立地类型和定位模式对精准林业GPS定位的影响

利用Trimble AgGPS132定位试验装置,采用单机模式和信标差分模式分别在空地和林地中进行了静态定位和动态定位试验,通过多次测量结果散点分布和真值位置图,检验立地类型和定位模式对卫星可见性、位置精密度、准确度、精确度和动态测试范围周长及面积的影响。静态定位试验结果表明:信标差分定位的准确度和精确度比单机定位高,当定位地点由空地变为林地时,卫星可见数减少2～3颗,PDOP值增大0.8～1.2,准确度降低0.30～0.31 m,精确度降低0.92～1.01 m。对动态定位试验结果进行方差分析表明,立地类型、定位模式以及二者的交互作用对周长、面积等定位精度的影响差异均显著。精准林业生产作业时,林分密度、树冠形状引起的多路径效应致使信噪比降低、载波信号被拦截,降低了定位精度。因此,林地中需采用差分定位技术提高定位精度以满足精准林业的生产作业要求。

Effects of the site condition and positioning mode on GPS performance for precision forestry

The main purpose of the study was to test GPS equipment receivers used for open sky and forest condition with non differential and RBN differential mode, and to quantify satellite availability, PDOP, accuracy, and precision under different factors, the objective being to assist GPS's application in precision forestry. Results of stationary test showed that the RBN DGPS mode improved the accuracy and precision both in open sky and forest condition. Comparing to the open sky, forestry GPS application decreased the number of satellites availability by 2-3, increased PDOP by 0.8-1.2, reduced accuracy by 0.30-0.31 m, and reduced precision by 0.92-1.01 m. In mobile test, analysis of variance(ANOVA)with SPSS16.0 was used to clarify the effects of positioning mode and site condition on the precision of GPS. According to the ANOVA test, the GPS positioning perimeter and area were affected significantly by positioning mode, site condition and their interaction. Based on the research, it is clearly possible to obtain good accuracy of a RBN GPS in forest, and forest observational conditions made extremely different conditions for GPS observation owing to forestry canopy causing strong multipath effect and satellites signals reception.