1. Epochs 20 0 mm -20 1 2 3 4 5 Hours Elevation angle and phase residuals for single satellite

2. Simple geometry for incidence of a direct and reflected signal Multipath contributions to observed phase for an antenna at heights (a) 0.15 m, (b) 0.6 m, and (c ) 1 m. [From Elosegui et al, 1995]

4. Antenna Phase Patterns

5. Top: PBO station near Lind, Washington. Bottom: BARD station CMBB at Columbia College, California

6. Left: Phase residuals versus elevation for Westford pillar, without (top) and with (bottom) microwave absorber. Right: Change in height estimate as a function of minimum elevation angle of observations; solid line is with the unmodified pillar, dashed with microwave absorber added [From Elosequi et al.,1995]

7. Correlation between estimates of height and zenith delay as function of minimum elevation angle observed (VLBI, from Davis [1986])

8. Uncertainty in estimated height as function of minimum elevation angle observed (VLBI, from Davis [1986]; dotted line with no zenith delay estimated)

9. GPS adjustments to atmospheric zenith delay for 29 June, 2003; southern Vancouver Island (ALBH) and northern coastal California (ALEN). Estimates at 2-hr intervals.