GPS and Surveying Space Segment Control Segment User

GPS and Surveying

Space Segment

Control Segment

User Segment

Satellite Signal Structure L 1 = 19 cm L 2 = 24 cm Carrier Code

Satellite Signal Structure Carrier Frequency Wavelength L 1 1575. 42 MHz 19 cm L 2 1227. 60 MHz 24 cm Code Modulation C/A-code P(Y)-code NAVDATA C/A - Coarse Acquisition Code P - Precise Code (Y-Code when encrypted) NAVDATA - Satellite health, satellite clock corrections, ephemeris parameters and SV orbital parameters.

Satellite Ranging Fourth measurement will decide between two points

Satellite Range based on Code Measurement measure time difference between same part of code from satellite from ground receiver

The Integer Ambiguity Dl = First Partial Wavelength N = Integer Ambiguity N Dl Solving for the Integer Ambiguity yields centimeter precision

Carrier Phase Results d e r u s Mea ce u d e d R Baseline or Vector (cm precision) Azi = 212 o 42’ 49. 8244” Dist = 557. 053 m DElev = 4. 875 m OR D X = -408. 251 m D Y = -84. 830 m D Z = -369. 413 m

ECEF Coordinate System +Z ECEF X = -2691542. 5437 m Y = -4301026. 4260 m Z = 3851926. 3688 m Z Y X -Y +X

Reference Ellipsoid a = semi-major axis b = semi-minor axis H b WGS-84 Ellipsoid a = 6378137. 000000 m b = 6356752. 314245 m 1/f = 298. 2572235630 a a l f

ECEF and WGS-84 +Z ECEF X = -2691542. 5437 m Y = -4301026. 4260 m Z = 3851926. 3688 m H Z f X WGS-84 f = 37 o 23’ 26. 38035” N l = 122 o 02’ 16. 62574” W H = -5. 4083 m b Y l a -Y +X

GPS Heights vs. Elevations ce a f r H e N e = Orthometric Height H = Ellipsoid Height N = Geoid Height e=H-N e H N Su s h’ t r Ea e H N id o ips Ell id o Ge

Good Satellite Geometry

Poor Satellite Geometry

Atmospheric Effects Ionosp here Tropos phere < 10 km > 10 km

Multipath

GPS Surveying Techniques

Technique for Survey Task

Questions ?