6. RTCM Format 3. Relative Positioning Radio Technical Commission for Maritime Services Static Relative Positioning Observation periods depending on C/A-code differential corrections baseline length number of visible satellites rrelated with the I Delta differential corrections geometric configuration, andt baseline length and · he method used. (or even better). 10 P-code differential corrections Rapid Static Technique pecial message Use code and carrier phase combinations on both Dual frequency receivers and optimum satellite geometry are required. e corrections Restricting 20 km baselines, with sub cm level Semi-Kinematic Relative Positioning(Stop-&-Go) The semikinematic(stop-and-go)is characterized by stopping In practice. it is best to use a mixture of the three methods and moving one receiver. The most important feature is several measurement epochs at when using single frequency receivers. the stop locations are accumulated and averaged This technique is often referred to as simply kinematic survey. Static and pseudokinematic methods can be used to Relative positional accuracies at the centimeter level can establish a broad framework of control and to set for baselines up to some 20 km points on either side of obstructions such as bridges Phase ambiguities of Kinematic positioning: Kinematic surveys can then be employed to The initialization by static or kinematic technique etermine the coordinates of the major portion of are(for dual points, using the static points as control and check requires 1-2 minutes(baselines up to 20 km) kinematically Lock must be maintained over 4 satellites all entire survey A thorough reconnaissance is required for these Best suited for wide open areas. mixed surveys. 1.3 Impact of SA on Positioning SA Impact Reduction 1. Authorized P-code by decrypting Sa to get SA has two components correction d-process dithers the satellite clock frequency(some 2. Differentia 3. Relative te 4. Modeling the behavior of sa and to remove its effect E-process truncates the ephemerides data in the by appropriate filters. navigation message(some hours) Both processes induce variations in the code and phase 1.Impact on Point Positioning: pseudoranges which in turn translate into like position errors 2. with SA on, the poston cror:1 m level.3 6. RTCM Format Radio Technical Commission for Maritime Services 21 Code range corrections 20 Carrier phase corrections 19 Raw code range measurements 18 Raw carrier phase measurements 16 Special message 10 P-code differential corrections 6 Null frame 3 Reference station parameters 2 Delta differential corrections 1 C/ A-code differential corrections Type Meaning RTCM Message Types 64 Message Types 3. Relative Positioning Static Relative Positioning • Observation periods depending on • baseline length, • number of visible satellites, • geometric configuration, and t • he method used. The accuracy is correlated with the baseline length and amounts to 1-0.1ppm (or even better). Rapid Static Technique: • Based on fast ambiguity resolution techniques • Use code and carrier phase combinations on both frequencies. • Dual frequency receivers and optimum satellite geometry are required. • Restricting 20 km baselines, with sub cm level Semi-Kinematic Relative Positioning (Stop-&-Go): • The semikinematic (stop-and-go) is characterized by stopping and moving one receiver. • The most important feature is several measurement epochs at the stop locations are accumulated and averaged. • This technique is often referred to as simply kinematic survey. • Relative positional accuracies at the centimeter level can be achieved for baselines up to some 20 km. Phase Ambiguities of Kinematic Positioning: • The initialization by static or kinematic techniques. • Commercial software (for dual frequency receivers) only requires 1-2 minutes (baselines up to 20 km) kinematically. • Lock must be maintained over 4 satellites all entire survey. • Best suited for wide open areas. In practice, it is best to use a mixture of the three methods when using single frequency receivers. For example: • Static and pseudokinematic methods can be used to establish a broad framework of control and to set points on either side of obstructions such as bridges. • Kinematic surveys can then be employed to determine the coordinates of the major portion of points, using the static points as control and check points. • A thorough reconnaissance is required for these mixed surveys. 1.3 Impact of SA on Positioning SA has two components. • δ-process dithers the satellite clock frequency (some minutes) • ε-process truncates the ephemerides data in the navigation message (some hours). Both processes induce variations in the code and phase pseudoranges which in turn translate into like position errors. 1. Authorized P-code user by decrypting SA to get correction data from the navigation message 2. Differential techniques 3. Relative techniques 4. Modeling the behavior of SA and to remove its effect by appropriate filters. SA Impact Reduction: 1. Impact on Point Positioning: 1. With SA off, the position errors: 15 m level 2. With SA on, the position errors: 100 m level