Ahmed Ragheb, Stuart Edwards, Peter John Clarke

Multipath is a major sidereally-repeating error affecting precise GPS positioning and deformation monitoring. Because satellite-receiver geometry repeats almost exactly every sidereal day, filtering can reduce multipath in near-static situations. Here, we investigate how sidereal filtering can be used in a switched multi-antenna array system providing semi-continuous GPS data, which may be adopted in order to reduce hardware costs. Depending on the receiver’s set-up, the optimum session switching interval is 119 seconds or a multiple thereof. This provides sufficient reliable epochs using a short switching interval, and is synchronized with the appropriate geometry repeat interval for sidereal filter application. The semi-continuous sidereally-filtered GPS technique is efficient in detecting horizontal and vertical displacements, surpassing 5 mm and 8 mm precision respectively per epoch in near-static environments with moderately high multipath. This provides the capability of monitoring deformations occurring at periods greater than double the switching interval, although it can also be used for monitoring rapid structural deformations despite data gaps which may affect temporal resolution. Consequently, this combined method presents an efficient, cost-effective and precise GPS technique.