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Formular 2.21, discuss, what speed is v? For GPS?
U = newtonian gravitationl potential at the location of the clock // va = velocity of the atomic clock // c = speed of light // delta_tau_geo = purely geometrical (or newtonian) delay difference between the arrival times of a wavefront at both telescopes. v ist die Geschwindigkeit der Atomuhr verglichen mit dem Massenzentrum des Systems. ca. 4km/s (Speed of a GPS-Satellite with respect to the Earth) ca. 29km/s (Speed of Earth with respect to the sun)
Charactericits of the GPS satellite constellation?
(clear access / coarse acquisition), 1023bits (chips), repeats after 1ms,
chip length (1 bit) = 293m, only modulated on L1, each GPS-Satellite sends own code-sequence.
(protected / precise), repeats after 266.4 days (=2.35*10^14 chips), chip length = 29.3m, transmitted on L1 and L2
Nav-Message of GPS Signal?
on L1 and L2, contains broadcast ephemerides (pseud-keplerian elements), satellite clock corrections (polynomial of 2nd degree), almanach data (approximate orbit info for long-term predictions), information about ionosphere, health status of the satellites
Which mechanisms exist for the artificial degradation of the GPS signals?
Selective Availability (SA): The accuracy of the positioning is degraded. This works with the so called dithering. There the satellite clock is manipulated in the range of 2 s, witch correspond to 60m. With relative positioning the SA wasn’t a problem. The SA was switched off at May 2, 2000. Anti-Spoofing (AS): The P-Code is encrypted by superposing a additional W-code. => Y-code. The AS was implemented to avoid that position quality can be degraded by a “wrong” artificial GPS-signal. Because of the AS there is an increased noise level in the code measurements ans especially in the carrier phase measurements.
Which mechanisms exist for the artificial degradation of the GLNASS signals?