Lester, Trenton (2018) Evaluation of the Effect of Vegetation Sky Obstructions and Multipath on AUSPOS and Trimble CenterPoint RTX Post-Processing. [USQ Project]
Abstract
Surveyors are often required to establish coordinates for survey control stations using data logged with Global Navigation Satellite Systems (GNSS) and processed using online GNSS post-processing services. Often these survey control stations are obstructed by vegetation, which may cause errors due to multipath. Previous research testing online GNSS post-processing has focussed on ideal unobstructed mark selection and therefore it is unclear how much vegetation sky obstruction is acceptable and what observation durations are necessary to achieve results that meet the relevant surveying standards when obstructed marks are observed.
Observations were taken over three 24-hour periods on five survey control stations with different amounts of sky obstruction including one with artificially induced multipath and one ideal unobstructed station. The observation files were divided into eight shorter duration files and submitted to AUSPOS (processing American GPS satellites only) and Trimble CenterPoint RTX Post-Processing (processing all five currently orbiting GNSS constellations) to test the uncertainty and repeatability of results. The differences in the processed coordinates and reported uncertainties of each observation file were compared to the Cadastral Survey Requirements v7.1 (DNRM 2016) requirement of cadastral surveys creating 10 or more lots to be connected to the State control survey with horizontal positional uncertainty of any mark coordinated for this purpose to be less than 50mm and the Surveying Standards - Part 2 (TMR 2016) requirement that PSMs used as project reference frame marks have coordinates with horizontal positional uncertainty of less than 30mm.
All stations tested were able to achieve acceptable results with sufficient observation duration. There was little difference in required observation durations between AUSPOS and Trimble CenterPoint RTX Post-Processing even though the satellite constellations in use by each service are so different. The first station had 90% obstructed sky and was surrounded by trees and provided repeatable, acceptable results with 12 hours of observation duration. The second station had 75% obstructed sky near a cleared edge of bush and needed 6 hours of observation duration. The third station had 45% obstructed sky near the cleared edge of bush and only needed 4 hours of observation duration to repeatably meet the TMR less than 30mm requirement. The fourth station involved artificial multipath which was averted by the receiver and the fifth station was unobstructed and provided repeatable, acceptable results with 2 hours of observation duration.
With usual caution and independent checks, surveyors may use these results to influence control station site selection and to indicate required observation durations in similar situations. More observations would be useful to boost confidence in repeatability and different vegetation types in other regions could be tested to create more universal guidelines for allowable vegetation sky obstruction and corresponding observation durations for online GNSS post-processing.
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| Item Type: | USQ Project |
|---|---|
| Item Status: | Live Archive |
| Faculty/School / Institute/Centre: | Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021) |
| Supervisors: | Gibbings, Peter |
| Qualification: | Bachelor of Spatial Science (Honours) (Surveying) |
| Date Deposited: | 05 Sep 2022 04:42 |
| Last Modified: | 29 Jun 2023 01:50 |
| Uncontrolled Keywords: | vegetation sky obstruction; surveying |
| URI: | https://sear.unisq.edu.au/id/eprint/40763 |
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