02 / WHY IT WORKS

Atmosphere is not empty space

The ionosphere is dispersive: its leading effect depends on frequency. Code delay and carrier-phase advance have opposite leading signs. The neutral atmosphere contributes tropospheric delay to both. Low-elevation paths often traverse more atmosphere, but rejecting them also changes geometry.

What a reflection changes

A reflected path is longer than the direct route between the same endpoints. A receiver can track a mixture of the two. The resulting bias depends on amplitudes, delay, phase and the tracking algorithm; it is not simply the full extra path length. Blocking the direct path can create a different non-line-of-sight problem.

03 / UNDER THE SURFACE

From intuition to a model

Length becomes delay

The experiment computes a specular reflection from a vertical wall by mirroring the satellite point across the wall and intersecting the receiver-to-image ray. Both pulses travel at the same illustrated speed. The meter scale is a chosen local geometry, not a satellite-to-ground scale drawing.

ΔL=∥S−W∥+∥W−R∥−∥S−R∥\begin{aligned}\Delta L&=\lVert S-W\rVert+\lVert W-R\rVert\\&\quad-\lVert S-R\rVert\end{aligned}Δt=ΔLc\Delta t=\frac{\Delta L}{c}

S: source; W: reflection point; R: receiver; lengths in meters. One extra meter gives about 3.34 ns of delay.

Code and carrier are different observations

Code correlation gives pseudorange. Carrier phase measures the phase of a much shorter wavelength and can be very precise, but includes an unknown integer cycle ambiguity. Precision of an observable does not by itself mean an ambiguity-resolved, unbiased position.

L=r+c(δtr−δts)−I+T+λN+εL\begin{aligned}L&=r+c(\delta t_r-\delta t_s)\\&\quad-I+T+\lambda N+\varepsilon_L\end{aligned}

L: carrier phase expressed in meters; λ: wavelength in meters; N: integer ambiguity. This is a simplified model.

04 / A WORKED EXAMPLE

A 30 m detour

If a reflected route is 30 m longer, its extra propagation delay is 30 / 299,792,458 seconds, about 100 ns. In the experiment, move the wall outward and observe the recomputed path difference. Turn reflection off to isolate the direct route. Do not label the displayed delay as a measured receiver error: no receiver tracking process is simulated here.

Return to the experiment and try it ↑

05 / PUT IT TO WORK

Try it in GNSS View

  1. Use the skyplot to inspect directions, then assess the real surrounding skyline.
  2. Compare mask settings while watching the loss of count and change in DOP.
  3. For actual quality assessment, consult receiver observations and correction status.
Open the observatory ↗

06 / COMMON QUESTIONS

Can low DOP remove multipath?

No. DOP describes geometry under an error model. It does not correct biased measurements.

Does dual frequency solve every error?

Frequency combinations can address major ionospheric terms, but do not remove all atmosphere, multipath, noise or hardware effects.

Why is carrier phase useful?

Its fine phase measurement supports high precision when ambiguities, models and corrections are handled appropriately.

07 / FURTHER READING

An original GNSS View explanation. These references document the models, terminology and system context.

ESA Navipedia · GNSS Basic Observables ↗ESA Navipedia · Positioning Error ↗