DETERMINATION OF PSEUDORANGE- AND CARRIER PHASE NOISE
With the current quality of GPS receivers, multipath on the pseudorange may
very well be the determining factor for (sub) meter level code differential
GPS, and multipath and receiver noise on both pseudorange and carrier phase
may determine the ability of the receiver for cm level carrier phase differential
GPS. It is therefore required: A. to gain knowledge about these quantities
and B. to control multipath by a careful antenna selection and antenna location.
This page gives guidelines on how to determine pseudorange- and carrier phase
noise. For guidelines on the determination of multipath, go to the
Experience shows, that the noise level of both pseudorange and carrier phase often depends on the satellite elevation: low elevation satellites have a longer path through the atmosphere, and are thus more damped, and can be more noisy because of ionospheric scintillation, and thus deliver more noisy observations than high elevation satellites.
Forming double differences (DD's) removes common errors such as satellite
clock error, satellite position error, ionospheric error, tropospheric error,
receiver multipath error and receiver clock error. Remaining errors are the
DD receiver noise, and, in case of the carrier phase, the DD cycle ambiguity.
However, the noise level on a DD is higher than the noise level on an
Usually, the noise of observations of satellites with a high elevation (say more than 60 deg) is constant, say S.
If one assumes that the noise between satellites and between receivers is uncorrelated and gaussian (a reasonable assumption), the noise of a Double Differenced (DD) observation of two high satellites can be determined with the propagation law: SDD = sqrt(S2 + S2 + S2 + S2) = 2 * S, or : S = SDD / 2.
This property is used to determine the noise of high satellites first.
Next, the noise of lower satellites is determined using the high sat noise and again the propagation law.