Zenith delay The zenith delay is determined by the integration of refractivity vertically The atmospheric is very close to hydrostatic equilibrium meaning that surface pressure is given by the vertical integration of density. Since the first term in refractivity depends only on density, its vertical integration will depend only on surface pressure. This integral is called the "zenith hydrostatic delay(zHD) Often referred to as "dry delay "but this is incorrect because has water vapor contribution 04/09/03 12540Lec15 Zenith hydrostatic delay The Zenith hydrostatic delay is given by ZHD=10k.8m Ps =0.00228 m/mbar Where gm is mean value of gravity in column of air (Davis et al. 1991) gm=98062(1000265c0s(2中)3.1×107(0.92+7300)ms2 Ps is total surface pressure(again water vapor contribution included Since Ps is 1013 mbar at mean sea level; typical ZHD =2. 3 meters 04903 12540Lec15Zenith delay • The zenith delay is determined by the integration of refractivity vertically. • The atmospheric is very close to hydrostatic equilibrium meaning that surface pressure is given by the vertical integration of density. Since the first term in refractivity depends only on density, its vertical integration will depend only on surface pressure. This integral is called the “zenith hydrostatic delay (ZHD)”. (Often referred to as “dry delay” but this is incorrect because has water vapor contribution). 04/09/03 12.540 Lec 15 9 Zenith hydrostatic delay • The Zenith hydrostatic delay is given by: ZHD =10-6 k1 M R d gm -1 P ª 0.00228 m/mbar s • Where gm is mean value of gravity in column of air (Davis et al. 1991) gm=9.8062(1-0.00265cos(2f)-3.1x10-7(0.9Z+7300)) ms-2 • Ps is total surface pressure (again water vapor contribution included) • Since Ps is 1013 mbar at mean sea level; typical ZHD =2.3 meters 04/09/03 12.540 Lec 15 10 5