Refractivity of air Air is made up of specific combination of gases, the most important ones being oxygen and nitrogen Each gas has its own refractive index that depends on re and temp For the main air constituents, the mixing ratio of the constituents is constant and so the refractivity of a packet of air at a specific pressure and temperature The one exception to this is water vapor which has a very variable mixing ratio Water vapor refractivity also depends on density/temperature due to dipole component 0409/03 12540Lec15 Refractivity of air The refractivity of moist air is given by N=k tk k1=77.60±0.05K/mbar k,=70.4±22 k2=(3.730±0.012)×105K2/mba For most constituents, refractivity depends on density (ie, number of air molecules ). Water vapor dipole terms depends on temperature as well as density 12540Lec15Refractivity of air • Air is made up of specific combination of gases, the most important ones being oxygen and nitrogen. • Each gas has its own refractive index that depends on pressure and temperature. • For the main air constituents, the mixing ratio of the constituents is constant and so the refractivity of a packet of air at a specific pressure and temperature can be defined. • The one exception to this is water vapor which has a very variable mixing ratio. • Water vapor refractivity also depends on density/temperature due to dipole component. 04/09/03 12.540 Lec 15 5 04/09/03 12.540 Lec 15 6 Refractivity of air • The refractivity of moist air is given by: • For most constituents, refractivity depends on density (ie., number of air molecules). Water vapor dipole terms depends on temperature as well as density N = k1 Pd T Zd -1 Density of dry air + k2 Pw T Zd -1 Density of water vapor + k3 Pw T2 Zd -1 Dipole compoent of water vapor r/T k1 = 77.60 ± 0.05 k2 = 70.4 ± 2.2 k3 = (3.730 ± 0.012) ¥105 K2 123 123 123 K/mbar K/mbar /mbar 3