Veripos LD6 Operation Manual page 77

Procedure Title: LD6 Operations Manual (B Variant)
File Ref.: AB-V-MA-00589
"It is essential to assess the precision and reliability of each position in order to
ensure the quality of the DGPS measurements. Thus is recommends that the
following processing steps be implemented: -



Where accuracy and precision statistical parameters are generated these all represent a
95% (2σ) confidence region.
Appendix A of the UKOOA guidelines emphasises this by listing 'Suggested parameters to
be specified by a system user for typical marine survey operations' and states that 'In order
to carry out rigorous QC, the covariance matrix generated by the least squares computation
should be used to generate test statistics and quality measures'.
It recommends the following Test Statistics:
1. w-test
2. F-test
It recommends also the following Quality Measures:
1. Error Ellipse
2. External Reliability
These recommendations are particularly aimed at survey applications but could be applied
equally to DP applications.
Rev No: A4
w-test for outliers carried out for each position fix
F-test for unit variance carried out for each position fix
When no more outliers are identified in any fix, precision and reliability
measures will be calculated:
o Precision:
a-posteriori error ellipse
o Reliability:
external reliability (positional MDE using a power of
test of 80%)"
used to detect outliers
used to verify the model which is being used to account for
'errors' in the DGPS observations
an approximate graphical representation of the positional
standard deviation in two dimensions
the effect of the maximum MDE (Marginally Detectable Error)
on the computed position
Page 77