12. 540 Principles of the Global Positioning System Lecture 09 Prof. Thomas Herring 03/06/02 12.540Lec09
03/06/02 12.540 Lec 09 1 12.540 Principles of the Global Positioning System Lecture 09 Prof. Thomas Herring
Summary · Review Examined definitions of pseudorange and carrier pnase Looked at some actual raw measurements from a RINEX file · Today we look at: Combinations of range and phase measurements Simple differences between observed and rough calculation of expected range and phase measurements Sources of gPs data 03/06/02 12.540Lec09
03/06/02 12.540 Lec 09 2 Summary • R e vie w: – Examined definitions of pseudorange and carrier phase – Looked at some actual raw measurements from a RINEX file • Today we look at: – Combinations of range and phase measurements – Simple differences between observed and rough calculation of expected range and phase measurements – Sources of GPS data
Range and phase data As we have seen with real data there are drops out of data missing data and often associated with this cycle slips in the phase data The difference between the L1 and L2 range measurements reflects noise and the ionospheric delay ( grew by 5 meters in the hour of data we looked at) Difference between L1 and L2 phase, when converted to distance using standard frequencies and speed of light, also reflects noise(much smaller than range) and ionospheric delay but with opposite sign to range ionospheric delay This difference can be used to check for cycles slips independent of ionosphere and movement of receivers. called the Melbourne -Wubena wide lane 03/06/02 12.540Lec09
03/06/02 12.540 Lec 09 3 Range and phase data • As we have seen, with real data there are drops out of data (missing data) and often associated with this cycle slips in the phase data. • The difference between the L1 and L2 range measurements reflects nois e and the ionospheric delay (grew by 5 meters in the hour of data we looked at) • Difference between L1 and L2 phase, when converted to distance using standard frequencies and speed of light, also reflects nois e (much smaller than range) and ionospheric delay but with opposite sign to range ionospheric delay. • This diffe rence can be used to check for cycles slips independent of ionosphere and movement of receivers. Called the Melbourne-Wubena Wide Lane
Melbourne-Wubena wide lane The difference between L1 and l2 phase with the l2 phase scaled to the L1 wavelenth is often called simply the widelane and used to detect cycle slips However it is effected fluctuations in the ionospheric delay which in delay is inversely proportional to frequency squared The lower frequency L2 has a larger contribution than the higher frequency L1 The mw-w removes both the effects on the ionspheric delay and changes in range by using the range measurements to estimate the difference in phase between L1 and L2 03/06/02 12.540Lec09
03/06/02 12.540 Lec 09 4 Melbourne-Wubena Wide Lane • The difference between L1 and L2 phase with the L2 phase scaled to the L1 wavelenth is often called simply the widelane and used to detect cycle slips. However it is effected fluctuations in the ionospheric delay which in delay is inversely proportional to frequency squared. • The lower frequency L2 has a larger contribution than the higher frequency L1 • The MW-WL removes both the effects on the ionspheric delay and changes in range by using the range measurements to estimate the difference in phase between L1 and L2
Melbourne-Wubena Wide Lane(Mw-WL mw-wI [Rf/c+R,/2/c] (f+f2) Equation for the Mw-WL. The term Rf/ c are the range in cycles(notice the sum due to change of sign ionospheric delay) The Af/Ef term for GPS is -0 124 which means range noise is reduced by a about a factor of ten Because of phase and biases range biases, the ML WL should be integer(within noise)when data from differerent sites and satellites double differences )are used. (EXample shown later) 03/06/02 12.540Lec09
03/06/02 12.540 Lec 09 5 Melbourne-Wubena Wide Lane (MW-WL) • Equation for the MW-WL. The term Rf/c are the range in cycles (notice the sum due to change of sign ionospheric delay) • T h e ∆f/ Σf term for GPS is ~0.124 which means range noise is reduced by a about a factor of ten. • Because of phase and biases range biases, the MLWL should be integer (within noise) when data from differerent sites and satellites (double differences) are used. (Example shown later) mw − wl = φ1 − φ2 − ( f1 − f2 ) ( f1 + f2 ) R1 f1 / c + R 2 f2 [ ] / c