Sect_10.4.1

10.4.1 Quality Control Procedures for GPS Networks

INTRODUCTION

In relation to GPS surveying, "QUALITY CONTROL" refers to those procedures or indicators that provide a measure of the quality (accuracy and reliability) of a GPS survey. Quality Control therefore has as much to do with detecting observational errors, as in interpreting the primary and secondary Least Squares adjustments peculiar to GPS surveying.

There are three categories of quality control measures that can be applied sequentially:

Quality control measures related to evidence gleaned from the station logs, as well as that obtained from other sources (for example, relating to the GPS system health).

Those quality control measures that relate to the internal consistency of the GPS-only network adjustment (the so-called "minimally constrained" solution). Only when the quality of this solution is assured is the third phase of quality assessment commenced.

Those quality control measures that incorporate external position information from geodetic control stations or other previously coordinated points.

For the moment the focus will be on those quality control issues related to the field operations and the minimally constrained GPS network solution. With regard to the latter, it is possible, in addition, to distinguish between:

Those procedures and quality indicators that are relevant for single session (perhaps even single baseline) results. These involve DATA QUALITY and SUFFICIENCY issues.
Those relevant for multi-session solutions. These test the CONSISTENCY and RELIABILITY of the COORDINATE RESULTS.

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