Carrier phase null space monitor for ionospheric gradient detection

A new carrier phase-based monitor is developed to instantaneously detect two-dimensional ionospheric gradients. In order to detect gradients at satellite acquisition, it is necessary for ground-based fault detection to rely directly on instantaneous ground facility measurements. The paper proposes a new monitor (termed the null space monitor) by combining measurements from multiple, spatially separated ground antennas through a null space transformation. In addition, comparison results with previously published monitors show that the null space monitor covers the largest possible range of detectable ionospheric gradients.