Tropospheric Effects(cont Tropospheric refraction accommodates only the systematic part of the effect, and some small un-modeled effects remain Moreover, errors are introduced into the tropospheric correction via inappropriate meteorological data(if applied )as well as via errors in the zenith mapping function These errors are propagated into station coordinates in the boint positioning and into base components in the relative positioning For example, the relative tropospheric refraction errors affects mainly a baseline's vertical component(error in the relative tropospheric delay at the level of 10 cm implies errors of a few millimeters in the horizontal components, and more than 20 cm in the vertical direction) Principles of the Global Positioning System 20054-1(1 Tropospheric Effects(cont If the zenith delay error is I cm, the effect on the horizontal coordinates will be less than l mm but the ffect on the vertical component will be significant about 2.2 cm The effect of the tropospheric refraction error increases with the latitude of the observing station and reaches its maximum for the polar sites. It is a natural consequence of a diluted observability at high latitudes where satellites are visible only at low elevation angles s The scale of a baseline derived from observations tha are not corrected for the effect of the tropospheric delay is distorted; the baseline is measured too long. NEV Principles of the Global Positioning System 20054110 Principles of the Global Positioning System 2005-4-1 19 Tropospheric Effects (cont.) ¾ Tropospheric refraction accommodates only the systematic part of the effect, and some small un-modeled effects remain ¾ Moreover, errors are introduced into the tropospheric correction via inappropriate meteorological data (if applied) as well as via errors in the zenith mapping function ¾ These errors are propagated into station coordinates in the point positioning and into base components in the relative positioning ¾ For example, the relative tropospheric refraction errors affects mainly a baseline’s vertical component (error in the relative tropospheric delay at the level of 10 cm implies errors of a few millimeters in the horizontal components, and more than 20 cm in the vertical direction) Principles of the Global Positioning System 2005-4-1 20 Tropospheric Effects (cont.) ¾ If the zenith delay error is 1 cm, the effect on the horizontal coordinates will be less than 1 mm but the effect on the vertical component will be significant, about 2.2 cm ¾ The effect of the tropospheric refraction error increases with the latitude of the observing station and reaches its maximum for the polar sites. It is a natural consequence of a diluted observability at high latitudes where satellites are visible only at low elevation angles ¾ The scale of a baseline derived from observations that are not corrected for the effect of the tropospheric delay is distorted; the baseline is measured too long