PW and zwd Relationship ZWD=10(2+k,/Tm)PW P/Tdz T ∫P./ridz The factor for conversion is -6.7 mm delay/mm PW This relationship is the basis of ground based GPS meteorology where gPs data are used to determine water vapor content of atmosphere ZWD is usually between 0-30cn 0409/03 12540Lec15 Mapping functions Zenith delays discussed so far; how to relate to measurements not at zenith Problem has been studied since 1970s In simplest form, for a plain atmosphere, elevation angle dependence would behave as 1/sin(elev).(At the horizon, elev=0 and this form goes to infinity For a spherically symmetric atmosphere, the 1/sin(elev) term is"tempered" by curvature effects Most complete form is"continued fraction representation"(Davis et aL., 1991) 04903 12540Lec1504/09/03 12.540 Lec 15 13 PW and ZWD • Relationship: • The factor for conversion is ~6.7 mm delay/mm PW • This relationship is the basis of ground based GPS meteorology where GPS data are used to determine water vapor content of atmosphere. • ZWD is usually between 0-30cm. ZWD =10-6 R Mw (k' 2 +k3 /Tm )PW Tm = Pw Ú /Tdz Pw /T2 Ú dz Mapping functions • Zenith delays discussed so far; how to relate to measurements not at zenith • Problem has been studied since 1970’s. • In simplest form, for a plain atmosphere, elevation angle dependence would behave as 1/sin(elev). (At the horizon, elev=0 and this form goes to infinity. • For a spherically symmetric atmosphere, the 1/sin(elev) term is “tempered” by curvature effects. • Most complete form is “continued fraction representation” (Davis et al., 1991). 04/09/03 12.540 Lec 15 14 7