GPS

Keplerian Motion (Satellite Orbits) (GPS) Part 1

The principle of the GPS system is to measure the signal transmitting paths from the satellites to the receivers. Therefore, the satellite orbits are very important topics in GPS theory. In this topic, the basic orbits theory is briefly described. For the GPS applications in orbits correction and orbits determination, the advanced orbits perturbation theory […]

Keplerian Motion (Satellite Orbits) (GPS) Part 2

Keplerian Equation Up to now, five integration constants have been derived. They are inclination angle i, right ascension of ascending node ,semimaj or axis a, eccentricity e of the ellipse, and argument of perigee w. Parameters i and1 decide the place of the orbital plane, a and e decide the size and shape of the […]

Disturbed Satellite Motion (GPS)

Keplerian motion of the satellite is a motion under the assumption that the satellite is only attracted by the central force of the Earth. This is, of course, an approximation. The Earth cannot be considered a mass point or a homogenous sphere for a satellite problem. The total attracting force of the Earth can be […]

GPS Broadcast Ephemerides (Satellite Orbits)

GPS broadcast ephemerides are forecasted, predicted or extrapolated satellite orbits data which are transmitted from the satellite to the receiver in the navigation message. Because of the nature of the extrapolation, broadcast ephemerides do not have enough high qualities for precise applications. The predicted orbits are curve fitted to a set of relatively simple disturbed […]

IGS Precise Ephemerides (Satellite Orbits) (GPS)

GPS satellite precise orbits are available through the International GPS Service (IGS) in the form of post-proceeded results. Such orbits data are called IGS precise ephemerides. They can be downloaded for free from several internet homepages (e.g., www.gfz-potsdam.de). IGS data are given in the ECEF coordinate system. For all possible satellites, the position vectors are […]

GLONASS Ephemerides (Satellite Orbits) (GPS)

GLONASS broadcast ephemerides are forecasted, predicted or extrapolated satellite orbit data which are transmitted from the satellite to the receiver in the navigation message. The broadcast messages include the following: satellite number, reference epoch of the ephemerides, relative frequency offset, satellite clock offset, satellite position, satellite velocity, satellite acceleration, time system correction with respect to […]

Ionospheric Effects (Physical Influences of GPS Surveying) Part 1

This topic covers all physical influences of GPS observations, including ionospheric effects, tropospheric effects, relativistic effects, Earth tide and ocean loading tide effects, clock errors, antenna mass centre and phase centre corrections, multipath effects, anti-spoofing and historical selective availability, as well as instrumental biases. Theories, models and algorithms are discussed in detail. The ionospheric effect […]

Ionospheric Effects (Physical Influences of GPS Surveying) Part 2

Ionospheric Models The Broadcast Ionospheric Model The GPS broadcast message includes the parameters of a predicted ionospheric model (Klobuchar 1996; Leick 1995). Using the model parameters, the ionospheric effects can be computed and corrected. The input parameters of the broadcast ionospheric model are the eight model coefficients ofgeodetic latitudeand longitudeof the GPS antenna, GPS observing […]

Tropospheric Effects (Physical Influences of GPS Surveying)

Troposphere is the lower part of atmosphere over the Earth’s surface. Unlike the ionosphere, the troposphere is a non-dispersive medium at GPS carrier frequencies. That is, the tropospheric effects on the GPS signal transmission are independent from the working frequency. The electromagnetic signals are affected by the neutral atoms and molecules in the troposphere. The […]

Relativistic Effects (Physical Influences of GPS Surveying)

Special Relativity and General Relativity Einstein’s special relativity is based on two postulates. The first one is called the principle of relativity, i.e., "No inertial system is preferred. The equations expressing the laws of physics have the same form in all inertial systems." The second one is called the principle of the constancy of the […]

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