DESIGNING A MULTI-SESSION NETWORK |
|
The "technical requirements" referred to relate to the propagation
of the network from session to session. Surveying more stations than the
minimum necessary for the adjustment is an added expense that must be justified
on grounds such as "quality control", generally in the form of
a contractual obligation, possibly arising from some specification relating
to the degree of redundancy that is required (section
10.3.2). An example will illustrate the principles of designing redundancy
into a GPS survey, and how this may impact on multi-session processing.
A GPS survey was carried out to coordinate 12 survey control stations, to Australian class "A" standard. Each tracking session involved observations by four receivers, and there were a total of seven sessions. The session deployment strategy is summarised in Table below (the numbers in the columns under the heading "SESSION" refer to the field party number).
| Station | SESSION |
|---|
| A | B | C | D | E | F | G | |
|---|---|---|---|---|---|---|---|
| PM69992 | 1 | 1 | |||||
| PM9920 | 1 | 1 | |||||
| PM69993 | 2 | 2 | 2 | ||||
| PM43517 | 3 | 3 | 3 | ||||
| PM43494 | 4 | 2 | 2 | ||||
| Vale Hd. Trig | 4 | 4 | 3 | ||||
| Molong Trig | 1 | 1 | 1 | ||||
| Brymedura Trig | 3 | 4 | |||||
| Goanna Trig | 2 | 2 | 4 | ||||
| Canobolas Trig | 3 | 3 | |||||
| Yuranigh Trig | 4 | ||||||
| Nandillyan Trig | 4 |
Note that although there are only 11 independent baselines in this network,
seven observation sessions were required in order to ensure a significant
amount of redundancy. Four stations (33% of the total) were occupied
twice, six stations (50%) were occupied three times, while only two stations
were occupied once.
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© Chris Rizos, SNAP-UNSW, 1999