للكاتب :
Ashraf Farah
Aswan-Faculty of Engineering, South Valley University, EGYPT
ABSTRACT
Tropospheric delay is the second major source of error after the ionospheric delay for satellite
navigation systems. The transmitted signal could face a delay caused by the troposphere of over
2m at zenith and 20m at lower satellite elevation angles of 10 degrees and below. Positioning
errors of 10m or greater can result from the inaccurate mitigation of the tropospheric delay. Many
techniques are available for tropospheric delay mitigation consisting of surface meteorological
models and global empirical models. Surface meteorological models need surface meteorological
data to give high accuracy mitigation while the global empirical models need not. Different
satellite based augmentation systems use this type of models such as EGNOS model for the
EGNOS augmentation system. This paper presents an assessment study of the behaviour of the
EGNOS model compared with highly accurate IGS-tropospheric estimation for South Egypt
region (Aswan city). The study was assessed for TNML station in China as it has similar latitude
and height with Aswan station for the lake of IGS-trop. Estimates for Aswan station. The study
was performed over four non-consecutive weeks on different seasons over one year. It can be
concluded that the EGNOS tropospheric correction model has shown acceptable level of
accuracy in describing the average tropospheric delay model as it agrees reasonably well with the
IGS-tropospheric estimates based on GPS measurements. The mean difference in total zenith
delay between the EGNOS model and the precise IGS-estimations of the tropospheric delay is
about 3.9 cm with maximum difference of up to 5.8 cm. The root mean square of the difference
in total zenith delay is 6.5 cm.
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