TITLE:
Impact of Tropospheric Delay Gradients on Total Tropospheric Delay and Precise Point Positioning
AUTHORS:
Mohamed Elsobeiey, Mohamed El-Diasty
KEYWORDS:
Precise Point Positioning, Electromagnetic Waves, Tropospheric Delay, Tropospheric Gradients
JOURNAL NAME:
International Journal of Geosciences,
Vol.7 No.5,
May
18,
2016
ABSTRACT: GPS signals are
electromagnetic waves that are affected by the Earth’s atmosphere. The Earth’s
atmosphere can be categorized, according to its effect on GPS signals, into the
ionosphere (ionospheric delay) and neutral atmosphere (tropospheric delay). The
first-order ionospheric delay can be eliminated by linear combination of GPS
observables on different frequencies. However, tropospheric delay cannot be
eliminated because it is frequency-independent. Thetotal tropospheric delay can be
divided into three components. The first is the dry component, the second part
is the wet component, and the third part is the horizontal gradients which
account for the azimuthal dependence of tropospheric delay. In this paper, the
effect of modeling tropospheric gradients on the estimation of the total
tropospheric delay and station position is investigated. Long session, one
month during January 2015, of GPS data is collected from ten randomly selected
globally distributed IGS stations. Two cases are studied: thefirst case, the coordinates of
stations are kept fixed to their actual values and the tropospheric delay is
estimated twice, with and without tropospheric gradients. In the second case,
the station position is estimated along with the total tropospheric delay with
and without tropospheric gradients. It is shown that the average bias of the
estimated total tropospheric delay when neglecting tropospheric gradients
ranges from ?1.72 mm to 2.14 mm while the average bias when estimating
gradients are ?0.898 mm to 1.92 mm which means that the bias is reduced by about
30%. In addition, the average standard deviation of the bias is 4.26 mm
compared with 4.52 mm which means that the standard deviation is improved by
about 6%.