Mapping functions Basic problem with forming a mapping function is determining the coefficient a, b,c etc for specific weather conditions There are different parameterization Niell mapping function uses a, b, c that are latitude height and time of year dependent MTT(MIT Temperature)model uses temperature as proxy for atmospheric conditions Recent Niell work uses height of 500mbar surface (needs to be determined from assimilation models 0409/03 12540Lec15 Coefficients in mapping function The typical values for the coefficients are Hydrostatic a=1232e-3,b=316e-3;c=712e-3 Wet delay a=0.583e-3;b=1.402e3;c=45.85e3 Since coefficients are smaller for wet delay, this mapping function increases more rapidly at low elevation angles At0 degrees, hydrostatic mapping function is 36. Total delay -82 meter 12540Lec1504/09/03 12.540 Lec 15 17 Mapping functions – height and time of year dependent – MTT (MIT Temperature) model uses temperature as proxy for atmospheric conditions. – 04/09/03 12.540 Lec 15 18 Coefficients in mapping function – a=1.232e-3, b=3.16e-3; c=71.2e-3 – a =0.583e-3; b=1.402e-3; c=45.85e-3 ~36. • Basic problem with forming a mapping function is determining the coefficient a,b, c etc for specific weather conditions. • There are different parameterizations: Niell mapping function uses a, b,c that are latitude, Recent Niell work uses height of 500mbar surface (needs to be determined from assimilation models). • The typical values for the coefficients are • Hydrostatic: • Wet delay • Since coefficients are smaller for wet delay, this mapping function increases more rapidly at low elevation angles. • At 0 degrees, hydrostatic mapping function is Total delay ~82 meter 9