Use of global positioning systems (GPS) for topographic surveys and the development of management units for precision farming
The use of Global Positioning System (GPS) technology has become common in situations requiring spatial and topographic information. Many of the receivers currently available offer sub-meter accuracy in two dimensions when correction is applied, whether realtime or post processing. The vertical dimension tends to be less accurate than the horizontal. To determine the relative accuracy of commonly available GPS receivers, four sites east of Saskatoon were surveyed using both conventional survey techniques (Total Station) and GPS (Trimble Pro XRS). The topography of the sites ranged from level (slope class 2) to hummocky (slope class 5). The GPS data were corrected using both real-time differential satellite correction and post processing data provided by local base stations. Digital Elevation Models (DEM) were derived for each of the following: the Total Station elevations, the GPS elevations corrected in real-time, and the post-processed GPS elevations. Comparing the GPS topographic surfaces with the Total Station surface reveals that there are substantial differences in the two, limiting the application of GPS to landform segmentation procedures. The errors present in the GPS surfaces tended to be linear, corresponding with the orientation of the survey transects, rather than random. In landform segmentation, this creates artificial ridges or draws in the landscape. Given these limitations, producers using combination GPS/yield monitor systems will not be able to produce high quality management unit maps, particularly when no differential correction is applied.
Soils and Crops Workshop