2. Impact on DGPS The errors induced by Sa are similar for the reference and remote receiver over distances of 500 km 2. In practice, time delay cannot be completely avoided Differential corrections calculating at reference station Signal propagation delay in transmitting these 2. US GPS Network Order corrections to the remote receiver 3. But this delay plays a much less stringent role in the absence of sa because the pseudoranges change smoothly and do not show the short variations caused by the dithering process. The differential pseudorange corrections accumulate ar error of about I m after 10 s 2.1 US GPS Survey Order 2.2 Observation for GPS Survey Observation Order Distance Relative Minimum time(minutes) 240120120 Pose Accuracy Accuracy Minimum satellites A0.5cm 0. 1ppm US Geodetic Reference Network. Elevation angle() Earth Surface Deformation Site number B 0.8 cm I ppm Local Earth Surface Deformation, imum baseline c 1.0 cm 10 ppm Engineering Surveying, Urban Max sides of non-synchronic loop Control Max length of non-synchronic loop 500300200 Number of atm eric measureme 2.3 Synchronic Loop Construction Definition: Several GPS receiver simultaneously survey 6 S=n(n-1)2 Radial Surveying4 2. Impact on DGPS: 1. The errors induced by SA are similar for the reference and remote receiver over distances of 500 km. 2. In practice, time delay cannot be completely avoided because of • Differential corrections calculating at reference station • Signal propagation delay in transmitting these corrections to the remote receiver. 3. But this delay plays a much less stringent role in the absence of SA because the pseudoranges change smoothly and do not show the short variations caused by the dithering process. The differential pseudorange corrections accumulate an error of about 1 m after 10 s. 2. US GPS Network Order 2.1 US GPS Survey Order Engineering Surveying, Urban Control Surveying C 1.0 cm 10 ppm Local Earth Surface Deformation, high-accuracy Engineering Surveying B 0.8 cm 1 ppm US Geodetic Reference Network, Earth Surface Deformation A 0.5 cm 0.1ppm Relative Purpose Accuracy Distance Accuracy Order 2.2 Observation for GPS Survey Number of atmospheric measurement 2 2 1 Number of antenna measurement 2 2 1 Max length of non-synchronic loop 500 300 200 Max sides of non-synchronic loop 8 10 10 Minimum baseline 15 5 5 10 30 20 50 40 80 Site number • Over 3 • Over 2 Elevation angle (°) 15 20 20 Minimum satellites 4 3~4 3 Minimum time (minutes) 240 120 120 Observation A B C 2.3 Synchronic Loop Construction Definition: Several GPS receiver simultaneously survey S=n(n-1)/2 Radial Surveying