Slant Residual Plots
As part of the daily processing we are computing slant path residuals
for selected sites is regions with a high density of sites. The slant
path residuals show azimuthal and elevation variations from the zenith
wet delay mapped to Line of site elevation of the satellite. We compute
a multipath map by stacking the residuals from many previous solutions
and subtract the multipath before generating these plots. Thus the plots
represent primarily atmospheric signal. Although they are also affected
by errors in the multipath map and measurement noise in the GPS delays.
Keeping in step with the general color bar scheme, blue represents
atmosphere drier than the mapped zenith average and red represents
wetter than the zenith pwv estimate.
We are computing a direct mapping function for each site using the AVN
weather model analysis prediction. Standard mapping functions tend to
break down for low elevation angles, but the Direct Mapping technique
works to very low angles. (Please refer to the document: "Improved
Mapping of Tropospheric Delays")
Our processing is based on station differencing methods, generating
differenced residuals. Line of sight residuals are generated by applying
statistical constraints + a linear inversion method to the double
difference residuals. (Please refer to the document:
"Obtaining singlepath phase delays from GPS double differences")
Currently only Suominet sites
and selected FSL sites are processed for slant residual plots.