Quality Standards - Veripos LD6 Operation Manual

Procedure Title: LD6 Operations Manual (B Variant)
File Ref.: AB-V-MA-00589
5.7

QUALITY STANDARDS

A number of standards offer marine satellite navigation system users DGNSS
(DGPS/DGPS+DGLONASS) quality information. The most well-known and frequently
referred to standards are:
1. UKOOA
2. NMEA-0183
Each standard is explained in more detail in the following sections.
NMEA have recently introduced the NMEA-2000 interface standard. This standard falls
outside the scope of this document. See
References
[1] Guidelines for the use of Differential GPS in offshore surveying, UKOOA, 1994
[2] NMEA 0183 Standard for interfacing marine electronic devices, version 3.01,
January 1, 2002
[3] Guidelines on the use of DGPS as a positioning reference in control systems, IMCA
M 141, October 1997
UKOOA STANDARD
The UK Offshore Operator Association (UKOOA) issued 'Guidelines for the use of
Differential GPS in offshore surveying' in 1994. These guidelines set out what is generally
regarded as good practise in the offshore industry. They are not mandatory and operators
are free to adopt different guidelines or standards.
These guidelines are now dated in certain areas due to advancements in positioning
technology and algorithms. However, they contain useful suggestions for quality monitoring
as indicated below [see 1]: -
"To assist DGPS operators and client representatives to monitor the quality of the
DGPS system in real-time the following information should be continuously
available:
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The UKOOA guidelines present a set of test statistics and quality measures recommended
for use with DGPS. In its final recommendations [see 1] it states: -
Rev No: A4
Pseudo-range residuals of all SV's and observation weight values used
Unit variance
Number of satellites in view and number used in solution
Redundancy of least squares solution
DOP values (HDOP, PDOP and VDOP)
Latency of differential correction data
Position comparisons derived from different reference stations
Derived antenna height with respect to "known" height
Monitor station information, especially position error measured at the monitor
station. All data should be time tagged
Maximum external reliability figure and observation carrying it"
www.nmea.org for further information.
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