Feature: Avionics
on GPS accuracy. For this software to be effective as a mitigation, the person in charge must know the GPS location certitude of its UAS system, and factor that in to his or her planning. For example, if the GPS location certitude of the UAS is ±10 feet, then add 10 feet to the buffers between the UAS and filming personnel.” These requirements point to a future
Screenshot of Spirent’s GNSS Foresight Visualisation Tool in downtown Indianapolis, the US, showing line-of-sight satellites at a given point. Position Dilution of Precision (PDOP) is calculated and shown to help users understand GNSS quality and performance
subject to this waiver must cease if, at any time, GPS signal is lost or GPS location information is degraded”. For Part 61/91 exemptions relating to
larger and heavier drones, the FAA states that the flight must not even start if GPS reliability is not assured throughout the flight. The exemption issued to A-Cam Aerials, for example, states that: “The PIC may not begin or continue a flight
if any global positioning system (GPS) outage, signal fault, integrity issue, Notice to Airmen in effect for any part of the planned operational area, or any other condition that affects or could affect the functionality or validity of the GPS signal”. To highlight a related consideration
of GPS reliability and performance, the waiver also states: “Geo-fencing relies
where navigation will form a crucial part of any defined regulation. That may not be much of an issue for operations in open rural spaces, but for services in urban or suburban areas, it could be a deal-breaker. That’s because the drone needs radio line of sight to at least four satellites – or six, if it’s also using an augmentation service like Wide Area Augmentation System (WAAS) or Satellite-based Augmentation System (SBAS) – to accurately calculate its position. If line of sight to those satellites is blocked or distorted by trees or buildings, even for a few seconds, the drone’s GPS receiver may temporarily lose lock on the signal.
GPS reliability Clearly, GPS reliability could be a deal- breaker for UAS-based business models. If a drone has to land unexpectedly, the costs of recovery and mission failure could become punitive. Hence, a solution is needed to address GPS signal degradation. Without one, regulators may not be convinced that a drone can operate safely in certain areas, businesses may find it tough to gain approval to fly in those areas, and operations that do obtain authorisation for BVLOS flight may be disrupted if GPS problems occur. As a provider of GNSS (Global
Navigation Satellite Systems) test, measurement and assurance solutions, Spirent Communications offers a two- fold solution to GPS signal degradation, developed in close cooperation with the aviation industry:
Screenshot of Spirent’s GNSS Foresight Visualisation Tool in downtown Detriot, US. In urban- canyon environments, where tall buildings surround the user, GNSS performance can be very unpredictable. GNSS Foresight forecasts these signals, creating a heatmap of GNSS performance. All constellations (GPS, Galileo, GLONAS,and BeiDou) were used to create this heatmap
Solution 1 GNSS availability forecasting solution, in the form of Spirent’s GNSS Foresight, which uses advanced 3D modelling and
www.electronicsworld.co.uk June 2022 19
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