Two phases of a precision farming project are described. Phase I consists of the collection of data from four test fields across Alberta using differential GPS (DGPS) combined with crop yield monitors and electromagnetic (EM) ground conductivity meters for measuring salinity. A geographic information system (GIS) is used to analyze and combine various layers of information obtained from each field in order to analyze yield variation. Positions better than 50 cm horizontally and 1 m vertically are obtained in DGPS mode using a robust carrier‐phase smoothing of the code approach. The accuracy of the DGPS positions is verified independently through a crossover point analysis and a comparison with an ambiguity resolution on the fly (OTF) solution. DGPS positions are used to generate maps, which indicate that fields are not homogeneous in crop yield when they have been treated without consideration for variability of soil, salinity, topography, or field history. Phase II, which consists of the application of variable‐rate fertilizer based on the information gathered in Phase I, is summarized.
The main characteristics of both GPS (UHF) and Loran-C (LF) navigation systems are reviewed, with emphasis on vehicular navigation applications. The effect of the GPS line-of-sight requirement and that of Loran-C signal interfcrence and attenuation in urban and mountainous areas are discussed.Unaided GPS and Loran-C signal availability statistics sufficient for 2-D positioning with HDOP < 5 are presented using GPS and Loran-C signal statistics obtained from tests conducted in Calgary and along roads of British Columbia. In Calgary, GPS availability is found to be better than Loran-C. This is attributed to a near complete satellite constellation and to the use of a fast signal acquisition GPS receiver. The use of integrated GPS/Loran-C improve GPS availability by only a few percents. In the mountains, the use of an integrated system increases availability to 95% as compared to 65% for GPS and 75% for multi-chain Loran-C.
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