(i.e. the nearby building southwest of the GNSS antenna) which appears to degrade
the quality of observations. The C/N0 values obtained at P4 change slowly with
elevation only. The values at site P1 (especially the C/N0 value for PRN30) depart
significantly from those at P4 and vary independently of the change in elevation.
Note that the colors of the C/N0 plots for the same PRN numbers are not identical in
Figures 6a and 6b. On the other hand, both stations are equipped equally and
situated one hundred meter apart only, i.e. the satellite elevations are equal at P1 and
P4 therefore the C/N0 values should be equal. At the site P1, the relatively low values
indicate the effect of signal distortion, see Figsures 6 and 8. Especially, the standard
deviation value of the height difference between P1 and P4 is significantly greater
than the others. The concrete building for P1 caused a significant bias in the phase
measurements. Figure 7 shows the positions of GNSS satellites as observed by the
antenna P1. For instance, the antenna P1 was able to track the satellite signals of
PRN 25 during 13:20-13:50 hours although propagation along the line-of-sight was
not possible. The same assessment is also valid for PRN 15. These are typical cases
of signal diffraction where a satellite signal is received, although the direct line-ofsight
is obstructed. The C/N0 values of PRN 25 indicate this diffraction effect for P1,
see Figure 6. During 13:20-13:50 hours the template suggests a C/N0 value for PRN
25 around 50 dB-Hz for P4 (see Figure 6b), however the actual C/N0 measurement
for P1 is about 10 dB-Hz less. Beside the C/N0 values, also the double-difference
residuals (DD) display the diffraction effect (see Figure 8b).
Figure 6 - L1 C/N0 of PRN 25 and PRN 30, measured simultaneously at P1 and P4
sites, at equal antenna/receiver combination. C/N0 of observations at site P1 indicate
signal distortion.