Manual Title:
LD7 Operations Manual
Ref.:
AB-V-MA-00555
Rev No:
A9
Page 42
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
www.nmea.org
for further information.
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:
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”
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: -
