Ray-traced slant factors for mitigating the tropospheric delay at the observation level |
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Authors: | Email author" target="_blank">Landon?UrquhartEmail author Felipe?G?Nievinski Marcelo?C?Santos |
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Institution: | (1) Geodetic Survey Division, Natural Resources Canada (NRCan), 615 Booth Street, Ottawa, ON, Canada, K1A 0E9 |
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Abstract: | Three-dimensional ray tracing through a numerical weather model has been applied to a global precise point positioning (PPP)
campaign for modeling both the elevation angle- and azimuth-dependence of the tropospheric delay. Rather than applying the
ray-traced slant delays directly, the delay has been parameterized in terms of slant factors, which are applied in a similar
manner to traditional mapping functions, but which can account for the azimuthal asymmetry of the delay. Five strategies are
considered: (1) Vienna Mapping Functions 1 (VMF1) and estimation of a residual zenith delay parameter; (2) VMF1, estimation
of a residual zenith delay and estimation of two tropospheric gradient parameters; (3) three-dimensional ray-traced slant
factors and estimation of a residual zenith delay; (4) using only ray-traced slant factors and no estimation of any tropospheric
parameters and; (5) using both ray-traced slant factors and estimating a residual zenith delay and two tropospheric gradient
parameters. The use of the ray-traced slant factors (solution 3) showed a 3.8% improvement in the repeatability of the up
component when compared to the assumption of a symmetric atmosphere (solution 1), while the estimation of two tropospheric
gradient parameters gave the best results showing an 7.6% improvement over solution 1 in the up component. Solution 4 performed
well in the horizontal domain, allowing for sub-centimeter repeatability but the up component was degraded due to deficiencies
in the modeling of the zenith delay, particularly for stations located at equatorial latitudes. The magnitude of the differences
in the mean coordinates between solution 2 and solution 3, and the strong correlation with the differences between the north
component and the ray-traced gradients (coefficient of correlation of 0.83), as well as the impact of observation geometry
on the gradient solution indicate that the use of the ray-traced slant factors could have an implication on the realization
of reference frames. The estimated tropospheric products from the PPP solutions were compared to those derived from ray tracing.
For the zenith delay, a root mean square (RMS) of 5.4 mm was found, while for the gradient terms, a correlation coefficient
of 0.46 for the N–S and 0.42 for the E–W was found for the north–south and east–west components, suggesting that there are
still important differences in the gradient parameters which could be due to either errors in the NWM or to non-tropospheric
error sources leaking into the PPP-estimated gradients. |
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