UBC Theses and Dissertations

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UBC Theses and Dissertations

An investigation of single channel, global positioning system receivers for forestry applications Shannon, Tim


The forest industry in British Columbia is converting much of its spatial data to digital format for input into Geographic Information Systems. The updating of these large databases stil l involves digitizing of analog data. This thesis examines the suitability of a single channel hand held Global Positioning System (GPS) receiver in the forests of British Columbia. GPS provides a means of directly capturing digital spatial attributes in the field. Field trials to evaluate the effects of forest canopy on the reception of satellite signals were conducted at the Malcolm Knapp Research Forest in Maple Ridge. Issues that need to be considered when implementing GPS in capturing spatial information are: 1) the frame of reference from which positions are calculated, (datums) 2) methods used to calculate the accuracy of position, 3) the accuracy of single point positions, 4) the accuracy of differential positioning, and 5) the effects of the forest canopy on the reception of signals from the satellites. The effect of choosing a different datum than that used to produce the base map can lead to positioning errors of several hundred metres. While commonly the largest source of error, it is preventable. Single point positions can be expected to be within 25-metres, in two dimensions, when Selective Availability is not enabled. When Selective Availability is enabled the accuracy will be degraded to 100 metres. To regain the accuracy lost due to Selective Availability, differential GPS will need to be used. Differentially corrected positions can be expected to be within 10-metres in two dimensions. The effect of the canopy on attenuating the signals emitted from the satellites is of concern. At best, the user can only expect intermittent signals under a closed canopy with the equipment tested. Evolving technologies are increasing the accuracy, speed and sensitivity of receivers, while decreasing the size, power consumption, and cost. The integration of GPS with other positioning and navigational aids shows the most promise for implementing GPS into forest management in British Columbia.

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