SX BLUE GPS iSXblue II+ GNSSTM, User Manual

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SXblue Series User Manual 89
correction services, including many private reference stations and DGPS beacon
systems. The SXblue receiver supports this correction protocol via either of its
communication ports.
In addition to the RTCM standard, the Radio Technical Commission for
Aeronautics has a differential service intended for wide area correction services,
designated RTCM SC-159. The United States Federal Aviation Administration’s
Wide Area Augmentation System (WAAS) and other compatible Space Based
Augmentation Systems (SBAS) such as the European Geostationary Navigation
Overlay System (EGNOS), the
Japanese MT-SAT Satellite-based Augmentation
System (MSAS) and the Indian Space Research Organization’s GPS Aided Geo-
Augmented Navigation system (GAGAN) system use this data format. The SXblue
receiver is compatible with each of these differential services.
Note – When using a differential correction service, the resultant position
may be referenced to a local datum rather than the current WGS-84 ellipsoid.
Please refer to your signal provider for more information.
Post Processing
Post processing is a method to compute accurate positions in post mission by
logging raw measurement data at the base station and the rover simultaneously.
The differential processing can then be performed later in the office using
sophisticated processing software tools. There are a small variety of
methodologies available to the operator, such as static, rapid static, kinematic, etc.
Describing in detail the various post processing techniques is beyond the scope of
this document, however, generally, post processing is more complicated from a
procedural perspective and requires more skill to successfully operate than real-
time systems.
Factors Affecting DGPS Accuracy
Many factors affect the positioning accuracy that a user may expect from a DGPS
system. The most significant of these influences include:
•
Proximity of the remote user to the reference station (atmospheric and orbit errors)
•
Age of the received differential corrections
•
Atmospheric conditions at the beacon and remote user locations
•
Satellite constellation geometry, often expressed as a Dilution of Precision (DOP)
•
Magnitude of GPS signal multipath present at the remote station
•
Quality of the GPS receiver being used at both the reference and remote stations
Proximity of the Reference Station
The distance between a remote user and the reference station can sometimes be