GNSS PPP

GNSS PPP Experiments - Cockle Park Farm

The world of satellite navigation has been undergoing dramatic changes with the rapid development of multi-constellation Global Navigation Satellite System (GNSS). More than 70 GNSS satellites are now in orbit around the Earth, and about 120 satellites will be available once all the four GNSS systems (i.e. GPS, GLONASS, BeiDou and Galileo) are fully deployed in the near future, which will bring abundant opportunities and challenges for GNSS scientific and engineering applications. In precision agriculture (PA), it is well recognized that GNSS is the major enabler of 'precision'. High precision GNSS (cm level) can be used for auto-steering systems on tractors and self-propelled machines (harvesters and sprayers) and for precision operations such as precision guidance, controlled traffic farming, mechanical inter-row weed control, inter-row sowing or crop thinning. Real Time Kinematic (RTK) GNSS is currently most commonly used for high precision GNSS applications in real time, producing typical errors of less than 2 cm with carrier phase measurements, but it requires at least one reference station. In contrast with RTK GNSS, precise point positioning (PPP) GNSS does not require access to observations from reference stations and it can provide an absolute positioning at the same accuracy level as RTK, with higher flexibility and potentially lower capital and running costs.

In this study, the feasibility of multi-GNSS PPP for PA applications is demonstrated by assessing the improvement of satellite visibility, spatial geometry, dilution of precision, convergence, accuracy, continuity and reliability that a combining utilization of multi-GNSS brings to precise positioning (against a single GNSS system). Our results in two farms (one in the UK and one in China) suggested that the addition of the BeiDou, Galileo and GLONASS systems to the standard GPS-only processing reduced the convergence time by approximately 70%, while the positioning accuracy was achieved in the 1-2cm level with an improvement of ~25% against the GPS-only PPP results. Some outliers in the GPS-only solutions disappeared when multi-GNSS observations are processed simultaneously. In space constrained and harsh environments (e.g., farms surrounded with dense trees), the availability and reliability of precise positioning decreased dramatically for the GPS-only PPP results, but limited impacts were observed for multi-GNSS PPP.

Last modified: Wed, 14 Oct 2015 17:09:18 BST