Introduction to GNSS Base-Station
Dinesh ManandharCenter for Spatial Information Science
The University of Tokyo
Contact Information: dinesh@iis.u-tokyo.ac.jp
Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 1

Introduction• GPS or GNSS observation has many types of errors. Due to these errors, theaccuracy of a GPS receiver is limited. Currently about 10m accuracy is possible
with Single Observation.
• However, some of these errors can be removed and reduced by using properobservation techniques to provide few millimeter accuracy. This can be done byusing a Base-Station within a limited base-length from the Rover (user) receiver.
• In the next few slides, we will see types of errors and how they can be removed.

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

2Slide : 2What is a Base-Station?
• A Base-Station is a station where a GNSS receiver is installed
at a known location.
• Also called Reference Station• CORS (Continuously Operating Reference Station)• The location is pre-surveyed by either traditional methods orby GNSS observation for multiple days.
• The Base-station then provides error data for every
observation compared to it’s known location.

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

3Slide : 3

• Accuracy

Accuracy vs. Precision• Capable of providing a correct measurement• Measurement is compared with true value• Affected by systematic error• Precision• Capable of providing repeatable and reliable measurement• Statistical analysis of measurement provides the precision• Measure of random error• Systematic error has no effect

Neither Precise nor Accurate Precise but Not Accurate

Accurate but Not Precise

Precise and Accurate

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

4Slide : 4

How accurate is GPS Position?

50 cm grid

50 cm grid

5 cm grid

SPP (Single Point Position)

DGPS (Differential GPS)RTK (Real Time Kinematic)

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

5Slide : 5

Errors in GPS Observation (L1C/A Signal)
Error Sources
Satellite Orbit
Satellite Clock
Ionosphere Error
Troposphere Error

One-Sigma Error , mTotal
DGPS
2.1
2.1
4.0
0.7

0.0
0.0
0.40.2

Comments
Common errors are
removedCommon errors are
reducedMultipath
1.4
1.4
Receiver Circuits
0.5
0.5
If we can remove common errors, position accuracy can be increased.
Common errors are: Satellite Orbit Errors, Clock Errors and Atmospheric Errors (within few km)
Table Source : http://www.edu-observatory.org/gps/gps_accuracy.html#Multipath

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

6Slide : 6

How to Remove the Errors?
• Averaging of Repeated Observation• Modeling of Phenomena that Causes Errors• Differential Corrections• DGPS, SBAS, GBAS

• Single frequency observation is OK• Code Observation• RTK• Normally multi-frequency observations• Single frequency RTK is also performed for smaller base-length• Code and Carrier Observation• PPP• Precise Point Positioning
Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

7

Slide : 7

Principle of Differential Correction
30

Send Correction Data to RoverFor Real-Time Position

Rover
For RTK, both rover and base receivers
need to use the same satellites
Antenna is installed at aUser in the Field
known-position(Either fixed or moving)Base-Station

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

8Slide : 8

Principle of QZSS MADOCA / CLAS Service
QZSS

GPSCorrection Data:
Satellite Orbit Error of GPS and Other Satellites
Satellite Clock Error of GPS and Other Satellites
Rover
Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

9Slide : 9

Which Method: DGPS, SBAS, RTK, PPP?

http://www.novatel.com/an-introduction-to-gnss/chapter-5-resolving-errors/

Training on GNSS – Course (T151-30), Organized by: GIC/AIT, CSIS/UT and ICG, held at: GIC/AIT, Thailand from 14 – 18 JAN 2019
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

10

Slide : 10