=input('Please, give me the sea level temperature (degrees C):');
fprintf ( 1, 'Thank you.\n' );
cslap=input('Please, give me the sea level atmospheric pressure (mb):');
fprintf ( 1, 'Thank you.\n' );
cpsap=input('Please, give me the atmospheric pressure of your position (mb):');
fprintf ( 1, 'Thank you.\n' );
alt=8.31447*(cslt+273.15)*log(cslap/cpsap)/(9.80665*0.0289644);
altf= alt*3.2808399;
fprintf('Your altitude is %d m or %d feet\n', alt, altf);

In reply to:
>> altitude
Hello, I will calculate your altitude.
Please, give me the sea level temperature (degrees C):17
Thank you.
Please, give me the sea level atmospheric pressure (mb):1017.9
Thank you.
Please, give me the atmospheric pressure of your position (mb):999.9
Thank you.
Your altitude is 1.515332e+002 m or 4.971562e+002 feet
>>

Density Altitude:

In reply to:
CODE --> Matlab

fprintf ( 1,'Hello, I will calculate your density altitude.\n' );
ts=input('Please, give me the sea level temperature (degrees C):');
fprintf ( 1, 'Thank you.\n' );
ps=input('Please, give me the sea level atmospheric pressure (mb):');
fprintf ( 1, 'Thank you.\n' );
tm=input('Please, give me the temperature of your position (degrees C):');
fprintf ( 1, 'Thank you.\n' )
pm=input('Please, give me the atmospheric pressure of your position (mb):');
fprintf ( 1, 'Thank you.\n' );
da=145442.156*(1-((pm/ps)/((tm+273.15)/(ts+273.15)))^0.234969);
dam= da/3.2808399;
fprintf('Your density altitude is %d m or %d feet\n', dam, da);

In reply to:
>> Density_Altitude
Hello, I will calculate your density altitude.
Please, give me the sea level temperature (degrees C):17
Thank you.
Please, give me the sea level atmospheric pressure (mb):1017.9
Thank you.
Please, give me the temperature of your position (degrees C):23.5
Thank you.
Please, give me the atmospheric pressure of your position (mb):999.9
Thank you.
Your density altitude is 4.146678e+002 m or 1.360459e+003 feet
>>

Soon, I will buy a weather multimeter. Its instructions say: The DENSITY ALTITUDE screen is calculated from the absolute values of station pressure, relative humidity and temperature. And my mind is confused. Why it depends on relative humidity? What formula it uses?

Thank you in advance.


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