Module 2 : Global Positioning System
  Lecture 13 : GPS Measurements Techniques II
Summary of GPS survey requirements
Survey type
Baseline length
(km)
#
satellites
GDOP
Observation
time
Accuracy
Static
20-50
≥ 4
≤6
2 - 3 hr
5 mm + 1 ppm
50-100
≥ 4
≤6
min. 3 hr
5 mm + 1 ppm
> 100
≥ 4
≤6
min. 4 hr
5 mm + 1 ppm
Rapid Static
0 - 5
≥ 4
≤5
5 - 10 min
5 - 10 mm + 1 ppm
5 - 10
≥ 4
≤5
10 - 15 min
5 - 10 mm + 1 ppm
10 - 20
≥ 4
≤5
10 - 30 min
5 - 10 mm + 1 ppm
Reoccupation
0 - 5
4
≤8
5 min
10 mm + 1 ppm
5 - 10
   4
≤8
5 - 10 min
10 mm + 1 ppm
10 - 20
   4
≤8
10 - 20min
10 mm + 1 ppm
 
Remarks :
  • 3 mm + 0.5 ppm accuracy achievable using choke-ring antenna & long observation period in static mode
Stop and Go
  • Rapid Static fix should be determined
  • Few epochs are only necessary on known points
Kinematic
  • Rapid Static Fix should be determined
  • No stopping after the rover is in movement.
 
Recommended Recording Intervals
Mode Observation time Accuracy
SPP 30 - 60 sec 10 - 100 m
SPP with PP 5 - 10 hrs 3 - 5 mm
Static 1 - 4 hr (recording interval: 15 sec) 5 mm + 1 ppm
Rapid Static 5 minutes (min) (recording interval: 5 sec) 5 mm + 1 ppm
Reoccupation 5 minutes (min) 1 cm + 1 ppm
Stop and Go 2 epochs (recording interval: 1-5 sec) 1 - 2 cm + 1 ppm
Kinematic & AROF 1 sec (recording interval: 0.2 sec) 1 - 2 cm + 1 ppm
Code difference with RT 1 sec 0.3 - 0.5 m
Phase difference with RT 1 sec 1 - 2 cm + 2 ppm
 
SPP: Single point positioning; PP: Post processing; RT: Real time
The recording/sampling or data interval refers to downloading interval of GPS data. It may be as high as between 0 - 1 second and as slow as 999 to 3600 seconds. High rate results in large volume of data and needs large storage. It also helps detection of cycle slips and results in improved accuracies for long baselines (> 50 km) when detection and repair of cycle slips is difficult.
 
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