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Which terms are present in the observation equation of GPS?
receiver position at reception time, satellite position at emission time, tropospheric delay, ionospheric delay, relativistic correction, influence of multi-path, light travel time, light velocity
What is the meaning of the terms in equation (2.43)
re(tE): Receiver position at reception time (tE), rs(tS): =rs(tE-tES): Satellite position at the time of emission tS, trp: signal delay in troposphere, ion, signla delay in ionosphere, rel: relativistic correction, mul: infuence of multi-path
Differences between the phase and code observation equations
Vorzeichen für Ionosphären-Korrektur (pase advane, group delay), andere Wert für Multipath-Korrektur.
Why are often differences formed in GPS analyses (especially double-differences)?
to improve the accuracy: get rid of the satellite clock error, receiver clock error and other effects
Explain single Diff in GPS measurements?
2 Reveivers observe simultanous the same satellite // calculate the difference of the two observation equations // eliminated satellite clock error (it’s not totally eliminated - but nearly) // other errors are reduced as well, if baseline is not too long (sallite orbit errors, atmospherical and relativistic effects) // system noise increases by a factor of sqrt(2)
Explain double Diff in GPS measurements?
2 receivers, 2 satellites // differences of the observation eqations // eliminates receiver clock error (you still need to know the clock error to calculate the satellite positions in the correct epoch!) // system noise increases by a factor of 2
Explain tripple Diff in GPS measurements?
2 reveivers, 2 satellites measured in two epochs // eliminates the ambiguity // first robust solution for relativ-coordinates // system noise increases by a factor of 2*sqrt(2)
What type of instrumental effects have to be considered in GPS? What can be done to reduce their adverse effects?
a) multipath-effects b)phasecenter of GPS antenna: actual point of reception. Depending on azimuth and elevation of the GPS satellites. // 1) combining different antenna types: mainly affecting the height component (up to 10cm), horizontal position maximally a few millimeters if tropospheric zenith delays are estimated in the adjustment // 2) long baselines, errors even present if identical antenna types are used! due to different elevtion angle to the same satellite. //
ant(z,a) = -(r0e+(a,z)),
e = unit vector pointing from receiver to satellite,
Corrections are also necessary for the satellite antenna phase center!