Mapping functions The basic form of the continued fraction fit raytracing through radiosonde temperature pressure and humidity profiles to a few millimeters at 3deg elevation angle Basic problem is parameterizing a, b, c in terms of observable meteorological parameters Comparison on mapping functions http://gauss.gge.unb.ca/papers.pdf/igs97tropo.pdf 04/09/03 12540Lec15 Gradients In recent years; more emphasis put on deviation of tmospheric delays from azimuthal symmetry. S Chen, G. and T A Herring, Effects of atmospheric azimuthal asymmetry of the analysis of space geodetic data, J Geophys These effects are much smaller(usually <30mm)but do effect modern gPSmlbl measurements There is a mean ns gradient that is latitude dependent and probably due to equator to pole temperature grader Parameterized as cos(azimuth) and sin(azimuth)terms with a" tilted"atmosphere model (1/(sin(E)+0.032) 12540Lec15Mapping functions • The basic form of the continued fraction fit raytracing through radiosonde temperature, pressure and humidity profiles to a few millimeters at 3deg elevation angle. • Basic problem is parameterizing a,b,c in terms of observable meteorological parameters. • Comparison on mapping functions: http://gauss.gge.unb.ca/papers.pdf/igs97tropo.pdf 04/09/03 12.540 Lec 15 19 Gradients • In recent years; more emphasis put on deviation of atmospheric delays from azimuthal symmetry. See: Chen, G. and T. A. Herring, Effects of atmospheric azimuthal asymmetry of the analysis of space geodetic data, J. Geophys. Res., 102, 20,489–20,502, 1997. • These effects are much smaller (usually <30mm) but do effect modern GPS/VLBI measurements. • There is a mean NS gradient that is latitude dependent and probably due to equator to pole temperature gradient. • Parameterized as cos(azimuth) and sin(azimuth) terms with a “tilted” atmosphere model (1/(sin(e)+0.032) 04/09/03 12.540 Lec 15 20 10